JP2008309749A - Device and method for measuring electronic spin resonance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure electronic spin resonance without using a cavity resonator. <P>SOLUTION: A device for measuring electronic spin resonance includes: a magnetic field generator 8 for splitting an energy level in an electronic spin system by applying a magnetic field to the electronic spin system; an effective vibration magnetic field generating light source 6 for generating, by irradiating the electronic spin system with light at the split energy level, an effective vibration magnetic field resonating the energy of the split width, or that in the vicinity of the split width; an electronic spin detector 7 for detecting changes in physical phenomena with the resonance to the energy of or in the vicinity of the split width of the energy level, in which a sample 9 is irradiated with laser light with the beats generated by the effective vibration magnetic field generating light source 6 and changes in the optical characteristics or the electric characteristics of the sample 9 at that time are detected by the electronic spin detector 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electron spin resonance measurement apparatus and an electron spin resonance measurement method, and is particularly suitable for application to a method of causing electron spin resonance by irradiating light having a plurality of frequency components.

In a substance having unpaired electrons, the energy level splits (Zeeman splitting) when a magnetic field is applied, and the phenomenon that the oscillating magnetic field that resonates with the splitting is absorbed is called electron spin resonance (ESR). Are known.
By measuring this electron spin resonance, it is possible to detect the characteristics of a substance with high sensitivity without decomposing the sample. Therefore, it is frequently used for the analysis of various substances such as semiconductors and organic substances in addition to magnetic substances. Has been.

  In order to measure this electron spin resonance, a conventional electron spin resonance measuring apparatus is provided with a cavity resonator for measuring absorption of electromagnetic waves. Then, the sample is placed in this cavity resonator, the static energy is applied to cause Zeeman splitting of the energy level in the sample, and the electromagnetic waves are applied to this sample to resonate unpaired electrons. By measuring the absorbed energy, the property of the substance can be detected with high sensitivity.

That is, when an electromagnetic wave is applied to a sample in which Zeeman splitting has occurred and the unpaired electrons are in a resonance state, the electromagnetic wave is absorbed and the Q value of the cavity resonator changes, so the frequency of the electromagnetic wave applied to the sample Is fixed, and the intensity of the static magnetic field applied to the sample is swept, whereby the magnetic field intensity satisfying the resonance condition can be observed.
Here, the frequency of the electromagnetic wave applied to the sample is generally used in the 10 GHz band (the magnetic field strength is about 0.3 Tesla or less), but in order to obtain higher resolution, W In addition to the band (95 GHz band), higher frequency electromagnetic waves are beginning to be used. Note that when an X-band 9 GHz electromagnetic wave is used, the wavelength is several centimeters.

Further, for example, Non-Patent Document 1 adopts the principle of an atomic force microscope (AFM) to measure electron spin resonance, and determines the amount of bending of the cantilever due to a change in magnetic torque due to electron spin resonance. A method of detecting is disclosed.
http: // www. kobe-u. biz / seeds / ppdoc / rigakubu / bunya2 / oottahissensei / slide0003. htm

  However, in the conventional electron spin resonance measuring apparatus, in order to increase the spatial resolution, when the frequency of the electromagnetic wave applied to the sample is lowered, it is necessary to reduce the size of the cavity resonator, and the sample size is accordingly reduced. As a result, the intensity of the signal obtained at the time of electron spin resonance becomes weak, and there is a problem that it is difficult to analyze physical properties peculiar to a fine structure such as a carbon nanotube or a quantum dot.

In addition, in the conventional electron spin resonance measuring apparatus, there is a problem that in the semiconductor element having the electrode structure on the surface, the electromagnetic wave does not enter the sample due to the skin effect of the electromagnetic wave, so that the analysis inside the sample is difficult.
In addition, the method disclosed in Non-Patent Document 1 has a problem in that it is necessary to apply a strong pulsed magnetic field in order to measure electron spin resonance with high sensitivity, which complicates the configuration of the apparatus. It was.

On the other hand, in the nuclear magnetic resonance used for the analysis of various substances with the same operation principle, the weight of the nucleus is about 2000 times heavier than that of the electron, so that the electromagnetic wave having a relatively low frequency on the order of MHz. Even when using, high-accuracy analysis is possible. Even in electron spin resonance, if the frequency of electromagnetic waves can be increased, more accurate analysis becomes possible. Therefore, there is a method that can measure electron spin resonance without using a cavity resonator that limits the increase in frequency. Development is desired.
Therefore, an object of the present invention is to provide an electron spin resonance measuring apparatus and an electron spin resonance measuring method capable of measuring electron spin resonance without using a cavity resonator.

  In order to solve the above-described problem, according to the electron spin resonance measuring apparatus according to claim 1, the energy level splitting means for splitting the energy level of the electron spin system and irradiating the electron spin system with light. And an effective oscillating magnetic field generating means for generating an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width, and an electron spin detection means for detecting a change in a physical phenomenon accompanying the resonance. It is characterized by.

According to the electron spin resonance measuring apparatus of claim 2, the energy level splitting means is a magnetic field applying means for applying a magnetic field to the electron spin system.
According to the electron spin resonance measuring apparatus of claim 3, the effective oscillating magnetic field generating means is a first light that irradiates the electron spin system with light having at least two frequency components or intensity-modulated light. Irradiation means is provided.

According to the electron spin resonance measuring apparatus of claim 4, the electron spin detection means forms an electron spin system having a higher polarization degree than that of light or thermal equilibrium for measuring the degree of polarization of electron spin. It is characterized by comprising a second light irradiation means for irradiating light for the purpose.
The electron spin resonance measuring apparatus according to claim 5, wherein the electron spin detection means detects light emitted from a sample having the electron spin system or light transmitted or reflected by the sample. It is characterized by providing.

Further, according to the electron spin resonance measuring apparatus of claim 6, the electron spin detecting means includes an electric characteristic measuring means for measuring an electric characteristic reflecting the degree of polarization of the electron spin in the electron spin system. Features.
According to the electron spin resonance measuring method of claim 7, the step of splitting the energy level of the electron spin system by applying a magnetic field to the electron spin system and irradiating the electron spin system with light Thus, the method includes a step of generating an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width, and a step of detecting a change in a physical phenomenon accompanying the resonance.

  According to the electron spin resonance measuring method of claim 8, the step of splitting the energy level of the electron spin system by applying a magnetic field to the electron spin system and the light having at least two frequency components or Irradiating the electron spin system with intensity-modulated light to generate an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width; and light having the at least two frequency components Or a step of detecting light emitted from a sample having the electron spin system or light transmitted or reflected by the sample while irradiating the electron spin system with intensity-modulated light.

  According to the electron spin resonance measurement method of claim 9, the step of splitting the energy level of the electron spin system by applying a magnetic field to the electron spin system and the light having at least two frequency components or Irradiating the electron spin system with intensity-modulated light to generate an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width; and light having the at least two frequency components Or measuring the electrical characteristics reflecting the degree of polarization of electron spin in the electron spin system while irradiating the electron spin system with intensity-modulated light.

  According to the electron spin resonance measuring method of claim 10, when the electron spin system is irradiated with the light having the at least two frequency components or the intensity-modulated light, the degree of polarization of the electron spin is measured. Or light for forming an electron spin system having a higher degree of polarization than that of the light or thermal equilibrium state.

  As described above, according to the present invention, by irradiating the electron spin system with light, an effective oscillating magnetic field that resonates with the energy corresponding to the Zeeman split width is generated, and the optical property change of the sample at that time or By detecting a change in electrical characteristics, electron spin resonance can be measured without providing a cavity resonator. Therefore, by narrowing down the light irradiation area, it is possible to reduce the size of the measurement area, and it is possible to prevent the deterioration of sensitivity associated with the reduction in the size of the cavity resonator, thereby increasing the spatial resolution. On the other hand, since it is possible to measure electron spin resonance with high sensitivity, physical properties peculiar to a fine structure such as a carbon nanotube or a quantum dot can be analyzed with high accuracy.

Hereinafter, an electron spin resonance measuring apparatus according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram conceptually showing a method for generating an effective oscillating magnetic field in photoexcited electron spin resonance of the present invention.
In FIG. 1, the principle of the spin-dependent AC Stark effect can be applied as a method for generating an effective oscillating magnetic field that resonates with the energy level split width of the electron spin system or the energy in the vicinity of the split width. This spin-dependent AC Stark effect is a phenomenon in which the energy level is split according to the direction of the electron spin when the electron spin system is irradiated with a laser beam having a circular polarization state having an energy smaller than the resonance excitation energy. As for the spin-dependent AC Stark effect, for example, “J.A. Gupta, R. Knobel, N. Samart, DD Awscharom,“ Ultrafast Manipulation Electron Spin Coherence ”29 June 2001, 29 VOL29. .

That is, when a laser beam having a circular polarization state having an energy smaller than the resonance excitation energy is irradiated to the energy level 1 of a conduction band electron having an upward spin and a downward spin, the conduction band electron having a downward spin Is split into energy level 2 and conduction level electron energy level 3 having an upward spin.
Here, when laser beams having a plurality of frequency components are superimposed, a beat corresponding to the difference between the frequencies is generated. When the circularly polarized light having the beat with energy smaller than the resonance excitation energy is irradiated to the energy levels 2 and 3 of the conduction band electrons having the upward spin and the downward spin, the energy splitting oscillates at the beat frequency. By doing so, an effective oscillating magnetic field 5 corresponding to the frequency is generated. Then, this effective oscillating magnetic field 5 is used in place of the oscillating magnetic field used in the conventional electron spin resonance, and by detecting the change in the optical characteristic or the electric characteristic of the sample at that time, the electron can be obtained without providing the cavity resonator. Spin resonance can be measured.

  As a result, by narrowing down the light irradiation region, it is possible to reduce the size of the measurement region, and it is possible to prevent deterioration in sensitivity due to the reduction in size of the cavity resonator. For this reason, it is possible to measure electron spin resonance with high sensitivity while increasing spatial resolution, and it is possible to accurately analyze physical properties peculiar to a fine structure such as a carbon nanotube or a quantum dot.

FIG. 2 is a block diagram showing a schematic configuration of the electron spin resonance measuring apparatus according to the first embodiment of the present invention.
In FIG. 2, the electron spin resonance measuring apparatus applies a magnetic field to the electron spin system, thereby splitting the energy level of the electron spin system, the magnetic field generator 8 that splits the energy level of the electron spin system, Is applied to generate an effective oscillating magnetic field generating light source unit 6 that generates an effective oscillating magnetic field that resonates with the split width or the energy in the vicinity of the split width, and the energy level split width or the energy in the vicinity of the split width. An electron spin detector 7 is provided for detecting a change in a physical phenomenon associated with resonance to the.

  Then, the energy level of the electron spin system of the sample 9 is split by applying the magnetic field generated by the magnetic field generator 8 to the sample 9. Then, the effective oscillating magnetic field generating light source unit 6 generates laser light having a plurality of frequency components and superimposes these laser lights to generate a beat corresponding to the difference between the frequencies. The sample 9 is irradiated with a circularly polarized component given to the laser beam. Note that polarization control may be performed before superposing laser beams having a plurality of frequency components. Then, the electron spin detection unit 7 measures electron spin resonance by detecting a change in optical characteristics or a change in electrical characteristics of the sample 9 at that time.

  Here, when the sample 9 is irradiated with a laser beam having a beat having a circularly polarized component, an effective oscillating magnetic field corresponding to the beat frequency is generated in the sample 9 by applying the spin-dependent AC Stark effect. be able to. An electron spin resonance spectrum is obtained by applying a magnetic field to the sample 9 in a direction crossing the effective direction of the oscillating magnetic field and sweeping the beat frequency of the laser beam or the strength of the magnetic field applied to the sample 9. Can do.

The effective oscillating magnetic field generating light source unit 6 can be provided with a light irradiating means for irradiating the sample 9 with light having at least two frequency components or intensity-modulated light.
Further, the electron spin detector 7 may be provided with a light detecting means for detecting light emitted from the sample 9 or light transmitted or reflected through the sample 9, and the degree of polarization of electron spin in the sample 9 is determined. You may make it provide the electrical property measurement means which measures the reflected electrical property. The electron spin detector 7 is provided with light irradiation means for irradiating light for measuring the degree of polarization of electron spin in the sample 9 or light for forming an electron spin system having a higher degree of polarization than the thermal equilibrium state. You may make it provide.

  This method eliminates the need to use microwave electromagnetic waves to cause electron spin resonance, eliminating the need for cavity resonators and microwave circuits, and effectively oscillating magnetic fields only in the light irradiation region. Can be generated in the sample 9. For this reason, it is possible to measure electron spin resonance with high sensitivity while increasing spatial resolution, and it is possible to accurately analyze physical properties peculiar to a fine structure such as a carbon nanotube or a quantum dot. In particular, by using a high-sensitivity photodetector as the electron spin detector 7, single spin electron spin resonance can also be detected, and can be applied to analysis of various substances and nanostructures.

  In addition, by using light to generate an effective oscillating magnetic field, it is not necessary to use microwave band electromagnetic waves or cavity resonators, so that the frequency matching characteristics and the skin effect due to the electrode metal on the surface of the sample 9 can be reduced. The influence can be eliminated, and even when an electrode is formed on the surface like a semiconductor element, the electron spin resonance can be detected as it is.

  Furthermore, by sweeping the frequency of light that generates an effective oscillating magnetic field, the frequency of the effective oscillating magnetic field can be controlled, eliminating the need to sweep the magnetic field intensity, simplifying the device configuration In addition, by sweeping the frequency difference of light, the resonance frequency can be increased to the terahertz region, and a complicated substance system with slightly different g factors can be accurately identified.

FIG. 3 is a diagram showing a configuration example of an effective oscillating magnetic field generating light source unit used in the electron spin resonance measuring apparatus of FIG.
In FIG. 3A, the effective oscillating magnetic field generation light source unit 6 includes single frequency light sources 10 and 11 that generate laser beams of frequencies f1 and f2, respectively, and a polarization control element 12a that controls a circularly polarized component of the laser beams. Can be provided.
Then, after the laser beams of the frequencies f1 and f2 emitted from the single frequency light sources 10 and 11 are superimposed, the laser light is incident on the polarization control element 12a, and a circularly polarized light component is given by the polarization control element 12a. By entering the sample 9 in FIG. 2, an effective oscillating magnetic field corresponding to the difference between the frequencies f1 and f2 can be generated.

Alternatively, in FIG. 3B, the effective oscillating magnetic field generating light source unit 6 includes a single frequency light source 13 that generates laser light having a frequency f, an optical frequency shifter 14 that shifts the frequency f of the laser light by Δf, and laser light. It is possible to provide a polarization control element 12a for controlling the circularly polarized light component.
Then, the laser beam having the frequency f emitted from the single frequency light source 13 enters the optical frequency shifter 14, is shifted by the frequency Δf by the optical frequency shifter 14, and then enters the polarization control element 12a. Then, after the laser light having the frequency f and the laser light having the frequency f−Δf shifted by the frequency Δf by the polarization control element 12a are superimposed, the light is incident on the polarization control element 12a and circularly polarized by the polarization control element 12a. An effective oscillating magnetic field corresponding to the frequency Δf can be generated by entering the sample 9 shown in FIG.

Alternatively, in FIG. 3C, the effective oscillating magnetic field generating light source unit 6 includes a single frequency light source 13 that generates laser light having a frequency f, a light modulator 15 that modulates laser light, and a circularly polarized component of the laser light. A polarization control element 12a to be controlled can be provided.
The laser light having the frequency f emitted from the single frequency light source 13 enters the light modulation element 15, is modulated by the light modulation element 15, and then enters the polarization control element 12 a. Then, the laser beam having the frequency f modulated by the light modulation element 15 enters the polarization control element 12a, is given a circularly polarized component by the polarization control element 12a, and then enters the sample 9 in FIG. Thus, an effective oscillating magnetic field corresponding to the modulation frequency can be generated.

Alternatively, in FIG. 3D, the effective oscillating magnetic field generating light source unit 6 is provided with a two-frequency mode light source 16 that generates laser light of two frequencies and a polarization control element 12a that controls the circularly polarized component of the laser light. Can do.
The two-frequency laser light emitted from the dual-frequency mode light source 16 enters the polarization control element 12a, is given a circularly polarized light component by the polarization control element 12a, and then enters the sample 9 in FIG. Thus, an effective oscillating magnetic field corresponding to the frequency difference of the laser light can be generated.

FIG. 4 is a diagram illustrating a configuration example of an electron spin detection unit used in the electron spin resonance measuring apparatus of FIG.
In FIG. 4A, the electron spin detector 7 can be provided with a photodetector 18 for detecting the light emission 17 generated from the sample 9 due to electron spin resonance. Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 in FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and the sample 9 Electron spin resonance can be measured by detecting the light emission 17 generated from the light by the photodetector 18.

As the effective oscillating magnetic field generation light source unit 6 combined with the electron spin detection unit 7 of FIG. 4A, any configuration of FIG. 3A to FIG. 3D may be used.
Alternatively, in FIG. 4B, the electron spin detector 7 includes an excitation light source 19 for forming an electron spin system having a higher degree of polarization than the thermal equilibrium state on the sample 9 and the sample 9 along with electron spin resonance. A light detector 18 for detecting the generated light emission 17 can be provided.

  Then, by irradiating the sample 9 with excitation light emitted from the excitation light source 19, electron / hole pairs contributing to the light emission 17 are generated in the sample 9, and the electron spin system has a higher degree of polarization than the thermal equilibrium state. Is formed on the sample 9. Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 in FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and the sample 9 Electron spin resonance can be measured by detecting the light emission 17 generated from the light by the photodetector 18.

As the effective oscillating magnetic field generating light source unit 6 combined with the electron spin detecting unit 7 of FIG. 4B, any configuration of FIG. 3A to FIG. 3D may be used.
Alternatively, in FIG. 4C, the electron spin detector 7 includes a probe light source 20 that generates probe light for measuring the degree of polarization of electron spin, a polarization control element 12b that controls the circularly polarized component of the laser light, and A polarimeter 21 for measuring the Faraday rotation angle of the probe light transmitted through the sample 9 can be provided.

  Then, the probe light emitted from the probe light source 20 is incident on the polarization control element 12b, the polarization is controlled by the polarization control element 12b, and the sample 9 is irradiated. Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 in FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and the sample 9 Electron spin resonance can be measured by measuring the Faraday rotation angle of the probe light that has passed through the measuring device 21.

In addition, as the effective oscillating magnetic field generation light source unit 6 combined with the electron spin detection unit 7 of FIG. 4C, any configuration of FIG. 3A to FIG. 3D may be used.
4D, the electron spin detector 7 includes a probe light source 20 that generates probe light for measuring the degree of polarization of electron spin, a polarization control element 12b that controls the circularly polarized component of the laser light, and A polarimeter 21 for measuring the Kerr rotation angle of the probe light reflected by the sample 9 can be provided.

  Then, the probe light emitted from the probe light source 20 is incident on the polarization control element 12b, the polarization is controlled by the polarization control element 12b, and the sample 9 is irradiated. Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 in FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and the sample 9 Electron spin resonance can be measured by measuring the Faraday rotation angle of the probe light reflected at 1 with the measuring device 21.

In addition, as the effective oscillating magnetic field generation light source unit 6 combined with the electron spin detection unit 7 of FIG. 4D, any configuration of FIG. 3A to FIG. 3D may be used.
Alternatively, in FIG. 4E, the electron spin detection unit 7 includes an excitation light source 19 for forming an electron spin system having a higher degree of polarization than the thermal equilibrium state on the sample 9, and an electric for measuring the electrical characteristics of the sample 9. An electric signal line 23 connecting the characteristic measuring instrument 22 and the sample 9 and the electric characteristic measuring instrument 22 can be provided.

  Then, by irradiating the sample 9 with excitation light emitted from the excitation light source 19, electron / hole pairs are generated in the sample 9, and an electron spin system having a higher degree of polarization than the thermal equilibrium state is formed in the sample 9. To do. Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 of FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and at that time Electron spin resonance can be measured by measuring the electrical properties of the sample 9 with the electrical property measuring instrument 22.

In addition, as the effective oscillating magnetic field generation light source unit 6 combined with the electron spin detection unit 7 of FIG. 4 (e), any configuration of FIG. 3 (a) to FIG. 3 (d) may be used.
Alternatively, in FIG. 4 (f), the electron spin detector 7 is provided with an electric characteristic measuring device 22 that measures the electric characteristics of the sample 9 and an electric signal line 23 that connects the sample 9 and the electric characteristic measuring device 22. Can do.

Then, by irradiating the sample 9 with the light generated by the effective oscillating magnetic field generating light source unit 6 of FIG. 2, an effective oscillating magnetic field corresponding to the beat frequency of the light is generated in the sample 9, and at that time Electron spin resonance can be measured by measuring the electrical properties of the sample 9 with the electrical property measuring instrument 22.
In addition, as the effective oscillating magnetic field generation light source unit 6 combined with the electron spin detection unit 7 of FIG. 4 (f), any configuration of FIG. 3 (a) to FIG. 3 (d) may be used.

FIG. 5 is a diagram showing a schematic configuration of an electron spin resonance measuring apparatus according to the second embodiment of the present invention.
In the embodiment of FIG. 5, the single-frequency light source 13, the frequency shifter 14, and the polarization control element 12 a of FIG. 3B are provided as the effective oscillating magnetic field generating light source unit 6 of FIG. 2, A configuration in which the probe light source 20 and the polarization measuring device 21 of FIG. Also, a GaAs / AlGaAs multiple quantum well structure 34 is used as the sample 9 in FIG. 2, and a normal conducting magnet 32 is used as the magnetic field generator 8 in FIG.

  That is, in FIG. 5, a titanium sapphire ring laser 24 is provided as the single frequency light source 13 in FIG. 3B, an acoustic modulation element 25 is provided as the frequency shifter 14, and a quarter wavelength plate 28 is provided as the polarization control element 12a. The frequency line width of the titanium sapphire ring laser 24 used as the single frequency light source 13 can be 100 kHz or less. The photon energy can be 1.651 eV, which is lower than the vicinity of the absorption edge of the exciton.

  Further, a titanium sapphire laser 29 is provided as the probe light source 20 in FIG. 4C, and a polarization beam spirit 30 and an optical balance detector 31 are provided as the polarization measuring device 21. The probe light emitted from the titanium sapphire laser 29 is not intended to generate carriers but to observe the magneto-optical effect caused by electron spin polarization. Also, the photon energy of the probe light can be adjusted to 1.680 eV in the vicinity of the absorption edge of the exciton of the quantum well, and the polarization can be linearly polarized.

  Sample 9 can be grown by molecular beam epitaxy, and a GaAs quantum well layer having a thickness of 3 nm and an AlGaAs barrier layer having a thickness of 15 nm can be stacked on the GaAs substrate for 100 periods. After the growth, the GaAs substrate can be removed by a selective etching method in order to prevent the probe light emitted from the titanium sapphire laser 29 from being absorbed by the sample 9.

  Then, the sample 9 is cooled to 4.2 K in a cryostat 33 with an optical window, and is arranged so that the sample surface is inclined with respect to the direction of the magnetic field generated by the normal conducting magnet 32. Here, by tilting the sample surface with respect to the direction of the magnetic field generated by the normal magnet 32, the spin quantization axis by the magnetic field can be made different from the spin axis that can be excited by circularly polarized light. The polarization state of electron spin can be observed by the magneto-optic effect.

  Then, by applying a magnetic field generated by the normal magnet 32 to the sample 9, the energy level of the electron spin system of the sample 9 is split. Then, a laser beam having a frequency f is emitted from the titanium sapphire ring laser 24 while irradiating the sample 9 with the probe light emitted from the titanium sapphire laser 29. The laser beam having the frequency f emitted from the titanium sapphire ring laser 24 is incident on the acoustic modulation element 25, and the first-order diffracted light diffracted by the acoustic modulation element 25 is shifted by 1.7 GHz in frequency Δf. Reflected by the mirror 26 and enters the beam spiriter 27. Then, the laser light having the frequency f that has passed through the acoustic modulation element 25 and the laser light having the frequency f−Δf diffracted by the acoustic modulation element 25 are superimposed on each other by the beam spiriter 27, so that the frequency Δf = 1. Light with a beat corresponding to .7 GHz is generated. Then, light having a beat corresponding to the frequency Δf = 1.7 GHz is incident on the quarter-wave plate 28 and converted into circularly polarized light by the quarter-wave plate 28, and then overlaps with the irradiation region of the probe light. Is incident on the sample 9.

Then, light having a beat corresponding to the frequency Δf = 1.7 GHz is incident on the sample 9, so that an effective oscillating magnetic field corresponding to the frequency Δf = 1.7 GHz can be generated. When an effective oscillating magnetic field corresponding to the frequency Δf = 1.7 GHz is generated in the sample 9, the polarization rate of the electron spin changes, and the Faraday rotation angle of the probe light transmitted through the sample 9 changes. Then, the probe light transmitted through the sample 9 is demultiplexed by the polarization beam splitter 30, and the Faraday rotation angle is measured by the optical balance detector 31, whereby the electron spin resonance can be measured.
Here, the Faraday rotation angle indicates the relative angle of the linear polarization axis after passing through the sample 9 with respect to the linear polarization axis before passing through the sample 9, and the magnitude thereof is the polarization rate of the electron spin in the thermal equilibrium state. Is proportional to

In the embodiment of FIG. 5, the configuration of FIG. 4C is applied to the electron spin detector 7 of FIG. 2, and the electron spin resonance is measured by utilizing the Faraday effect using the transmitted light of the probe light. The electron spin resonance is measured by applying the configuration of FIG. 4D to the electron spin detection unit 7 of FIG. 2 and utilizing the Kerr effect using the reflected light of the probe light. It may be.
In addition, in order to improve the S / N ratio of the measurement data, the light that generates an effective oscillating magnetic field and the probe light are modulated with different light intensities, and the Faraday rotation angle is measured by heterodyne detection. You may do it.

FIG. 6 is a diagram illustrating an example of an observation result of an electron spin resonance spectrum by the electron spin resonance measuring apparatus of FIG.
In FIG. 6, when the Faraday rotation angle of the probe light is measured while sweeping the magnetic field generated by the normal conducting magnet 32, when the magnetic field strength is 0.27 T, the polarization rate of the electron spin decreases. A change in the Faraday rotation angle was observed. The peak of the change amount Δθ _F of the Faraday rotation angle coincided with the resonance condition of ESR calculated from the electron g factor value of the sample 9 = 0.45.

FIG. 7 is a diagram showing a schematic configuration of an electron spin resonance measuring apparatus according to the third embodiment of the present invention.
In the embodiment shown in FIG. 7, the single-frequency light sources 10 and 11 and the polarization control element 12a shown in FIG. 3A are provided as the effective oscillating magnetic field generating light source unit 6 shown in FIG. 2, and the electron spin shown in FIG. A configuration in which the excitation light source 19 and the photodetector 18 of FIG. In addition, an InAs quantum dot structure 42 is used as the sample 9 in FIG. 2, and a superconducting magnet 43 is used as the magnetic field generator 8 in FIG.

  That is, in FIG. 7, the wavelength variable semiconductor lasers 35 and 36 with external resonators are provided as the single frequency light sources 10 and 11 in FIG. The frequency line widths of the wavelength-tunable semiconductor lasers 35 and 36 with external resonators used as the single frequency light sources 10 and 11 can be 300 kHz or less. In addition, the photon energy of the wavelength tunable semiconductor laser 35 with an external resonator can be set to 1.319 eV (wavelength 940 nm), which is lower than the absorption energy of negatively charged excitons. Further, the photon energy of the wavelength tunable semiconductor laser 36 with the external resonator can be varied in the range of 200 GHz from the photon energy of the wavelength tunable semiconductor laser 35 with the external resonator.

  Also, an argon ion laser 37 is provided as the excitation light source 19 in FIG. 4B, and a spectroscope 40 and a CCD detector 41 are provided as the photodetector 18. The excitation light emitted from the argon ion laser 37 is intended to generate electron-hole pairs that contribute to light emission from the sample 9, and its photon energy is larger than the absorption edge energy of the quantum dots. It can be 2.54 eV.

  Sample 9 can be produced by metal organic vapor phase epitaxy, and a quantum dot made of InAs can be embedded in a quantum well made of InGaAs / GaAs having a thickness of 5 nm. After the quantum dots are formed, a 200 nm square mesa structure can be formed by electron beam lithography and dry etching. Here, by forming the mesa structure, the number of quantum dots existing in the mesa can be limited to several, and by analyzing the light emitted when the sample 9 is irradiated with light, Only light emitted from one quantum dot can be identified.

  Then, the sample 9 is cooled to 4.2 K in a cryostat 33 with an optical window, and a 10 T magnetic field generated by the superconducting magnet 43 is applied to the sample 9, whereby the electron spin system energy level of the sample 9 is applied. Divide the rank. Then, the excitation light emitted from the argon ion laser 37 is condensed by the objective lens 38 and the excitation light is irradiated onto one mesa structure of the sample 9. When the excitation light emitted from the argon ion laser 37 is irradiated onto one mesa structure of the sample 9, photoluminescence 39 from a single quantum dot is generated, and the photoluminescence 39 passes through the spectroscope 40. By entering the CCD detector 41, the spectrum of the photoluminescence 39 is measured.

  Here, while irradiating the sample 9 with the excitation light emitted from the argon ion laser 37, the laser light having the frequencies f1 and f2 are emitted from the wavelength tunable semiconductor lasers 35 and 36 with external resonators, respectively. Then, the laser beam having the frequency f 1 emitted from the wavelength tunable semiconductor laser 35 with the external resonator is reflected by the mirror 26 and enters the beam spiriter 27. Then, the laser light having the frequency f 1 emitted from the wavelength tunable semiconductor laser 35 with the external resonator and the laser light having the frequency f 2 emitted from the wavelength tunable semiconductor laser 36 with the external resonator are superimposed by the beam spiriter 27. Thus, light having a beat corresponding to the difference between the frequencies f1 and f2 is generated. Light having a beat corresponding to the difference between the frequencies f1 and f2 is incident on the quarter-wave plate 28, converted into circularly polarized light by the quarter-wave plate 28, and then incident on the objective lens 38. By being condensed by the lens 38, it is incident on the sample 9 so as to overlap the irradiation region of the excitation light.

  Then, when light having a beat corresponding to the difference between the frequencies f1 and f2 enters the sample 9, an effective oscillating magnetic field corresponding to the difference between the frequencies f1 and f2 can be generated. When an effective oscillating magnetic field corresponding to the difference between the frequencies f1 and f2 is generated in the sample 9, the spectrum of the photoluminescence 39 changes. The change in the spectrum of the photoluminescence 39 is detected by the CCD detector 41, whereby the electron spin resonance can be measured.

  Here, the Zeeman splitting of electron spin can be read from the peak splitting from negatively charged excitons. Negatively charged excitons are composed of two electrons and one hole, and it is known that Zeeman splitting is almost zero. The state in which this negatively charged exciton ejects only one photon becomes one electron with Zeeman splitting, and information on electron spin is reflected in light emission at that time. The magnitude of the Zeeman splitting at 10T calculated from the value of g factor of electrons in the quantum dots in Sample 9 = 1.1 is 0.637 meV. The state of spin polarization in a thermal equilibrium state can be observed in the form of a strong peak on the high energy side among the peaks of split charged excitons.

  In the embodiment of FIG. 7, the configuration of FIG. 4B is applied to the electron spin detection unit 7 of FIG. 2, and the sample 9 is irradiated with excitation light emitted from the excitation light source 19. The method of generating electron / hole pairs contributing to the emission of light has been described. However, when sufficient electron / hole pairs are generated by two-photon absorption or the like, the electron spin detection unit 7 of FIG. The configuration of (a) may be applied, and electron spin resonance may be measured without irradiating the sample 9 with excitation light.

FIG. 8 is a diagram showing an example of the observation result of the photoluminescence spectrum by the electron spin resonance measuring apparatus of FIG.
In FIG. 8, it can be seen that the spectrum of the photoluminescence 39 is different between the non-resonant state (beat frequency Δf = 153.90 GHz) and the resonance state (beat frequency Δf = 153.96 GHz). That is, it was observed that when the ESR resonance condition was satisfied, the two Zeeman split peak intensities changed in a direction approaching the same value.

FIG. 9 is a diagram showing a schematic configuration of an electron spin resonance measuring apparatus according to the fourth embodiment of the present invention.
In the embodiment of FIG. 9, the single-frequency light source 13, the light modulation element 15 and the polarization control element 12a of FIG. 3C are provided as the effective oscillating magnetic field generating light source unit 6 of FIG. 4 shows a configuration in which the excitation light source 19, the electrical property measuring instrument 22, and the electrical signal line 23 shown in FIG. Further, as the sample 9 in FIG. 2, an ni Schottky diode structure 48 in which GaAs / AlGaAs quantum dots are embedded, and a superconducting magnet 43 is used as the magnetic field generator 8 in FIG.

  That is, in FIG. 9, a titanium sapphire ring laser 24 is provided as the single frequency light source 13 in FIG. 3C, an EO modulator 44 is provided as the light modulation element 15, and a liquid crystal retarder 45 is provided as the polarization control element 12a. The frequency line width of the titanium sapphire ring laser 24 used as the single frequency light source 13 can be 100 kHz or less. The photon energy can be 1.648 eV (wavelength 752.4 nm) lower than the absorption energy of the negatively charged excitons.

Further, a titanium sapphire laser 29 is provided as the excitation light source 19 in FIG. 4E, and a DC voltage source 46 and a minute current measuring device 47 are provided as the electrical characteristic measuring device 22.
The purpose of the excitation light emitted from the titanium sapphire laser 29 is to generate electron-hole pairs that contribute to the light absorption of the sample 9 and the accompanying photocurrent.

  The sample 9 is grown by molecular beam epitaxy, and quantum dots are formed by introducing monoatomic layer fluctuations at the interface of a quantum well made of GaAs / AlGaAs having a quantum width of 3 nm. The quantum dots are arranged inside an AlGaAs-based ni Schottky diode fabricated on an n-type GaAs substrate. Further, a Ti / Au Schottky electrode with a thickness of 100 nm having a pinhole with a diameter of 250 nm is formed on the surface of the sample 9. Here, by forming a pinhole, it is possible to irradiate only a single quantum dot under the pinhole when light is incident on the sample 9, and only light absorption of the single quantum dot is possible. Can be measured as photocurrent.

Then, the sample 9 is cooled to 4.2 K in a cryostat 33 with an optical window, and the magnetic level generated by the superconducting magnet 43 is applied to the sample 9, so that the energy level of the electron spin system of the sample 9 is changed. Split. Further, the bias of the element is adjusted by the DC voltage source 46 so that the photocurrent flows with the generation of the negatively charged excitons in the sample 9.
Then, the excitation light emitted from the titanium sapphire laser 29 is condensed by the objective lens 38, and the excitation light is irradiated to the quantum dots under the pinhole of the sample 9. When the excitation light emitted from the titanium sapphire laser 29 is applied to the quantum dots below the pinhole of the sample 9, a photocurrent flows with the generation of negatively charged excitons in the sample 9, and the photocurrent Is measured by the minute current measuring device 47, whereby the excitation spectrum is measured.

Here, the laser light is emitted from the titanium sapphire ring laser 24 while irradiating the sample 9 with the excitation light emitted from the titanium sapphire laser 29. The laser light emitted from the titanium sapphire ring laser 24 enters the EO modulator 44 and is intensity-modulated at 20 GHz by the EO modulator 44.
Then, the laser light intensity-modulated at 20 GHz is incident on the liquid crystal retarder 45, converted into circularly polarized light by the liquid crystal retarder 45, then incident on the objective lens 38, and condensed by the objective lens 38. It enters the sample 9 so as to overlap with the irradiation region of the excitation light.

  Then, an effective oscillating magnetic field corresponding to the modulation frequency can be generated when the laser light whose intensity is modulated at 20 GHz is incident on the sample 9. When an effective oscillating magnetic field corresponding to the modulation frequency is generated in the sample 9, the photocurrent flowing through the sample 9 changes. Electron spin resonance can be measured by measuring the change in the excitation spectrum accompanying the change in the photocurrent with the minute current measuring device 47.

  Here, it is possible to observe Zeeman splitting of a single electron spin in a magnetic field by acquiring an excitation spectrum by photocurrent measurement in the energy region near the resonance excitation of the ground state of a negatively charged exciton. . The state of spin polarization in a thermal equilibrium state can be observed in the form of a strong peak on the high energy side among the peaks of split charged excitons.

  In the embodiment of FIG. 9, the configuration of FIG. 4E is applied to the electron spin detection unit 7 of FIG. 2, and the sample 9 is irradiated with the excitation light emitted from the excitation light source 19 to Although the method for generating electron-hole pairs has been described, the configuration shown in FIG. 4F is applied to the electron spin detection unit 7 in FIG. Electron spin resonance may be measured without irradiating the sample 9.

FIG. 10 is a diagram illustrating an example of an observation result of an electron spin resonance spectrum by the electron spin resonance measuring apparatus of FIG.
In FIG. 10, when two photocurrent peaks having Zeeman splitting are detected and plotted while sweeping the magnetic field applied to the sample 9, the ESR resonance condition is satisfied at 6.804T, and two Zeeman splitting two peaks are obtained. It was observed that the peak intensity changed toward the same value.
In the above-described embodiment, an example in which the light path from the light source to the sample is a free space is shown, but an optical fiber may be used for the light path from the light source to the sample. In order to obtain a high spatial resolution below the wavelength of light, a scanning near-field optical microscope (SNOM) technique may be adopted.

  The electron spin resonance measuring apparatus of the present invention can be widely used in fields such as chemistry and biology as one of the analysis apparatuses for substances such as materials. The ability to identify a substance can be increased, and the high sensitivity and high spatial resolution make it possible to detect a single spin in a minute region. be able to.

It is a figure which shows notionally the generation method of the effective oscillating magnetic field in the photoexcitation electron spin resonance of this invention. 1 is a block diagram showing a schematic configuration of an electron spin resonance measuring apparatus according to a first embodiment of the present invention. It is a figure which shows the structural example of the effective vibration magnetic field generation light source part used for the electron spin resonance measuring apparatus of FIG. It is a figure which shows the structural example of the electron spin detection part used for the electron spin resonance measuring apparatus of FIG. It is a figure which shows schematic structure of the electron spin resonance measuring apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows an example of the observation result of the electron spin resonance spectrum by the electron spin resonance measuring apparatus of FIG. It is a figure which shows schematic structure of the electron spin resonance measuring apparatus which concerns on 3rd Embodiment of this invention. It is a figure which shows an example of the observation result of the photoluminescence spectrum by the electron spin resonance measuring apparatus of FIG. It is a figure which shows schematic structure of the electron spin resonance measuring apparatus which concerns on 4th Embodiment of this invention. It is a figure which shows an example of the observation result of the electron spin resonance spectrum by the electron spin resonance measuring apparatus of FIG.

Explanation of symbols

1, 2, 3 energy level 4 beat laser beam 5 effective oscillating magnetic field 6 effective oscillating magnetic field generating light source unit 7 electron spin detecting unit 8 magnetic field generating unit 9 sample 10, 11, 13 single frequency light source 12 a, 12 b Polarization control element 14 Optical frequency shifter 15 Optical modulation element 16 Dual frequency mode light source 17 Light emission 18 Photo detector 19 Excitation light source 20 Probe light source 21 Polarization measuring instrument 22 Electrical property measuring instrument 23 Electric signal line 24 Titanium sapphire ring laser 25 Acoustic modulation element 26 Mirror 27 Beam Splitter 28 1/4 Wave Plate 29 Titanium Sapphire Laser 30 Polarized Beam Splitter 31 Optical Balance Detector 32 Normal Conductive Magnet 33 Cryostat 34 GaAs / AlGaAs Multiple Quantum Well Structure 35, 36 Wavelength Tunable Semiconductor Laser 37 Argonio Laser 38 objective lens 39 photoluminescence 40 spectrograph 41 CCD detector 42 InAs quantum dot structure 43 superconducting magnet 44 EO modulator 45 liquid crystal retarder 46 DC voltage source 47 micro current meter 48 n-i Schottky diode structure

Claims (10)

Energy level splitting means to split the energy level of the electron spin system,
By irradiating the electron spin system with light, an effective oscillating magnetic field generating means for generating an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width;
An electron spin resonance measuring apparatus comprising: an electron spin detection means for detecting a change in a physical phenomenon accompanying the resonance.   2. The electron spin resonance measuring apparatus according to claim 1, wherein the energy level splitting means is a magnetic field applying means for applying a magnetic field to the electron spin system.   The said effective oscillating magnetic field generation | occurrence | production means is provided with the 1st light irradiation means to irradiate the said electron spin system with the light which has at least two frequency components, or the intensity | strength modulation | alteration light, The Claim 1 or 2 characterized by the above-mentioned. Electron spin resonance measuring device.   The electron spin detecting means includes second light irradiating means for irradiating light for measuring the degree of polarization of electron spin or light for forming an electron spin system having a higher degree of polarization than a thermal equilibrium state. The electron spin resonance measuring apparatus according to any one of claims 1 to 3, wherein   5. The electron spin detection unit according to claim 1, further comprising a light detection unit configured to detect light emitted from a sample having the electron spin system or light transmitted through or reflected from the sample. The electron spin resonance measuring apparatus according to item.   6. The electron according to claim 1, wherein the electron spin detection unit includes an electric characteristic measurement unit that measures an electric characteristic that reflects a degree of polarization of an electron spin in the electron spin system. Spin resonance measuring device. Splitting the energy levels of the electron spin system by applying a magnetic field to the electron spin system;
Irradiating the electron spin system with light to generate an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width;
And a method of detecting a change in a physical phenomenon accompanying the resonance. Splitting the energy levels of the electron spin system by applying a magnetic field to the electron spin system;
Irradiating the electron spin system with light having at least two frequency components or intensity-modulated light, thereby generating an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width;
Detecting the light emitted from the sample having the electron spin system or the light transmitted through or reflected by the sample while irradiating the electron spin system with the light having the at least two frequency components or the intensity-modulated light. An electron spin resonance measurement method comprising: Splitting the energy levels of the electron spin system by applying a magnetic field to the electron spin system;
Irradiating the electron spin system with light having at least two frequency components or intensity-modulated light, thereby generating an effective oscillating magnetic field that resonates with the split width or energy in the vicinity of the split width;
Measuring electrical characteristics reflecting the degree of polarization of electron spin in the electron spin system while irradiating the electron spin system with light having at least two frequency components or intensity-modulated light. A method for measuring electron spin resonance.   When irradiating the electron spin system with light having at least two frequency components or intensity-modulated light, an electron spin system having a polarization higher than that of light or a thermal equilibrium state is used for measuring the degree of polarization of the electron spin. 10. The electron spin resonance measuring method according to claim 7, wherein the light for forming is irradiated simultaneously.

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