JP3442629B2 - Probe for optical near-field excited spin-polarized scanning tunneling microscope - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spin polarization probe used in a spin polarization scanning tunneling microscope (spin polarization STM).

[0002]

2. Description of the Related Art Recently, a fine semiconductor spin-polarized STM probe chip has been widely used because it can realize high resolution.

[0003]

However, the fine semiconductor spin-polarized STM probe chip capable of realizing high resolution is effective for efficient optical pumping by a method of propagating optical excitation that spin-polarizes an ordinary flat plate semiconductor sample. It was difficult to do. The present invention eliminates the above-mentioned problems, and provides an optical near-field excitation spin polarization scanning tunneling microscope probe capable of highly efficient spin polarization by optical pumping by excitation using polarization of the optical near field. With the goal.

[0004]

In order to achieve the above object, the present invention provides [1] a probe for an optical near-field excited spin polarized scanning tunneling microscope, in which two orthogonal evanescent waves are superposed, 1 optical near field with single polarization (circular polarization)
A high-efficiency optical pumping is provided by the pumping means, which is provided with a pumping means for generating stripes having a width of about / 4 wavelength, and a conical semiconductor probe whose symmetry axis is built to match the polarization axis of the optical near field. The electron spin polarization of is made possible.

[2] The optical near-field excitation spin polarization scanning tunneling microscope probe described in [1] above is provided with a phase modulation element for phase modulating one of the excitation lights emitted from one laser source, and The polarization of the optical near field that excites the conical semiconductor probe is modulated, and the electron spin polarization is modulated. In general, due to the property of the optical near field, the polarization direction of the evanescent wave is determined by the rotational symmetry of the related system, and is perpendicular to the light propagation direction for the flat waveguide. In the present invention, by superimposing two orthogonal evanescent waves, an optical near field having a single polarization (circular polarization) is generated in a striped pattern having a width of about 1/4 wavelength as shown in FIG. , Excite the semiconductor probe. The conical semiconductor probe has its symmetry axis built in alignment with the polarization axis of the optical near-field, and can achieve highly efficient spin polarization by optical pumping.

Further, one of the excitation lights emitted from one laser is phase-modulated to modulate the polarization of the optical near field that excites the probe, thereby modulating the electron spin polarization. Since it can be performed at high speed and easily, the sensitivity of spin polarized STM measurement can be significantly improved by using a method such as phase sensitive detection of tunnel current.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view of an essential part of a probe for optical near-field excitation spin polarization scanning tunneling microscope showing an embodiment of the present invention. In general, due to the property of the optical near field, the polarization direction of the evanescent wave is determined by the rotational symmetry of the related system, and is perpendicular to the light propagation direction for the flat waveguide.

As shown in this figure, a spin-polarized STM probe having a fine semiconductor probe such as GaAs, which is a compound semiconductor, is spin-polarized on the semiconductor substrate 1 in order to spin-polarize the probe by optical pumping. A processed conical semiconductor probe 2 is provided, and a thin film optical waveguide 3 whose normal direction is the symmetric axis direction of the conical semiconductor probe 2 is provided. Therefore, a linearly polarized laser beam emitted from a single laser source (not shown) and split into two by a beam splitter,
Adjust the incident direction using optical elements such as mirrors and prisms,
Through the respective independent prism couplers 5 and the like, TE polarized light (s-polarized light) 4 having incidence planes orthogonal to each other is incident on the thin film optical waveguide 3, and an evanescent wave 6 generated by total reflection is generated on the surface of the thin film optical waveguide 3.

Further, the frequency of the laser light is tuned to the transition frequency between electronic states at the tip of the probe in order to use it as the excitation light of the micro semiconductor probe, and the spin-orbit interaction and radiative decay of the electron system are used. Electron spin polarization is performed by the optical pumping performed. At this time, the phase of the two orthogonal evanescent waves 6 propagating in parallel to the surface is adjusted, and by the combined wave, the light which is single polarized (circularly polarized) in the conical semiconductor probe 2 portion in the symmetry axis direction. By generating a near field,
The conical semiconductor probe 2 is optically pumped, and the electron spin of the conical semiconductor probe 2 is polarized with high efficiency.

Further, by modulating the phase of the incident light with an electro-optical element, it is possible to control and modulate the electron spin polarization at the tip of the conical semiconductor probe 2 at high speed. FIG. 2 is a schematic plan view of an optical near-field excitation spin polarization scanning tunneling microscope probe showing an embodiment of the present invention. In the present invention, two orthogonal evanescent waves are superposed to generate an optical near field having a single polarization (circular polarization) in a striped pattern having a width of about 1/4 wavelength, as shown in FIG. , The conical semiconductor probe 2 is excited. The symmetry axis of the conical semiconductor probe 2 is made so as to match the polarization axis of the optical near field, and spin polarization can be performed with high efficiency by optical pumping.

Further, an optical element arrangement or an electro-optical phase modulator 11 for generating an optical path length difference of one of the two excitation lights emitted from one laser source (not shown) is used. Then, phase modulation is performed within a range of an equivalent optical path length difference of about 1/2 wavelength, and the spatial position of polarization generated in stripes is shifted (see FIG. 2), and optical proximity that excites the conical semiconductor probe 2 is obtained. Since the electron spin polarization can be modulated at high speed and easily by modulating the polarization of the field, a method such as phase sensitive detection of tunnel current is also used to improve the sensitivity of spin polarization STM measurement. It can be greatly improved.

As described above, according to the present invention, it is possible to realize an optically pumped spin polarized micro semiconductor probe which can be used as a scanning probe for spin polarized STM.
At the same time, by enabling polarization modulation, the spin polarization S
The sensitivity of TM measurement can be improved. The present invention is not limited to the above-mentioned embodiments, and various modifications can be made based on the spirit of the present invention, and these modifications are not excluded from the scope of the present invention.

[0013]

As described in detail above, according to the present invention, the following effects can be achieved. (1) According to the first aspect of the present invention, excitation utilizing the polarization of the optical near field enables highly efficient spin polarization by optical pumping.

(2) According to the second aspect of the invention, it is possible to improve the sensitivity of the spin polarization STM measurement by enabling polarization modulation.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an essential part of an optical near-field excited spin polarization scanning tunneling microscope probe showing an embodiment of the present invention.

FIG. 2 is a schematic plan view of a probe for optical near-field excitation spin polarized scanning tunneling microscope showing an embodiment of the present invention.

[Explanation of symbols]

1 Semiconductor substrate 2 Conical semiconductor probe 3 Thin film optical waveguide 4 TE polarized light (s polarized light) 5 prism coupler 6 evanescent waves 11 Phase modulator

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-9-145724 (JP, A) JP-A-9-280810 (JP, A) JP-A-9-43324 (JP, A) JP-A-62- 139240 (JP, A) JP 9-54101 (JP, A) JP 5-180756 (JP, A) JP 5-10819 (JP, A) JP 8-262253 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01N 13/10-13/24 G12B 21/00-21/24 JISST file (JOIS)

Claims (2)

(57) [Claims] 1. A probe for a spin-polarized scanning tunneling microscope excited by an optical near-field, wherein (a) two orthogonal evanescent waves are superposed to generate an optical near-field having a single polarization of about 1/4 wavelength. Excitation means for generating stripes of width,
(B) a conical semiconductor probe whose symmetry axis is made to match the polarization axis of the optical near field, and (c) the excitation means enables highly efficient electron spin polarization by optical pumping. Optical near-field excitation spin-polarized scanning tunneling microscope probe. 2. The optical near-field excitation spin polarization scanning tunneling microscope probe according to claim 1, further comprising a phase modulation element for phase-modulating one of the excitation light emitted from one laser source, A probe for an optical near-field excited spin polarization scanning tunneling microscope, which modulates the polarization of an optical near field that excites a semiconductor probe to modulate the electron spin polarization.