KR20060019203A - Aharonov-bohm device for measuring frequency of oscillating magnetic field and for amplifying current by frequency change - Google Patents

Abstract

According to the present invention, a first closed loop and a second closed loop on a semiconductor substrate, a lead wire connecting the first closed loop and the second closed loop, and extending in a direction opposite to the lead wire connecting the first closed loop and the second closed loop. A lead wire, and a bias voltage Δμ applied between the first closed loop and the second closed loop, and providing first and second magnetic fluxes varying in time in the first and second closed loops, respectively. Thus, an aharonov-spring device is disclosed in which a step of current occurs in a current-voltage characteristic curve.

Aharonov-Spring Device, Bias Voltage

Description

Aharonov-Bohm Device for measuring frequency of oscillating magnetic field and for amplifying current by frequency change}

Figure 1 shows one embodiment of the aronov-spring device of the present invention.

Figure 2 shows the current (I) -voltage (Δμ = eV) characteristic curve of the Arronov-spring device of the present invention.

FIG. 3 shows the transfer coefficients of the Aharonov-spring device of FIG. 1 for the case of FIG. 2.

4 shows a current (I) -voltage (V = Δμ / e) characteristic curve showing the current amplification by the frequency change of the Arronov-spring device of the present invention.

5 shows a current (I) -voltage (V = Δμ / e) characteristic curve showing the current amplification by the change in amplitude of the Arronov-spring device of the present invention.

The present invention relates to an Aharonov-Bohm device, which is a device for amplifying a current by measuring the frequency of a weakly vibrating magnetic field and changing the frequency or amplitude of the vibrating magnetic field. More specifically, the present invention is a micro or nano-sized frequency measuring instrument that can be used to measure the frequency of a weakly vibrating magnetic field, especially the measurement of the frequency of a weakly vibrating magnetic field which exists under strong static magnetic fields, such as magnetic resonance imaging (MRI) devices. The present invention relates to an aharonov-spring device, which is applicable to a remote switch or a communication device, which is a new concept transistor which is applicable to and which can amplify a current by a change in frequency or amplitude.

Recent highly developed manufacturing techniques have enabled the invention of new quantum devices that maintain quantum coherence. Some of these quantum devices provide new methods for measuring useful physical quantities or some basic physical constants, while others are expected to replace existing micrometer-sized field effect devices in the future.

The development of new quantum devices has been of interest to theorists and experimenters of nanoscale electronic devices, as well as to researchers in semiconductor labs. In addition to industrial interest, nanoscale systems that maintain quantum coherence are very promising in the field of nanoelectronics (nano electronics or mesoscopic physics), although not all theoretical ideas can be realized due to difficulties in manufacturing techniques. Made into fields.

Conventional techniques for measuring the frequency of weakly vibrating magnetic fields are known using the ac (or alternating) effect of Josephson junctions (D. R. Tilly and J. Tilly, superfluid and superconducting, John Willie & Sons, New York) , 1974). In addition, superconducting quantum interference devices (SQUID) using Josephson junctions are widely used, but this method uses superconductors, so SQUID is lost due to strong static magnetic field in magnetic resonance imaging (MRI) or nuclear magnetic resonance experiments. I cannot use it. Furthermore, to be useful for measuring the Fermi energy of the material (material) for use in a given device, because knowing the Fermi energy value, for the one-dimensional k _F = πn / 2 in, and for the two-dimensional k _F This is because the density of electrons dominating the Fermi wave vector can be known as (2πn) ^1/2 . There have been various methods of determining the electron density of a material, but a method of determining the electron density by measuring Fermi energy is not known until now.

Another conventional technology of the present invention discloses a "nano sensor" disclosed in the Republic of Korea Patent Publication No. 2003-55346 (Patent Application No. 2003-7007723) dated July 2, 2003 (disclose). The conventional nanosensor invention discloses an electrical device and a nano detector device composed of nano wires. This prior art nanoscale device is a sensor comprising at least one nanowire and a means for measuring a change in the properties of at least one nanowire, mainly for measuring the presence or amount of analyte in a chemical sample. will be.

The present invention provides a Haronov-spring device capable of measuring the frequency of a dynamic magnetic field of micro or nano size using a new type of current jump or steps in the current-voltage (IV) characteristics of a quantum device. Aharonov-Bohm device).

It is still another object of the present invention to provide a Haronov-spring device that can be applied to a remote switch, a communication receiver, a magnetic field sensor, and the like as a new concept transistor that amplifies a current through a change in frequency or amplitude of a dynamic magnetic field. .

It is still another object of the present invention to provide an aharonov-spring device that can be used to measure the frequency of weak dynamic magnetic fields generated in MRI or NMR, which is a medical device with a strong static magnetic field where superconducting devices cannot be used. .

In order to achieve the above object, the aharonov-spring device of the present invention is a lead wire connecting the first closed loop and the second closed loop, the first closed loop and the second closed loop on the semiconductor substrate, the first closed loop and A lead wire extending in a direction opposite to a lead wire connecting the second closed loop, and a bias voltage applied between the first closed loop and the second closed loop, wherein each of the first and second closed loops is provided at a time in the first and second closed loops. The first and second magnetic fluxes having the phases varying accordingly are provided, so that a step of the current occurs in the current-voltage characteristic.

The aharonov-spring device of the present invention comprises at least two closed loops connected to each other with simple nanoelectronic devices. The two closed loops have a power source that provides a potential difference ΔV = Δμ / e to lead wires in a direction opposite to the lines connected to each other. Static and dynamic magnetic fluxes pass through the closed loop, respectively, and the dynamic magnetic fluxes have the same or different phases. When a static magnetic field having a half (1/2) integer multiple of the magnetic flux quantum unit Φ ₀ = h / e is applied, the Aharonov-spring device of the present invention is completely canceled at the junction even with the potential difference applied. Because of this, no current flows. However, in this state, when dynamic magnetic flux is applied, electrons can move only at special energy value. This specific example is illustrated by the transfer coefficient of FIG. 3 as described below, which is represented by a stepped current (I) -voltage (Δμ) characteristic curve. As in quantum pumping, two dynamic magnetic fluxes having different phases may be used, or two dynamic magnetic fluxes having the same phase may be used. However, in the present embodiment, the latter is selected in consideration of the convenience of the apparatus.

Since the amplitude and frequency of the static or dynamic magnetic flux passing through each closed loop in the Aharonov-spring device of the present invention can serve as a gate voltage, the Aharonov-spring device of the present invention has three terminals. It can be operated as a transistor device having a.

The Aharonov-spring device of the present invention can be used as a current amplification device by a frequency change and a current amplification device by a change in amplitude, and thus can be used as a remote switch, a communication receiver, a remote magnetic field sensor, and the like.

The Aharonov-Spring device of the present invention has the advantage that it is possible to measure the frequency of weak dynamic magnetic field in place of the conventional superconducting quantum interferometer which cannot measure the weak dynamic magnetic field under strong static magnetic field. Can be used for frequency measurement.

Hereinafter, the present invention will be described in detail with reference to Examples.

1 shows one embodiment of the Aharonov-spring device of the present invention. In the preferred embodiment shown in FIG. 1, the Aharonov-spring device comprises two closed loops in the shape of a ring. However, the ring-shaped closed loop can have any other shape, such as square.

The two closed loops shown in FIG. 1 are connected by lines, and the two closed loops also have lead wires respectively facing the connecting line. A power supply providing an external bias potential difference ΔV = Δμ / e is connected between two closed loops (between the points A and B).

If a static magnetic flux with half integers of magnetic protons (ie 1/2, 3/2, 5/2, ...) is applied to each closed loop, the ring shown in FIG. After passing through the arm with the same length, current must not flow even though the bias voltage is applied due to full Aharonov-spring interference at the junction. However, if there is a weak additional magnetic flux that vibrates, electrons will overcome full interference and current will flow. The mechanism through which the current flows with the help of a vibrating magnetic field is called “photon assisted tunneling.” First observed by S. Shapiro (Physical Review 11, 80 (1963)). The sudden current jump in the ac Josephson effect is one of the typical cases of the photon assisted tunneling phenomenon.

In FIG. 1, the movement of electrons under the complete interference condition should be incident from the left lead line, proceed to the left closed loop, and then return to the left lead line. Thus, the possible wave vector k _n of electrons in the closed circuit must be quantized with k _n = (n + 1) π / 2ℓ, where n is 0,1,2, ... The length of the upper or lower arm (ie, semicircle in FIG. 1) of the closed loop. Thus, photon assisted tunneling can occur at an energy value of En ± ħω, where En is given by En = ħ ² k _n ² / 2m _e , m _e is the electron mass and ω is the angular frequency of the oscillating magnetic flux. , Decode ± means absorption (+) and emission (-) of photons.

As mentioned above, photon assisted tunneling occurs only at certain energies, and at other energy values, full interference limits the transmission, so if the strength (strength) of the oscillating magnetic field is sufficiently weak, the propagation spikes have an energy value of En ± ħω. Is expected to occur, and this spike occurrence in the transfer coefficient ensures the occurrence of a sudden current jump in the current-voltage (IV) characteristic.

Back to Figure 1, each closed loop vibrates magnetic flux

f (t) = fs + fd cos (ωt + φ ), f (t) = Φ (t) / Φ ₀

Is applied. The magnetic flux f is represented by φ ₀ = h / e , which is a magnetic flux quantum unit, and may introduce different phases φ for left and right closed loops.

In the present invention, the static flux fs and the dynamic flux fd of the same magnitude are applied to each closed loop to reduce the control parameters, and the same phase (ie, phase difference = 0) is applied to the left and right closed loops for the convenience of manufacturing the device. Take it.

In the Aharonov-spring arrangement of the present invention, the static flux fs, the dynamic flux fd, and the frequency ω can all control the strength of the current.

Each waste by providing a potential difference △ V = △ μ / e between loop currents flowing in the apparatus of the present invention _{△ μ = μ L -μ R>} 0 (μ L and μ _R is left, being chemical potential of the right lead) If is

I (△ μ) = (2e / h) ∫ ₀ ^EF [T _→ (E) -T _← (E)] dE + (2e / h) ∫ _EF ^{EF + △ μ} T _→ (E) dE (1)

Is given by In Equation (1), the first term on the right side is zero when the same phase is taken in the left and right closed loops. In Equation (1), E _F is a Fermi energy and T _→ (E) is a transfer probability in which electrons in an energy E state move from the left lead wire to the right lead wire. The energy values are expressed in units of the lowest intrinsic energy E ₀ = ħ ² π ² / (8ℓ ² m _e ) that may be present in the closed loop. Where l is half the closed loop length and m _e is the mass of the electron.

2 shows a current (I) -voltage (V) characteristic curve for the case of Fermi energy E _F = 9E ₀ . Specifically, FIG. 2A shows the current steps when fs = 0.5, fd = 0.05, angular vibration frequency ω = 2.8E ₀ / ħ of dynamic magnetic flux, and FIG. 2B shows fs = 0.49, fd = 0.05, dynamic magnetic flux The current step is shown when the angular vibration frequency of ω = 2.8E ₀ / ħ.

In the embodiment of the present invention, when the circumferential length of the closed loop is 200 nm, the energy shown in FIG. 2 is E ₀ = 9.4 meV (milli-electron volts), the current is I ₀ = 0.72 nA (nano amps), and the dynamic The frequency unit of the magnetic flux is ν ₀ = E ₀ /h=2.3 GHz. On the other hand, the strength of the magnetic field required to obtain the magnetic flux quantum unit Φ ₀ = h / e (that is, fs = 1) requires 0.3T (Tesla) when the circumferential length of the closed loop is 200 nm. Therefore, the magnetic field required for fs = 0.5 is 0.15T, and changing the circumferential length of the closed loop also changes the strength of the required static magnetic field.

FIG. 3 shows the transfer coefficient of the Aharonov-spring device of FIG. 1 when the Fermi energy is 9E ₀ . Specifically, Figure 3a is fs = 0.5, fd = 0.05, if the frequency ν = 2.8E ₀ / h of a dynamic magnetic flux, and Figure 3b is fs = 0.49, fd = 0.05, the frequency of the dynamic magnetic flux ν = 2.8E ₀ / h. The current staircase of FIG. 2 corresponds 1: 1 to the transfer spike of FIG. 3, the position of which is ħω from the left and right in the upward double arrow. In other words, the corresponding pair of current jumps are separated by 2? Ω. The position of the double arrow is the position of the intrinsic energy that electrons have in the closed loop, where E _n = n ² E ₀ , where n is a positive integer (ie, n = 1, 2, 3, ...). )to be. In FIG. 3B, extra spikes appear in the downward double arrow position, which appears when fs = 0.5, where the energy at that position is given by (2n-1) ² E ₀ .

2 and 3, it is possible to confirm that the voltage gap ΔV between any current steps corresponds to 2 ? Ω or 2h ν by matching the position of the current step with the spike of the transfer coefficient. Therefore, through the relation eΔV = 2h v , the frequency v of the dynamic magnetic flux is obtained from v = eΔV / 2h using the measurement of the corresponding voltage interval ΔV and a known e / h value. That is, when the measurement of the voltage interval DELTA V is made, a precise value of the unknown frequency v can be obtained using the known value e / h. In the case of using a vibrating magnetic field which knows the value of the frequency ν , a precise measurement value of the basic constant value h / e can be known by measuring the voltage interval ΔV.

Figure 4 shows a current (I) -voltage (V) characteristic curve showing current amplification by frequency change using the Aharonov-Spring device of the present invention. Specifically, Figure 4a is a case where the Fermi energy is fs = 0.5, fd = 0.05 when 9.2E _0, Fig. 4b is a case where the Fermi energy is fs = 0.49, fd = 0.05 when 9.2E _0. In each case of FIGS. 4A and 4B, the frequencies of the dynamic magnetic flux are ν = 3.48E ₀ / h, 1.8E ₀ / h, and 1.24E ₀ / h.

Referring again to FIG. 4, when the bias voltage ΔV is given by ΔV = 3E ₀ / e, that is, when each closed loop circumferential length is manufactured at 200 nm, a voltage corresponding to ΔV = 3E ₀ /e=28.2mV is applied. As a result, reducing the frequency from 8 GHz to 4 GHz increases the current by approximately 20 times from 2.9 pA (picoamps) to 58 pA. This current value can be obtained by drawing a vertical line at Δμ = 3E ₀ (ie, ΔV = 3E ₀ / e) in FIG. 4A, reading the current value and using the units given above for those values. Therefore, when fs = 0.5, when a dynamic magnetic field of 4 GHz is applied when there is no dynamic magnetic field and a current is 0, a current of 58 pA flows, so that the Aharonov-spring device of the present invention can function as a switch.

FIG. 5 shows a current (I) -voltage (V) characteristic curve showing current amplification by varying amplitude of dynamic magnetic flux using the Aharonov-Spring device of the present invention. Specifically, when the Fermi energy is 9.2E ₀ , fs = 0.5, and the frequency is ν = 3.48E ₀ / h, fd = 0.05, 0.1, 0.2, the current amplification increases as the amplitude fd increases. Is showing. As a specific example, it can be seen that when the amplitude fd is increased from fd = 0.05 to fd = 0.2, the current increases approximately 10 times.

In addition, Fermi energy for the material of the device can also be determined from experimental data. Since Fermi energy is the energy value where Δμ = 0, it is not directly shown in the experimental data.However, the Fermi energy value can be obtained by finding the closed loop eigenenergy value En in the current-voltage characteristic curve. As a simple example, if the first current jump occurs at bias potential V ₁ , the Fermi energy E _F is obtained as E _F = En + ħω-eV ₁ .

The Aharonov-Spring device of the present invention described above can be used as a new concept transistor that amplifies the current through a change in the frequency or amplitude of the dynamic magnetic field as well as the measurement of the weak dynamic magnetic field frequency. Specifically, it can be used to measure the frequency of weak dynamic magnetic fields generated by MRI or NMR, which is a medical device with a strong static magnetic field where superconducting devices cannot be used. Various applications such as magnetic field sensors are possible.                     

In addition, using the aharonov-spring device of the present invention, the electron density can be determined using the measured Fermi energy value obtained from the bias voltage at which the current jump occurs in the current-voltage characteristic curve.

The above embodiments of the present invention have been described as exemplary only, and are not intended to limit the scope of the present invention. It is intended that the scope of the invention only be limited by the appended claims.

Claims (21)

In the Aharonov-spring device, A first closed loop and a second closed loop on the semiconductor substrate, A lead wire connecting the first closed loop and the second closed loop, A lead wire extending in a direction opposite to a lead wire connecting the first closed loop and the second closed loop, and A bias voltage Δμ applied between the first closed loop and the second closed loop Including, Providing first and second magnetic fluxes varying with time in the first and second closed loops, respectively, such that a step of current occurs in the current-voltage characteristic curve. Aharonov-spring device. The method of claim 1, wherein the first magnetic flux and the second magnetic flux are respectively f (t) = fs + fd cosωt, f (t) = fs + fd cos (ωt + φ ) Where fs is a static magnetic flux, fd is a dynamic magnetic flux, ω and φ are the angular frequency and the phase difference, respectively, and are given by f (t) = Φ (t) / Φ ₀ , where Φ ₀ is the magnetic flux quantum Aharonov-spring device expressed in units of Φ ₀ = h / e . 3. The aharonov-spring device of claim 2 wherein the first and second magnetic fluxes are provided in a direction perpendicular to the first closed loop and the second closed loop, respectively. The aharonov-spring device according to any one of claims 1 to 3, wherein the phase difference is zero. The aharonov-spring device according to any one of claims 1 to 3, wherein the phase difference is π / 2. 4. The apparatus of any one of claims 1 to 3, wherein the first closed loop and the second closed loop are circular in shape. 5. The apparatus of claim 4, wherein the first closed loop and the second closed loop are circular in shape. 6. The apparatus of claim 5, wherein the first closed loop and the second closed loop are circular in shape. 4. The aharonov-spring device according to any one of claims 1 to 3, wherein the current step occurs at a position where a pair of voltage intervals satisfy DELTA V = 2h v / e. 5. The apparatus of claim 4, wherein the current step occurs at a position where a pair of voltage intervals satisfy DELTA V = 2h v / e. 6. The aharonov-spring device of claim 5 wherein the current step occurs at a location where a pair of voltage intervals satisfy DELTA V = 2h v / e. 7. The aharonov-spring device of claim 6, wherein the current step occurs at a position where a pair of voltage intervals satisfy DELTA V = 2h v / e. 8. The apparatus of claim 7, wherein the current step occurs at a location where a pair of voltage intervals satisfy DELTA V = 2h v / e. 10. The apparatus of claim 8, wherein the current step occurs at a position where a pair of voltage intervals satisfy DELTA V = 2h v / e. 4. An ahronov-spring device as set forth in claim 2 or 3, wherein decreasing the frequency of the dynamic magnetic flux increases the current. The method according to claim 2 or 3, wherein when the bias voltage ΔV is given by ΔV = 3E ₀ / e, the respective closed loop circumferential length is set to 200 nm and a voltage corresponding to ΔV = 28.2 mV is applied. Aharonov-spring device in which the current increases approximately 20 times when the frequency of the dynamic magnetic flux is reduced from 8 GHz to 4 GHz. 17. The aharonov-spring device according to claim 16, wherein the aharonov-spring device functions as a switch. 4. The apparatus of claim 2 or 3, wherein increasing the amplitude of the dynamic magnetic flux increases the current. 19. The Aharonov-Spring device according to claim 18, wherein the Aharonov-Spring device functions as a current amplifying device. The method according to claim 2 or 3, wherein when the bias voltage ΔV is given by ΔV = 15E ₀ / e, increasing the amplitude of the dynamic magnetic flux fd from fd = 0.05 to fd = 0.2 increases the current approximately 10 times. Ronov-spring device. The apparatus of claim 20, wherein the aharonov-spring device functions as a current amplifying device.

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