CN114199782A - Sb2Te3Circularly polarized light current regulation and control method for topological surface state - Google Patents
Sb2Te3Circularly polarized light current regulation and control method for topological surface state Download PDFInfo
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- 229910052738 indium Inorganic materials 0.000 claims description 9
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 claims description 9
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 claims description 5
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- GPXJNWSHGFTCBW-UHFFFAOYSA-N Indium phosphide Chemical compound [In]#P GPXJNWSHGFTCBW-UHFFFAOYSA-N 0.000 description 45
- 239000010408 film Substances 0.000 description 16
- VEALVRVVWBQVSL-UHFFFAOYSA-N strontium titanate Chemical compound [Sr+2].[O-][Ti]([O-])=O VEALVRVVWBQVSL-UHFFFAOYSA-N 0.000 description 16
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- BPDQXJZWVBPDSN-UHFFFAOYSA-N tellanylideneantimony;tellurium Chemical compound [Te].[Te]=[Sb].[Te]=[Sb] BPDQXJZWVBPDSN-UHFFFAOYSA-N 0.000 description 2
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Abstract
The invention relates to Sb2Te3The circularly polarized light current regulation and control method of the topological surface state comprises the following steps: step S1: growth of Sb on InP substrate by molecular beam epitaxy equipment2Te3And preparing a pair of dot electrodes on the surface of the sample, and step S2: constructing a stress device, and fixing the sample on the stress device by using epoxy resin; step S3: irradiating the geometric center of the sample, namely the center of the connecting line of the two electrodes, by using the emitted light of the laser, measuring and extracting circularly polarized light current; step S4: changing the stress application size through a stress device, and analyzing the change trend of the circularly polarized light current along with the stress; step S5: measurement of Sb2Te3XPS spectrum of sample, analysis, calculation of substrate and Sb2Te3The energy band distribution of the interface, if the band order is less than zero, the possibility of spin injection exists; comparison of Sb without substrate spin injection2Te3The CPGE current of the sample is regulated and controlled by stress, and the Sb is regulated and controlled by the synergistic effect of stress and substrate injection2Te3The regulation and control effect of the medium circular polarized photocurrent method. The invention regulates and controls Sb2Te3The circularly polarized light current effect of the topological surface state is obvious, and continuous regulation and control can be realized.
Description
Technical Field
The invention relates to the field of spintronics, in particular to Sb2Te3A circularly polarized light current regulation method of topological surface state.
Background
The spin electronic device has the advantages of low energy consumption, high processing speed, high integration degree and the like, and is one of the current research hotspots. Three-dimensional Topological Insulators (TIs) have Topological surface states protected by time reversal symmetry and locked by spin momentum, and are ideal platforms for realizing spintronics and quantum computing research. The circularly polarized light current effect (CPGE) is a powerful tool for studying the electron spin properties in topological surface states, since it can exclude D from TIs3dThe body state of symmetry, and the spin photocurrent was observed at room temperature. The control of CPGE in TIs is of great significance to the design of spin photoelectric devices.
Disclosure of Invention
In view of the above, the present invention provides a Sb2Te3The method for regulating and controlling circularly polarized light current in topological surface state can simply and effectively realize the regulation and control of CPGE in TIs.
In order to achieve the purpose, the invention adopts the following technical scheme:
sb2Te3The circularly polarized light current regulation and control method of the topological surface state comprises the following steps:
step S1: growth of Sb on InP substrate by molecular beam epitaxy equipment2Te3Preparing a pair of point electrodes on the surface of a sample by a mechanical indium pressing method;
step S2: constructing a stress device, and fixing the sample on the stress device by using epoxy resin;
step S3: laser emitted by a laser sequentially passes through a chopper, a polarizer and a quarter-wave plate and irradiates the geometric center of a sample, namely the center of a connecting line of two electrodes, and circular polarized light current is measured and extracted;
step S4: changing the stress application size through a stress device, and analyzing the change trend of the circularly polarized light current along with the stress;
step S5: measurement of Sb2Te3XPS spectrum of sample, analysis, calculation of substrate and Sb2Te3The energy band distribution of the interface, if the band order is less than zero, the possibility of spin injection exists; comparison of Sb without substrate spin injection2Te3The CPGE current of the sample is regulated and controlled by stress, and the Sb is regulated and controlled by the synergistic effect of stress and substrate injection2Te3The regulation and control effect of the medium circular polarized photocurrent method.
Furthermore, the stress device comprises a rectangular polycarbonate plastic strip, a steel stress table, a stress thimble and a differential sleeve; fixing a sample in the center of a rectangular polycarbonate plastic strip by using epoxy resin, installing the sample on a steel stress table, applying uniaxial stress to the sample by rotating a differential sleeve through a stress thimble, measuring the distance from the left edge to the right edge of the steel stress table of the polycarbonate plastic strip as 2a, and measuring the thickness of the polycarbonate plastic strip as h.
Further, in step S4, specifically, the step includes:
and step S41, rotating the differential sleeve of the stress device to bend the sample, thereby applying stress to the sample. Reading the forward moving distance of the stress thimble from the differential sleeve and recording the forward moving distance as JzBy the formula ex＝3hJz/2a2Calculating the magnitude of the applied stress;
step S42, rotating the quarter-wave plate by the stepping motor, collecting the photocurrent by the electrode, inputting the collected photocurrent to the preamplifier and the lock-in amplifier in turn, inputting the signal output by the lock-in amplifier to the computer by the data acquisition card; the rotation angle of the quarter-wave plate is changed from 0 degree to 360 degrees, the step length is 5 degrees, namely data J of one photocurrent is collected every 5 degrees;
and step S43, fitting the measured photocurrents J under different quarter-wave plate rotation angles by using the following formula:
wherein, JCIs circularly polarized light current, L1And L2Is photocurrent due to linearly polarized light, J0Is photocurrent caused by photovoltaic effect, thermoelectric effect and Danpei effect, which is simply referred to as background current; obtaining circularly polarized light current J by fittingC；
Step S44 repeating steps S41 to S43 to measure Sb2Te3Circular polarized light current J of film under different stressC。
Further, the step S5 is specifically:
step S51 measuring InP/Sb by X-ray photoelectron spectroscopy2Te3Band step at the interface, measured conduction band step Δ EcLess than zero, indicating that electrons can be injected from InP into Sb2Te3In the layer;
step S52, fixing the InP substrate at the center of a rectangular polycarbonate plastic strip by using epoxy resin, installing the sample on a self-made steel stress table, and applying uniaxial stress to the sample by rotating a differential sleeve; repeating the steps S3 to S4 to measure circularly polarized light current J of the InP substrate under different stressesc0(ii) a Measured change trend of the circularly polarized light current of the InP substrate along with stress and Sb2Te3The film has the same change trend with stress, which shows that Sb2Te3The circularly polarized light current of the film is affected by the spin injection of the InP substrate.
Further, said Sb2Te3The sample is in a rectangular single crystal structure, the short side of the sample is more than or equal to 3mm, the long side of the sample is more than or equal to 5mm, and the thickness of the sample is 7-30 nm; the point-shaped electrodes are a pair of point-shaped indium electrodes, are pressed on the middle lines of the inner sides of the two long sides of the rectangle through thin needles, are approximately circular with the diameter of about 0.25mm, and have the electrode spacing of about 2 mm.
Furthermore, the power of the laser is 30-200mW, and the incidence plane of the laser is vertical to the connecting line of the two electrodes; the laser beam is at an angle of between 10 and 45 degrees to the normal to the sample surface.
Compared with the prior art, the invention has the following beneficial effects:
1. sb is regulated and controlled through synergistic effect of strain and substrate injection2Te3The method for the medium CPGE current is simple and easy to implement, has low cost, does not relate to the energy band engineering in the material growth process and the preparation of an additional grid in the device preparation, and is favorable for popularization and application in the future;
2. the invention has obvious regulation effect and large regulation range, and is easy to realize continuous regulation.
Drawings
Fig. 1 is a schematic structural diagram of a self-stress-control apparatus according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of a test system and an optical path distribution for measuring CPGE in an embodiment of the present invention.
FIG. 3 shows 30nm Sb grown on an InP substrate measured in an example of the present invention2Te3Graph of CPGE current versus stress for the sample. Where the black rectangle is the experimental data and the solid line is the linear fit result.
FIG. 4 shows the measured 12nm Sb growth on (a) Strontium Titanate (STO) substrate in an example of the present invention2Te3Sample and (b) 30nm Sb grown on InP substrate2Te3Graph of resistance of the sample as a function of stress. Where the black rectangle is the experimental data and the solid line is the linear fit result.
Fig. 5 is an XPS spectrum obtained In an example of the present invention, which is a characteristic peak core energy level In3d and a valence band top (VBM) of In element of an InP substrate; 7nm Sb2Te3Te element characteristic peak core energy level Te3d and In element characteristic peak core energy level In3d of the InP sample; 30nm Sb2Te3Te element characteristic peak core energy level Te3d and valence band top (VBM) of the InP sample; 7nm Sb2Te3Te element characteristic peak core energy level Te3d and In element characteristic peak core energy level In3d of the InP sample.
FIG. 6 shows InP/Sb measured in examples of the present invention2Te3The interface band distribution.
Fig. 7 is a graph showing the measurement of CPGE current in an InP substrate as a function of stress in an embodiment of the present invention. Where the black rectangle is the experimental data and the solid line is the linear fit result.
FIG. 8 shows InP/Sb in an embodiment of the present invention2Te3Schematic representation of an interfacial spin injection model.
FIG. 9 shows 18nm Sb measured in an example of the present invention2Te3CPGE current under normal incidence and back incidence conditions of polarized light in the/STO sample is plotted as a function of incidence angle. Where the black rectangle is the experimental data and the solid line is the linear fit result. The inset is a schematic diagram of the back incident light path.
FIG. 10 shows Sb grown on a strontium titanate substrate as a comparative sample in an example of the present invention2Te3CPGE current versus stress curve for the sample. Where the black rectangle is the experimental data and the solid line is the linear fit result.
Detailed Description
The invention is further explained below with reference to the drawings and the embodiments.
Referring to FIG. 1, the present invention provides Sb2Te3The circularly polarized light current regulation and control method of the topological surface state comprises the following steps:
step S1: growth of Sb on indium phosphide (InP) substrates using molecular beam epitaxy equipment2Te3A pair of point electrodes is manufactured on the surface of a sample by a mechanical indium pressing method.
In a preferred embodiment of the present invention, the Sb is2Te3The sample is in a rectangular single crystal structure, the short side of the sample is more than or equal to 3mm, the long side of the sample is more than or equal to 5mm, and the thickness of the sample is 7-30nm (including 7nm and 30 nm). The pair of point-like indium electrodes are pressed on the middle lines of the inner sides of the two long sides of the rectangle through thin needles, are approximately round with the diameter of 0.25mm, and the distance between the inner sides of the two electrodes is more than or equal to 2 nm. And pressing a platinum wire on the indium electrode by using indium, wherein the platinum wire is used as an electrode lead.
Step S2: the sample was fixed in the center of a rectangular polycarbonate plastic strip using epoxy, mounted on a self-made steel stress table, and uniaxial stress was applied to the sample by rotating a differential sleeve, the stress apparatus being shown in fig. 1. The distance of the polycarbonate plastic strip from the left edge to the right edge of the steel stress stage was measured and recorded as 2a, as shown in fig. 1. The thickness of the polycarbonate plastic strip was measured and recorded as h.
The polycarbonate plastic strips used had a length of 38mm, a width of 5mm and a thickness of 2 mm. The effective width 2a of the stress table for applying stress is 20mm in the present example, the epoxy resin curing process is annealing at 60 ℃ for 2 hours in a vacuum environment.
Step S3: the laser emitted by the laser sequentially passes through the chopper, the polarizer and the quarter-wave plate and irradiates the geometric center of the sample, namely the center of the connecting line of the two electrodes.
Preferably, in the embodiment, the power of the laser is 30-200mW, the laser can excite the band edge of the InP substrate or can excite the InP internal defects to generate circularly polarized light current, and the diameter of the light spot impinging on the sample is smaller than the distance between two dot-shaped indium electrodes. The incident plane of the laser is vertical to the connecting line of the two electrodes; the laser beam is at an angle of between 10 and 45 degrees to the normal to the sample surface.
Preferably, in this embodiment, the power of the laser used is 100mW, the spot diameter of the laser is 1mm, and the wavelength of the laser is 1064 nm. The laser beam was angled 30 degrees from the normal to the sample surface.
Step S4: the differential sleeve of the stressing device is rotated to bend the sample, thereby stressing the sample. Reading the forward moving distance of the stress thimble from the differential sleeve and recording the forward moving distance as Jz. By the formula ex＝3hJz/2a2The magnitude of the applied stress is calculated. The longitudinal compressive strain to which the sample is subjected can be determined by the formula: e.g. of the typez＝-(C12/C13)exIs calculated to obtain wherein C12、C13Is Sb2Te3The modulus of elasticity of the sample. In this embodiment, let step length Jz0When the thickness is 0.01mm, e is calculated0＝3×10-4With ex/e0The magnitude of stress application is described.
The quarter-wave plate is rotated by the stepping motor, the photocurrent is collected by the electrode and is sequentially input into the preamplifier and the lock-in amplifier, and the signal output by the lock-in amplifier is input into the computer by the data acquisition card. The quarter-wave plate rotates from 0 degree to 360 degrees in steps of 5 degrees, namely collecting data J of one photocurrent every 5 degrees.
Fitting the measured photocurrents J at different quarter-wave plate rotation angles by using the following formula:
formula (1)
Wherein, JCIs circularly polarized light current, L1And L2Is photocurrent due to linearly polarized light, J0Is photocurrent caused by photovoltaic effect, thermoelectric effect and Danpei effect, which is simply referred to as background current; obtaining circularly polarized light current J by fittingC。
Repeating the steps S41 to S43 to obtain Sb2Te3Circular polarized light current J of film under different stressC. The measurement results are shown in fig. 3, where the black rectangle is the experimental data and the solid line is the result of the linear fit. It can be seen that Sb is increased with increasing applied strain2Te3The CPGE current in the thin film sample shows a linear monotonically decreasing trend.
In this example, Sb was measured on different substrates2Te3The resistance of the film varies with stress as shown in fig. 4. It can be seen that Sb is increased with increasing stress2Te3The resistance of the film also increases because the fermi level in the topological surface states shifts into the bandgap with increasing strain, causing the dirac point to shift to the middle of the bandgap, resulting in an increase in resistance. The Fermi level moves towards the band gap, the concentration of bulk carriers can be reduced, the scattering of the bulk carriers on spin-polarized photon-generated carriers is reduced, and CPGE current is improved. However, the change in resistance with strain is very small, indicating that the shift in fermi level is small, and the experiment observed that CPGE current decreased with an increase in strain, so the shift in fermi level was not the cause of CPGE change.
Through literature investigations, it was found that Sb is present as the applied strain increases2Te3Spin orbit of topological surface statesThe coupling strength decreases and the magnitude of CPGE is positively compared to the spin-orbit coupling strength, resulting in a concomitant decrease in CPGE current. Thus, the decrease in CPGE current with stress is due to Sb2Te3The spin-orbit coupling of topological surface states is induced with reduced stress.
Step S5: measurement of InP/Sb by X-ray photoelectron spectroscopy2Te3Band step at the interface, measured conduction band step Δ EcLess than zero, indicating that electrons can be injected from InP into Sb2Te3In the layer
In this example, 7nm Sb was grown on InP substrates by molecular beam epitaxy equipment, respectively2Te3Thin film, 30nm Sb2Te3Thin film, then, for 7nm Sb grown on InP substrate2Te3Film and 30nm Sb2Te3X-ray photoelectron spectroscopy (XPS) was performed on the thin film and the InP substrate, and XPS1, XPS2, and XPS3 spectra were obtained, and the results of the measurements are shown in fig. 5. The core energy level Te3d of Te element characteristic peak and the core energy level In3d of In element characteristic peak In XPS1 were measured
Note that the core energy level Te3d and the top of the valence band of Te element characteristic peak in XPS2 are respectively
Note that the core energy level In3d and the top of the valence band of the In characteristic peak In XPS3 are
In the present embodiment, measured
572.65 + -0.05 eV and 444.75 + -0.05 eV, respectively
572.65 + -0.05 eV and-0.38 + -0.1 eV, respectively
444.1 + -0.05 eV and 0.34 + -0.1 eV, respectively. InP substrate and Sb were calculated by the following formula (2)2Te3Top band order Δ E of valence bandvObtaining Δ Ev＝-1.37±0.1eV。
By the formula
InP substrate and Sb can be obtained2Te3The difference Δ Ec of the conduction band bottom. Wherein,
and
InP substrate and Sb respectively2Te3The band gaps of the film are respectively 1.34eV and 0.23 eV. Calculating to obtain: Δ Ec is-2.48 ± 0.1 eV. Thereby obtaining InP substrate and Sb2Te3The energy band distribution of the heterojunction is shown in fig. 6. It can be seen that Sb2Te3The band orientation of the/InP heterostructure is of type III, and due to the absence of a potential barrier, electrons in the InP conduction band can be transferred and injected into Sb2Te3In the film. Thus, Sb2Te3The energy band distribution of the/InP heterostructure is such that spin-polarized carriers can be injected from the substrate into Sb2Te3In the film.
Step S6: the InP substrate is fixed at the center of a rectangular polycarbonate plastic strip by epoxy resin, the sample is arranged on a self-made steel stress table, and uniaxial stress is applied to the sample by rotating a differential sleeve. Repeating the steps S3 to S4 to measure circularly polarized light current J of the InP substrate under different stressesc0As shown in fig. 7. Measured change trend of the circularly polarized light current of the InP substrate along with stress and Sb2Te3The change trend of the film along with the stress is the sameShowing that Sb2Te3The circularly polarized light current of the film is affected by the spin injection of the InP substrate.
A schematic diagram of a substrate injection spin-polarized carrier model is shown in fig. 8. Although the bandgap of InP (1.35eV) is larger than the photon energy of 1064nm light, there are some defects in the InP substrate, introducing some defect levels in the bandgap. Thus, under excitation by 1064nm light, electrons in the defect level will absorb light and transition into the conduction band, generating spin-polarized carriers. Spin polarized electrons will be injected from the substrate into Sb2Te3Thin film of and Sb2Te3The spin-polarized carriers of the lower surface recombine, thereby reducing the CPGE current of the lower surface state. Due to Sb2Te3The spin diffusion length of (a) is short, and spin injected electrons will mainly affect the lower surface of the sample. Since the spin-orbit coupling coefficients of the upper and lower surface states are of opposite sign, the CPGE currents they generate will be opposite. If our sample is such that the contribution of the upper surface states to the CPGE current dominates, then a decrease in the lower surface state signal will increase the total CPGE current. Next, we analyzed whether our samples are dominated by the contribution of the upper surface state to the CPGE current by laser front and back incidence CPGE measurements.
For Sb with the thickness of 18nm2Te3the/STO samples were subjected to a variable incidence angle CPGE measurement under circularly polarized front and back incidence conditions. Because STO does not absorb 1064nm light, CPGE current measurements at laser back incidence can be made. The experimental results are shown in fig. 9, and the data were fitted by the following formula (3).
Where n is Sb2Te3Refractive index of the film, ACPGEIs a constant related to the spin-orbit coupling strength of the sample. The dependence of the CPGE current on the angle of incidence can be well fitted by phenomenological equation (3). It can be seen that for 18nm Sb2Te3STO sample, front and back entryThe incident CPGE currents are of the same sign, and the CPGE amplitude at normal incidence is greater than that at back incidence. This phenomenon indicates that the upper surface state will dominate in both the case of circularly polarized light at normal and back incidence. The reason is as follows: sb2Te3Surface state of (D) is of3vPoint clusters, CPGE can be represented by phenomenological formulas
Here, JCPGEyIs the CPGE current in the y-direction and gamma is the second order pseudotensor, proportional to the spin-orbit coupling of the material.
Is a unit vector pointing in the direction of light propagation. In the optical path we use, for a certain angle of incidence,
will remain unchanged at normal incidence and back incidence, which can be derived from comparing the directions of the incident angles in the insets of fig. 3 and 9. Thus, if the sign of the CPGE current remains the same in both the front and back incidence cases, the major contribution of CPGE must come from the same topological surface state. Considering that at circularly polarized front incidence the intensity of light absorbed by the top surface is greater than that absorbed by the top surface state when light is incident from the back, resulting in a greater CPGE current generated by the top surface at normal incidence. Therefore, Sb having an upper surface state of 18nm can be inferred2Te3the/STO samples play a dominant role. Since other samples showed Sb at 18nm at a given angle of incidence2Te3the/STO samples are of the same sign, so it can be concluded that the contribution of the upper surface state to the CPGE current is dominant in these samples.
Due to Sb2Te3The coefficients of the upper and lower surface spin-orbit couplings are opposite and therefore will produce oppositely directed CPGE currents, while the total CPGE current is dominated by the upper surface states and therefore the lower surface state contribution reduction will enhance the net CPGE current. Thus, spin injection into the InP substrate will increase the total CPGE current, but the CPGE of the InP substrate will also increase under stressDecrease or even inversion, as shown in FIG. 8, proving it to Sb2Te3The injected spin electrons in the film will decrease with increasing stress; further result in Sb2Te3CPGE in the film decreased. In conclusion, Sb grown on InP substrate2Te3Under the synergistic action of spin injection, the amplitude of the current regulated by the stress is larger under the condition of no spin injection, namely under the condition of the same stress, if the synergistic action of substrate injection exists, the amplitude of the change of the CPGE current is larger, and the regulation effect is more obvious.
To verify the regulation of substrate implantation, we measured Sb without substrate implantation effect2Te3The CPGE current of the sample is along with the change curve of the stress, namely, Sb with the thickness of 12 nanometers grown on the strontium titanate substrate is measured2Te3The change curve of sample CPGE current with stress is shown in FIG. 10. The band gap of the strontium titanate substrate is 1.9eV, which is far larger than the photon energy of a 1064nm laser, and no CPGE current is experimentally measured in the presence of the strontium titanate substrate under the excitation of the 1064nm laser, which indicates that no circularly polarized light current in a defect state exists. Thus, Sb grown on a strontium titanate substrate2Te3The current contribution of the substrate spin injection is absent in the CPGE current of the sample. Comparative growth of 12nm Sb on STO substrates2Te3And growing 30nm Sb on InP substrate2Te3It can be seen that the magnitude of the CPGE current decreases with increasing uniaxial strain. In particular, in uniaxial strain e compared to the unstressed samplexIn the case of 0.0066, 12nm Sb2Te3The CPGE of the/STO sample decreased to 44% of the original value. However, 30nm Sb2Te3The magnitude of CPGE in the InP samples can be tuned to zero by a uniaxial strain of 0.0033, i.e. a tuning range up to 100%. As can be seen, Sb grown on InP substrate2Te3The CPGE regulating effect of the sample is better, which is caused by the synergistic effect of the stress and the spin injection of the InP substrate.
In summary, the invention utilizes the synergistic effect of uniaxial stress and substrate implantation effect to realize Sb2Te3Middle CPThe purpose of GE current regulation. Because Sb is increased with the applied strain2Te3The spin-orbit coupling strength of the topological surface state is reduced, and the CPGE size is in positive correlation with the spin-orbit coupling strength, so that the CPGE current is reduced; in addition, spin injection of the InP substrate will increase the total CPGE current, but the InP substrate is stressed towards Sb2Te3The injected spin electrons in the film decrease with increasing stress, so Sb grown on InP substrate2Te3The effect of stress regulation of the CPGE current on the STO substrate is more obvious than that of the CPGE current on the STO substrate under the synergistic action of spin injection. Therefore, the synergistic effect of uniaxial stress and substrate injection effect can be used for better realizing Sb2Te3The method provided by the invention is convenient to realize, low in cost, good in regulation effect and easy to realize continuous regulation.
The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the claims of the present invention should be covered by the present invention.
Claims (6)
1. Sb2Te3The circularly polarized light current regulation and control method of the topological surface state is characterized by comprising the following steps of:
step S1: growth of Sb on InP substrate by molecular beam epitaxy equipment2Te3Preparing a pair of point electrodes on the surface of a sample by a mechanical indium pressing method;
step S2: constructing a stress device, and fixing the sample on the stress device by using epoxy resin;
step S3: laser emitted by a laser sequentially passes through a chopper, a polarizer and a quarter-wave plate and irradiates the geometric center of a sample, namely the center of a connecting line of two electrodes, and circular polarized light current is measured and extracted;
step S4: changing the stress application size through a stress device, and analyzing the change trend of the circularly polarized light current along with the stress;
step S5: measurement of Sb2Te3XPS spectrum of sample, analysis, calculation of substrate and Sb2Te3The energy band distribution of the interface, if the band order is less than zero, the possibility of spin injection exists; comparison of Sb without substrate spin injection2Te3The CPGE current of the sample is regulated and controlled by stress, and the Sb is regulated and controlled by the synergistic effect of stress and substrate injection2Te3The regulation and control effect of the medium circular polarized photocurrent method.
2. Sb according to claim 12Te3The method for regulating and controlling circularly polarized light current in a topological surface state is characterized in that the stress device comprises a rectangular polycarbonate plastic strip, a steel stress table, a stress thimble and a differential sleeve; fixing a sample in the center of a rectangular polycarbonate plastic strip by using epoxy resin, installing the sample on a steel stress table, applying uniaxial stress to the sample by rotating a differential sleeve through a stress thimble, measuring the distance from the left edge to the right edge of the steel stress table of the polycarbonate plastic strip as 2a, and measuring the thickness of the polycarbonate plastic strip as h.
3. Sb according to claim 12Te3The method for regulating circularly polarized light current in a topological surface state is characterized in that, in the step S4, the method specifically comprises the following steps:
and step S41, rotating the differential sleeve of the stress device to bend the sample, thereby applying stress to the sample. Reading the forward moving distance of the stress thimble from the differential sleeve and recording the forward moving distance as JzBy the formula ex＝3hJz/2a2Calculating the magnitude of the applied stress;
step S42, rotating the quarter-wave plate by the stepping motor, collecting the photocurrent by the electrode, inputting the collected photocurrent to the preamplifier and the lock-in amplifier in turn, inputting the signal output by the lock-in amplifier to the computer by the data acquisition card; the rotation angle of the quarter-wave plate is changed from 0 degree to 360 degrees, the step length is 5 degrees, namely data J of one photocurrent is collected every 5 degrees;
and step S43, fitting the measured photocurrents J under different quarter-wave plate rotation angles by using the following formula:
wherein, JCIs circularly polarized light current, L1And L2Is photocurrent due to linearly polarized light, J0Is photocurrent caused by photovoltaic effect, thermoelectric effect and Danpei effect, which is simply referred to as background current; obtaining circularly polarized light current J by fittingC；
Step S44 repeating steps S41 to S43 to measure Sb2Te3Circular polarized light current J of film under different stressC。
4. Sb according to claim 12Te3The method for regulating and controlling circularly polarized light current in a topological surface state is characterized in that the step S5 specifically comprises the following steps:
step S51 measuring InP/Sb by X-ray photoelectron spectroscopy2Te3Band step at the interface, measured conduction band step Δ EcLess than zero, indicating that electrons can be injected from InP into Sb2Te3In the layer;
step S52, fixing the InP substrate at the center of a rectangular polycarbonate plastic strip by using epoxy resin, installing the sample on a self-made steel stress table, and applying uniaxial stress to the sample by rotating a differential sleeve; repeating the steps S3 to S4 to measure circularly polarized light current J of the InP substrate under different stressesc0(ii) a Measured change trend of the circularly polarized light current of the InP substrate along with stress and Sb2Te3The film has the same change trend with stress, which shows that Sb2Te3The circularly polarized light current of the film is affected by the spin injection of the InP substrate.
5. Sb according to claim 12Te3The method for regulating and controlling circularly polarized light current of topological surface state is characterized in that Sb2Te3The sample is in a rectangular single crystal structure, the short side of the sample is more than or equal to 3mm, the long side of the sample is more than or equal to 5mm, and the thickness of the sample is 7-30 nm; the point-like electrodes are a pair of point-like indium electrodesThe electrodes are pressed on the midline of the inner sides of two long sides of the rectangle through fine needles, the diameter of each electrode is approximately 0.25mm, and the electrode spacing is approximately 2 mm.
6. Sb according to claim 12Te3The circularly polarized light current regulation and control method of the topological surface state is characterized in that the power of the laser is between 30 and 200mW, and the incidence plane of the laser is vertical to the connecting line of the two electrodes; the laser beam is at an angle of between 10 and 45 degrees to the normal to the sample surface.
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