CN114199782A - A circularly polarized photocurrent regulation method for Sb2Te3 topological surface states - Google Patents

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

A circularly polarized photocurrent regulation method for Sb2Te3 topological surface states

technical field

The invention relates to the field of spintronics, in particular to a circularly polarized photocurrent regulation method of Sb ₂ Te ₃ topological surface state.

Background technique

Spintronic devices have the advantages of low energy consumption, fast processing speed, and high integration, and are one of the current research hotspots. Because 3D topological insulators (TIs) possess topological surface states protected by time-reversal symmetry and locked by spin-momentum, they are ideal platforms for realizing spintronics and quantum computing research. The circularly polarized photogalvanic effect (CPGE) is a powerful tool to study the spin properties of electrons in topological surface states because it can exclude the contribution of bulk states belonging to D _3d symmetry in TIs and can be observed at room temperature Spin photocurrent. The regulation of CPGE in TIs is of great significance for designing spin optoelectronic devices.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a circularly polarized photocurrent regulation method of Sb ₂ Te ₃ topological surface state, which can easily and effectively realize regulation of CPGE in TIs.

To achieve the above object, the present invention adopts the following technical solutions:

A method for regulating circularly polarized photocurrent of Sb ₂ Te ₃ topological surface state, comprising the following steps:

Step S1: growing a Sb ₂ Te ₃ sample on an indium phosphide substrate with molecular beam epitaxy equipment, and fabricating a pair of point electrodes on the surface of the sample by mechanically pressing indium;

Step S2: constructing a stress device, and fixing the sample on the stress device with epoxy resin;

Step S3: emit laser light through the chopper, polarizer and quarter-wave plate in sequence, and irradiate the geometric center of the sample, that is, the center of the line connecting the two electrodes, to measure and extract the circularly polarized photocurrent;

Step S4: changing the magnitude of the stress applied by the stress device, and analyzing the variation trend of the circularly polarized photocurrent with the stress;

Step S5: measure and analyze the XPS spectrum of the Sb ₂ Te ₃ sample, calculate the energy band distribution of the interface between the substrate and Sb ₂ Te ₃ , if the band order is less than zero, there is the possibility of spin injection; The CPGE current of the Sb ₂ Te ₃ sample is regulated by stress, which verifies the regulation effect of the method of controlling the circularly polarized photocurrent in Sb ₂ Te ₃ by the synergistic effect of stress and substrate injection.

Further, the stress device includes a rectangular polycarbonate plastic strip, a steel stress table, a stress thimble and a differential sleeve; the sample is fixed in the center of the rectangular polycarbonate plastic strip using epoxy resin, and is mounted on the steel stress table , apply uniaxial stress to the sample through the stress top by rotating the differential sleeve, measure the distance of the polycarbonate plastic strip from the left edge to the right edge of the steel stress table, denoted as 2a, measure the thickness of the polycarbonate plastic strip, denoted as h.

Further, the step S4 is specifically:

Step S41: Rotate the differential sleeve of the stress device to bend the sample to apply stress to the sample. Read the distance that the stress thimble moves forward from the differential sleeve, denoted as J _z , and calculate the magnitude of the applied stress by the formula ex _{= 3hJ z /} 2a ² ;

Step S42: rotate the quarter-wave plate by the stepping motor, collect the photocurrent through the electrodes, the collected photocurrent is sequentially input to the preamplifier and the lock-in amplifier, and the signal output by the lock-in amplifier is input to the computer through the data acquisition card; The rotation angle of one wave plate is from 0 degrees to 360 degrees, and the step size is 5 degrees, that is, a photocurrent data J is collected every 5 degrees;

Step S43: Fit the measured photocurrent J under different quarter-wave plate rotation angles with the following formula:

Among them, J _C is the circularly polarized photocurrent, _L1 and L2 are the photocurrents caused by _linearly polarized light, and J0 is the photocurrent caused by the photovoltaic effect, the thermoelectric effect, and the _Danpe effect, referred to as the background current for short; , obtain the circularly polarized photocurrent J _C ;

Step S44: Repeat steps S41 to S43, and measure the circularly polarized photocurrent J _C of the Sb ₂ Te ₃ film under different stresses.

Further, the step S5 is specifically:

Step S51: measuring the energy band order at the InP/Sb ₂ Te ₃ interface by X-ray photoelectron spectroscopy, and the measured conduction band order ΔE _c is less than zero, indicating that electrons can be injected from InP into the Sb ₂ Te ₃ layer;

Step S52: Fix the InP substrate with epoxy resin to fix the sample in the center of the rectangular polycarbonate plastic strip, install it on the self-made steel stress stage, and apply uniaxial stress to the sample by rotating the differential sleeve; Repeat steps S3 to S4 , the circularly polarized photocurrent J _c0 of the InP substrate under different stresses was measured; the variation trend of the measured circularly polarized photocurrent with the stress of the InP substrate was the same as that of the Sb ₂ Te ₃ film, indicating that the Sb The circularly polarized photocurrent _of the _2Te3 film is influenced by the spin injection into the InP substrate.

Further, the Sb ₂ Te ₃ sample has a rectangular single crystal structure, the short side of the sample is ≥3mm, the long side is ≥5mm, and the thickness is 7-30nm; Pressed on the midline of the inside of the two long sides of the rectangle, the diameter is about 0.25mm, and the electrode spacing is about 2mm.

Further, the power of the laser is between 30-200 mW, the incident surface of the laser is perpendicular to the line connecting the two electrodes; the angle between the laser beam and the normal line of the sample surface is between 10 degrees and 45 degrees.

Compared with the prior art, the present invention has the following beneficial effects:

1. The method of controlling the CPGE current in Sb ₂ Te ₃ through the synergistic effect of strain and substrate injection in the present invention is very simple and easy to implement, with low cost, and does not involve the energy band engineering in the material growth process and the preparation of the external gate in the device preparation, It is beneficial to promote the application in the future;

2. The control effect of the present invention is obvious, the control range is large, and it is easy to realize continuous control.

Description of drawings

FIG. 1 is a schematic structural diagram of a self-stressing device in an embodiment of the present invention.

FIG. 2 is a schematic diagram of a test system and optical path distribution for measuring CPGE in an embodiment of the present invention.

3 is a graph of CPGE current as a function of stress measured for a 30 nm Sb ₂ Te ₃ sample grown on an InP substrate in an embodiment of the present invention. The black rectangle is the experimental data, and the solid line is the linear fitting result.

FIG. 4 is the measured resistance of (a) a 12 nm Sb ₂ Te ₃ sample grown on a strontium titanate (STO) substrate and (b) a 30 nm Sb ₂ Te ₃ sample grown on an InP substrate, measured in embodiments of the present invention Graph of stress as a function of stress. The black rectangle is the experimental data, and the solid line is the linear fitting result.

Fig. 5 is the XPS spectrum measured in the embodiment of the present invention, it is InP substrate In element characteristic peak core energy level In3d and valence band top (VBM) respectively; 7nm Sb ₂ Te ₃ /InP sample Te element characteristic peak core Energy level Te3d and In element characteristic peak core energy level In3d; 30nm Sb ₂ Te ₃ /InP sample Te element characteristic peak core energy level Te3d and valence band top (VBM); 7nm Sb ₂ Te ₃ /InP sample Te element characteristic peak core Energy level Te3d and In element characteristic peak core energy level In3d.

FIG. 6 is the energy band distribution of the InP/Sb ₂ Te ₃ interface measured in the embodiment of the present invention.

FIG. 7 is a curve of measuring CPGE current in InP substrate as a function of stress in an embodiment of the present invention. The black rectangle is the experimental data, and the solid line is the linear fitting result.

FIG. 8 is a schematic diagram of an InP/Sb ₂ Te ₃ interface spin injection model in an embodiment of the present invention.

FIG. 9 is the variation curve of the CPGE current with the incident angle in the 18 nm Sb ₂ Te ₃ /STO sample under normal incidence and back incidence conditions of polarized light measured in the embodiment of the present invention. The black rectangle is the experimental data, and the solid line is the linear fitting result. The inset is a schematic diagram of the back-incidence light path setup.

FIG. 10 is a curve of CPGE current as a function of stress of the Sb ₂ Te ₃ sample grown on the strontium titanate substrate of the comparative sample in the embodiment of the present invention. The black rectangle is the experimental data, and the solid line is the linear fitting result.

Detailed ways

The present invention will be further described below with reference to the accompanying drawings and embodiments.

Please refer to FIG. 1 , the present invention provides a circularly polarized photocurrent regulation method of Sb ₂ Te ₃ topological surface state, comprising the following steps:

Step S1 : growing a Sb ₂ Te ₃ sample on an indium phosphide (InP) substrate with molecular beam epitaxy equipment, and fabricating a pair of point electrodes on the surface of the sample by a mechanical indium pressing method.

In a preferred embodiment of the present invention, the Sb ₂ Te ₃ sample has a rectangular single crystal structure, the short side of the sample is ≥ 3 mm, the long side is ≥ 5 mm, and the thickness is 7-30 nm (including 7 nm and 30 nm). The pair of point-shaped indium electrodes are pressed on the midline of the inner sides of the two long sides of the rectangle by thin needles, and are approximately circular with a diameter of 0.25 mm, and the distance between the inner sides of the two electrodes is greater than or equal to 2 nm. Then, the platinum wire is pressed on the indium electrode with indium, and the platinum wire is the electrode lead.

Step S2: Use epoxy resin to fix the sample in the center of the rectangular polycarbonate plastic strip, install it on a self-made steel stress stage, and apply uniaxial stress to the sample by rotating the differential sleeve. The stress device is shown in Figure 1. Measure the distance of the polycarbonate plastic strip from the left edge to the right edge of the steel stress table, denoted as 2a, as shown in Figure 1. Measure the thickness of the polycarbonate plastic strip and denote it as h.

The polycarbonate plastic strip used is 38mm in length, 5mm in width and 2mm in thickness. The effective width 2a of the stress table applied to the stress is 20 mm. In this embodiment, the curing process of the epoxy resin is annealing at 60° C. for 2 hours in a vacuum environment.

Step S3: the laser is emitted by the laser to pass through the chopper, the polarizer and the quarter-wave plate in sequence, and is irradiated on the geometric center of the sample, that is, the center of the connection line between the two electrodes.

Preferably, in this embodiment, the power of the used laser is between 30-200 mW, and the used laser can excite the band-edge excitation of the InP substrate or can excite the internal defects of the InP to generate a circularly polarized photocurrent, which is then hit on the sample. The diameter of the spot is smaller than the distance between the two point-like indium electrodes. The incident surface of the laser is perpendicular to the line connecting the two electrodes; the angle between the laser beam and the normal to the surface of the sample is between 10 degrees and 45 degrees.

Preferably, in this embodiment, the power of the used laser is 100 mW, the spot diameter of the laser is 1 mm, and the wavelength of the laser is 1064 nm. The angle between the laser beam and the normal to the sample surface is 30 degrees.

Step S4: Rotate the differential sleeve of the stress device to bend the sample to apply stress to the sample. The distance the stress thimble moved forward was read from the differential sleeve and recorded as J _z . The magnitude of the applied stress is calculated by the formula ex _{= 3hJ z /} 2a ² . The longitudinal compressive strain of the sample can be calculated by the formula: _{ez =} -(C ₁₂ /C ₁₃ ) _ex , where C ₁₂ and C ₁₃ are the elastic coefficients of the Sb ₂ Te ₃ sample. In this embodiment, let the step length J _z0 =0.01mm, e ₀ =3 _× 10 ^-4 is calculated, and the stress applied magnitude is described by ex /e ₀ .

The quarter-wave plate is rotated by the stepping motor, and the photocurrent is collected through the electrodes. The collected photocurrent is input to the preamplifier and the lock-in amplifier in turn, and the output signal of the lock-in amplifier is input to the computer through the data acquisition card. The rotation angle of the quarter-wave plate is from 0 degrees to 360 degrees, and the step size is 5 degrees, that is, a photocurrent data J is collected every 5 degrees.

Fit the measured photocurrent J at different quarter-wave plate rotation angles with the following formula:

Formula 1)

Among them, J _C is the circularly polarized photocurrent, _L1 and L2 are the photocurrents caused by _linearly polarized light, and J0 is the photocurrent caused by the photovoltaic effect, the thermoelectric effect, and the _Danpe effect, referred to as the background current for short; , the circularly polarized photocurrent J _C is obtained.

Repeat steps S41 to S43 to measure the circularly polarized photocurrent J _C of the Sb ₂ Te ₃ film under different stresses. The measurement results are shown in Figure 3, where the black rectangle is the experimental data, and the solid line is the result of linear fitting. It can be seen that with the increase of the applied strain, the CPGE current in the Sb ₂ Te ₃ thin film sample exhibits a linear monotonically decreasing trend.

In this example, the resistance of Sb ₂ Te ₃ films on different substrates was measured as a function of stress, as shown in FIG. 4 . It can be seen that with the increase of stress, the resistance of Sb ₂ Te ₃ film also increases, which is because the Fermi level in the topological surface state moves into the band gap with the increase of strain, and at the same time causes the Dirac point to move towards the middle of the band gap. move, resulting in an increase in resistance. The shift of the Fermi level to the band gap can reduce the concentration of bulk carriers, thereby reducing the scattering of spin-polarized photogenerated carriers by bulk carriers and increasing the CPGE current. However, the change of resistance with strain is very small, indicating that the shift of the Fermi level is small, and the CPGE current is experimentally observed to decrease with increasing strain, so the shift of the Fermi level is not the cause of the CPGE change.

Through literature investigation, it is found that with the increase of applied strain, the spin-orbit coupling strength of Sb ₂ Te ₃ topological surface states decreases, while the size of CPGE is proportional to the spin-orbit coupling strength, resulting in a decrease in CPGE current. Therefore, the decrease of CPGE current with stress is due to the decrease of the spin _- orbit coupling _of the topological surface states of Sb2Te3 with stress.

Step S5: measure the energy band order at the InP/Sb ₂ Te ₃ interface by X-ray photoelectron spectroscopy, the measured conduction band order ΔE _c is less than zero, indicating that electrons can be injected from InP into the Sb ₂ Te ₃ layer

记XPS2中Te元素特征峰核心能级Te3d与价带顶分别为

记XPS3中In元素特征峰核心能级In3d与价带顶分别为

In this embodiment, a 7nm Sb ₂ Te ₃ film and a 30nm Sb ₂ Te ₃ film were grown on the InP substrate by molecular beam epitaxy equipment. Then, the 7 nm Sb ₂ Te ₃ film and The 30nm Sb ₂ Te ₃ film and the InP substrate were measured by X-ray photoelectron spectroscopy (XPS). The XPS spectra I remember are XPS1, XPS2, and XPS3 spectra, respectively. The measurement results are shown in Figure 5. The core energy level Te3d of the characteristic peak of Te element and the core energy level In3d of the characteristic peak of In element in the measured XPS1 are recorded as

The core energy level Te3d and the top of the valence band of the characteristic peak of Te element in XPS2 are written as

The core energy level In3d and valence band top of the characteristic peak of In element in XPS3 are written as

分别为572.65±0.05eV和444.75±0.05eV，所测得的

分别为572.65±0.05eV和-0.38±0.1eV，所测得的

分别为444.1±0.05eV和0.34±0.1eV。通过如下的公式(2)计算InP衬底与Sb₂Te₃的价带顶带阶ΔE_v，得ΔE_v＝-1.37±0.1eV。In this example, the measured

572.65±0.05eV and 444.75±0.05eV, respectively, the measured

572.65±0.05eV and -0.38±0.1eV, respectively, the measured

are 444.1 ± 0.05 eV and 0.34 ± 0.1 eV, respectively. The valence top band order ΔE _v of the InP substrate and Sb ₂ Te ₃ is calculated by the following formula (2), and ΔE _v =−1.37±0.1 eV is obtained.

可以得出InP衬底与Sb₂Te₃的导带底差值ΔEc。其中，

和

分别为InP衬底和Sb₂Te₃薄膜的带隙，大小分别为1.34eV和0.23eV。计算得出：ΔEc＝-2.48±0.1eV。从而得到InP衬底与Sb₂Te₃异质结的能带分布，如图6所示。可以看出，Sb₂Te₃/InP异质结构的能带取向属于III型，由于不存在势垒，InP导带中的电子可以转移注入到Sb₂Te₃薄膜中。因此，Sb₂Te₃/InP异质结构的能带分布使得自旋极化载流子可以从衬底注入到Sb₂Te₃薄膜中。by formula

The conduction band bottom difference ΔEc between InP substrate and Sb ₂ Te ₃ can be obtained. in,

and

are the band gaps of the InP substrate and the Sb ₂ Te ₃ film, which are 1.34 eV and 0.23 eV, respectively. Calculated: ΔEc=-2.48±0.1eV. Thus, the energy band distribution of the InP substrate and the Sb ₂ Te ₃ heterojunction is obtained, as shown in FIG. 6 . It can be seen that the energy band orientation of the Sb ₂ Te ₃ /InP heterostructure belongs to type III, and electrons in the conduction band of InP can be transferred and injected into the Sb ₂ Te ₃ film due to the absence of potential barriers. Therefore, the energy band distribution of the Sb ₂ Te ₃ /InP heterostructure enables the injection of spin-polarized carriers from the substrate into the Sb ₂ Te ₃ thin film.

Step S6: Fix the InP substrate with epoxy resin to fix the sample in the center of a rectangular polycarbonate plastic strip, mount it on a self-made steel stress stage, and apply uniaxial stress to the sample by rotating the differential sleeve. Steps S3 to S4 are repeated, and the circularly polarized photocurrent J _c0 of the InP substrate under different stresses is measured, as shown in FIG. 7 . The variation trend of the measured circularly polarized photocurrent of the InP substrate with stress is the same as that _of the _Sb2Te3 film, indicating that the circularly polarized photocurrent _of the _Sb2Te3 film is affected by the spin injection of the InP substrate .

A schematic diagram of the substrate injection model of spin-polarized carriers is shown in Figure 8. Although the band gap (1.35 eV) of InP is larger than the photon energy of 1064 nm light, there are some defects in the InP substrate, which introduce some defect energy levels in the band gap. Therefore, under the excitation of 1064 nm light, the electrons in the defect level will absorb the light and transition into the conduction band, generating spin-polarized carriers. The spin _- polarized electrons will be injected into the _Sb2Te3 film from the substrate and recombine with the spin _- polarized carriers _on the lower surface of Sb2Te3, thereby reducing the CPGE current in the lower surface state. Due to the short spin diffusion length of Sb ₂ Te ₃ , the 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 have opposite signs, the CPGE currents they generate will be opposite. If our sample is dominated by the contribution of the upper surface states to the CPGE current, then the decrease in the signal of the lower surface state will enhance the overall CPGE current. Next, we analyze whether the contribution of the top surface state to the CPGE current is dominant in our sample by the CPGE measurements at the front and back side of the laser.

The variable incident angle CPGE measurements were performed on the Sb ₂ Te ₃ /STO samples with a thickness of 18 nm under the conditions of front and rear incidence of circularly polarized light. Because STO does not absorb light at 1064 nm, CPGE current measurements under laser back-incidence can be performed. The experimental results are shown in Figure 9, and the data are fitted by the following formula (3).

这里，J_CPGEy是沿y方向的CPGE电流，γ是二阶赝张量，与材料的自旋轨道耦合成正比。

是指向光传播方向的单位矢量。在我们所采用的光路中，对于某一个入射角，

在正入射和背入射下将保持不变，这可从对比图3和图9插图中入射角的方向得到。因此，如果CPGE电流的符号在正、背入射两种情况下保持相同，则CPGE的主要贡献必然来自相同的拓扑表面态。考虑到在圆偏振光正面入射下，上表面吸收的光强度大于当光从背面入射时上表面态吸收的光强度，导致在正入射下上表面产生更大的CPGE电流。因此，可以推断上表面态在此18nm的Sb₂Te₃/STO的样品中起主导作用。由于其他样品在某一给定入射角下显示出与18nmSb₂Te₃/STO样品相同的符号，因此可以推断，在这些样品中上表面态对CPGE电流的贡献占主导。Here, n is the refractive index _of the _{Sb2Te3 film, and ACPGE is} a constant related to the spin-orbit coupling strength of the sample. The dependence of the CPGE current on the incident angle can be well fitted by the phenomenological formula (3). It can be seen that for the 18nmSb ₂ Te ₃ /STO sample, the CPGE currents of the forward and back incidents show the same sign, and the CPGE amplitude under the normal incidence is larger than that of the back incident CPGE. This phenomenon indicates that the upper surface state will play a dominant role in both cases of circularly polarized light with forward and backward incidence. The reasons are as follows: the surface state of Sb ₂ Te ₃ belongs to the C _3v point group, and CPGE can be expressed by the phenomenological formula as

Here, J _CPGEy is the CPGE current along the y direction, and γ is the second-order pseudotensor proportional to the spin-orbit coupling of the material.

is the unit vector pointing in the direction of light propagation. In the light path we adopted, for a certain incident angle,

It will remain the same under normal and back incidence, which can be obtained by comparing the orientation of the incidence angles in the insets of Figures 3 and 9. Therefore, if the sign of the CPGE current remains the same for both forward and backward incidence, the main contribution of CPGE must come from the same topological surface states. Considering that under the frontal incidence of circularly polarized light, the light intensity absorbed by the upper surface is greater than that absorbed by the upper surface state when the light is incident from the backside, resulting in a larger CPGE current on the upper surface under normal incidence. Therefore, it can be inferred that the upper surface state plays a dominant role in this 18 nm sample of Sb ₂ Te ₃ /STO. Since the other samples show the same sign as the 18 nmSb ₂ Te ₃ /STO sample at a given incident angle, it can be inferred that the contribution of the upper surface states to the CPGE current dominates in these samples.

Since the coefficients of the spin-orbit coupling between the upper and lower surfaces of Sb ₂ Te ₃ are opposite, CPGE currents in opposite directions will be generated, while the total CPGE current is dominated by the upper surface states, so the reduced contribution of the lower surface states will enhance the net CPGE current. Therefore, the spin implantation of the InP substrate will increase the total CPGE current, but the _{CPGE of} the InP substrate will also decrease or even reverse the sign under the action of stress, as shown in Fig. The spintronics will decrease with increasing stress; further resulting in a decrease in _CPGE in the _Sb2Te3 film. In summary, the Sb ₂ Te ₃ grown on the InP substrate is more regulated by the stress under the synergistic effect of spin implantation without spin implantation, that is, under the same stress, if there is substrate implantation The greater the amplitude of CPGE current change, the more obvious the regulation effect.

In order to verify the regulation effect of substrate implantation, we measured the CPGE current versus stress curve of the Sb ₂ Te ₃ sample without substrate implant effect, that is, we measured the Sb 12 nm thick grown on the strontium titanate substrate The variation curve of CPGE current with stress of ₂ Te ₃ sample is shown in Fig. 10. The band gap of the strontium titanate substrate is 1.9eV, which is much larger than the photon energy of the 1064nm laser, and we have not measured the CPGE current of the strontium titanate substrate under the excitation of the 1064nm laser, indicating that there is no circular defect state. Polarized photocurrent. Therefore, there is no current contribution from substrate spin injection in the CPGE current _of Sb2Te3 samples grown _on strontium titanate substrates. Comparing the growth of 12 nm Sb _{2 Te 3 on the STO substrate and the growth of 30 nm Sb 2 Te 3 on the} InP substrate, it can be seen that the magnitude of the CPGE current decreases with the increase of the uniaxial strain. Specifically, when the uniaxial strain ex _is 0.0066, the CPGE of the 12 nm Sb ₂ Te ₃ /STO sample drops to 44% compared to the unstressed sample. However, the size of the CPGE in the 30 nm Sb ₂ Te ₃ /InP sample can be tuned to zero by a uniaxial strain of 0.0033, i.e., the tuning range is up to 100%. It can be seen that the Sb ₂ Te ₃ samples grown on the InP substrate have better CPGE regulation effect, which is caused by the synergistic effect of the stress and the spin injection of the InP substrate.

To sum up, the present invention utilizes the synergistic effect of uniaxial stress and substrate injection effect to achieve the purpose of regulating the current of CPGE in Sb ₂ Te ₃ . Because the spin-orbit coupling strength of the Sb ₂ Te ₃ topological surface state decreases with the increase of applied strain, and the size of CPGE is positively correlated with the spin-orbit coupling strength, resulting in a decrease in CPGE current; Spin injection will increase the total CPGE current, but the spin electrons injected into the Sb ₂ Te ₃ film by the InP substrate under the action of stress decrease with the increase of the stress, so the Sb ₂ Te ₃ grown on the InP substrate is in the spin Under the synergistic effect of implantation, the effect of stress regulation of CPGE current is more significant than that on STO substrates. Therefore, the purpose of regulating the CPGE current in Sb ₂ Te ₃ can be better achieved by using the synergistic effect of uniaxial stress and substrate injection effect. The method provided by the invention is convenient to implement, low in cost, good in regulation effect, and easy to realize continuous regulation. .

The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of 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 J_zBy the formula e_x＝3hJ_z/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, J_CIs 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 fitting_C；

Step S44 repeating steps S41 to S43 to measure Sb₂Te₃Circular polarized light current J of film under different stress_C。

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 E_cLess 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 stresses_c0(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.

Images