A method for enhancing valley polarization of monolayer tungsten disulfide by using lanthanum manganese oxide substrate

Abstract

This invention relates to a method for enhancing the valley polarization of monolayer tungsten disulfide using a ferromagnetic lanthanum manganese oxide substrate. A lanthanum manganese oxide (LMO) thin film is prepared using laser pulse deposition. The LMO thin film has the structural formula LaMnO3 and a thickness of 30 nm to 40 nm. A thin layer of tungsten disulfide (WS2) is prepared. The WS2 thin layer is 1-10 WS2 molecule-thickness WS2 material. The thin layer of WS2 is transferred to the LMO thin film using a dry transfer method. WS2 molecules are transferred to the LMO thin film through van der Waals forces, forming a material structure with a monolayer of WS2 molecules on the LMO substrate, thereby enhancing the valley polarization of the monolayer tungsten disulfide using the lanthanum manganese oxide substrate. The material structure with a monolayer of WS2 molecules on the LMO substrate is a monolayer WS2 / LMO van der Waals heterojunction.

Description

Technical Field

[0001] This invention relates to the field of materials information, specifically to enhancing the valley polarization of monolayer tungsten disulfide by constructing a lanthanum manganese ferromagnetic material with a monolayer tungsten disulfide van der Waals heterostructure. Background Technology

[0002] Due to the breaking of inversion symmetry, monolayer tungsten disulfide (WS2) possesses two degenerate but unequal energy valleys, providing electrons with a new degree of freedom in addition to charge and spin. Selectively pumping one of these valleys with circularly polarized light can generate an unbalanced carrier population between the +K and -K valleys, leading to valley-polarized light emission. Achieving high valley polarization is a necessary step in realizing valley devices; however, due to inter-valley scattering, the reported valley polarization degrees are currently relatively low.

[0003] Currently reported methods for improving valley polarization mainly include using strong magnetic fields, resonant excitation, heterojunctions, and defect stress modulation. These methods either require stringent experimental conditions or result in low valley polarization. For example, applying a strong magnetic field linearly increases valley polarization, but at a strong magnetic field of 15 Tesla and a temperature of 4K, the valley polarization of monolayer WS2 only increases to 30%. This method not only requires a strong magnetic field but also does not significantly enhance valley polarization. Resonant excitation can increase valley polarization to 40% at 10K, but this method requires complex experimental equipment to filter out pump light, and the enhancement is still low. Constructing heterojunctions, such as in a WS2-graphene heterojunction, can achieve a valley polarization of 41% at 4K, but the preparation of such heterojunctions is difficult and the enhancement is not significant. Defect and stress modulation can also control valley polarization, and in CVD-grown, defect-rich monolayer WS2, the valley polarization can reach 90% at 80K, but this method is not easy to control precisely and may even reduce polarization. The above methods either require stringent conditions, such as strong magnetic fields, resonant excitation testing devices, or complex preparation processes, or their valley polarization optimization efficiency is low.

[0004] Therefore, a simple and effective method for manipulating valley polarization is very important and urgently needed. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the existing methods by proposing a method for improving the valley polarization of a monolayer tungsten disulfide using a lanthanum manganese oxide substrate.

[0006] Therefore, this invention proposes a method for enhancing the valley polarization of a monolayer tungsten disulfide using a lanthanum manganese oxide substrate, the method comprising:

[0007] Lanthanum manganese oxide (LMO) thin films were prepared using laser pulse deposition; the LMO thin films had the structural formula LaMnO3 and a thickness of 30 nm to 40 nm.

[0008] Preparation of thin-layer tungsten disulfide (WS2); the thin-layer WS2 is a WS2 material with a thickness of 1-10 WS2 molecules;

[0009] The thin WS2 layer is transferred to the LMO film using a dry transfer method. WS2 molecules are transferred to the LMO film through van der Waals forces, forming a material structure with a monolayer of WS2 molecules on the LMO substrate. This enhances the valley polarization of the monolayer tungsten disulfide using a lanthanum manganese oxide substrate. The material structure with a monolayer of WS2 molecules on the LMO substrate is a monolayer WS2 / LMO van der Waals heterojunction.

[0010] Preferably, the preparation of LMO thin films using the laser pulse deposition method specifically involves depositing LMO thin films on (001) oriented SrTiO3 (STO) substrates using a pulsed laser deposition (PLD) system at 700-750°C.

[0011] More preferably, during the deposition process, the pulsed laser deposition PLD system uses a XeCl laser with a center wavelength of 308 nm at a frequency of 2-4 Hz to provide 1.2-1.8 J cm⁻¹. -2 The laser density is set at 7-10 cm between the target material and the STO substrate, and the oxygen partial pressure is maintained at 0.5-2 Pa. The deposition process lasts for 15-20 min, followed by cooling to room temperature at a rate of 20-30 °C / min.

[0012] Preferably, the LMO film is a ferromagnetic material with a Curie temperature of 130K-180K.

[0013] Preferably, the method for preparing the thin-layer tungsten disulfide is a mechanical exfoliation method, specifically including:

[0014] Cut sheets of 0.2-0.3cm in length and width from the block of WS2 material, place them on 3M Scotch tape, fold the tape in half and then unfold it, repeating this process 5-8 times.

[0015] Press a polydimethylsiloxane (PDMS) film onto the side of an unfolded tape containing the WS2 material, and peel the PDMS with the WS2 material attached off the tape to obtain the thin layer of tungsten disulfide.

[0016] More preferably, after obtaining the thin layer of tungsten disulfide, the method further includes: placing the PDMS film with WS2 material attached under an optical microscope to qualitatively determine the thickness of the thin layer of WS2.

[0017] More preferably, the method of transferring the thin WS2 layer onto the LMO film by dry transfer specifically includes:

[0018] Press the WS2 side of the thin WS2 layer onto the LMO film with the WS2 side facing the LMO film;

[0019] Place the LMO film on a hot plate and heat it at 90 to 100°C for 1-2 minutes. The PDMS film becomes deadhesive through heating. Peel off the PDMS film and transfer WS2 onto the LMO film using van der Waals forces.

[0020] More preferably, after forming a material structure with a monolayer of WS2 molecules on the LMO substrate, the method further includes: measuring the thickness of the WS2 material on the LMO substrate by atomic force microscopy (AFM) to determine that the thickness is less than 1 nm.

[0021] Preferably, the method further includes testing the valley polarization of a single layer of tungsten disulfide; the test temperature is 4.2K, the test device is a micro-area confocal fluorescence test device, the excitation method is non-resonant excitation, the excitation light is a 532nm continuous laser, and the excitation light power is 1-3mW;

[0022] The method for testing the valley polarizability of the monolayer tungsten disulfide is as follows: an excitation light with a fixed circular polarization direction is used to collect a pair of fluorescence signals with orthogonal circular polarization directions; wherein, the excitation light polarization direction is left-handed or right-handed circularly polarized light; the pair of orthogonal fluorescence signals are left-handed and right-handed fluorescence signals; the polarization direction is selected by a combination of a polarizer and a quarter-wave plate.

[0023] The valley polarization of the monolayer tungsten disulfide is the valley polarization of the detected intrinsic neutral excitons, and the calculation method is as follows:

[0024] P v =(I left -I right ) / (I left +I right );

[0025] The P v For valley polarization, the I left The intensity of the intrinsic neutral exciton left-handed fluorescence signal, wherein I right The intensity of the intrinsic neutral exciton dextrorotatory fluorescence signal is denoted as α.

[0026] Preferably, the method for testing the valley polarizability of the monolayer tungsten disulfide is as follows:

[0027] The laser light is converted into linearly polarized light by passing it through a polarizer. Then, a quarter-wave plate is placed at an angle of 45 degrees or -45 degrees to the direction of linear polarization. After passing through the quarter-wave plate, the laser light becomes left-handed or right-handed circularly polarized light.

[0028] The fluorescence signal of a monolayer of tungsten disulfide on an LMO substrate is sequentially passed through a quarter-wave plate and a polarizer. By setting the angle between the quarter-wave plate and the polarizer to 45 degrees or -45 degrees, left-handed and right-handed fluorescence signals are collected.

[0029] This invention constructs a monolayer WS2 / LMO van der Waals heterojunction by forming a monolayer of tungsten disulfide on a lanthanum manganese oxide substrate. Employing a non-resonant excitation method, it eliminates the need for complex experimental setups. The use of the lanthanum manganese oxide substrate significantly enhances the valley polarization of the monolayer tungsten disulfide, achieving a substantial increase of up to 80%. Furthermore, the construction of the van der Waals heterojunction in this invention is simple and easy to perform, facilitating large-area fabrication and application. The method significantly improves valley polarization, providing a novel approach and concept for valley polarization manipulation, which is beneficial for the development and application of valley devices. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating a method for improving the valley polarization of a monolayer tungsten disulfide using a lanthanum manganese oxide substrate, as described in an embodiment of the present invention.

[0031] Figure 2 (a) is a schematic diagram of the crystal structure of the LMO thin film according to an embodiment of the present invention;

[0032] Figure 2 (b) High-resolution X-ray diffraction (XRD) characterization of the crystallinity of the LMO thin film in the embodiment of the present invention;

[0033] Figure 2 (c) is an X-ray reflectance (XRR) pattern of the LMO thin film in the embodiment of the present invention;

[0034] Figure 3 (a) An optical micrograph of the WS2 / LMO heterojunction prepared in the embodiment of the present invention;

[0035] Figure 3 (b) An atomic force microscope (AFM) image of the WS2 / LMO heterojunction prepared in the embodiment of the present invention;

[0036] Figure 4 This is a graph showing the measurement results of the valley polarization of a single layer of tungsten disulfide in the WS2 / LMO heterojunction prepared in the embodiments of the present invention. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0038] This invention proposes a method for enhancing the valley polarization of a monolayer tungsten disulfide using a lanthanum manganese oxide substrate, the main steps of which are as follows: Figure 1 As shown, it includes:

[0039] Step 110: Prepare lanthanum manganese oxide (LMO) thin films using laser pulse deposition.

[0040] Specifically, the LMO thin film was prepared using pulsed laser deposition (PLD) at 700-750°C on a (001) oriented SrTiO3 (STO) substrate. During deposition, the PLD system used a XeCl laser with a center wavelength of 308 nm at a frequency of 2-4 Hz, providing 1.2-1.8 J / cm². -2 The laser density is controlled, the distance between the target material and the STO substrate is 7-10 cm, and the oxygen partial pressure is maintained at 0.5-2 Pa. The deposition process takes 15-20 min, followed by cooling to room temperature at a rate of 20-30 °C / min. This method can yield LMO films with large area, good quality, and suitable thickness.

[0041] The structure of LMO thin films is LaMnO3, which is a ferromagnetic material with a thickness of 30 nm to 40 nm and a Curie temperature of 130 K to 180 K.

[0042] Step 120: Prepare a thin layer of tungsten disulfide (WS2);

[0043] Among them, thin-layer WS2 refers to WS2 material with a thickness of 1-10 WS2 molecules;

[0044] The specific method for preparing thin-layer tungsten disulfide is mechanical exfoliation, including:

[0045] Step 121: Cut sheets of 0.2-0.3 cm in length and width from the block of WS2 material, place them on 3MScotch tape, fold the tape in half and unfold it, repeat 5-8 times.

[0046] Step 122: Gently press the polydimethylsiloxane (PDMS) film onto the side of the unfolded tape containing the WS2 material, and slowly peel the PDMS with the WS2 material adhering to it off the tape to obtain a thin layer of tungsten disulfide.

[0047] After obtaining a thin layer of tungsten disulfide, the PDMS film with the WS2 material attached can be placed under an optical microscope, and the thickness of the WS2 layer can be qualitatively determined by observing the film's color. A near-transparent color indicates a WS2 layer with a thickness of 1-10 WS2 molecules. This step is not the final step in WS2 transfer, therefore the WS2 thickness requirement is not very strict; a near-transparent thin layer is sufficient, typically 1-10 layers, and does not necessarily have to be a single layer.

[0048] Steps 110 and 120 can be executed either sequentially or simultaneously.

[0049] Step 130: A thin layer of WS2 is transferred onto an LMO film using a dry transfer method. WS2 molecules are transferred onto the LMO film by van der Waals forces to form a material structure with a single layer of WS2 molecules on an LMO substrate, thereby enhancing the valley polarization of the single layer of tungsten disulfide using a lanthanum manganese oxide substrate.

[0050] Among them, the material structure with a single layer of WS2 molecules on the LMO substrate is a single-layer WS2 / LMO van der Waals heterojunction.

[0051] The dry transfer method for transferring thin WS2 layers onto LMO films specifically includes:

[0052] Step 131: Press the WS2 side of the thin WS2 layer onto the LMO film with the WS2 side facing it.

[0053] Step 132: Place the LMO film on a hot plate and heat it at 90 to 100°C for 1-2 minutes. The PDMS film will become de-adhesive through heating. Slowly peel off the PDMS film and transfer WS2 onto the LMO film through van der Waals forces.

[0054] After forming a material structure with a monolayer of WS2 molecules on an LMO substrate, a thin layer of WS2 with a color close to that of the LMO substrate can be found first by using an optical microscope. Then, the thickness of the WS2 material on the LMO substrate can be measured by atomic force microscopy (AFM). If the thickness is less than 1 nm, the monolayer WS2 / LMO van der Waals heterostructure is considered to have been successfully constructed.

[0055] Then the valley polarization of a single layer of tungsten disulfide can be tested.

[0056] The test temperature was 4.2K, the test device was a micro-area confocal fluorescence test device, the excitation method was non-resonant excitation, the excitation light was a 532nm continuous laser, and the excitation light power was 1-3mW.

[0057] The method for testing the valley polarizability of monolayer tungsten disulfide is as follows: an excitation light with a fixed circular polarization direction is used to collect a pair of fluorescence signals with orthogonal circular polarization directions; wherein, the excitation light polarization direction is left-handed or right-handed circularly polarized light; the pair of fluorescence signals with orthogonal directions are left-handed and right-handed fluorescence signals; the polarization direction is selected by a combination of a polarizer and a quarter-wave plate.

[0058] Specifically, the laser light is converted into linearly polarized light by passing it through a polarizer. Then, a quarter-wave plate is placed at an angle of 45 degrees or -45 degrees to the linear polarization direction. After passing through the quarter-wave plate, the laser light becomes left-handed or right-handed circularly polarized light. The fluorescence signal of a monolayer of tungsten disulfide on the LMO substrate is sequentially passed through a quarter-wave plate and a polarizer. By setting the angle between the quarter-wave plate and the polarizer to 45 degrees or -45 degrees, left-handed and right-handed fluorescence signals are collected.

[0059] The valley polarizability of a monolayer tungsten disulfide is the valley polarizability of the detected intrinsic neutral excitons, calculated as follows: P v =(I left -I right ) / (I left +I right ); where P v For valley polarization, I left I represents the intensity of the intrinsic neutral exciton left-handed fluorescence signal. right The intensity of the intrinsic neutral exciton dextrorotatory fluorescence signal is denoted as α.

[0060] The following is a specific example of a method for improving the valley polarization of a monolayer tungsten disulfide using a lanthanum manganese oxide substrate. The process includes:

[0061] 1. Preparation of LMO thin films:

[0062] LMO thin films were deposited at 730 °C on (001) oriented STO substrates using a pulsed laser deposition (PLD) system. During deposition, a XeCl laser with a center wavelength of 308 nm was used to provide 1.4 J / cm² at a frequency of 3 Hz. -2 The laser density was [value missing]. The distance between the target material and the substrate was 9 cm, and the oxygen partial pressure was maintained at 1.6 Pa. After 18 min of growth, an LMO film was obtained, and then [value missing] was grown at 25 °C for [value missing] min. -1 Cooled to room temperature at a rate of [missing information].

[0063] Figure 2 Characterization of the LMO thin film in this embodiment. Wherein, Figure 2 (a) is a schematic diagram of the LMO thin film crystal structure. The crystallinity of the LMO thin film is determined by... Figure 2(b) shows the high-resolution X-ray diffraction (XRD) characterization. Only peaks from the LMO film and the STO substrate are observed in the figure, demonstrating the purity of the LMO film. The X-ray reflectance (XRR) results of the LMO film are as follows: Figure 2 As shown in (c), the thickness of the LMO film is approximately 35 nm.

[0064] 2. Preparation of thin-layer tungsten disulfide:

[0065] First, use a blade to cut a piece about 0.3cm long and 0.2cm wide from the WS2 block, which is about 1cm in size. Place the piece on 3M Scotch tape, then fold the tape in half and unfold it. Repeat this process 7 times.

[0066] Gently press the PDMS film onto the tape that has been folded and unfolded 7 times and has WS2 material attached to it, and then slowly peel the PDMS with WS2 material attached off the tape.

[0067] 3. Preparation of van der Waals heterojunctions of monolayer tungsten disulfide and LMO thin films:

[0068] The PDMS film with the WS2 material attached was placed under an optical microscope to locate the thin WS2 layer, which was nearly transparent in color. The PDMS film with the WS2 layer attached was then gently pressed onto the LMO substrate with the WS2 side facing up. The film was placed on a hot stage and heated to 95 degrees Celsius for 1 minute. After that, it was removed from the hot stage, and the PDMS film was slowly peeled off the LMO substrate.

[0069] 4. Result Confirmation:

[0070] The LMO substrate containing WS2 was placed under an optical microscope to locate a thin layer of WS2 with a color close to that of the LMO substrate. Using an anodizing process (AFM), the thickness was measured; a thickness less than 1 nm was considered a monolayer of WS2. This process yielded a monolayer WS2 / LMO van der Waals heterojunction.

[0071] Figure 3 This is a characterization of the heterojunction of the present invention. Wherein, Figure 3 (a) is an optical micrograph of WS2 on an LMO substrate. Figure 3 (b) is the corresponding AFM image. The thickness of a single-layer WS2 can be confirmed by its thickness, which is approximately 0.9 nm.

[0072] 5. Characterization of valley polarization of monolayer tungsten disulfide in heterojunctions:

[0073] The heterojunction sample was placed in a continuous-flow cryogenic chamber, and the sample temperature was lowered to 4.2 K using a continuous flow of liquid helium. A micro-area confocal fluorescence testing system was constructed, and a monolayer of tungsten disulfide was non-resonantly excited using a 532 nm continuous-wave laser. Polarizers and quarter-wave plates were placed in the excitation and collection optical paths to achieve polarization excitation and collection, obtaining the left-handed and right-handed polarized fluorescence intensities, and calculating the valley polarization: P v =(I left -I right ) / (I left +I right ); where P v For valley polarization, I left I represents the intensity of the intrinsic neutral exciton left-handed fluorescence signal. right The intensity of the intrinsic neutral exciton dextrorotatory fluorescence signal is denoted as α. Figure 4 The results of the measurement of the valley polarization of a single layer of tungsten disulfide in this embodiment show that the valley polarization can reach 80% through non-resonant excitation.

[0074] This invention constructs a monolayer WS2 / LMO van der Waals heterojunction by forming a monolayer of tungsten disulfide on a lanthanum manganese oxide substrate. Employing a non-resonant excitation method, it eliminates the need for complex experimental setups. The use of the lanthanum manganese oxide substrate significantly enhances the valley polarization of the monolayer tungsten disulfide, achieving a substantial increase of up to 80%. Furthermore, the construction of the van der Waals heterojunction in this invention is simple and easy to perform, facilitating large-area fabrication and application. The method significantly improves valley polarization, providing a novel approach and concept for valley polarization manipulation, which is beneficial for the development and application of valley devices.

[0075] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for enhancing the valley polarization of a monolayer of tungsten disulfide using a lanthanum manganese oxide substrate, the method comprising: providing a substrate comprising a layer of lanthanum manganese oxide; and depositing a monolayer of tungsten disulfide on the substrate. The method comprises: Preparation of lanthanum manganese oxide film by laser pulse deposition method; the structural formula of the lanthanum manganese oxide film is LaMnO3, and the thickness is 30-40 nm; Preparation of thin layer of tungsten disulfide; the thin layer of tungsten disulfide is a tungsten disulfide material with a thickness of 1-10 layers of tungsten disulfide molecules; Transfer of the thin layer of tungsten disulfide to the lanthanum manganese oxide film by mechanical exfoliation method; the tungsten disulfide molecules are transferred to the lanthanum manganese oxide film by van der Waals force to form a material structure with single-layer tungsten disulfide molecules on the lanthanum manganese oxide substrate, thereby enhancing the valley polarization degree of the single-layer tungsten disulfide by using the lanthanum manganese oxide substrate; wherein the material structure with single-layer tungsten disulfide molecules on the lanthanum manganese oxide substrate is a single-layer tungsten disulfide / lanthanum manganese oxide van der Waals heterojunction; The method further comprises testing the valley polarization degree of the single-layer tungsten disulfide; the testing temperature of the testing is 4.2 K, the device of the testing is a micro-confocal fluorescence testing device, the excitation mode is non-resonant excitation, the excitation light is 532 nm continuous laser, and the power of the excitation light is 1-3 mW.

2. The method of claim 1, wherein the LaMnO substrate enhances the valley polarization of the monolayer WS2. The preparation of the lanthanum manganese oxide film by the laser pulse deposition method is specifically deposition of the lanthanum manganese oxide film on a (001) oriented SrTiO3 substrate by a pulsed laser deposition system at 700-750 DEG C.

3. The method of claim 2, wherein the LaMnO substrate enhances the valley polarization of the monolayer tungsten disulfide. In the process for preparing the lanthanum manganate oxide thin film by using the laser pulse deposition method, the pulse laser deposition system uses a XeCl laser with a central wavelength of 308 nm to provide a laser density of 1.2-1.8 J cm -2 at a frequency of 2-4 Hz, the distance between the target material and the SrTiO3 substrate is 7-10 cm, and the oxygen partial pressure is kept at 0.5-2 Pa; the process for preparing the lanthanum manganate oxide thin film by using the laser pulse deposition method lasts for 15-20 min, and then is cooled to room temperature at a rate of 20-30 ℃ / min.

4. The method of claim 1, wherein the LaMnO substrate enhances the valley polarization of the monolayer tungsten disulfide. The lanthanum manganese oxide film is a ferromagnetic material, and the Curie temperature is 130-180 K.

5. The method of claim 1, wherein the single layer of tungsten disulfide is grown on a LaMnO3 substrate. The mechanical exfoliation method specifically comprises: Cutting a piece of material with a size of 0.2-0.3 cm in length and width from a bulk tungsten disulfide material, and placing the piece on a 3M Scotch tape; folding the tape in half and then unfolding it repeatedly for 5-8 times; Pressing a polydimethylsiloxane film on the side of the unfolded tape with the tungsten disulfide material, and then taking the polydimethylsiloxane with the tungsten disulfide material off the tape to obtain the thin layer of tungsten disulfide.

6. The method of claim 5, wherein the LaMnO substrate enhances the valley polarization of the monolayer WS2. After obtaining the thin layer of tungsten disulfide, the method further comprises placing the polydimethylsiloxane film with the tungsten disulfide material under an optical microscope to qualitatively determine the thickness of the thin layer of tungsten disulfide.

7. The method of claim 5, wherein the LaMnO substrate enhances the valley polarization of the monolayer of tungsten disulfide. The transfer of the thin layer of tungsten disulfide to the lanthanum manganese oxide film by the mechanical exfoliation method specifically comprises: Pressing the thin layer of tungsten disulfide on the lanthanum manganese oxide film with the tungsten disulfide side facing the lanthanum manganese oxide film; Placing the lanthanum manganese oxide film on a hot stage, heating at 90-100 DEG C for 1-2 minutes to make the polydimethylsiloxane film lose adhesion, taking the polydimethylsiloxane film off, and transferring the tungsten disulfide to the lanthanum manganese oxide film by van der Waals force.

8. The method of claim 6, wherein the LaMnO substrate enhances the valley polarization of the monolayer tungsten disulfide. After forming the material structure with single-layer tungsten disulfide molecules on the lanthanum manganese oxide substrate, the method further comprises measuring the thickness of the tungsten disulfide material on the lanthanum manganese oxide substrate by an atomic force microscope to determine that the thickness is below 1 nm.

9. The method of claim 1, wherein the LaMnO substrate enhances the valley polarization of the monolayer tungsten disulfide. The testing method of the valley polarization degree of the single-layer tungsten disulfide is: fixing the excitation light with a circular polarization direction, and collecting a pair of fluorescence signals with orthogonal circular polarization directions; wherein the polarization direction of the excitation light is left-handed or right-handed circularly polarized light; the pair of fluorescence signals with orthogonal circular polarization directions are left-handed and right-handed fluorescence signals; and the selection of the polarization direction is a combination of a polarizer and a quarter-wave plate. The monolayer tungsten disulfide valley polarization degree is the valley polarization degree of the intrinsic neutral exciton detected, and the calculation method is as follows: P v = (I left + I right ) / (I left + I right ); The P v is the degree of valley polarization, the I left is the intensity of the left-handed fluorescence signal of the intrinsic neutral excitons. The I right is the intensity of the right-handed fluorescence signal of the intrinsic neutral excitons.

10. The method of claim 9, wherein the LaMnO substrate enhances the valley polarization of the monolayer WS2. The test method of the monolayer tungsten disulfide valley polarization degree is as follows: The laser is changed into linear polarization by a polarizer, then a quarter-wave plate is arranged at an angle of 45 degrees or-45 degrees with the linear polarization direction, and the laser is changed into left-handed or right-handed circularly polarized light after passing through the quarter-wave plate; The monolayer tungsten disulfide fluorescent signal on the lanthanum manganese oxygen substrate is sequentially passed through a quarter-wave plate and a polarizer, left-handed and right-handed fluorescent signals are collected by setting the angle between the quarter-wave plate and the polarizer to 45 degrees or-45 degrees.

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