Active control method and device for spin-momentum locking of topological insulator surface state

Abstract

The application discloses a kind of topological insulator surface state spin-momentum locking active regulation method and device thereof.The device includes topological insulator material layer with nontrivial topological surface state, projection angle modulation system (projection angle θ is modulated by light field, electric field, magnetic field, stress field or microwave field), spin-momentum locking monitoring system and feedback control system.The method is by external field modulation projection angle θ, make topological number C occur quantization change, change the Dirac cone dispersion relation and spin texture of surface state, realize the reversible, programmable control of spin-momentum locking intensity (adjustable ±30% to ±60%), direction (adjustable ±90 ° to ±180 °) and spatial distribution.The application also provides closed-loop feedback control based on stability criterion γ_SML θ̇² ≥ |1-k_SML||∂C / ∂θ||θ̇|·h / 2.The application first promotes spin-momentum locking from fixed attribute to active controllable dynamic variable, and can be applied to low-power spin electronic device, topological quantum computing, spin logic circuit, magnetic random memory, terahertz spin emitter, spin neuromorphic computing and other fields.

Description

Technical Field

[0001] This invention relates to the fields of topological quantum material manipulation technology, spintronics, and quantum information processing technology, specifically to an active manipulation method and apparatus for spin-momentum locking of surface states in topological insulators. This invention can be applied to low-power spintronic devices, topological quantum computing, spin logic circuits, microwave / terahertz signal processing, quantum information transmission, and other fields. Background Technology

[0002] 3.1 Spin-momentum locking properties of surface states in topological insulators Three-dimensional topological insulators (such as Bi₂Se₃, Bi₂Te₃, Sb₂Te₃, etc.) are a class of quantum materials with nontrivial topological band structures. Their bulk states possess an insulator band gap, but their surface states contain gapless metallic states protected by time-reversal symmetry—i.e., topological surface states. These surface states exhibit a Dirac cone-shaped linear dispersion relation, and their most prominent feature is spin-momentum locking. The core physical concept of spin-momentum locking is that the spin direction of electrons in the surface states of a topological insulator is locked in a plane perpendicular to their momentum direction. Specifically: For a surface electron with a certain momentum direction, its spin orientation is determined in the direction perpendicular to that momentum, forming a helical spin texture; This locking relationship is protected by time-reversal symmetry, is robust to non-magnetic impurities, and prevents backscattering. This locking relationship results in extremely high carrier mobility and extremely low transmission loss on the surface of the topological insulator. These properties make topological insulators promising for applications in low-power spintronic devices and topological quantum computing. 3.2 Limitations of existing control technologies Although the spin-momentum locking property of the surface states of topological insulators has been experimentally confirmed, existing techniques for controlling this property are very limited: (1) Lack of active control methods: Existing technologies mainly focus on "utilizing" spin-momentum locking characteristics to construct specific devices, such as Josephson devices based on the topological superconductivity of double surfaces and non-reciprocal spintronic devices based on the surface states of topological insulators. These technical solutions all regard spin-momentum locking as a fixed physical property, rather than a dynamic variable that can be actively controlled. (2) Lack of optical field manipulation schemes: In recent years, Floquet engineering has been shown to induce non-equilibrium topological states in topological materials through periodic optical field driving. Circularly polarized light can open the band gap at the Dirac point of graphene to realize Floquet Chern insulators. However, existing research mainly focuses on the overall manipulation of band topological properties by optical fields, and no technical scheme has been proposed for precise, reversible, and programmable manipulation of spin-momentum locking itself. (3) Lack of stress / strain control schemes: Studies have shown that charge redistribution, strain, and atomic displacement at the interface of topological insulators affect the properties of surface states. Topological properties can be controlled by changing the film thickness and applied stress. However, existing technologies have not yet systematically established a quantitative control relationship between stress / strain and spin-momentum locking strength and direction. (4) Lack of multi-field coordinated control scheme: Existing technologies mostly use single control methods (such as using only electric field or only magnetic field), which fail to achieve coordinated control of multiple external fields such as light field, stress field, electric field, and magnetic field, thus limiting the flexibility and accuracy of control. 3.3 Latest Research Progress In recent years, significant progress has been made in the study of active manipulation of surface states in topological insulators: In 2025, research revealed that high-frequency linearly polarized light can be used to suppress backscattering and dissipation caused by magnetic impurities in magnetic topological insulators, thereby recovering dissipation-free surface states. This research shows that the optical field can actively modulate the transport properties of topological surface states, providing a theoretical basis for spin-momentum locked optical manipulation. Concurrently, optically driven strain-induced topological phase transitions were achieved in Bi₂Se₃ using ultrafast optics and terahertz spectroscopy. Experiments revealed ultrafast and reversible switching from a topological insulator with a spin-momentum locked surface to hybrid states and normal insulating phases. This discovery demonstrates that topological surface states and their spin-momentum locking properties can be reversibly controlled on a femtosecond timescale using an optical field. The aforementioned research progress indicates that spin-momentum locking is not an immutable static property, but a dynamic variable that can be actively controlled by an external field—this is precisely the core technical solution that this invention aims to protect. 3.4 The formula system of the applicant's prior application The applicant has previously filed a series of invention patent applications (SG0028, SG0030, G0036, N0095) on a topological material control method based on the theory of geometric projection fiber bundles (projection axiom), and established a general methodology system of "projection angle θ modulation → topological Chern number C change → physical effect control". 3.5 Shortcomings of existing technologies In summary, the existing technology has the following shortcomings: Spin-momentum locking is considered a fixed property, and there is a lack of technical understanding of it as a variable that can be actively controlled. There is a lack of technical solutions for precisely controlling the strength, direction, and chirality of spin-momentum locking through optical fields (Floquet engineering); There is a lack of technical solutions for quantitatively controlling spin-momentum locking through stress / strain. There is a lack of a spin-momentum locking control scheme that coordinates multiple fields including light field, stress field, electric field, and magnetic field; There is a lack of real-time monitoring and closed-loop feedback mechanisms for the spin-momentum locking control effect. To address the above problems, this invention provides an active control method and apparatus for spin-momentum locking of surface states in topological insulators. Summary of the Invention

[0003] (a) Purpose of the invention This invention aims to address the technical problems in the prior art, such as the lack of active control methods for spin-momentum locking of surface states of topological insulators, the single control dimension, and the lack of real-time monitoring and feedback. It provides an active control method and device for spin-momentum locking of surface states of topological insulators. Through the coordinated modulation of multiple external fields such as light field, stress field, electric field, and magnetic field, it achieves precise, reversible, and programmable control of spin-momentum locking strength, direction, chirality, and spin texture. (II) Technical Solution This invention provides an active control device for spin-momentum locking of surface states in a topological insulator, characterized in that it comprises: A topological insulator material layer is disposed on a substrate and has nontrivial topological surface states, wherein the surface states have spin-momentum locking properties; A projection angle modulation system modulates the projection angle θ of the topological insulator material layer through an external field, wherein the external field includes at least one of an optical field, an electric field, a magnetic field, a stress field, or a microwave field; A spin-momentum locking monitoring system is used to measure the spin texture, spin polarizability and spin-momentum locking strength of the surface states of the topological insulator. A feedback control system is connected to the projection angle modulation system and the spin-momentum lock monitoring system, and dynamically adjusts the projection angle θ according to the measurement results of the spin-momentum lock parameters; The projection angle θ is defined as θ = arctan(β_s / β_r), where β_r and β_s satisfy β_r² + β_s² = 1; The feedback control system determines whether the spin-momentum lock-in control state is in a stable topology protection state based on the following stability criterion: Where γ_SML is the decoherence rate of spin-momentum locking, θ̇ is the rate of change of projection angle, k_SML is the restitution coefficient, C is the topological Chern number, and h is Planck's constant; when the criterion is not met, the feedback control system automatically triggers an adjustment operation to bring the system back to a stable control state. Core mathematical principles: 0. The projection angle θ is used as a unified control parameter for spin-momentum locking. In this invention, the spin-momentum locking relationship of the surface states of the topological insulator originates from the projection geometry of the total space fiber bundle in momentum space. The projection angle θ is defined as: Where β_r and β_s are the radial and axial projection weights, respectively, satisfying the projection constraints: The spin-momentum locking strength λ_SML is a function of the projection angle θ: Where λ_max is the theoretical maximum locking strength, θ_0 is the optimal projection angle (corresponding to the maximum locking strength), and σ_θ is the topology protection bandwidth. The spin-momentum locked orientation angle φ_SML is also modulated by the projection angle θ: Where φ_0 is the intrinsic locking direction and Δφ is the maximum directional deflection. The topological Chern number C and the spin-momentum locking strength satisfy the following: Where Ω(k) is the Berry curvature in momentum space, FS is the Fermi surface, and C_max is the maximum topological Chern number. When |θ - θ0| ≤ 2σ_θ, |C| ≥ 1, the system is in a topologically nontrivial phase, and spin-momentum locking is strongest; when |θ - θ0| > 2σ_θ, |C| → 0, the system approaches a topologically trivial phase, and spin-momentum locking weakens or disappears. 1. Geometric description of spin-momentum locking relationship The Hamiltonian of the surface states of a topological insulator can be written as: Where k is the momentum of the surface electron, σ is the Pauli matrix vector, v_F is the Fermi velocity, and ẑ is the surface normal direction. The eigenstates of this Hamiltonian have a definite spin-momentum locking relationship: 2. Spin-momentum-locked modulation controlled by optical field Under light field illumination, the Floquet project introduces an effective correction term: Spin-momentum locking strength λ_SML varies with optical field parameters: 3. Stress-controlled spin-momentum-locked modulation The stress-induced Hamiltonian is corrected as follows: Spin-momentum locking orientation angle φ_SML as a function of strain: 4. Magnetic field-controlled spin-momentum locking modulation Magnetic field B modulates the Dirac cone gap and spin texture of the surface states by disrupting time-reversal symmetry, which is equivalent to changing the projection angle θ: 5. A unified framework for multi-field coordinated regulation The combined effect of light field, stress field, electric field, and magnetic field on spin-momentum locking can be uniformly expressed as: (III) Beneficial Effects For the first time, active control of spin-momentum locking has been achieved: the spin-momentum locking of surface states of topological insulators has been transformed from a "fixed property" to a "dynamic variable that can be actively controlled"; Multidimensional control: The intensity, direction and spatial distribution of spin-momentum locking can be controlled through the independent or synergistic effects of light fields, electric fields, magnetic fields, stress fields or microwave fields; Ultra-fast modulation speed: Light field modulation can achieve femtosecond to picosecond level response speed; Reversible and programmable: The intrinsic state can be restored after the external field is turned off, and the programmable design of spin texture can be achieved through spatial resolution control; Closed-loop feedback control: The control state is always kept in a stable operating range through stability criteria and feedback control system. Low power consumption: All control methods are non-contact or low-power methods; Compatible with existing processes: The material preparation is compatible with existing semiconductor processes. Attached Figure Description

[0004] Figure 1 This is a schematic diagram of the overall structure of the active control device for spin-momentum locking of surface states of a topological insulator provided in an embodiment of the present invention. Figure 2This is a schematic diagram of the surface state spin texture of a topological insulator provided in an embodiment of the present invention, wherein (a) is the intrinsic spin texture and (b) is the spin texture after optical field modulation. Figure 3 A schematic diagram illustrating the principle of spin-momentum locking controlled by optical field as provided in an embodiment of the present invention (Floquet project). Figure 4 This is a schematic diagram illustrating the principle of stress / strain modulation spin-momentum locking provided in an embodiment of the present invention. Figure 5 The graph showing the change of spin-momentum locking strength with projection angle θ and the schematic diagram of feedback control principle are provided for embodiments of the present invention. Figure 6 This is a schematic diagram of the feedback control system provided in an embodiment of the present invention. Detailed Implementation

[0005] Example 1: A method for controlling the projection angle θ based on the Floquet project of a twisted double-layer MoTe2 optical field Step 1: Select topological insulator material A twisted bilayer MoTe2 (molybdenum ditelluride) homojunction was selected as the topologically nontrivial lattice material. The twist angle between the two MoTe2 layers was precisely controlled within the range of 3.5° ± 0.1° (near the magic angle), giving the system a non-zero topological Chern number C≠0, and the surface states exhibiting Dirac cone dispersion and spin-momentum locking characteristics. Step 2: Integrating the light field application system and projection angle modulation An optical window and polarization control module are integrated above the MoTe2 thin film. Adjustable optical field parameters: - Wavelength: 0.5-10 THz (terahertz band) or 800-1550 nm (near-infrared band); - Optical power density: 1 μW / cm² - 100mW / cm²; - Polarization state: linear polarization, circular polarization (left-handed / right-handed), or elliptical polarization. By modulating the projection angle θ through Floquet engineering of the light field, θ is varied near its optimal value θ0, thereby controlling the spin-momentum locking strength: Step 3: Spin-momentum locking monitoring and closed-loop feedback Spin-resolved angle-resolved photoelectron spectroscopy (Spin-ARPES) was used to monitor spin texture in real time, and stability criteria were established. The system automatically adjusts the optical field parameters to ensure that it is always in a stable topology protection state. Step 4: Performance Verification The expected spin-momentum locking strength is adjustable within a range of ±30%, the spin texture direction is adjustable within a range of ±90°, and the control response time is ≤ 1 ps. Example 2: Projection Angle θ Modulation Method Based on Stress / Strain Control Step 1: Selecting the topological insulator material and piezoelectric substrate Bi2Te3 or Bi2Se3 thin films are deposited on piezoelectric substrates (such as PMN-PT or PZT). Step 2: Integrated stress application system Electrodes are fabricated on the upper and lower surfaces of a piezoelectric substrate, and uniaxial or biaxial strain of ±0.1% to ±0.5% is generated by applying a voltage of ±100 V. Step 3: Stress-controlled projection angle θ and spin-momentum locking The strain tensor ε changes the projection angle θ: Spin-momentum locking direction angle rotates with strain: Step 4: Performance Verification The expected strain control can achieve adjustment of spin-momentum locking strength by ±20% and rotation of locking direction by ±30°, with a response time ≤ 100 ns. Example 3: Projection Angle θ Modulation Method Based on Electric Field / Gate Voltage Step 1: Fabrication of a field-effect transistor (FET) structure A high-k dielectric layer (such as HfO2) and a top gate electrode are deposited on top of a topological insulator film. Step 2: Integrated Gate Voltage Application System A gate voltage V_g, ranging from -10 V to +10 V, is applied between the top gate electrode and the back gate electrode. Step 3: Electric field modulates projection angle θ and spin-momentum locking The gate voltage V_g changes the carrier concentration and band bending, which is equivalent to modulating the projection angle θ: Step 4: Performance Verification It is expected that the electric field manipulation can achieve a spin-momentum locking strength adjustment of ±15% with a response time ≤ 1 μs. Example 4: Projection Angle θ Modulation Method Based on Magnetic Field Control Step 1: Determine the method of applying the magnetic field This embodiment is applicable to spin-momentum locking of surface states in topological insulators via magnetic field modulation. The magnetic field application module is an electromagnet or a superconducting magnet, used to apply a static or alternating magnetic field to the topological insulator material layer. Step 2: Magnetic field manipulation of projection angle θ and spin-momentum locking Magnetic field B modulates the Dirac cone gap and spin texture of the surface states by disrupting time-reversal symmetry, which is equivalent to changing the projection angle θ: Spin-momentum locking strength as a function of magnetic field: Where α_B is the magnetic field-projection angle coupling coefficient, η_B is the magnetic field-spin coupling coefficient, and B_0 is the reference magnetic field strength. Step 3: Performance Verification The magnetic field strength ranges from 0.01 T to 10 T, and its direction can be arbitrary, either in-plane or out-of-plane. It is expected that the magnetic field can be modulated to achieve ±20% adjustment of the spin-momentum locking strength and ±45° rotation of the spin texture direction. Example 5: Multi-field coordinated regulation (preferred example) Step 1: Fabrication of multi-field integrated devices Four control modules—optical field, stress field, electric field, and magnetic field—are integrated into a single device. Step 2: Independently adjust the parameters of each external field. The parameters of four external fields are independently controlled by a multi-channel signal generator. Step 3: Coordinated control of projection angle θ and spin-momentum locking The combined effect is: Step 4: Performance Verification With the four-field coordinated control enabled, the expected spin-momentum locking strength is adjustable within a range of ±60%, the direction is adjustable within a range of ±180°, the control response time is ≤ 1 ps, and the control accuracy is better than 1%. Example 6: Topological spintronic devices with programmable spin textures Step 1: Fabrication of spatially resolved modulation devices An electrode array (spacing 1-10 μm) is fabricated on the surface of a topological insulator thin film, and each electrode is independently controlled to achieve spatially resolved projection angle θ modulation. Step 2: Programming Spin Textures By independently controlling the gate voltage V_g(r) and optical field parameter E0(r) of each electrode region, a programmable spin texture can be constructed on the surface: Step 3: Real-time reconstruction of spin texture By updating the control signals of each electrode, the spin texture pattern can be reconstructed in microseconds to milliseconds. Example 7: Closed-loop control method based on stability criterion Step 1: Initial state setting The system is set to the target projection angle θ_target through an external field, so that the spin-momentum locking reaches the target state. Step 2: Real-time monitoring The spin-momentum locking monitoring system is used to measure λ_SML and its rate of change λ̇_SML, θ and its rate of change θ̇, as well as the topological Chern number C in real time. Step 3: Calculating the stability criterion The control unit calculates in real time: Compare the magnitudes of L and R. Step 4: State judgment and feedback When L ≥ R: the system is in a stable topological protection state, and the current parameters are maintained; When L < R: the system tends to be unstable, and the feedback control system automatically adjusts the external field parameters to return the system to the stable state where L ≥ R. Step 5: Continuous closed-loop control Repeat Steps 2 to 4 to form a continuous closed-loop control loop, ensuring that the spin-momentum locking is always in a stable topological protection state. Eighth Embodiment: Active Regulation Device for Spin-Charge Conversion Efficiency Step 1: Determine the device structure This embodiment is applicable to a spin-charge conversion device of a topological insulator / ferromagnetic metal heterostructure or a topological insulator / heavy metal heterostructure. The device structure is: ferromagnetic layer (CoFeB or Py) / topological insulator layer (Bi2Se3 or Bi2Te3) / substrate. Step 2: Integrate the projection angle modulation system A gate electrode or optical field application module is integrated above the device, and the projection angle θ in the topological insulator layer is modulated by an external field, so as to regulate the spin-momentum locking strength λ_SML. Step 3: Active regulation of spin-charge conversion efficiency The spin-charge conversion efficiency η_SCC and the spin-momentum locking strength λ_SML satisfy: By modulating θ, the conversion efficiency can be continuously regulated within the range of ±50%. Step 4: Performance verification It is expected that under the topological protection enabled state (|C|≥1), the spin-charge conversion efficiency is increased by 2-5 times compared with the unregulated state, and the regulation response time is ≤ 1 ps. Ninth Embodiment: Active Regulation of Spin-Orbit Torque (SOT) Device Step 1: Determine the device structure This embodiment applies to SOT devices based on topological insulator surface states. The device structure is: heavy metal layer (Pt or Ta) / topological insulator layer (Bi2Se3) / ferromagnetic layer (CoFeB or Pt / Co multilayer film). Step 2: Integrate the projection angle modulation system The gate electrode is integrated on top of the device, and the projection angle θ in the topological insulator layer is modulated by the gate voltage V_g, thereby controlling the SOT efficiency. Step 3: Dynamic Adjustment of SOT Efficiency SOT efficiency ξ_SOT and spin-momentum locking strength λ_SML satisfy the following: The critical current density J_c for magnetization reversal varies with θ: By modulating θ, the magnetization reversal current density can be 3.0 × 10⁻⁶. 5 Up to 1.0×10 6 Adjustable within the range of A / cm². Step 4: Performance Verification The SOT efficiency is expected to be 2-3 times higher than that of the uncontrolled state, and the magnetization reversal current density is expected to be reduced by 50%-70%. Example 10: Reconfigurable Spin-Orbit Torque Magnetic Random Access Memory (SOT-MRAM) Step 1: Determine the memory cell structure This embodiment applies to SOT-MRAM memory cell arrays. The cell structure is: magnetic tunnel junction (MTJ) / topological insulator layer / heavy metal layer, where the MTJ consists of a reference layer / tunneling layer / free layer. Step 2: Integrate global / local projection angle modulation Integrating a global gate (controlling all cells) or a local gate array (independently controlling each cell) in the memory array allows for the regulation of SOT efficiency by modulating the projection angle θ. Step 3: Dynamic optimization of write current Based on the actual process deviations and operating temperature of the memory cell, the write current is dynamically optimized by modulating θ: Step 4: Performance Verification The expected write current is reduced by 50%-70%, write power consumption is reduced by 60%-80%, and device lifespan is extended by 3-5 times. Example 11: Spin-FET Step 1: Determine the transistor structure This embodiment is applicable to quantum spin Hall state spin field-effect transistors based on two-dimensional topological insulators (such as single-layer or double-layer WTe2, MoTe2). The device structure is: source / drain (ferromagnetic contact) / channel (topological insulator) / top gate (high-k dielectric) / substrate. Step 2: Integrated gate projection angle modulation Using the gate voltage V_g as an external field control method for the projection angle θ, the spin-momentum locking strength λ_SML in the channel is changed by changing θ through V_g. Step 3: Active control of channel spin polarization The spin polarizability P_Spin in the channel satisfies the following relationship with the projection angle θ: The source-drain current I_DS is modulated by the spin polarization: Step 4: Performance Verification The expected on / off ratio is improved by 2-3 times, the subthreshold swing is reduced by 30%-50%, and the operating power consumption is reduced by 40%-60%. Example 12: Ultrafast Terahertz Spin Emitter Step 1: Determine the transmitter structure This embodiment applies to a terahertz spin emitter based on topological insulator surface states. The device structure is: a topological insulator thin film (Bi2Se3 or Bi2Te3) / non-magnetic substrate, with an integrated femtosecond laser irradiation system. Step 2: Integrated projection angle pre-modulation system Before terahertz emission, the spin-momentum locking strength λ_SML is optimized by pre-modulating the projection angle θ in the topological insulator using the gate voltage or optical field. Step 3: Terahertz Spin Current Emission Spin-polarized photocurrent is generated through spin-momentum locking under femtosecond laser pulse (pulse width ≤ 100 fs) irradiation: Spin polarization is adjustable in the range of 30%-90%. Step 4: Performance Verification The expected improvement in terahertz emission efficiency is 3-5 times, and the spin polarization is adjustable from 30% to 90%. Example 13: Topology-protected spin qubit manipulation interface Step 1: Determine the interface structure This embodiment is applicable to spin-momentum locking-based spin qubit manipulation interfaces in topological quantum computing. The device structure is: a topological insulator nanowire or quantum dot / superconducting electrode / gate array. Step 2: Integrating projection angle modulation and quantum bit manipulation The local spin texture can be altered by modulating the local projection angle θ(r) using a local gate or optical field. Coherent manipulation of spin qubits (single-qubit rotation gate, two-qubit entanglement gate) can be achieved by temporal control of θ(r). Step 3: Topology Protection and Decoherence Suppression The topological protection provided by topological nontrivial states (|C|≥1) reduces the decoherence rate of qubits by 2-3 orders of magnitude. Example 14: Spin Logic Circuit Based on Programmable Spin Texture Step 1: Determine the logic circuit structure This embodiment is applicable to spin logic circuits based on programmable spin textures on the surface of topological insulators. The device structure is: a topological insulator thin film / electrode array (achieving spatially resolved theta control). Step 2: Programming Spin Textures to Implement Logical Functions By independently controlling the projection angle θ_i of each region through the electrode array, spin texture patterns of different functional regions are constructed on the surface. Step 3: Restructuring of logical functions By updating the control signals of the electrode array, logic functions can be reconstructed within microseconds to milliseconds: - Parallel arrangement of spin textures: implements AND logic - Anti-parallel arrangement of spin textures: implements OR logic - Swirl arrangement of spin textures: implements NOT logic Step 4: Performance Verification Expected logic operation speed ≤ 100 ps, ​​single logic operation energy consumption ≤ 1 aJ, and reconstruction time ≤ 1 μs. Example 15: Programmable Spin Waveguide and Spin Beamsplitter Step 1: Determine the waveguide / beam splitter structure Construct one-dimensional spin textured channels (waveguides) or Y-shaped bifurcated structures (beam splitters) on the surface of a topological insulator. Step 2: Program the spin waveguide path By modulating the spatial distribution of θ, the propagation path and direction of the spin wave are defined. Step 3: Spin beam splitting and spin separation In the Y-shaped bifurcation structure, the incident spin flow is separated according to the spin direction by spin-momentum locking, and the spin separation ratio is adjustable from 10:1 to 1:10. Example 16: High-sensitivity topological spin sensor Step 1: Determine the sensor structure This embodiment is applicable to a spin sensor with high sensitivity to the projection angle θ based on spin-momentum locking. The device structure is: topological insulator thin film / electrode pair / signal processing circuit. Step 2: Sensing Principle The rate of change of the spin-momentum locking strength λ_SML with respect to θ is maximum near θ0: The physical quantities to be measured (magnetic field B, stress σ, temperature T, electric field E) are sensed by converting them into changes in θ. Step 3: Performance Verification The sensitivity is expected to be improved by 2-4 orders of magnitude, and the detection limit will be reduced to fT-level magnetic fields, nN-level forces, and μK-level temperatures. Example 17: Spin Neuromorphic Computing Device Step 1: Determine the device structure This embodiment applies to a spin neuromorphic computing device based on tunable spin-momentum locking. The device structure is: topological insulator / ferromagnetic multilayer film array / electrode array. Step 2: Spin realization of synaptic plasticity By continuously adjusting the spin-orbit torque efficiency through modulation of θ, the weight variation of biological synapses (synaptic plasticity) is simulated. Step 3: Neural Network Inference and Learning The neural network achieves inference (forward propagation) and online learning (weight update) through reconfigurable spin textures. Terminology Explanation

[0006] Meaning of terms and symbols Topological insulators (TI) are quantum materials that possess a nontrivial topological band structure, exhibiting bulk insulation and surface conductivity. Spin-momentum locked (SML) property: The property of electron spin direction being perpendicular to momentum direction locked in the surface states of a topological insulator. The projection angle θ is a geometric parameter describing the projection direction in fiber bundle projection mapping. Spin-momentum locking strength λ_SML is a quantitative indicator characterizing the degree of spin-momentum locking. The topological Chern number C describes the topological invariants that can carry topological nontriviality. Topology protection bandwidth σ_θ is the parameter width between nontrivial and trivial phases in the topology phase diagram. Floquet Project—A Method for Inducing Non-Equilibrium Topological States Using Periodic Optical Fields Spin-orbit torque (SOT) is the torque applied to magnetization by the spin current through spin-orbit coupling. The decoherence rate γ_SML is the rate at which spin-momentum locking degrades due to environmental perturbations.

Claims

1. Claim 1 (Independent claim, core device + method + criterion) An active control device for spin-momentum locking of surface states of a topological insulator, characterized in that it comprises: A topological insulator material layer is disposed on a substrate and has nontrivial topological surface states, wherein the surface states have spin-momentum locking properties; A projection angle modulation system modulates the projection angle θ of the topological insulator material layer through an external field, wherein the external field includes at least one of an optical field, an electric field, a magnetic field, a stress field, or a microwave field; A spin-momentum locking monitoring system is used to measure the spin texture, spin polarizability and spin-momentum locking strength of the surface states of the topological insulator. A feedback control system is connected to the projection angle modulation system and the spin-momentum lock monitoring system, and dynamically adjusts the projection angle θ according to the measurement results of the spin-momentum lock parameters; The projection angle θ is defined as θ = arctan(β_s / β_r), where β_r and β_s satisfy β_r² + β_s² = 1; The feedback control system determines whether the spin-momentum lock-in control state is in a stable topology protection state based on the following stability criterion: Where γ_SML is the decoherence rate of spin-momentum locking, θ̇ is the rate of change of projection angle, k_SML is the restitution coefficient, C is the topological Chern number, and h is Planck's constant; when the criterion is not met, the feedback control system automatically triggers an adjustment operation to bring the system back to a stable control state.

2. Claim 2 (dependent, materials and structure) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: The topological insulator material layer is at least one of Bi2Se3, Bi2Te3, Sb2Te3, twisted bilayer MoTe2, or twisted bilayer WSe2; the modulation timescale of the external field is from femtosecond to nanosecond.

3. Claim 3 (dependent, light field manipulation) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: When the external field is an optical field, the optical field is linearly polarized light, left-handed circularly polarized light, right-handed circularly polarized light, or elliptically polarized light, with a wavelength range of 0.5-10 THz or 800-1550 nm, and the projection angle θ is modulated by Floquet engineering.

4. Claim 4 (dependent, magnetic field control) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: When the external field is a magnetic field, the magnetic field is a static magnetic field or an alternating magnetic field with an intensity range of 0.01 T to 10 T and a direction along any direction in-plane or out-of-plane. The projection angle θ is modulated by breaking the time-reversal symmetry.

5. Claim 5 (dependent, stress / electric field modulation) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: When the external field is a stress field, the stress field is a uniaxial or biaxial mechanical strain with an amplitude range of ±0.1% to ±0.5%; when the external field is an electric field, the electric field is applied through a gate voltage with a gate voltage range of ±10 V.

6. Claim 6 (dependent, regulatory effect) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: The spin-momentum locking strength λ_SML and the projection angle θ satisfy: Where λ_max is the theoretical maximum locking strength, θ0 is the optimal projection angle, and σ_θ is the topology protection bandwidth; the spin-momentum locking direction angle φ_SML and the projection angle θ satisfy: The spin-momentum locking strength is adjustable from ±30% to ±60%, the direction is adjustable from ±90° to ±180°, and the control response time is ≤ 1 ps.

7. Claim 7 (dependent, programmable spin texture) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: The external field application system includes a spatially resolved control array that enables programmable spin texture distribution on the surface of the topological insulator by independently controlling the projection angle θ(r) at each spatial location. The programmable spin texture includes at least one of spin helix, spin vortex, spin domain wall, or arbitrary spin pattern, with a reconstruction time ≤ 1 μs.

8. Claim 8 (Dependent, Multilayer Extension Stability Criterion) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: The topological insulator material layer is a multilayer heterojunction structure, comprising at least two material layers with different topological Chern numbers. The stability criterion for the multilayer heterojunction structure is: The subscript i represents the corresponding parameter of the i-th layer material; when each layer is in a constructive interference state, the topological protection effect of each layer is coherently superimposed.

9. Claim 9 (dependent, field of application) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 1 is characterized in that: The active control of spin-momentum locking is applied to at least one of spin-charge conversion devices, spin-orbit torque devices, magnetic random access memory, spin field-effect transistors, terahertz spin emitters, or topological quantum bit manipulation interfaces.

10. Claim 10 (dependent, spin logic / waveguide / sensor) The active control device for spin-momentum locking of surface states of a topological insulator according to claim 7 is characterized in that: The programmable spin texture is applied to spin logic circuits, spin waveguides, spin beam splitters, spin sensors, or spin neuromorphic computing devices; the logic function of the spin logic circuit can be reconstructed between AND, OR, NOT, NAND, NOR, and XOR, with a reconstruction time ≤ 1 μs; the sensitivity of the spin sensor is improved by 2-4 orders of magnitude.

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