A novel spin terahertz emitter and a method for regulating the same

Abstract

The present application relates to a kind of novel spin terahertz emitter and its regulation method, and spin terahertz emission structure includes: electrode, and by sequentially arranged substrate layer, first topological material layer, first ferromagnetic material layer, barrier layer, second topological material layer and second ferromagnetic material layer from bottom to top, first, second topological material layer includes topological insulator and topological semimetal, electrode is used to input current to the first topological material layer.New regulation method of novel spin terahertz emitter includes: by electrode, input current to the first topological material layer, by changing the polarity and size of current, change the magnetic moment direction of first ferromagnetic material layer, and then switch superfast regulation to spin terahertz, enrich the type of prior art in spin terahertz emitter and the regulation means of spin terahertz switch.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of spin terahertz emitter and spin terahertz emission regulation, and particularly relates to a novel spin terahertz emitter and a regulation method thereof. BACKGROUND

[0002] In recent years, with the development of THz technology, its unique advantages and great application prospects in many important fields such as physics, chemistry, electronic information, life science, material science, astronomy, atmospheric and environmental monitoring, communication radar, national security, etc. gradually revealed.

[0003] Terahertz wave switch is an important terahertz wave functional device, and with the development of practical application environment, higher requirements are put forward for the switching effect and regulation speed of terahertz wave switch. SUMMARY

[0004] The purpose of the present application is to provide a novel spin terahertz emitter capable of switching and ultrafast regulating spin terahertz and a regulation method thereof.

[0005] In order to achieve the above purpose, the novel spin terahertz emitter provided by the present application comprises a spin terahertz emission structure, which comprises an electrode, and a substrate layer, a first topological material layer, a first ferromagnetic material layer, a barrier layer, a second topological material layer and a second ferromagnetic material layer arranged in order from bottom to top; the first topological material layer and the second topological material layer comprise a topological insulator and a topological semimetal, and the electrode is used to input current to the first topological material layer or apply voltage to the substrate layer.

[0006] The spin terahertz emission structure further comprises an antiferromagnetic pinning layer arranged above the second ferromagnetic material layer.

[0007] The first topological material layer, the first ferromagnetic material layer, the barrier layer, the second topological material layer and the second ferromagnetic material layer all contain van der Waals materials.

[0008] The topological insulator is selected from one of van der Waals materials Bi2Se3, Bi2Te3, Bi x Sb 1-x , Sb2Te3, (Bi x Sb 1-x )2Te3 or an alloy composed of multiple materials.

[0009] The first ferromagnetic material layer and the second ferromagnetic material layer comprise a two-dimensional ferromagnetic material, and the two-dimensional ferromagnetic material is selected from one of van der Waals materials Fe x GeTe2 and CrTe2.

[0010] The barrier layer is selected from one of an oxide and a two-dimensional material, the oxide includes one of MgO and Al2O3, and the two-dimensional material is selected from one of van der Waals materials h-BN, MoS2, WSe2, and GaSe.

[0011] The electrode is connected to the first topological material layer, and the electrode is configured to be connected to an external power source.

[0012] The electrode is arranged below the substrate layer, and the substrate layer is a lead magnesium niobate-lead titanate or strontium titanate substrate.

[0013] A method for regulating a novel spin terahertz emitter, comprising the following steps:

[0014] The electrode is connected to the first topological material layer, and the electrode is configured to be connected to an external power source.

[0015] By changing the polarity and size of the input current, the magnetic moment direction of the first ferromagnetic material layer is changed, and the waveform, amplitude and phase of the spin terahertz are regulated.

[0016] For the novel spin terahertz emitter structure in which the electrode is arranged below the substrate layer, the method further comprises:

[0017] A voltage is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate through the electrode, so that the lead magnesium niobate-lead titanate or strontium titanate substrate produces a tensile or shrinkage deformation, and the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes.

[0018] Specifically, when a voltage of a certain size is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate to make the lead magnesium niobate-lead titanate or strontium titanate substrate produce a specified deformation, the deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes by a specified amount, the magnetic moment direction of the first ferromagnetic material layer is parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz amplitude is maximum, the waveform and phase of the terahertz exist, and the corresponding switch state is open.

[0019] When a voltage of a certain size is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate to make the lead magnesium niobate-lead titanate or strontium titanate substrate produce a deformation opposite to the specified deformation, the deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes by a specified amount, the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz amplitude is minimum, the waveform and phase of the terahertz tend to zero, and the corresponding switch state is closed.

[0020] According to the specific embodiments of the present application, the following technical effects are disclosed: a new type of spin terahertz emitter and a regulation method thereof are developed, wherein the emission structure of the new type of spin terahertz emitter comprises an electrode, and a substrate layer, a first topological material layer, a first ferromagnetic material layer, a barrier layer, a second topological material layer and a second ferromagnetic material layer arranged in order from bottom to top; when regulating the terahertz emitted by the new type of spin terahertz emitter, a current of a certain size and different polarity is passed through the first topological material layer in the structure of the new type of spin terahertz emitter, so as to regulate the switch of the spin terahertz, or a voltage of a specified size is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate layer, so as to regulate the switch of the spin terahertz. Compared with the prior art, since the polarity and size of the current or the size of the voltage is used to control the switch of the spin terahertz, the regulation method does not need to rely on the optimization of the film layer thickness, the periodic arrangement of the film layer and the presence or absence of external experimental conditions or the rotation angle to regulate the switch of the spin terahertz, so the regulation method is more simple. At the same time, the polarity of the current or the voltage is changed to realize the flip of the magnetic moment of the first ferromagnetic material layer, and then the switch of the spin terahertz is realized. That is, the switch of the spin terahertz is regulated by the magnetic moment, so the switch of the spin terahertz has the characteristics of superfast, low consumption and easy operation. BRIEF DESCRIPTION OF DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0022] Figure 1 A schematic diagram for regulating the emission structure without an antiferromagnetic pinning layer based on the spin-orbit torque effect through an external power supply;

[0023] Figure 2 A schematic diagram for regulating the emission structure without an antiferromagnetic pinning layer based on the spin-orbit torque effect through a piezoelectric effect

[0024] Figure 3 A schematic diagram for regulating the emission structure with an antiferromagnetic pinning layer based on the spin-orbit torque effect through an external power supply;

[0025] Figure 4 A schematic diagram for regulating the emission structure with an antiferromagnetic pinning layer based on the spin-orbit torque effect through a piezoelectric effect. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0027] The present application aims to provide a novel spin terahertz emitter capable of switching and ultrafast regulating spin terahertz and a regulating method thereof.

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0029] In the present application, the novel spin terahertz emitter comprises an electrode, and a substrate layer, a first topological material layer, a first ferromagnetic material layer, a barrier layer, a second topological material layer and a second ferromagnetic material layer arranged in order from bottom to top; the first and second topological material layers comprise a topological insulator and a topological semimetal, and the electrode is used to input current to the first topological material layer or apply voltage to the substrate layer.

[0030] When the novel spin terahertz emitter needs to be turned on, a current of a certain size and a specified polarity is input to the first topological material layer through the electrode, under the action of the current, the first ferromagnetic material layer and the second ferromagnetic material layer generate magnetic moments in parallel directions, at this time, the terahertz radiated by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, the two terahertz signals superimpose on each other, the terahertz amplitude is maximum, the terahertz waveform and phase exist, and the turning on of the novel spin terahertz emitter is realized. When the novel spin terahertz emitter needs to be turned off, a current opposite in polarity to the above-mentioned current is input to the first topological material layer through the electrode, and when the amplitude of the current increases to a certain size, the magnetic moment direction of the first ferromagnetic material layer instantaneously flips, and is anti-parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz radiated by the first ferromagnetic material layer and the second ferromagnetic material layer are in opposite directions, the two terahertz signals cancel each other out, the terahertz amplitude is minimum, the terahertz waveform and phase tend to zero, and the turning off of the novel spin terahertz emitter is realized.

[0031] It should be noted that, when the novel spin terahertz emitter is turned on, the terahertz signals generated by the first ferromagnetic material layer and the second ferromagnetic material layer superimpose on each other, thereby increasing the amplitude of the terahertz signal. When the novel spin terahertz emitter is turned off, the terahertz signals generated by the first ferromagnetic material layer and the second ferromagnetic material layer cancel each other out, the terahertz amplitude is minimum, and the terahertz waveform and phase tend to zero, thereby realizing the more obvious switching effect of the novel spin terahertz emitter.

[0032] In addition, it can be known from the above analysis that the opening of the terahertz emitter is realized by the instantaneous flipping of the magnetic moment, that is, the process from opening to closing is realized instantaneously, that is, the terahertz emitter can realize the ultrafast regulation and control of opening and closing.

[0033] It should be noted that when it is necessary to close the new spin terahertz emitter, in the process of continuously increasing the current amplitude of the opposite polarity input into the first ferromagnetic material layer, the magnetic moment direction of the first ferromagnetic material layer is first flipped, but if the current amplitude continues to increase, the magnetic moment direction of the second ferromagnetic material layer will also be flipped, at this time, the switch will fail. That is, within a certain current amplitude range (hereinafter referred to as a first current amplitude range), the closing of the new spin terahertz emitter can be realized. The lower limit of the first current amplitude range is greater than the current amplitude that causes the flipping of the magnetic moment direction of the first ferromagnetic material layer, and the upper limit is less than the current amplitude that causes the flipping of the magnetic moment direction of the second ferromagnetic material layer.

[0034] In some embodiments, in order to reduce the difficulty of the operation of flipping the magnetic moment of the first ferromagnetic material layer by using the current, the spin terahertz emission structure shown in Figure 1 、 Figure 2 Before regulating the switch of the spin terahertz, the second ferromagnetic material layer of the spin terahertz emitter is saturated magnetized, so that when the current is input into the first topological material layer, a spin polarization current perpendicular to the upward direction is generated to fix the magnetic moment direction of the second ferromagnetic material layer. In this way, when the terahertz emitter is closed, due to the fixing effect of the spin polarization current on the magnetic moment direction of the second ferromagnetic material layer, if the magnetic moment direction of the second ferromagnetic material layer is to be flipped, the corresponding current amplitude is increased, at this time, the current amplitude range corresponding to the closing of the terahertz emitter (hereinafter referred to as a second current amplitude range) is expanded. The lower limit of the second current amplitude range is greater than the current amplitude that causes the flipping of the magnetic moment direction of the first ferromagnetic material layer, and the upper limit is less than the current amplitude that causes the flipping of the magnetic moment direction of the second ferromagnetic material layer.

[0035] In other embodiments, an antiferromagnetic pinning layer can also be used to replace the saturation magnetization of the second ferromagnetic material layer. Specifically, as shown in Figure 3 、 Figure 4An antiferromagnetic pinning layer is arranged above the second ferromagnetic material layer, and the antiferromagnetic pinning layer is made of an antiferromagnetic material such as IrMn, NiO, CrSb, Co / Pt multilayer film, etc. The function of the antiferromagnetic pinning layer is to fix the direction of the magnetic moment of the second ferromagnetic material layer, so that when the terahertz emitter is turned off, due to the fixing effect of the antiferromagnetic pinning layer on the direction of the magnetic moment of the second ferromagnetic material layer, if the direction of the magnetic moment of the second ferromagnetic material layer is to be reversed, the corresponding current amplitude is increased, at this time, the current amplitude range corresponding to the turn-off of the terahertz emitter (hereinafter referred to as the third current amplitude range) is expanded, and the lower limit of the third current amplitude range is greater than the current amplitude that causes the direction of the magnetic moment of the first ferromagnetic material layer to be reversed, and the upper limit is less than the current amplitude that causes the direction of the magnetic moment of the second ferromagnetic material layer to be reversed.

[0036] In some embodiments, the first topological material layer, the first ferromagnetic material layer, the barrier layer, the second topological material layer, and the second ferromagnetic material layer can each contain a van der Waals material.

[0037] Specifically, the topological insulator is selected from one of van der Waals materials Bi2Se3, Bi2Te3, Bi x Sb 1-x , Sb2Te3, (Bi x Sb 1-x )2Te3 or an alloy composed of multiple materials therefrom, and the topological semimetal is selected from one of van der Waals materials PtTe2, WTe2, PtSe2, WSe2.

[0038] The first ferromagnetic material layer and the second ferromagnetic material layer include a two-dimensional ferromagnetic material, and the two-dimensional ferromagnetic material is selected from one of van der Waals materials Fe x GeTe2, CrTe2.

[0039] The barrier layer is selected from one of an oxide and a two-dimensional material, the oxide includes one of MgO and Al2O3, and the two-dimensional material is selected from one of van der Waals materials h-BN, MoS2, WSe2, and GaSe.

[0040] Due to the interaction with adjacent layers through weak van der Waals forces, the two-dimensional ferromagnetic material can be free from the restrictions of lattice matching and compatibility, and at the same time, the two-dimensional ferromagnetic material can obtain a high-quality interface without dangling bonds at the interface and with atomic-level flatness, which is expected to significantly reduce the interface spin loss, greatly improve the emission efficiency, and realize high mechanical flexibility and integrability of the spin terahertz.

[0041] In some embodiments, the antiferromagnetic pinning layer is made of an antiferromagnetic material such as IrMn, NiO, CrSb, Co / Pt multilayer film, etc.

[0042] In some embodiments, the electrode is connected to the first topological material layer, and the electrode is used to connect to an external power source. As shown in Figure 1 、 Figure 3 the lower surface of the electrode is in contact with the first topological material layer. When the external power source is connected to the electrode and a current is passed to the first topological material layer, the direction of the magnetic moment of the first ferromagnetic material layer is controlled by the spin-orbit effect, and the direction of the magnetic moment of the first ferromagnetic material layer is parallel to the direction of the magnetic moment of the second ferromagnetic material layer. There are two cases of parallel and anti-parallel.

[0043] Specifically, when a certain size and specified polarity current is passed to the first topological material layer by connecting the external power source to the electrode, the direction of the magnetic moment of the first ferromagnetic material layer is parallel to the direction of the magnetic moment of the second ferromagnetic material layer, at this time the terahertz amplitude is maximum, the waveform and phase of terahertz exist, and the corresponding switch state is on.

[0044] When a certain size and opposite polarity current is passed to the first topological material layer by connecting the external power source to the electrode, the direction of the magnetic moment of the first ferromagnetic material layer is anti-parallel to the direction of the magnetic moment of the second ferromagnetic material layer, the terahertz amplitude is minimum, the waveform and phase of terahertz tend to zero, and the corresponding switch state is off.

[0045] In other embodiments, as shown in Figure 2 、 Figure 4 the electrode is arranged below the substrate layer, and the substrate layer is a lead magnesium niobate-lead titanate or strontium titanate substrate. At this time, the electrode is used to apply an electric field to the lead magnesium niobate-lead titanate or strontium titanate substrate (i.e. piezoelectric material). A certain size voltage is applied to the electrode by an external power source, and a specified electric field is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate, wherein the generated electric field ranges from -10kV / cm to 10kV / cm, thereby generating a specified size voltage on the lead magnesium niobate-lead titanate or strontium titanate substrate, resulting in a tensile or shrinkage deformation of the lead magnesium niobate-lead titanate or strontium titanate substrate. Since the lead magnesium niobate-lead titanate or strontium titanate substrate is closely connected to the first topological material layer, and the first topological material layer is closely connected to the first ferromagnetic material layer, when the substrate layer is deformed under the action of the voltage, the deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, causing the lattice constant of the magnetic thin film in the first ferromagnetic material layer to change, realizing the magnetic moment flip, thereby making the direction of the magnetic moment of the first ferromagnetic material layer parallel to the direction of the magnetic moment of the second ferromagnetic material layer. There are two cases of parallel and anti-parallel.

[0046] Specifically, a certain size of voltage is applied to the electrode by an external power supply to apply a certain size of electric field to the lead magnesium niobate-lead titanate or strontium titanate substrate, for example, an electric field of-10 kV / cm is applied, which causes the lead magnesium niobate-lead titanate or strontium titanate substrate to generate a specified size of voltage, causing the lead magnesium niobate-lead titanate or strontium titanate substrate to appear a deformation in a tensile state, at this time, the magnetic moment direction of the first ferromagnetic material layer is parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz amplitude is the largest, the waveform and phase of the terahertz exist, and the corresponding switch state is on.

[0047] When a certain size of voltage is applied to the electrode by an external power supply to apply a certain size of electric field to the lead magnesium niobate-lead titanate or strontium titanate substrate, for example, an electric field of-10 kV / cm is applied, which causes the lead magnesium niobate-lead titanate or strontium titanate substrate to generate a specified size of voltage, causing the lead magnesium niobate-lead titanate or strontium titanate substrate to appear a deformation in a compression state, at this time, the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz amplitude is the smallest, the waveform and phase of the terahertz tend to zero, and the corresponding switch state is off.

[0048] For the above-mentioned new spin terahertz emitter, the control method is as follows:

[0049] The current is input to the first topological material layer through the electrode;

[0050] By changing the polarity and size of the input current, the magnetic moment direction of the first ferromagnetic material layer is changed, and the spin terahertz is switched and controlled.

[0051] Specifically, when a certain size and specified polarity of current is input, the magnetic moment direction of the first ferromagnetic material layer is parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz amplitude is the largest, the waveform and phase of the terahertz exist, and the corresponding switch state is on.

[0052] When a certain size of current opposite to the above-mentioned current polarity is input, the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the magnetic moment direction of the second ferromagnetic material layer, the terahertz amplitude is the smallest, the waveform and phase of the terahertz tend to zero, and the corresponding switch state is off.

[0053] For the new spin terahertz emitter structure in which the electrodes are arranged below the substrate layer, as shown in the spin terahertz emission structure of Figure 2 and Figure 4 The control method further comprises: applying a voltage to the lead magnesium niobate-lead titanate or strontium titanate substrate through the electrode to cause the lead magnesium niobate-lead titanate or strontium titanate substrate to generate a tensile or shrinkage deformation, and the generated deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, so that the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes.

[0054] The following isFigures 1-4 The regulation schematic diagram of the terahertz emission structure based on the spin-orbit torque effect is specifically illustrated.

[0055] As shown in the figure, for the terahertz emission structure containing the antiferromagnetic pinning layer and the terahertz emission structure not containing the antiferromagnetic pinning layer, the spin-orbit effect is regulated by the external power supply and the piezoelectric effect respectively. Figures 1-4 The spin-orbit torque effect is based on the spin-orbit coupling, and the spin flow induced by the charge flow is used to generate the spin-orbit torque, and then the fast and reliable magnetization reversal is realized; the piezoelectric effect refers to that the voltage is applied to the piezoelectric material, and under the action of the voltage, the piezoelectric material shows stretching or shrinking deformation, and the deformation is transmitted to the ferromagnetic layer, so that the lattice constant of the magnetic thin film changes, and the purpose of voltage regulating the magnetization reversal is achieved.

[0056]

[0057] As shown in the figure, the terahertz is emitted by irradiating the terahertz emission structure not containing the antiferromagnetic pinning layer with the ultra-short pulse laser, and when the magnetic moment direction of the first ferromagnetic material layer is parallel or anti-parallel to the second ferromagnetic material layer, the terahertz amplitude emitted respectively is shown. When the magnetic moment direction of the first ferromagnetic material layer is parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, and the terahertz signal is enhanced; when the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in opposite directions, and the terahertz signals emitted on both sides will cancel each other out, and the terahertz signal tends to zero. Figure 1

[0058] As shown in the figure, the terahertz is emitted by irradiating the terahertz emission structure not containing the antiferromagnetic pinning layer with the ultra-short pulse laser, and the voltage is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate through the electrodes, and the lead magnesium niobate-lead titanate or strontium titanate substrate produces stretching or shrinking deformation under the action of the voltage, and the deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, so that the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes, and when the magnetic moment direction of the first ferromagnetic material layer is parallel or anti-parallel to the second ferromagnetic material layer, the terahertz amplitude emitted respectively is shown. When the magnetic moment direction of the first ferromagnetic material layer is parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, and the terahertz signal is enhanced; when the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in opposite directions, and the terahertz signals emitted on both sides will cancel each other out, and the terahertz signal tends to zero. Figure 2

[0059] Figure 3 ​As shown, the terahertz is emitted by the ultra-short pulse laser irradiating to the terahertz emission structure containing the anti-ferromagnetic pinning layer. When the magnetic moment direction of the first ferromagnetic material layer is parallel or anti-parallel to the second ferromagnetic material layer, the terahertz amplitude emitted respectively is shown. When the magnetic moment direction of the first ferromagnetic material layer is parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, and the terahertz signal is enhanced. When the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in opposite directions, and the terahertz signals emitted by the two sides will cancel each other out, and the terahertz signal tends to be zero.

[0060] Figure 4 As shown, the terahertz is emitted by the ultra-short pulse laser irradiating to the terahertz emission structure containing the anti-ferromagnetic pinning layer. The voltage is applied to the lead magnesium niobate-lead titanate or strontium titanate substrate through the electrode, and the lead magnesium niobate-lead titanate or strontium titanate substrate produces tensile or shrinkage deformation under the action of the voltage. The deformation is transmitted to the first ferromagnetic material layer through the first topological material layer, so that the lattice constant of the magnetic thin film in the first ferromagnetic material layer changes. When the magnetic moment direction of the first ferromagnetic material layer is parallel or anti-parallel to the second ferromagnetic material layer, the terahertz amplitude emitted respectively is shown. When the magnetic moment direction of the first ferromagnetic material layer is parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, and the terahertz signal is enhanced. When the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the second ferromagnetic material layer, the terahertz signals emitted by the first ferromagnetic material layer and the second ferromagnetic material layer are in opposite directions, and the terahertz signals emitted by the two sides will cancel each other out, and the terahertz signal tends to be zero.

[0061] As shown, Figures 1-4 The left side of the figure shows that when the magnetic moment direction of the first ferromagnetic material layer is parallel to the second ferromagnetic material layer, the terahertz signal is enhanced because the terahertz signals emitted are in the same direction, which is equivalent to the spin terahertz being in the on state. The right side of the figure shows that when the magnetic moment direction of the first ferromagnetic material layer is anti-parallel to the second ferromagnetic material layer, the terahertz signal tends to be zero because the terahertz signals emitted are in opposite directions, which is equivalent to the spin terahertz being in the off state.

[0062] For the above-mentioned new type of spin terahertz emitter, the method for regulating the emitted terahertz waves further comprises using the photovoltaic effect to radiate terahertz waves with different polarization states by changing external conditions such as laser polarization state and sample azimuth angle. The principle is as follows: the process of generating photocurrent includes two parts, i.e., an excitation process in which light excites electrons from an initial state i to an excited state j, and a relaxation process in which electrons recover from the excited state to the equilibrium state. In the excitation process, since the energy of laser photons (1.57 eV) is greater than the band gap of the topological material (0.4 eV), vertical band transition (different from non-vertical band transition assisted by phonons and impurities) dominates. The relaxation process generally includes non-centrosymmetric potential scattering, asymmetric recombination and intrinsic surface field (drift current). When the incident laser is linearly polarized, the photocurrent is related to the sample azimuth angle φ and the incident angle θ. When the incident laser is circularly or elliptically polarized, the photocurrent is mainly determined by the helicity of the incident laser (quarter-wave plate rotation angle α) and the incident angle θ.

[0063] In some embodiments, the terahertz emission structure based on spin-orbit effect in the above-mentioned new type of spin terahertz emitter adopts a molecular beam epitaxy technique and a magnetron sputtering technique to grow a suitable thin film structure. The specific preparation process is as follows:

[0064] Thin film growth: Taking a sapphire substrate as an example, since the sapphire substrate has stable properties and is not easy to be corroded by acid and alkali, it is first cleaned before growth. Generally, it is first ultrasonically treated in acetone and isopropyl alcohol for 5-6 minutes respectively, and then ultrasonically treated in deionized water for 5-6 minutes to remove organic matter on the surface of the substrate. After blowing dry with nitrogen, it is placed in the growth chamber of the molecular beam epitaxy. Before growth, the substrate is temperature checked. After slowly increasing the substrate temperature, it is monitored by a thermocouple, and the thermocouple temperature is calibrated by a pyrometer to achieve maximum temperature accuracy. After preparation, thin film growth is started.

[0065] First, the growth conditions of the growth chamber are determined:

[0066] 1. The vacuum degree is kept at about 10 -10 Torr.

[0067] 2. The ultrahigh vacuum chamber is equipped with required evaporation sources such as bismuth (Bi), antimony (Sb), tellurium (Te), selenium (Se), iron (Fe), germanium (Ge), tellurium (Te), chromium (Ge), platinum (Pt), tungsten (W), nickel (Ni) and all required materials.

[0068] 3. The evaporation rate is determined by a film thickness monitor (FDC) to control the flux ratio during the growth process. After the substrate temperature reaches 600 DEG C, annealing is performed for 40-60 min, and then the substrate temperature is reduced to the appropriate growth temperature corresponding to each material. The topological material, ferromagnetic material, barrier layer, topological material, ferromagnetic material, and antiferromagnetic material are sequentially grown, the thickness of the topological material is 5-10 nm, the thickness of the two-dimensional ferromagnetic material is 2-10 nm, and the thickness of the barrier layer is 0.2-5 nm. After the growth is completed, a 2-3 nm protective layer is coated, and then the substrate is rapidly cooled to room temperature and taken out.

[0069] Device processing: for the device using the piezoelectric effect, the thin film is placed in an evaporation chamber of electron beam evaporation, and a bottom electrode of 20 nm Ti and 100 nm Au is evaporated on the back of the substrate; for the device using the spin-orbit torque effect, the thin film is patterned by using photolithography technology, dry etching technology, electron beam evaporation technology and peeling technology. After processing, the processing effect is characterized by an optical microscope.

[0070] After the device is prepared, electrodes are prepared on the basis of the thin film under the irradiation of 800 nm or 1560 nm femtosecond laser. The device radiates broadband terahertz (the frequency band width is in the range of 0-3 THz), and at the same time, appropriate different amplitude currents (-30 MA / cm 2 ~ 30 MA / cm 2 ) are input to each unit device through a current source. The current is applied to the metal electrode and flows into the bottom topological material to control the magnetic moment direction of the two-dimensional ferromagnetic layer close to the substrate layer by using the spin-orbit torque effect. When the magnetic moment direction of the layer is parallel to the magnetic moment direction of the upper ferromagnetic layer, the terahertz amplitude is the largest, and when the magnetic moment direction of the layer is anti-parallel to the magnetic moment direction of the upper ferromagnetic layer, the terahertz amplitude is the smallest.

[0071] The present application discloses the following technical effects: (1) the topological material and the two-dimensional ferromagnetic material are used as the spin source non-ferromagnetic layer and the ferromagnetic layer material, respectively. Since the two-dimensional ferromagnetic material is combined with the adjacent layer through the weak van der Waals force interaction, the two-dimensional ferromagnetic material can break away from the limitation of lattice matching and compatibility. At the same time, the two-dimensional ferromagnetic material can obtain a high-quality interface without dangling bonds at the interface and an atomic-level flatness, which is expected to significantly reduce the interface spin loss, greatly improve the emission efficiency, and realize the high mechanical flexibility and integration of the spin terahertz; (2) the spin-orbit torque effect or the piezoelectric effect is used to perform ultrafast regulation and control on the waveform, amplitude and phase of the terahertz, which promotes the development and realization of the terahertz on-chip device; (3) the terahertz emission module and the regulation and control module are perfectly integrated, which greatly improves the integration of the terahertz device and system.

[0072] The principles and implementation manners of the present application are described by using specific examples in the present application, and the above examples are only used to help understand the method of the present application and its core idea; meanwhile, for the general technical personnel in the art, the specific implementation manners and application ranges will be changed according to the idea of the present application. In conclusion, the content of the present specification should not be understood as the limitation of the present application.

Claims

1. A spin terahertz emitter, characterized by, The spin terahertz emission structure comprises an electrode, and a substrate layer, a first topological material layer, a first ferromagnetic material layer, a barrier layer, a second topological material layer and a second ferromagnetic material layer arranged in order from bottom to top; the first topological material layer and the second topological material layer comprise a topological insulator and a topological semimetal, and the electrode is used for inputting a current to the first topological material layer or applying a voltage to the substrate layer; the spin terahertz emission structure further comprises an antiferromagnetic pinning layer arranged above the second ferromagnetic material layer; the first topological material layer, the first ferromagnetic material layer, the barrier layer, the second topological material layer and the second ferromagnetic material layer all contain van der Waals materials; By inputting a current of a certain size and a specified polarity to the first topological material layer, under the action of the current, the first ferromagnetic material layer and the second ferromagnetic material layer generate magnetic moments in parallel directions, at this time, the terahertz radiated by the first ferromagnetic material layer and the second ferromagnetic material layer are in the same direction, the two terahertz signals are superimposed on each other, the terahertz amplitude is maximum, the terahertz waveform and phase exist, and the new spin terahertz emitter is turned on; When it is necessary to turn off the new spin terahertz emitter, by inputting a current opposite in polarity to the above-mentioned current to the first topological material layer, when the amplitude of the current increases to a certain size, the magnetic moment direction of the first ferromagnetic material layer instantaneously flips, and is anti-parallel to the magnetic moment direction of the second ferromagnetic material layer, at this time, the terahertz radiated by the first ferromagnetic material layer and the second ferromagnetic material layer are opposite in direction, the two terahertz signals cancel each other out, the terahertz amplitude is minimum, the terahertz waveform and phase tend to zero, and the new spin terahertz emitter is turned off; The adjustment process from turning on to turning off is realized through the instantaneous flipping of the magnetic moment.

2. The spin terahertz emitter of claim 1, the topological insulator is selected from one of or an alloy of a plurality of the materials Bi2Se3, Bi2Te3, Bi x Sb 1-x , Sb2Te3, (Bi x Sb 1-x )2Te3, the topological semimetal is selected from one of the van der Waals materials PtTe2, WTe2, PtSe2, WSe2.

3. The spin terahertz emitter of claim 1, wherein, The first ferromagnetic material layer and the second ferromagnetic material layer comprise two-dimensional ferromagnetic material, and the two-dimensional ferromagnetic material is selected from van der Waals materials Fe x one of GeTe2 and CrTe2.

4. The spin terahertz emitter of claim 1, wherein, The barrier layer is selected from one of an oxide and a two-dimensional material; the oxide comprises one of MgO and Al2O3, and the two-dimensional material is selected from one of van der Waals materials h-BN, MoS2, WSe2 and GaSe.

5. The spin terahertz emitter of claim 1, wherein, The electrode is connected to the first topological material layer, and the electrode is used for being connected to an external power supply.

6. The spin terahertz emitter of claim 1, wherein, The electrode is arranged below the substrate layer, and the substrate layer is a lead magnesium niobate-lead titanate or strontium titanate substrate.

7. A method of tuning the spin terahertz emitter of any one of claims 1-6, wherein, The method comprises the following steps: The electrode is connected to the first topological material layer, and the electrode is used for being connected to an external power supply. The method further comprises the following steps:

8. The method of claim 7, wherein the spin terahertz emitter is a spintronic terahertz emitter. The electrode is connected to the first topological material layer, and the electrode is used for being connected to an external power supply. The electrode is connected to the first topological material layer, and the electrode is used for being connected to an external power supply.

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