A terahertz emission device and a method for amplitude regulation thereof

Abstract

The present application relates to a kind of terahertz emitter and its amplitude regulation method, belong to terahertz regulation field, the terahertz emitter includes from bottom to top sequentially stacked substrate, ferromagnetic layer, non-ferromagnetic layer and antiferromagnetic layer, or including from bottom to top sequentially stacked substrate, antiferromagnetic layer, non-ferromagnetic layer and ferromagnetic layer, can be changed by the direction of applied magnetic field, applied current or applied electric field to the amplitude regulation of above-mentioned terahertz emitter, to change the direction of applied magnetic field, applied current or applied electric field to the amplitude regulation of above-mentioned terahertz emitter, so that the present application designs a kind of terahertz emitter of new structure, and corresponding amplitude regulation method is designed for the terahertz emitter, can realize the efficient regulation of terahertz amplitude.

Description

Technical Field

[0001] This invention relates to the field of terahertz modulation technology, and in particular to a terahertz emitting device and its amplitude modulation method. Background Technology

[0002] Currently, commonly used terahertz emission schemes include photoconductive antenna terahertz sources and spin terahertz sources. The photoconductive antenna terahertz source consists of a semiconductor substrate and electrodes. Its working principle is that an ultrashort laser pulse is focused onto the semiconductor material between the electrodes. If the laser photon energy is greater than the band gap width of the semiconductor substrate, electrons can be excited into the conduction band to form photogenerated carriers. These photogenerated carriers move under the influence of a bias electric field, forming a transiently changing current within the laser penetration depth range, thus radiating terahertz waves. The spin terahertz source is generally composed of a ferromagnetic / non-ferromagnetic heterojunction. Its working principle is that when a femtosecond laser pulse irradiates the ferromagnetic / non-ferromagnetic heterobilayer, an ultrafast spin current is excited in the ferromagnetic layer. When the spin current enters the non-ferromagnetic layer, the inverse spin Hall effect converts it into a transient charge current, thereby radiating terahertz waves.

[0003] When controlling spin terahertz sources, the commonly used schemes include: (1) using a ferromagnetic layer / metal layer / oxide barrier layer / pinning layer / antiferromagnetic pinning layer as the basic emission structure, and controlling the terahertz radiation efficiency, bandwidth and polarization state by controlling different materials and film thicknesses in the composite film structure without applying an external magnetic field; (2) using a ferromagnetic layer / non-ferromagnetic layer / ferromagnetic layer / antiferromagnetic pinning layer as the basic emission structure, and controlling the terahertz amplitude by changing the direction of the external magnetic field and utilizing the tunneling magnetoresistance effect.

[0004] Therefore, there is an urgent need for a new type of terahertz transmitting device and its amplitude control method, which can achieve efficient control of terahertz amplitude. Summary of the Invention

[0005] The purpose of this invention is to provide a terahertz transmitting device and its amplitude control method. A novel terahertz transmitting device is designed, and a corresponding amplitude control method is designed for the terahertz transmitting device, which can achieve efficient control of the terahertz amplitude.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] A terahertz emitting device, the terahertz emitting device comprising a substrate, a ferromagnetic layer, a non-ferromagnetic layer and an antiferromagnetic layer stacked sequentially from bottom to top; or, the terahertz emitting device comprising a substrate, an antiferromagnetic layer, a non-ferromagnetic layer and a ferromagnetic layer stacked sequentially from bottom to top.

[0008] In some embodiments, the ferromagnetic layer is made of a two-dimensional ferromagnetic material, a ferromagnetic metal, or a ferromagnetic metal alloy; the non-ferromagnetic layer is made of a topological insulator, a topological half-metal, or a heavy metal; the antiferromagnetic layer is made of a single-crystal antiferromagnetic material; and the ferromagnetic metal alloy is an alloy containing the ferromagnetic metal.

[0009] In some embodiments, the two-dimensional ferromagnetic material includes Fe x GeTe2, CrTe2; the ferromagnetic metals include Co, Fe, Ni; the topological insulators include Bi2Se3, Bi2Te3, Bi x Sb 1-x Sb2Te3, (Bi x Sb 1-x )2Te3; the topological half-metal includes PtTe2 and WTe2; the heavy metal includes W, Ta, and Pt; the single-crystal antiferromagnetic material includes NiO.

[0010] In some embodiments, the thickness of the ferromagnetic layer is 2nm-10nm; the thickness of the non-ferromagnetic layer is 2nm-10nm; and the thickness of the antiferromagnetic layer is 10nm-200nm.

[0011] In some embodiments, the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer are all prepared by molecular beam epitaxy, magnetron sputtering, or pulsed laser deposition.

[0012] In some embodiments, the terahertz emitting device further includes two electrodes; both electrodes are located on the substrate; one electrode is located at a first end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer, and is in contact with the end face of the first end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer; the other electrode is located at a second end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer, and is in contact with the end face of the second end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer.

[0013] An amplitude modulation method for the above-mentioned terahertz transmitting device, the amplitude modulation method comprising:

[0014] A magnetic field is applied to a terahertz emitting device, and the terahertz amplitude of the terahertz emitting device is controlled by changing the direction of the magnetic field;

[0015] A current is applied to the terahertz emitting device, and the terahertz amplitude of the terahertz emitting device is controlled based on the spin orbital moment effect;

[0016] And / or, apply an electric field to the terahertz emitting device to modulate the terahertz amplitude of the terahertz emitting device based on the piezoelectric effect.

[0017] In some embodiments, the magnetic flux of the magnetic field is -200mT to 200mT.

[0018] In some embodiments, the current is -30mA / cm 2 ~30MA / cm 2 .

[0019] In some embodiments, the electric field is -10KV / cm to 10KV / cm.

[0020] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0021] This invention provides a terahertz emitting device and its amplitude modulation method. The terahertz emitting device comprises a substrate, a ferromagnetic layer, a non-ferromagnetic layer, and an antiferromagnetic layer stacked sequentially from bottom to top, or comprises a substrate, an antiferromagnetic layer, a non-ferromagnetic layer, and a ferromagnetic layer stacked sequentially from bottom to top. The amplitude of the terahertz emitting device can be modulated by changing the direction of the applied magnetic field, applying a current, or applying an electric field. Thus, this invention designs a novel terahertz emitting device and a corresponding amplitude modulation method for the terahertz emitting device, which can achieve efficient modulation of the terahertz amplitude. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of the terahertz transmitting device provided by the present invention;

[0024] Figure 2 This is a schematic diagram illustrating the manipulation of a terahertz emission device by a rotating magnetic field in the substrate / ferromagnetic layer / non-ferromagnetic layer / antiferromagnetic layer structure provided by the present invention.

[0025] Figure 3 This is a schematic diagram illustrating the manipulation of a terahertz emission device by a rotating magnetic field in the substrate / antiferromagnetic layer / nonferromagnetic layer / ferromagnetic layer structure provided by the present invention.

[0026] Figure 4 A schematic diagram illustrating the manipulation of terahertz emission devices by the spin orbital moment effect provided by this invention;

[0027] Figure 5 This is a schematic diagram illustrating the piezoelectric effect used to control terahertz transmitting devices according to the present invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The purpose of this invention is to provide a terahertz transmitting device and its amplitude control method. A novel terahertz transmitting device is designed, and a corresponding amplitude control method is designed for the terahertz transmitting device, which can achieve efficient control of the terahertz amplitude.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1:

[0032] This embodiment provides a terahertz emission device, which is a spin terahertz emission device. It employs a three-layer structure of ferromagnetic layer / non-ferromagnetic layer / antiferromagnetic layer as the emission structure. The ferromagnetic layer and non-ferromagnetic layer form a heterojunction, and the non-ferromagnetic layer and antiferromagnetic layer also form a heterojunction. Specifically, as shown... Figure 1 As shown, the terahertz emitting device includes a substrate, a ferromagnetic layer, a non-ferromagnetic layer and an antiferromagnetic layer stacked sequentially from bottom to top, or the terahertz emitting device includes a substrate, an antiferromagnetic layer, a non-ferromagnetic layer and a ferromagnetic layer stacked sequentially from bottom to top.

[0033] The materials of each layer of the terahertz transmitting device in this embodiment are as follows:

[0034] The substrate can be a double-sided polished alumina substrate, a double-sided polished magnesium oxide substrate, a sapphire substrate, a lead magnesium niobate-lead titanate substrate, or a strontium titanate substrate.

[0035] The ferromagnetic layer can be made of two-dimensional ferromagnetic materials, ferromagnetic metals, or ferromagnetic metal alloys, with the latter being alloys containing ferromagnetic metals. Two-dimensional ferromagnetic materials may include Fe. x GeTe2 and CrTe2 are ferromagnetic metals, which may include Co, Fe, and Ni. Ferromagnetic metal alloys may be alloys containing Co, Fe, or Ni.

[0036] The material of the non-ferromagnetic layer can be a topological material, including topological insulators, topological half-metals, and heavy metals, with heavy metals preferably having a large spin Hall angle. Topological insulators may include Bi₂Se₃, Bi₂Te₃, and Bi₂Se₃. x Sb 1-x Sb2Te3, (Bix Sb 1-x )2Te3 and alloys containing any of the aforementioned topological insulators, the topological half-metals may include PtTe2 and WTe2, and the heavy metals may include W, Ta and Pt.

[0037] The antiferromagnetic layer can be a single-crystal antiferromagnetic material, including NiO.

[0038] The materials selected for the terahertz emitting device in this embodiment have a wide applicable temperature range. The materials are stable in the temperature range of 0K-300K, which can ensure the reliability of the terahertz emitting device. Therefore, the terahertz emitting device in this embodiment is applicable to a wide range of conditions and can achieve high-efficiency spin terahertz radiation with a wide bandwidth between 0K-300K.

[0039] Preferably, the thickness of the ferromagnetic layer is 2nm-10nm, the thickness of the non-ferromagnetic layer is 2nm-10nm, and the thickness of the antiferromagnetic layer is 10nm-200nm. By optimizing the thickness, a higher amplitude terahertz can be radiated, avoiding the problem of very small or no terahertz amplitude caused by using other thicknesses.

[0040] In this embodiment, the ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer are all prepared by growth methods such as molecular beam epitaxy, magnetron sputtering, or pulsed laser deposition. The ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer are all thin film shapes, that is, the ferromagnetic layer is a ferromagnetic thin film, the non-ferromagnetic layer is a non-ferromagnetic thin film, and the antiferromagnetic layer is an antiferromagnetic thin film.

[0041] The terahertz emitting device in this embodiment may further include two electrodes, both located on the substrate. One electrode is located at the first end of the ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer, and is in contact with the end face of the first end of the ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer. The other electrode is located at the second end of the ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer, and is in contact with the end face of the second end of the ferromagnetic layer, non-ferromagnetic layer, and antiferromagnetic layer. Using two electrodes facilitates the subsequent control process. The two electrodes are the positive and negative electrodes, respectively.

[0042] Based on the above structure, when the terahertz emitting device includes a substrate, a ferromagnetic layer, a non-ferromagnetic layer, and an antiferromagnetic layer stacked sequentially from bottom to top, the fabrication method of the terahertz emitting device in this embodiment may include:

[0043] (1) A ferromagnetic thin film of 2nm-10nm is grown on a double-polished alumina substrate or a double-polished magnesium oxide substrate by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition.

[0044] (2) Non-ferromagnetic films of 2nm-10nm are grown on ferromagnetic films by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition;

[0045] (3) Antiferromagnetic films of 10 nm-200 nm are grown on nonferromagnetic films by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition;

[0046] (4) Two electrodes are deposited on the substrate. One electrode is located at the first end of the ferromagnetic thin film, the non-ferromagnetic thin film, and the antiferromagnetic thin film, and is in contact with the end face of the first end of the three films at the same time. The other electrode is located at the second end of the ferromagnetic thin film, the non-ferromagnetic thin film, and the antiferromagnetic thin film, and is in contact with the end face of the second end of the three films at the same time.

[0047] When the terahertz emitting device comprises a substrate, an antiferromagnetic layer, a nonferromagnetic layer, and a ferromagnetic layer stacked sequentially from bottom to top, the fabrication method of the terahertz emitting device in this embodiment may include:

[0048] (1) An antiferromagnetic thin film of 15 nm-100 nm is grown on a double-polished alumina substrate or a double-polished magnesium oxide substrate by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition.

[0049] (2) Non-ferromagnetic films of 2nm-10nm are grown on antiferromagnetic films by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition;

[0050] (3) 2nm-10nm ferromagnetic thin films are grown on non-ferromagnetic thin films by growth methods such as molecular beam epitaxy, magnetron sputtering or pulsed laser deposition;

[0051] (4) Two electrodes are deposited on the substrate. One electrode is located at the first end of the antiferromagnetic thin film, the nonferromagnetic thin film, and the ferromagnetic thin film, and is in contact with the end face of the first end of the three films. The other electrode is located at the second end of the antiferromagnetic thin film, the nonferromagnetic thin film, and the ferromagnetic thin film, and is in contact with the end face of the second end of the three films.

[0052] This embodiment provides a novel terahertz emission device. Based on traditional spin terahertz emission, it achieves efficient spin terahertz radiation using a NiO antiferromagnetic / nonferromagnetic heterojunction with a specific crystal phase (such as NiO(111) / Pt, NiO(001) / Pt). Under femtosecond laser irradiation, due to nonlinear effects and ultrafast demagnetization, a spin current pointing towards the nonferromagnetic layer is generated in the NiO and ferromagnetic layers. Due to the inverse spin Hall effect, the spin current is converted into a picosecond-level charge flow in the ferromagnetic layer, thereby radiating terahertz waves. Since the generation of NiO / nonferromagnetic layers does not depend on an external magnetic field, under the condition of applying a magnetic field in a suitable direction, the two currents can be superimposed to achieve high terahertz emission efficiency.

[0053] Example 2:

[0054] In this embodiment, the terahertz amplitude modulation mechanism is as follows: based on the characteristic that the emission of the antiferromagnetic layer / nonferromagnetic layer heterojunction does not depend on the magnetization direction, when the magnetic moment of the ferromagnetic layer is magnetized in a suitable direction, the terahertz amplitude will be greatly increased. Therefore, this embodiment controls the magnetization direction of the magnetic moment of the ferromagnetic layer to achieve the modulation of the terahertz amplitude, so as to develop a terahertz radiation switching device.

[0055] This embodiment proposes three methods to control the magnetization direction of the ferromagnetic layer's magnetic moment: changing the external magnetic field arrangement; utilizing the spin orbital moment effect; and utilizing the piezoelectric effect. By employing these three methods, terahertz radiation is modulated by controlling the reversal of the ferromagnetic layer's magnetic moment. This embodiment represents a significant innovation in terahertz modulation methods, enabling on-chip ultrafast and low-power terahertz modulation.

[0056] Based on the above principles, this embodiment provides an amplitude control method for the terahertz emitting device described in Embodiment 1. The amplitude control method includes: applying a magnetic field to the terahertz emitting device and controlling the terahertz amplitude of the terahertz emitting device by changing the direction of the magnetic field; applying a current to the terahertz emitting device and controlling the terahertz amplitude of the terahertz emitting device based on the spin-orbit moment effect; and / or applying an electric field to the terahertz emitting device and controlling the terahertz amplitude of the terahertz emitting device based on the piezoelectric effect.

[0057] In this embodiment, the magnetic flux of the applied magnetic field can be -200mT to 200mT. When the magnetic moment reversal of the ferromagnetic layer is achieved through the spin orbital moment effect or the piezoelectric effect, the applied current ranges from -30mA / cm. 2 ~30MA / cm 2 The applied electric field ranges from -10 kV / cm to 10 kV / cm. The values ​​of the magnetic field, current, and electric field are preferably determined from the above range; exceeding these ranges may damage the terahertz transmitting device.

[0058] To facilitate a clearer description of the directions later, three directions are first defined for the structure of the terahertz emitting device, such as... Figure 1 As shown, one direction is vertical, defined as the direction from the antiferromagnetic layer to the substrate. Figure 1 The vertical direction is defined as up and down; the horizontal direction is defined as the line connecting the two electrodes. Figure 1 The horizontal direction is left-right; the third is the front-back direction, which is defined as the direction that is perpendicular to both the up-down and left-right directions, that is, the direction perpendicular to the paper.

[0059] Specifically, in this embodiment, the direction of the applied magnetic field can be changed manually. When the direction of the applied magnetic field is parallel to the left and right direction, the magnetic moment of the ferromagnetic layer can be rotated by 180°; when the direction of the applied magnetic field is parallel to the front and back direction, the magnetic moment of the ferromagnetic layer can be rotated by 90°.

[0060] In this embodiment, a current is applied to the terahertz transmitting device via a current source, specifically by electrically connecting the current source to two electrodes. This process can be performed manually or automatically through programming. The method of applying the current relies on the spin-orbit moment effect, which can achieve a 180° rotation of the ferromagnetic layer's magnetic moment.

[0061] In this embodiment, a voltage is applied to the terahertz transmitting device via a voltage source, specifically by electrically connecting the voltage source to two electrodes. This process can be performed manually or automatically through programming. The method of applying the voltage relies on the piezoelectric effect, which can achieve a 90° rotation of the magnetic moment of the ferromagnetic layer.

[0062] To demonstrate the effectiveness of the amplitude control method provided in this embodiment, a specific experiment is conducted to prove it:

[0063] This experiment includes a spin terahertz emission device based on a heterojunction of ferromagnetic, non-ferromagnetic, and antiferromagnetic materials, and a terahertz time-domain spectroscopy system capable of amplitude modulation. Suitable thin film structures are grown using molecular beam epitaxy, magnetron sputtering, or pulsed laser deposition. The thickness of the ferromagnetic layer is between 2 nm and 10 nm, the thickness of the non-ferromagnetic layer is between 2 nm and 10 nm, and the thickness of the antiferromagnetic layer is between 10 nm and 200 nm. The terahertz emission device samples prepared using the above methods are placed in a variable-temperature (0-300 K) terahertz time-domain spectroscopy system for performance testing. Under irradiation with an 800 nm or 1560 nm femtosecond laser at an experimental temperature between 0 K and 300 K, a magnetic field of -30 MA / cm is applied by rotating the magnetic field direction from -200 mT to 200 mT. 2 ~30MA / cm 2 The magnetic moment of the ferromagnetic layer is reversed by applying a current or an electric field of -10kV / cm to 10kV / cm, thereby achieving the modulation of the terahertz amplitude.

[0064] Experimental results are as follows Figures 2-5 As shown, the lower rhomboid lines in the diagram represent femtosecond lasers, while the upper single lines represent terahertz waves. The orientation in the diagram is based on the optical path, which is actually horizontal. The femtosecond laser is in front of the terahertz emitting device sample, and the terahertz waves are emitted from behind the sample. Therefore, the magnetic field can be distributed in the four directions of up, down, left, and right of the terahertz emitting device sample. Figure 2 This is a schematic diagram illustrating the manipulation of a terahertz emission device by a rotating magnetic field in a substrate / ferromagnetic layer / non-ferromagnetic layer / antiferromagnetic layer structure. Figure 2In (A), the magnetic field direction is from N to S, that is, the magnetic field direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped 180 degrees, and the magnetization direction of the magnetic moment is to the left. Figure 2 In (B), the magnetic field direction is from N to S, that is, the magnetic field direction is to the right. At this time, the magnetic moment of the ferromagnetic layer is flipped 180 degrees, and the magnetization direction of the magnetic moment is to the right. Figure 2 In (C), the magnetic field direction is from N to S, that is, the magnetic field direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped by 90 degrees, and the magnetization direction of the magnetic moment is to the left. Figure 2 In (D), the magnetic field direction is from N to S, that is, the magnetic field direction is downward. At this time, the magnetic moment of the ferromagnetic layer is reversed by 90 degrees, and the magnetization direction of the magnetic moment is downward. Figure 2 (A) Figure 2 (B) The magnetization direction is changed by 180° to switch the terahertz amplitude. Figure 2 (C) Figure 2 The magnetization direction of (D) is changed by 90° to adjust the magnitude of the terahertz amplitude.

[0065] Figure 3 This is a schematic diagram illustrating the manipulation of a terahertz emission device by a rotating magnetic field within a substrate / antiferromagnetic layer / nonferromagnetic layer / ferromagnetic layer structure. Figure 3 In (A), the magnetic field direction is from N to S, that is, the magnetic field direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped 180 degrees, and the magnetization direction of the magnetic moment is to the left. Figure 3 In (B), the magnetic field direction is from N to S, that is, the magnetic field direction is to the right. At this time, the magnetic moment of the ferromagnetic layer is flipped 180 degrees, and the magnetization direction of the magnetic moment is to the right. Figure 3 In (C), the magnetic field direction is from N to S, that is, the magnetic field direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped by 90 degrees, and the magnetization direction of the magnetic moment is to the left. Figure 3 In (D), the magnetic field direction is from N to S, that is, the magnetic field direction is downward. At this time, the magnetic moment of the ferromagnetic layer is reversed by 90 degrees, and the magnetization direction of the magnetic moment is downward. Figure 3 (A) Figure 3 (B) The magnetization direction is changed by 180° to switch the terahertz amplitude. Figure 3 (C) Figure 3 The magnetization direction of (D) is changed by 90° to adjust the magnitude of the terahertz amplitude.

[0066] Figure 4 (A) is a schematic diagram of the spin orbit moment effect in the substrate / ferromagnetic layer / non-ferromagnetic layer / antiferromagnetic layer structure on the modulation of terahertz emission device. The current direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped by 180 degrees and the magnetization direction of the magnetic moment is downward. Figure 4 (B) is a schematic diagram of the spin orbit moment effect in the substrate / antiferromagnetic layer / nonferromagnetic layer / ferromagnetic layer structure on the modulation of the terahertz emission device. The current direction is to the left. At this time, the magnetic moment of the ferromagnetic layer is flipped by 180 degrees and the magnetization direction of the magnetic moment is upward.

[0067] Figure 5 (A) is a schematic diagram of the piezoelectric effect on the modulation of the terahertz emission device in the substrate / ferromagnetic layer / non-ferromagnetic layer / antiferromagnetic layer structure. The electric field direction is forward or backward (originating from the bottom electrode or the top electrode). At this time, the magnetic moment of the ferromagnetic layer is flipped by 90 degrees, and the magnetization direction of the magnetic moment is downward. Figure 5 (B) is a schematic diagram of the piezoelectric effect in the substrate / antiferromagnetic layer / nonferromagnetic layer / ferromagnetic layer structure controlling the terahertz emission device. The electric field direction is forward or backward (originating from the bottom electrode or top electrode). At this time, the magnetic moment of the ferromagnetic layer is flipped by 90 degrees, and the magnetization direction of the magnetic moment is downward.

[0068] This embodiment proposes a spin terahertz emission device based on an antiferromagnetic / nonferromagnetic / ferromagnetic heterostructure. It achieves efficient terahertz radiation and ultrafast on-chip amplitude modulation based on spin materials, utilizing conventional spin terahertz emission mechanisms, antiferromagnetic terahertz emission mechanisms, spin orbital moment effects, and piezoelectric effects. Its advantages are as follows:

[0069] (1) It can achieve efficient terahertz radiation.

[0070] This embodiment can change the direction of the magnetic moment of the ferromagnetic layer by altering the magnetic field arrangement, applying current, or voltage, thereby changing the amplitude of the radiated terahertz waves. When external conditions are applied to make the terahertz waves radiated by the ferromagnetic / non-ferromagnetic heterojunction have the same phase as those radiated by the antiferromagnetic / non-ferromagnetic heterojunction, the superposition of the two terahertz waves can be achieved, greatly improving the terahertz emission efficiency. Since the emission of the antiferromagnetic / non-ferromagnetic layer does not depend on the magnetic field, i.e., changing the direction of the magnetic field does not change the amplitude or phase of the emitted terahertz waves. However, when the direction of the magnetic moment of the ferromagnetic layer is changed by altering the magnetic field arrangement (direction) or applying current or electric field, the phase of the terahertz waves at the ferromagnetic / non-ferromagnetic layer end will change. Therefore, when the magnetic moment arrangement is at a suitable angle, the terahertz waves radiated by this mechanism will have the same phase as those of NiO / Pt, i.e., the amplitudes of the emitted terahertz waves will be superimposed.

[0071] (2) On-chip terahertz amplitude modulation can be achieved through multiple means.

[0072] Based on the properties of NiO, for NiO thin films with specific crystal phases, taking the 111 crystal phase as an example, under femtosecond laser irradiation, the NiO thin film generates a laser-impact magnetic moment M through magnetic difference frequency generation. M automatically generates a spin-polarized current Js1. After the spin current is injected into the adjacent non-ferromagnetic layer, a transient charge current Jc is generated due to the inverse spin Hall effect, which then radiates terahertz waves. This radiation method is independent of the direction of the external magnetic field; that is, when the direction of the external magnetic field changes, the amplitude and phase of the radiated terahertz waves remain unchanged. When the direction of the magnetic moment of the ferromagnetic layer is changed by altering the direction of the external magnetic field, the spin orbital moment effect, or the piezoelectric effect, the phase of the terahertz waves radiated by the ferromagnetic layer / non-ferromagnetic heterojunction will also change accordingly. When the magnetic moment direction is changed by 180° through a rotating magnetic field or spin orbital moment effect, the terahertz phase radiated by the ferromagnetic / non-ferromagnetic heterojunction will also be flipped by 180°, thus achieving the superposition or subtraction of terahertz generated by the two mechanisms, thereby realizing terahertz amplitude modulation. When the magnetic moment direction is changed by 90° through a rotating magnetic field or piezoelectric effect, the terahertz phase radiated by the ferromagnetic / non-ferromagnetic heterojunction will also be deflected by 90°, that is, the phase difference between the two terahertz beams is 90°. Since the azimuth angle of the crystal at the detection end is fixed, only the terahertz amplitude at a certain polarization angle can be detected. In this case, only the terahertz radiated by the antiferromagnetic / non-ferromagnetic heterojunction can be detected. In contrast, the terahertz detected in the initial state is the result of the superposition or cancellation of the two terahertz beams. In comparison, there will be a large difference in amplitude in this case. Based on this, the amplitude modulation of on-chip terahertz can be achieved by changing the magnetic moment direction.

[0073] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0074] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A terahertz transmitting device, characterized in that, The terahertz emitting device comprises a substrate, a ferromagnetic layer, a non-ferromagnetic layer, and an antiferromagnetic layer stacked sequentially from bottom to top; or, the terahertz emitting device comprises a substrate, an antiferromagnetic layer, a non-ferromagnetic layer, and a ferromagnetic layer stacked sequentially from bottom to top; the ferromagnetic layer and the non-ferromagnetic layer form a heterojunction, and the non-ferromagnetic layer and the antiferromagnetic layer form a heterojunction. Under the irradiation of a femtosecond laser, due to nonlinear effects and ultrafast demagnetization effects, a spin current pointing towards the non-ferromagnetic layer is generated in the antiferromagnetic layer and the ferromagnetic layer. Due to the inverse spin Hall effect, the spin current is converted into a charge current in the ferromagnetic layer, radiating terahertz waves; The emission of a heterojunction composed of a non-ferromagnetic layer and an antiferromagnetic layer is independent of the magnetization direction. By controlling the magnetization direction of the magnetic moment of the ferromagnetic layer, the terahertz phase of the heterojunction composed of the ferromagnetic layer and the non-ferromagnetic layer changes, thereby achieving the modulation of the terahertz amplitude. A magnetic field is applied to the terahertz emitting device, and the terahertz amplitude of the terahertz emitting device is controlled by changing the direction of the magnetic field; Applying a current to a terahertz emitting device to modulate the terahertz amplitude of the terahertz emitting device based on the spin-orbit moment effect; and / or applying an electric field to a terahertz emitting device to modulate the terahertz amplitude of the terahertz emitting device based on the piezoelectric effect.

2. The terahertz transmitting device according to claim 1, characterized in that, The ferromagnetic layer is made of a two-dimensional ferromagnetic material, a ferromagnetic metal, or a ferromagnetic metal alloy; the non-ferromagnetic layer is made of a topological insulator, a topological half-metal, or a heavy metal; the antiferromagnetic layer is made of a single-crystal antiferromagnetic material; and the ferromagnetic metal alloy is an alloy containing the ferromagnetic metal.

3. The terahertz transmitting device according to claim 2, characterized in that, The two-dimensional ferromagnetic material includes Fe. x GeTe2, CrTe2; the ferromagnetic metals include Co, Fe, Ni; the topological insulators include Bi2Se3, Bi2Te3, Bi x Sb 1-x Sb2Te3, (Bi x Sb 1-x )2Te3; the topological half-metal includes PtTe2 and WTe2; the heavy metal includes W, Ta, and Pt; the single-crystal antiferromagnetic material includes NiO.

4. The terahertz transmitting device according to claim 1, characterized in that, The thickness of the ferromagnetic layer is 2nm-10nm; the thickness of the non-ferromagnetic layer is 2nm-10nm; and the thickness of the antiferromagnetic layer is 10nm-200nm.

5. The terahertz transmitting device according to claim 1, characterized in that, The ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer are all prepared by molecular beam epitaxy, magnetron sputtering, or pulsed laser deposition.

6. The terahertz transmitting device according to claim 1, characterized in that, The terahertz emitting device further includes two electrodes; both electrodes are located on the substrate; one electrode is located at the first end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer, and is in contact with the end face of the first end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer; the other electrode is located at the second end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer, and is in contact with the end face of the second end of the ferromagnetic layer, the non-ferromagnetic layer, and the antiferromagnetic layer.

7. An amplitude modulation method for a terahertz transmitting device according to any one of claims 1-6, characterized in that, The amplitude control method includes: A magnetic field is applied to a terahertz emitting device, and the terahertz amplitude of the terahertz emitting device is controlled by changing the direction of the magnetic field; A current is applied to the terahertz emitting device, and the terahertz amplitude of the terahertz emitting device is controlled based on the spin orbital moment effect; And / or, apply an electric field to the terahertz emitting device to modulate the terahertz amplitude of the terahertz emitting device based on the piezoelectric effect.

8. The amplitude control method according to claim 7, characterized in that, The magnetic flux of the magnetic field is -200mT to 200mT.

9. The amplitude control method according to claim 7, characterized in that, The current is -30mA / cm 2 ~30MA / cm 2 .

10. The amplitude control method according to claim 7, characterized in that, The electric field is -10KV / cm to 10KV / cm.

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