CN209658587U - A kind of spin terahertz transmitter - Google Patents

Abstract

An embodiment of the present invention provides a spin terahertz emitter, which at least includes a femtosecond laser, a topological thin film, and a magnetic field generator. The pump light output by the femtosecond laser passes through the topological thin film to generate The magnetic field generator generates terahertz waves in the direction of the magnetic field. The topological structure thin film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, ferromagnetic layer and non-ferromagnetic layer are arranged and bonded in sequence And form a heterogeneous structure. The transmitter provided by the embodiment of the utility model has the advantages of simple structure, simple transmitting principle, high transmitting frequency, wide pulse width and low cost.

Description

A spinning terahertz emitter

technical field

The embodiment of the utility model relates to the technical field of terahertz pulse generation, in particular to a spin terahertz transmitter.

Background technique

Terahertz (THz) waves are between far-infrared and microwaves, covering the frequency range from 0.1 to 10 THz. Hertzian pulses are resonant probes of the excitation of many low-energy elements in condensed matter. Terahertz waves have many unique properties, such as transmission, safety, strong spectral resolution, etc. These properties endow terahertz waves with a wide range of application prospects, including terahertz radar and communication, spectroscopy and imaging, non-destructive flaw detection, security detection etc.

However, terahertz applications still have a strong demand for terahertz radiation sources with high efficiency, high power, low cost, and room temperature operation. At present, the commonly used terahertz sources based on photonics methods mainly include: zinc telluride (ZnTe) photorectification effect and low temperature grown gallium arsenide (LT-GaAs) photoconductive antenna to generate terahertz pulses. These two methods have the advantages of high maturity, high electric field strength for generating THz pulses, and good stability, but the preparation of these two materials is complicated, and the high cost limits the wide application of THz devices. Therefore, it is of great significance to improve on the basis of existing sources, or to develop terahertz radiation sources that meet the above requirements based on new physical principles.

Spintronics refers to the discipline of controlling and manipulating electron spin, studying its transport properties and constructing new devices. Some physical phenomena of spintronics, such as exchange-type magnons, antiferromagnetic resonance and ultrafast spin dynamics, etc., have characteristic frequencies just in the terahertz frequency band; this makes the combination of terahertz and spintronics, Terahertz spintronics, an emerging interdisciplinary subject, has been formed. Based on the phenomena and principles of spintronics, researchers have discovered and established several new terahertz wave generation methods, mainly including: a) Spin injection to generate terahertz waves b) THz wave generation based on antiferromagnetic resonance; c) THz wave generation based on ultrafast spin dynamics.

At present, femtosecond laser pulses are mainly used to irradiate ferromagnetic/nonmagnetic metal heterostructures to generate terahertz waves. The ferromagnetic layer absorbs light energy to make electrons transition from the d-band below the Fermi surface to the energy band above the Fermi surface, resulting in non-equilibrium Electronic distribution; due to the obvious difference in the spin-up and down-spin electronic density of states, the result is an instantaneous spin-polarized transmission from the ferromagnetic layer to the adjacent non-ferromagnetic layer (tungsten or platinum), that is, an instantaneous spin current; Due to the inverse spin Hall effect, spin-up and down-spin electrons are scattered to opposite directions, and the instantaneous spin current injected into the nonmagnetic layer is transformed into a transient charge current, thereby radiating broadband THz pulses. However, although many studies have shown that ferromagnetic/nonmagnetic metal heterostructure bilayers can generate terahertz radiation under femtosecond laser irradiation, due to the small spin Hall angle of tungsten or platinum, they cannot generate enough terahertz radiation. The instantaneous charge flow, and finally the radiation effect of terahertz is not significant.

Utility model content

Aiming at the technical problems existing in the prior art, the embodiment of the utility model provides a spin terahertz emitter.

An embodiment of the present invention provides a spin terahertz emitter, which at least includes a femtosecond laser, a topological thin film, and a magnetic field generator. The pump light output by the femtosecond laser passes through the topological thin film to generate The magnetic field generator generates terahertz waves in the direction of the magnetic field. The topological structure thin film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, ferromagnetic layer and non-ferromagnetic layer are arranged and bonded in sequence And form a heterogeneous structure.

Optionally, the topological insulator layer and the ferromagnetic layer form a double-layer heterostructure.

Optionally, the topological insulator layer forms a three-layer heterojunction with the ferromagnetic layer and the non-ferromagnetic layer and makes the terahertz waves mutually amplify.

Optionally, the topological insulator layer is a group V-VI element compound, specifically Bi ₂ Se ₃ , Bi ₂ Te ₃ , Bi _x Sb _1-x , Sb ₂ Te ₃ , (Bi _x Sb _1-x ) ₂ Te ₃ and its alloys.

Optionally, the ferromagnetic layer is a transition metal or a corresponding ferromagnetic alloy.

Optionally, the non-ferromagnetic layer is a material with strong spin-orbit coupling, and the spin Hall angle of the topological insulator is opposite to that of the topological insulator.

Optionally, the femtosecond laser is specifically a femtosecond laser oscillator, a femtosecond laser amplifier, or a fiber femtosecond laser.

Optionally, the magnetic field generator is used to generate magnetic fields with different directions and different magnitudes, so as to change the magnitude and polarization state of the generated terahertz waves.

The spin terahertz emitter provided by the embodiment of the present invention at least includes a femtosecond laser, a topological thin film and a magnetic field generator. The pump light output by the femtosecond laser passes through the topological thin film to generate The generator generates a terahertz wave in the direction of the magnetic field, the topological structure thin film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, the ferromagnetic layer and the non-ferromagnetic layer are arranged in sequence and bonded together. form a heterogeneous structure. The transmitter provided by the embodiment of the utility model has the advantages of simple structure, simple transmitting principle, high transmitting frequency, wide pulse width and low cost.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the appended drawings in the following description The drawings show some embodiments of the utility model, and those skilled in the art can also obtain other drawings according to these drawings without creative work.

Fig. 1 is a side view of the topological thin film of the spin terahertz emitter provided by the embodiment of the present invention;

Fig. 2 is the top view of the topological structure film in the in-plane magnetic field provided by the embodiment of the utility model;

Fig. 3 is a graph showing the change of the magnetization intensity of the ferromagnetic layer caused by the spin terahertz emitter magnet provided by the embodiment of the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the utility model more clear, the technical solutions in the embodiments of the utility model will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the utility model. Obviously, the described The embodiments are some embodiments of the present utility model, but not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the scope of protection of the present utility model.

An embodiment of the present invention provides a spin terahertz emitter, which at least includes a femtosecond laser, a topological thin film, and a magnetic field generator. The pump light output by the femtosecond laser passes through the topological thin film to generate The magnetic field generator generates terahertz waves in the direction of the magnetic field. The topological structure thin film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, ferromagnetic layer and non-ferromagnetic layer are arranged and bonded in sequence And form a heterogeneous structure.

Specifically, the pump laser output by the femtosecond laser passes through the topological structure film to generate a terahertz wave polarized based on the direction of the magnetic field. The pulse width of the pump laser output by the femtosecond laser is less than 1 ps.

In the embodiment of the present invention, taking the magnetic field as the in-plane field as an example, the topological structure thin film is placed in a constant in-plane magnetic field H, and the topological structure thin film generates terahertz waves under the action of the magnetic field. The way of spin emission is based on the anomalous spin Hall effect, using external magnetization to generate terahertz pulse radiation with preset spectral width and preset radiation field strength.

As shown in FIG. 1 , it is also assumed that the magnetic field is a constant in-plane field, and the magnetization direction M of the ferromagnetic layer points to the direction of the magnetic field. The pump laser output by the femtosecond laser is incident on one surface of the topological structure film, and the spin current Js with the same direction and the same size will be injected into the topological insulator layer and the nonmagnetic layer in the ferromagnetic layer, due to the inverse spin Hall effect , will generate the same magnitude of charge flow Jc in the two layers of materials, and because the spin Hall angles of the two materials are opposite, the direction of the charge flow generated by the two materials is the same, and then generate terahertz waves with the same direction and mutual enhancement.

The high-efficiency new topology-protected spin terahertz transmitter provided by the embodiment of the utility model, terahertz is generated from a topological structure film, that is, a three-layer nano-film of topological insulator layer/ferromagnetic layer/non-ferromagnetic layer, and the topological insulator has stable properties and is easy to prepare. It is not limited by the crystal size in the traditional terahertz emission method, and due to its topologically protected surface state, this material has a large positive spin Hall angle, and in the nonferromagnetic layer with a negative spin Hall angle When used in combination, they can generate stronger terahertz waves than ordinary ferromagnetic layer/nonferromagnetic layer two-layer structure. Through material selection and sample structure optimization, the terahertz energy conversion efficiency of the three-layer film structure is even better than the terahertz radiation based on laser oscillators in 0.25mm GaP(110), 1mm ZnTe(110) and photoconductive antennas .

The high-efficiency new topology-protected spin terahertz wave transmitter provided by the embodiment of the utility model is based on the anomalous spin Hall effect. By applying a weak magnetic field, an ultra-fast spin current is obtained in the topological structure film, thereby generating terahertz pulse radiation. . Topological thin films can be prepared using a mature molecular beam epitaxy system. It does not need to adopt complex micro-nano processing technology for preparing large-aperture photoconductive antennas, and overcomes the shortcomings of traditional terahertz pulsed radiation transmitters that require high materials and complex structures.

Compared with the current emerging terahertz emitting devices with a ferromagnetic layer/non-ferromagnetic layer double-layer heterostructure as the main material, a topological insulator layer is added as a complement, and the topological protection characteristics of the surface state of the topological insulator are used to enhance the terahertz intensity and emission efficiency.

Since no external bias voltage is required, the cost and complexity of the transmitter are reduced. Moreover, the ferromagnetic nano-film growth technology adopted is simple and can be prepared in a large area. Compared with traditional nonlinear crystals and high-conductivity antennas, the cost of the transmitter is greatly reduced.

Since the terahertz emission mechanism in the topological insulator layer/ferromagnetic layer/non-ferromagnetic layer three-layer structure film does not depend on phonons, the spectral width of the generated terahertz wave is only limited by the pump laser generated by the femtosecond laser. The pulse width is independent of the phonon vibration frequency and absorption of the material itself, so the emission of ultra-broadband terahertz pulse radiation can be realized.

The spin terahertz emitter provided by the embodiment of the present invention at least includes a femtosecond laser, a topological thin film and a magnetic field generator. The pump light output by the femtosecond laser passes through the topological thin film to generate The generator generates a terahertz wave in the direction of the magnetic field, the topological structure thin film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, the ferromagnetic layer and the non-ferromagnetic layer are arranged in sequence and bonded together. form a heterogeneous structure. The transmitter provided by the embodiment of the utility model has the advantages of simple structure, simple transmitting principle, high transmitting frequency, wide pulse width and low cost.

Optionally, the topological insulator layer and the ferromagnetic layer form a double-layer heterostructure.

On the basis of the above-mentioned embodiments, due to the special energy band structure of the topological insulator, due to the topological protection of the electron transport process in the topological insulator to its special surface state, the material of the topological insulating layer has great spin-orbit coupling characteristics , when a single-layer topological insulating material and a ferromagnetic material form a double-layer heterostructure thin film, terahertz wave emission can also be performed.

Optionally, the topological insulator layer forms a three-layer heterojunction with the ferromagnetic layer and the non-ferromagnetic layer and makes the terahertz waves mutually amplify.

On the basis of the above-mentioned embodiments, since the topological insulator has a positive spin Hall angle, when a three-layer heterojunction is formed with a ferromagnetic material and a non-magnetic layer material with a negative spin Hall angle, the emitted terahertz wave will reinforce each other.

Specifically, the pulsed pump laser output by the femtosecond laser passes through the topological insulator layer/ferromagnetic layer/non-ferromagnetic layer three-layer structure film to generate spin current, and the spin current passes through the upper and lower two Hall with opposite spin The non-ferromagnetic material of the angle generates the charge flow in the same direction, which in turn generates mutually reinforcing terahertz waves.

Specifically, the topological insulator layer is a group V-VI element compound, specifically Bi ₂ Se ₃ , Bi ₂ Te ₃ , Bi _x Sb _1-x , Sb ₂ Te ₃ , (Bi _x Sb _1-x ) ₂ Te ₃ and its alloys.

Specifically, the ferromagnetic layer is a transition metal or a corresponding ferromagnetic alloy, for example, the material of the ferromagnetic layer may be cobalt-iron-boron alloy (CoFeB).

Specifically, the non-ferromagnetic layer is a material with strong spin-orbit coupling, and is opposite to the spin Hall angle of the topological insulator. For example, the non-ferromagnetic layer can be a heavy metal material with a large negative spin Hall angle. , such as tungsten (W) or tantalum (Ta).

In the embodiment of the present invention, the specific shape of the topological thin film is not specifically limited, it can be circular, oval, square, rectangular or other irregular shapes, as long as the spot of the pump laser can be completely irradiated on the thin film That's it.

In the embodiment of the utility model, only a circular three-layer structure film is taken as an example for illustration. Since the constant magnetic field is a uniform magnetic field along the surface of the film, the polarization state of the generated terahertz pulse radiation is a linear polarization state, and the polarization direction is perpendicular to the direction of the magnetic field, as shown in Figure 2.

Optionally, the femtosecond laser is specifically a femtosecond laser oscillator, a femtosecond laser amplifier, or a fiber femtosecond laser.

Specifically, the magnetic field generator is used to generate magnetic fields with different directions and sizes, so as to change the size and polarization state of the generated terahertz waves.

On the basis of the above-mentioned embodiments, in the plane where the topological thin film is located, there is a magnetic field whose direction is parallel or perpendicular to the thin film. By changing the direction and magnitude of the magnetic field, the size and polarization state of the generated terahertz wave can be changed.

When the magnetic field in the topological thin film region changes, the magnetization of the ferromagnetic layer changes, that is, with the change of the magnetic field, the direction and magnitude of the magnetization of the ferromagnetic layer will change, which in turn affects the injection of topological insulator layers and non-ferromagnetic layers. The swirling flow finally affects the intensity and polarization state of the emitted terahertz wave, as shown in Figure 3.

The embodiment of the present utility model also provides a method for generating a terahertz wave, which uses any of the above transmitters to generate a terahertz wave.

The spin terahertz emitter and the method for generating terahertz waves provided by the embodiments of the present invention at least include a femtosecond laser, a topological thin film and a magnetic field generator, and the pump light output by the femtosecond laser passes through the topological structure A film that generates a terahertz wave based on the direction of the magnetic field generated by the magnetic field generator, the topological structure film includes a topological insulator layer, a ferromagnetic layer and a non-ferromagnetic layer, and the topological insulator layer, the ferromagnetic layer and the non-ferromagnetic layer The magnetic layers are arranged and bonded in sequence to form a heterogeneous structure. The transmitter provided by the embodiment of the utility model has the advantages of simple structure, simple transmitting principle, high transmitting frequency, wide pulse width and low cost.

The device embodiments described above are only illustrative, and the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in One place, or it can be distributed to multiple network elements. Part or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. It can be understood and implemented by those skilled in the art without any creative efforts.

Through the above description of the implementations, those skilled in the art can clearly understand that each implementation can be implemented by means of software plus a necessary general-purpose hardware platform, and of course also by hardware. Based on this understanding, the essence of the above technical solution or the part that contributes to the prior art can be embodied in the form of software products, and the computer software products can be stored in computer-readable storage media, such as ROM/RAM, magnetic discs, optical discs, etc., including several instructions to make a computer device (which may be a personal computer, server, or network device, etc.) execute the methods described in various embodiments or some parts of the embodiments.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present utility model, and are not intended to limit it; although the utility model has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit of the technical solutions of the various embodiments of the present invention. and range.

Claims (5)

1. a kind of spin terahertz transmitter, which is characterized in that include at least femto-second laser, topological structure film and magnetic field hair Raw device, the pump light of the femto-second laser output are generated and are produced based on the magnetic field generator by the topological structure film The THz wave in the direction of magnetisation field, the topological structure film include topological insulator layer, ferromagnetic layer and non-ferromagnetic layers, and The topological insulator layer, ferromagnetic layer and non-ferromagnetic layers are arranged successively fitting and constitute heterojunction structure.

2. transmitter according to claim 1, which is characterized in that the topological insulator layer and ferromagnetic layer composition are double Layer heterojunction structure.

3. transmitter according to claim 1, which is characterized in that the topological insulator layer and the ferromagnetic layer, described Non-ferromagnetic layers constitute three layers of hetero-junctions and the THz wave are mutually enhanced.

4. transmitter according to claim 1, which is characterized in that the femto-second laser is specially femtosecond laser oscillation Device, femtosecond laser amplifier or optical fiber femtosecond laser.

5. transmitter according to claim 1, which is characterized in that the magnetic field generator is for generating different directions difference The magnetic field of size, to change the size and polarized state of the THz wave generated.