A tunable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure

Abstract

The present invention discloses an adjustable non-reciprocal absorber based on a graphene-Weyl semimetal plasmon structure, which relates to the field of nanophotonics, including a graphene film having a certain thickness; a polymer dielectric layer laid on the lower part of the graphene film; a germanium grating layer on the lower part of the polymer dielectric layer; a Weyl semimetal layer on the lower part of the germanium grating layer; a zinc selenide dielectric layer on the lower part of the Weyl semimetal layer; and a silver substrate arranged at the bottom of the Weyl semimetal layer. The adjustable non-reciprocal absorber of the present invention can improve the dynamic regulation of the non-reciprocal absorption coefficient by appropriately adjusting the graphene Fermi level and the incident light angle, thereby realizing the switching of the non-reciprocal and reciprocal states of the device, thereby achieving the effect of enhancing the practicality of the non-reciprocal device.

Description

Technical Field

[0001] The invention belongs to the field of nanophotonics, and in particular relates to an adjustable non-reciprocal absorber based on a graphene-Weyl semimetal plasmon structure. Background Art

[0002] In the field of thermal radiation, Kirchhoff's law, as a basic principle, clearly states that the spectral emissivity of an object, e(λ, θ), is exactly equal to its spectral absorptivity, α(λ, θ). This law is an important cornerstone for the advancement of thermal radiation theory and practice, and is widely used in fields such as solar energy collection and photothermal conversion, radiation cooling, and thermal camouflage, all of which implicitly rely on the validity of Kirchhoff's law. However, academic research in recent years has shown that the establishment of Kirchhoff's law in thermal radiation is not an inevitable result of the principles of thermodynamics, but is derived from Lorentz reciprocity. In the absence of Lorentz reciprocity, Kirchhoff's law no longer holds, resulting in differences in the emissivity and absorptivity of an object at specific wavelengths and directions. This discovery challenges the traditional understanding of the radiation transfer process and promotes the rapid development of new theories and applications. In recent years, researchers have explored and realized non-reciprocal radiation through various approaches. Among them, non-reciprocal devices based on Weyl semimetals have attracted much attention due to the Weyl points with opposite chirality inside them. These Weyl points induce an anomalous Hall effect, leading to an asymmetric dielectric tensor, which can exhibit optical nonreciprocity without the need for an external magnetic field, greatly simplifying the application conditions. Zhao et al. demonstrated that magnetic WS can be used to construct nonreciprocal thermal radiation devices [Prior Art 1: Zhao B, et al., Axion-field-enabled nonreciprocal thermal radiation in Weyl semimetals, NanoLetters 2020, 20, 1923].

[0003] However, conventional non-reciprocal devices often lack adjustability and flexibility, and have a small response angle range, which is obviously inconsistent with the current demand for wide-angle, adjustable optical systems. Summary of the invention

[0004] In order to solve the technical problems of existing non-reciprocal absorbers that the incident light angle range is small and they cannot be tuned, an adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure is proposed.

[0005] Technical solution: The present invention provides the following technical solution: an adjustable non-reciprocal absorber based on a graphene-Weyl semimetal plasmon structure, the adjustable non-reciprocal absorber comprising:

[0006] The graphene film has a certain thickness;

[0007] A low dielectric constant polymer dielectric layer is laid on the lower part of the graphene film;

[0008] A germanium grating layer is provided below the low dielectric constant polymer dielectric layer;

[0009] A Weyl semimetal layer, located below the germanium grating;

[0010] a zinc selenide dielectric layer, located below the Weyl semi-metal layer; and

[0011] The silver substrate is arranged at the bottom of the Weyl semi-metal layer.

[0012] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the thickness of the graphene film is 0.34 nanometers.

[0013] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the thickness of the polymer dielectric layer is 12 nanometers.

[0014] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the germanium grating layer has a period of 0.58 microns, a grating width of 0.26 microns, a height of 0.12 microns, and the grating gap is filled with polymer.

[0015] As a preferred solution of the adjustable non-reciprocal absorber based on the graphene-Weyl semimetal plasmon structure of the present invention, the thickness of the Weyl semimetal layer is 0.26 micrometers.

[0016] As a preferred solution of the adjustable non-reciprocal absorber based on the graphene-Weyl semimetal plasmon structure of the present invention, the thickness of the zinc selenide dielectric layer is 1.75 microns.

[0017] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the thickness of the silver substrate is greater than 1 micron.

[0018] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, wherein: the polymer dielectric layer is a low dielectric constant polymer material, and the material is a polyhydroxystyrene polymer.

[0019] As a preferred solution of the adjustable non-reciprocal absorber based on the graphene-Weyl semimetal plasmon structure of the present invention, a TM linear polarized light generator is arranged above the adjustable non-reciprocal absorber.

[0020] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the wavelength of the incident light wave emitted by the TM linear polarized light generator is 10 microns to 11.5 microns.

[0021] As a preferred solution of the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure described in the present invention, the angle of the incident light wave emitted by the TM linear polarized light generator is 40 degrees to 80 degrees.

[0022] Beneficial effect: The non-reciprocal absorber provided by the present invention can adjust the graphene plasmon mode by appropriately adjusting the graphene Fermi level and the incident light angle, thereby realizing the regulation of the non-reciprocal absorbing efficiency, achieving dynamic tuning, and enhancing the practicality of the non-reciprocal device. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the structure of the adjustable non-reciprocal absorber based on the graphene-Weyl semimetal plasmon structure described in Example 1;

[0024] Figure 2 It is a curve showing the variation of the absorption rate and the non-reciprocal coefficient with the wavelength of Example 1 of the present invention when the incident angle is 60 degrees and the graphene Fermi level is 1.2 electron volts under the irradiation of TM linear polarized light.

[0025] Figure 3 It is the non-reciprocal absorption spectra of Example 2 of the present invention under oblique incidence of TM linear polarized light at different wavelengths and different structural parameters.

[0026] Figure 4 It is a curve diagram of the variation of the non-reciprocal intensity with the Fermi level of graphene under oblique incidence of TM linear polarized light in Example 3 of the present invention.

[0027] Figure 5 It is the non-reciprocal absorption spectrum of Example 3 of the present invention at different wavelengths and different graphene Fermi levels under oblique incidence of TM linear polarized light.

[0028] Figure 6 It is a curve diagram of the variation of the non-reciprocal intensity with different incident angles under oblique incidence of TM linear polarized light of a specific incident wavelength in Example 4 of the present invention.

[0029] Figure 7 It is a curve diagram of the variation of the non-reciprocal intensity with different incident angles under oblique incidence of TM linear polarized light with a fixed incident wavelength in Example 4 of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below through embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0031] Example 1: Reference Figure 1 , this embodiment provides an adjustable non-reciprocal absorber based on a graphene-Weyl semimetal plasmon structure.

[0032] The adjustable non-reciprocal absorber is formed by stacking a graphene film 101, a polymer dielectric layer 102, a germanium grating layer 103, a Weyl semimetal layer 104, a zinc selenide dielectric layer 105 and a silver substrate 106 in sequence from top to bottom.

[0033] The graphene film 101 is 0.34 nanometers; the polymer dielectric layer 102 is 12 nanometers thick and is a low dielectric constant polymer material (dielectric constant is less than 3.9), the material is polyhydroxystyrene polymer, and its dielectric constant is 2.4; the period of the germanium grating layer 103 is 0.58 microns, the grating width is 0.26 microns, the height is 0.12 microns, the dielectric constant is 16, and the grating gap is filled with polyhydroxystyrene polymer; the thickness of the Weyl semimetal layer 104 is 0.26 microns, the thickness of the zinc selenide dielectric layer 105 is 1.75 microns, the refractive index is 2.4, and the thickness of the silver substrate 106 is 1 micron.

[0034] The graphene-Weyl semimetal plasmon structure works efficiently under TM polarized light. When TM linearly polarized light is incident on the structure, the graphene plasmon mode can be excited. At the same time, by adjusting the graphene Fermi level and the angle of the incident light, the non-reciprocal performance can be modulated.

[0035] The wavelength of the incident light wave emitted by the TM linear polarized light generator is 10 microns to 11.5 microns, and the incident angle is θ is 60 degrees, and the medium between the TM linear polarized light generator and the structure is air, that is, the incident area of ​​the incident light wave is air, and its refractive index is 1.

[0036] The thickness of graphene film (101) is 0.34 nanometers, the Fermi level is 1.2 electron volts, and its equivalent dielectric constant is:

[0037] (1)

[0038] Where, σ is the conductivity of graphene, ε 0 is the dielectric constant of vacuum, t gis the graphene thickness, and ω is the incident light angular frequency. The detailed parameter definitions and parameter values ​​can be referred to [Prior Art 2: Qing YM, et al., Theoretical analysis of tunable multimode coupling in a grating-assisted double-layergraphene plasmonic system, ACS Photonics 20119, 6(11), 2884].

[0039] The dielectric constant of Weyl semimetal materials in the infrared region can be expressed as:

[0040] (2)

[0041] The detailed parameter definitions and parameter values ​​can be found in [Prior Art 1: Zhao B, et al., Axion-field-enabled nonreciprocal thermal radiation in Weyl semimetals, Nano Letters2020, 20, 1923].

[0042] Non-reciprocal absorption coefficient ( η ) is defined as:

[0043] (3)

[0044] Among them, α ( θ )and e ( θ ) are respectively at the incident angle θ Absorption when it is positive and negative (i.e. to the left and right of the normal).

[0045] Figure 2 The absorber is a wave absorber with TM linear polarized light incident at an angle of plus or minus 60 degrees, a wavelength of 10 microns to 11.5 microns, and a graphene Fermi level of 1.2 electron volts. The curve of the device's absorptivity and non-reciprocity coefficient as a function of wavelength. It can be seen from the figure that under this setting, two obvious absorption peaks are achieved at wavelengths of 10.62 microns and 10.84 microns. θ The absorption peak is 0.98 when positive. θ When it is negative, the absorption peak is 0.94, and the corresponding non-reciprocal absorption rates are 0.89 and 0.83, achieving a larger amplitude of non-reciprocal absorption.

[0046] Embodiment 2: Based on Embodiment 1, Embodiment 2 sets different grating periods and different grating widths, and other conditions are the same as those of Embodiment 1:

[0047] Its non-reciprocal coefficient is Figure 3 As shown in the figure, it can be seen that with the increase of the germanium grating period and the germanium grating width, the resonance wavelength corresponding to the non-reciprocal absorption has a significant red shift. However, this adjustment method is passive, that is, once the device is prepared, it cannot be adjusted.

[0048] Example 3: Based on Example 1, Example 3 dynamically adjusts the non-reciprocal absorption spectrum of the system when the graphene Fermi level is adjusted. Other conditions are the same as those in Example 1:

[0049] Its non-reciprocal coefficient is Figure 4 As shown in the figure, it can be seen that as the Fermi level of graphene increases, the non-reciprocal resonance wavelength blueshifts, and the peak amplitude can still maintain a large value.

[0050] When the Fermi level is fixed at 1.1 electron volts, 1.2 electron volts, and 1.3 electron volts, the non-reciprocal coefficient curve is as follows: Figure 5 As shown in the figure, it can be seen that with the increase of the Fermi level, the non-reciprocal resonance wavelength does shift significantly, indicating that adjusting the graphene Fermi level can dynamically control non-reciprocal absorption.

[0051] Embodiment 4: Based on Embodiment 1, Embodiment 4 adjusts the incident angle to 0 to 80 degrees. Other conditions are the same as those of Embodiment 1:

[0052] Its non-reciprocal coefficient is Figure 6 As shown in the figure, it can be seen that when the incident angle is in the range of 40 degrees to 80 degrees, the non-reciprocal absorption is more obvious.

[0053] When the incident wavelength is fixed at 10.84 microns and the incident angle is adjusted, the non-reciprocal coefficient curve is as follows: Figure 7 As shown in the figure, it can be seen that with the increase of the incident angle, the non-reciprocal absorption coefficient gradually increases from 0 to the maximum value and then gradually decreases, indicating that the incident angle can dynamically control the non-reciprocal coefficient.

[0054] In manufacturing the adjustable non-reciprocal absorber based on graphene-Weyl semimetal plasmon structure for infrared band of the present invention, different germanium grating periods and different germanium grating widths are selected, the Fermi level is adjusted to 1.1 electron volts to 1.3 electron volts, and the incident light angle is 40 degrees to 80 degrees, so as to realize the regulation of non-reciprocal absorption coefficient and resonance wavelength.

[0055] The adjustable non-reciprocal absorber based on the graphene-Weyl semimetal plasmon structure of the present invention has the advantages of flexible and convenient use, wide-angle response, tunability, etc. It is a very practical light modulation device. It can be produced in large quantities and at low cost using a coating process. The manufactured modulator has stable and reliable performance and has important practical prospects.

[0056] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to the form and details without departing from the spirit and scope of the present invention.

Claims

1. A tunable non-reciprocal absorber based on a graphene-Weyl semimetal plasmon structure, characterized in that: The adjustable non-reciprocal absorber is formed by stacking a graphene film (101), a polymer dielectric layer (102), a germanium grating layer (103), a Weyl semimetal layer (104), a zinc selenide dielectric layer (105), and a silver substrate (106) in sequence from top to bottom.

2. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The graphene film (101) has a thickness of 0.34 nanometers.

3. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The thickness of the polymer medium layer (102) is 12 nanometers.

4. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The germanium grating layer (103) has a period of 0.58 microns, a grating width of 0.26 microns, a height of 0.12 microns, and a grating gap filled with polymer.

5. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The thickness of the Weyl semi-metal layer (104) is 0.26 micrometers.

6. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The thickness of the zinc selenide dielectric layer (105) is 1.75 microns.

7. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The thickness of the silver substrate (106) is greater than 1 micron.

8. The adjustable non-reciprocal absorber according to claim 1, characterized in that: The polymer dielectric layer (102) is a low dielectric constant polymer material, and the material is a polyhydroxystyrene polymer.

9. The adjustable non-reciprocal absorber according to any one of claims 1 to 8, characterized in that: A TM linear polarized light generator is arranged above the adjustable non-reciprocal absorber. The wavelength of the incident light wave emitted by the TM linear polarized light generator is 10 microns to 11.5 microns, and the angle of the incident light wave emitted by the light generator is 40 degrees to 80 degrees.

10. The adjustable non-reciprocal absorber according to claim 9, characterized in that: By selecting different germanium grating periods and different germanium grating widths, the Fermi level of the graphene film (101) is adjusted to 1.1 electron volts to 1.3 electron volts, and the incident light angle is 40 degrees to 80 degrees, thereby achieving regulation of the non-reciprocal absorption coefficient and the resonance wavelength.

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