# US 2018/0026185 A1 · Far-infrared detection using weyl semimetals

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- Number: US 2018/0026185 A1
- Document ID: US20180026185A1
- Status: Published application
- Kind: A1
- Application number: 15/656,373
- Filed: 2017-07-21
- Published: 2018-01-25
- Earliest claimed: 2016-07-21
- Assignees: Massachusetts Institute of Technology; California Institute of Technology; Technion R&D Foundation Ltd.
- Inventors: Ching-Kit CHAN; Patrick A. LEE; Netanel LINDNER; Gil REFAEL; Qiong MA; Suyang XU; Nuh GEDIK
- Web page: https://patentgrep.com/patent/US20180026185A1

## CPC

- H10N 99/03: {Devices using Mott metal-insulator transition, e.g. field-effect transistor-like devices}
- G01J 1/0429: {using polarisation elements}
- G01J 1/44: Electric circuits {(for command of an exposure part G03B7/02)}
- G01J 3/0224: {using polarising or depolarising elements}
- G01J 5/10: using electric radiation detectors
- H10F 77/12: Active materials
- G01J 2001/4446: {Type of detector}
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION

## Abstract

The generation of photocurrent in an ideal two-dimensional Dirac spectrum is symmetry forbidden. In sharp contrast, a three-dimensional Weyl semimetal can generically support significant photocurrent due to the combination of inversion symmetry breaking and finite tilts of the Weyl spectrum. To realize this photocurrent, a noncentrosymmetric Weyl semimetal is coupled to a pair of electrodes and illuminated with circularly polarized light without any voltage applied to the Weyl semimetal. The wavelength of the incident light can range over tens of microns and can be adjusted by doping the Weyl semimetal to change its chemical potential.

## Claims

### Claim 1

A detector comprising:
a detecting element comprising a noncentrosymmetric Weyl semimetal that produces a photocurrent in response to incident radiation; and
a pair of electrodes, in electrical communication with the detecting element, to conduct the photocurrent out of the noncentrosymmetric Weyl semimetal.

### Claim 2 (depends on 1)

The detector of claim 1, wherein the detecting element is configured to produce the photocurrent in an absence of an external bias voltage.

### Claim 3 (depends on 1)

The detector of claim 1, wherein the detecting element is configured to produce the photocurrent in an absence of an applied magnetic field.

### Claim 4 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal has a three-dimensional band structure comprising a plurality of tilted Weyl cones.

### Claim 5 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal has an energy band structure that lacks inversion symmetry.

### Claim 6 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal has a chemical potential within about 5 meV of a Weyl node of the noncentrosymmetric Weyl semimetal.

### Claim 7 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal has a thickness of substantially equal to or less than an absorption length of the noncentrosymmetric Weyl semimetal at a wavelength of the incident radiation.

### Claim 8 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal has a thickness of less than about 1 micron.

### Claim 9 (depends on 1)

The detector of claim 1, wherein the noncentrosymmetric Weyl semimetal comprises at least one of SrSi2, TaAs, WTe2, MoTe2, TaP, NbP, NbAs, Ag2Se, Ta3S2, LaAlGe, PrAlGe, CoSi, or RhSi.

### Claim 10 (depends on 1)

The detector of claim 1, wherein the pair of electrodes comprises:
a transparent electrode disposed on a first side of the Weyl semimetal; and
a back electrode disposed on a second side of the Weyl semimetal opposite the first side of the Weyl semimetal.

### Claim 11 (depends on 1)

The detector of claim 1, further comprising:
a polarizer to polarize the incident polarization in a linear polarization state; and
a quarter wave plate, in optical communication with the polarizer and the detecting element, to transform the incident radiation from the linear polarization state to a circular polarization state.

### Claim 12

A method of detecting incident radiation, the method comprising:
illuminating a noncentrosymmetric Weyl semimetal with the incident radiation, the noncentrosymmetric Weyl semimetal generating a photocurrent in response to the incident radiation; and
conducting the photocurrent out of the noncentrosymmetric Weyl semimetal via electrodes in electrical communication with the noncentrosymmetric Weyl semimetal.

### Claim 13 (depends on 12)

The method of claim 12, wherein illuminating the noncentrosymmetric Weyl semimetal occurs in an absence of a bias voltage.

### Claim 14 (depends on 12)

The method of claim 12, wherein illuminating the noncentrosymmetric Weyl semimetal occurs in an absence of a magnetic field.

### Claim 15 (depends on 12)

The method of claim 12, wherein illuminating the noncentrosymmetric Weyl semimetal comprises illuminating the noncentrosymmetric Weyl semimetal with near to far-infrared light.

### Claim 16 (depends on 12)

The method of claim 12, wherein illuminating the noncentrosymmetric Weyl semimetal comprises illuminating the noncentrosymmetric Weyl semimetal with Terahertz radiation.

### Claim 17 (depends on 12)

The method of claim 12, wherein illuminating the noncentrosymmetric Weyl semimetal comprises illuminating the noncentrosymmetric Weyl semimetal with circularly polarized radiation.

### Claim 18

A detector comprising:
a Weyl semimetal to produce a photocurrent in response to circularly polarized incident radiation, the Weyl semimetal having a tilted Weyl dispersion and an energy band structure lacking inversion symmetry at a wavelength of the circularly polarized incident radiation; and
a pair of electrodes, in electrical communication with the Weyl semimetal, to conduct the photocurrent out of the Weyl semimetal.

### Claim 19 (depends on 18)

The detector of claim 18, wherein:
the Weyl semimetal has a thickness of substantially equal to or less than an absorption length and defines a surface configured to receive the circularly polarized incident radiation; and
the pair of electrodes comprises a first electrode at a first edge of the surface and a second electrode at a second of the surface.

### Claim 20 (depends on 18)

The detector of claim 18, wherein:
the Weyl semimetal has a thickness greater than an absorption length and defines a first surface configured to receive the circularly polarized incident radiation; and
the pair of electrodes comprises a transparent electrode disposed on the first surface and a back electrode disposed on the a second surface of the Weyl semimetal, the second surface being opposite the first surface.