Schottky Electric Field Induced Circular Photogalvanic Eﬀect in Cd 3As2Nanobelts Bob Minyu Wang Yuqing Zhu Henry Clark Travaglini Sergey Y. Savrasov and

2025-05-03 0 0 1.59MB 22 页 10玖币

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Schottky Electric Field Induced Circular

Photogalvanic Eﬀect in Cd3As2Nanobelts

Bob Minyu Wang, Yuqing Zhu, Henry Clark Travaglini, Sergey Y. Savrasov, and

Dong Yu∗

Department of Physics and Astronomy, University of California, Davis

E-mail: yu@physics.ucdavis.edu

Abstract

Dirac semimetals are expected to forbid the manifestation of the circular photogal-

vanic eﬀect (CPGE) because of their crystal inversion symmetry. Here, we report the

observation of the CPGE in Cd3As2nanobelt ﬁeld eﬀect transistors, when the photoex-

citation is focused in the vicinity of the metal contacts up to room temperature. We

attribute the CPGE to the Schottky electric ﬁeld induced symmetry breaking, which

results in the photocurrent modulation by circularly polarized photoexcitation via spin-

momentum locking. The hypothesis is supported by a suite of experiments including

spatially and angularly resolved helicity dependent photocurrent, Kelvin probe force

microscopy, and gate voltage dependence. First principles calculations conﬁrmed a

topological phase transition upon ﬁeld induced structural distortion. This work pro-

vides key insights on the electrically controlled helicity dependent optoelectronics in

Dirac materials.

arXiv:2210.03819v1 [cond-mat.mes-hall] 7 Oct 2022

Keywords

Dirac semimetal, Weyl semimetal, topological insulator, circular photogalvanic eﬀect, spin-

momentum locking, photocurrent, quantum devices

The circular photogalvanic eﬀect (CPGE) has gained traction recently as a means to

study spin dependent carrier transport in crystals possessing spin-split bands1and spin-

momentum locked topological surface states (TSS).2,3 This requires breaking of crystal in-

version symmetry or time reversal symmetry. For example, the inherent noncentrosymmetry

of the lattice can satisfy inversion symmetry breaking, such as in the Weyl semimetal (WSM)

TaAs.4Crystal symmetry can also be lowered at a terminating surface as in the cases of the

Rashba spin-split bands of GaAs5and of inorganic-organic lead halide perovskites,6and

the TSS of topological insulators (TIs) such as Bi2Se3.2Furthermore, in centrosymmetric

materials, applied electric ﬁelds7,8 and lattice strain9can break crystal inversion symmetry,

and magnetic ﬁelds10,11 or ultrafast pumping of circularly polarized light can break time

reversal symmetry.7,12 CPGE not only oﬀers a valuable tool for examining spin-orbit in-

teraction in materials, but also provides an optical control of charge transport applicable

to spintronic and quantum devices. Recently, it has also been theoretically proposed that

the CPGE induced current may be quantized to a material-independent value, similar to

quantized conductance, potentially providing a direct detection of the topological charge of

Weyl points.13

Fundamentally, the CPGE relies on asymmetric contributions to photocurrent from inci-

dent helical photons and is dictated by angular momentum selection rules. In the case of the

Dirac materials that we focus on in this letter, excitations typically involve the Dirac cones

with linear dispersion in the vicinity of the Dirac point that exhibit strong coupling between

spin and momentum.14 Net helicity dependent photocurrent is induced if there exists an odd

number of Dirac cones in the Brillouin zone as in TIs2or if contributions from Weyl nodes

do not cancel as in WSMs.4In contrast, if a crystal obeys both time reversal and crystal

inversion symmetry, as in a Dirac semimetal (DSM), the CPGE is not expected to manifest

as Weyl nodes of opposite chirality are paired up at the same position in k-space and any

helical contributions to photocurrent will cancel. However, the CPGE can be achieved in

these materials via the addition of perturbations such as strain or electric ﬁeld to system-

atically break the inversion symmetry.15 The electric control is particularly attractive, as it

oﬀers unique opportunities for quantum applications of Dirac materials with in-situ tunabil-

ity. Electric ﬁeld induced topological phase transitions have been demonstrated in ultrathin

Na3Bi ﬁlms.16 Schottky electric ﬁeld induced CPGE has been demonstrated previously in

semiconductor nanowires, WSMs, and 2D transition metal dichalcogenides. Their proposed

mechanisms include the electron orbital mixing in Si nanowires,8the Fermi level tilting in

TaIrTe4,17 and the symmetry reduction and Berry phase in monolayer MoS2.18

Cd3As2is a prototypical DSM with chemical stability and unusually high carrier mobil-

ity.19 This material system exhibits a plethora of exotic fundamental phenomena such as 3D

quantum Hall eﬀect,20 Fermi arc spin transport,21 long spin coherence length,22 and giant

magnetoresistance.23 In addition to basic science, promising applications such as fast broad-

band photodetectors24 and topological electronics25 have been demonstrated using Cd3As2

and related semimetals. Understanding spin-dependent charge transport in this system is

paramount to utilizing its capabilities. Though lattice strain-induced CPGE in Cd3As2thin

ﬁlms has been experimentally demonstrated,9manipulation of TSS and bulk band structure

via electric ﬁelds in DSMs has only been proposed theoretically in Cd3As2.26,27 Here, we

experimentally demonstrate helicity dependent photocurrent (HDPC) observed at the inter-

face made by Cd3As2and the metal contact, where crystal inversion symmetry is broken

via the Schottky electric ﬁeld, conﬁrmed by surface potential measurements. The degree of

helicity dependence can be controlled by the electric ﬁeld strength through a gate voltage.

First principles calculations further support that the DSM can be tuned into a TI under the

ﬁeld induced distortion to the crystal structure.

Our Cd3As2nanobelts were grown by chemical vapor deposition (CVD) following a recipe

modiﬁed from previous reports.28,29 Brieﬂy, Cd3As2precursor was heated up to 640◦C and

carried downstream by Ar gas ﬂowing between 20-30 sccm to a Si substrate where vapor

deposited at 200-250◦C. The growths yielded nanobelts with thickness 80-100 nm, length

10-60 µm, and width 3-10 µm as shown in Figure S1(a) in the Supporting Information.

Figure 1: Cd3As2nanobelts and device characteristics. (a) Scanning electron microscopic

(SEM) image of a representative nanobelt FET. (b) Powder XRD spectrum of Cd3As2

nanobelts on an as-grown substrate, in agreement with the (142) phase. A small peak

indicated by (326) in blue implies the existence of a mixed phase (133). Inset: EDS of the

sample. (c) Electron mobility and concentration versus temperature, extracted from ﬁeld

eﬀect measurements. (d) Conductance versus gate voltage at various temperatures. (c) and

(d) were taken in Device #1.

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摘要：

SchottkyElectricFieldInducedCircularPhotogalvanicEectinCd3As2NanobeltsBobMinyuWang,YuqingZhu,HenryClarkTravaglini,SergeyY.Savrasov,andDongYuDepartmentofPhysicsandAstronomy,UniversityofCalifornia,DavisE-mail:yu@physics.ucdavis.eduAbstractDiracsemimetalsareexpectedtoforbidthemanifestationofthecircul...

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Schottky Electric Field Induced Circular Photogalvanic Eﬀect in Cd 3As2Nanobelts Bob Minyu Wang Yuqing Zhu Henry Clark Travaglini Sergey Y. Savrasov and

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