Photogalvanic effect in the HgTe/CdTe topological insulator due to edge-bulk optical transitions

Kaladzhyan, Vardan; Aseev, P. P.; Artemenko, S. N.

doi:10.1103/physrevb.92.155424

Cited by 38 publications

(54 citation statements)

References 35 publications

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“…There have been many theoretical and experimental works in the past few years on helicity-controlled photocurrents [14][15][16][17][18], the linear photogalvanic effect [19][20][21], local photocurrents [22,23], edge photocurrents in two-dimensional (2D) TIs [24,25], coherent control of injection currents [26,27], photon drag currents [19,28,29], second-harmonic generation [30], photoinduced quantum Hall insulators [31,32], cyclotron-resonance-assisted photocurrents [33,34], quantum oscillations of photocurrents [35], photogalvanic currents via proximity interactions with magnetic materials [36][37][38], and the photoelectromagnetic effect [39]. These phenomena, scaling in the second or third order of the radiation electric fields, open up new opportunities to study Dirac fermions, which has been already demonstrated for graphene (for a review see Ref.…”

Section: Introductionmentioning

confidence: 99%

Photon drag effect in(Bi1−xSbx)2Te3three-dimensional topological insulators

et al. 2016

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We report on the observation of a terahertz radiation-induced photon drag effect in epitaxially grown nand p-type (Bi 1−x Sb x ) 2 Te 3 three-dimensional topological insulators with different antimony concentrations x varying from 0 to 1. We demonstrate that the excitation with polarized terahertz radiation results in a dc electric photocurrent. While at normal incidence a current arises due to the photogalvanic effect in the surface states, at oblique incidence it is outweighed by the trigonal photon drag effect. The developed microscopic model and theory show that the photon drag photocurrent can be generated in surface states. It arises due to the dynamical momentum alignment by time-and space-dependent radiation electric field and implies the radiation-induced asymmetric scattering in the electron momentum space. We show that the photon drag current may also be generated in the bulk. Both surface states and bulk photon drag currents behave identically upon variation of such macroscopic parameters as radiation polarization and photocurrent direction with respect to the radiation propagation. This fact complicates the assignment of the trigonal photon drag effect to a specific electronic system.

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Section: Introductionmentioning

confidence: 99%

Photon drag effect in(Bi1−xSbx)2Te3three-dimensional topological insulators

et al. 2016

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“…Photocurrents caused by the Drude-like free-carrier absorption require additional scattering and k-dependent velocity and, therefore, seem to be weak. Comparing the efficiencies of all these processes we attribute the circular edge photocurrents in region II to the excitation of electrons from helical edge states to bulk conduction band states ("photoionization" of the edge channels) [29,30].…”

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confidence: 99%

“…[24]). In a simple four-subband model with inversion center, the coefficient K at k x = 0 is given by 2BD/(B 2 + D 2 ) [29], where B and D are the parameters of the Bernevig-Hughes-Zhang (BHZ) Hamiltonian [2]. PHYSICAL Calculations within the relaxation time approximation yield the following expression for the edge current:…”

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confidence: 99%

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Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

et al. 2017

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We report on the observation of a circular photogalvanic current excited by terahertz laser radiation in helical edge channels of two-dimensional (2D) HgTe topological insulators (TIs). The direction of the photocurrent reverses by switching the radiation polarization from a right-handed to a left-handed one and, for fixed photon helicity, is opposite for the opposite edges. The photocurrent is detected in a wide range of gate voltages. With decreasing the Fermi level below the conduction band bottom, the current emerges, reaches a maximum, decreases, changes its sign close to the charge neutrality point (CNP), and again rises. Conductance measured over a ≈3 μm distance at CNP approaches 2e 2 /h, the value characteristic for ballistic transport in 2D TIs. The data reveal that the photocurrent is caused by photoionization of helical edge electrons to the conduction band. We discuss the microscopic model of this phenomenon and compare calculations with experimental data. DOI: 10.1103/PhysRevB.95.201103 The quantum spin Hall (QSH) effect occurs in 2D TIs and rests on the existence of conducting helical edge states while the bulk is insulating [1][2][3][4]. In contrast to the quantum Hall effect, the formation of these edge states requires no magnetic field: they stem from the band inversion caused by strong spin-orbit interaction and are topologically protected by time reversal symmetry. Given that the spin-up and spin-down electrons propagate along an edge in opposite directions, i.e., the spin projection is locked to the k vector, the edge channels are helical in nature. The first experimental evidence for the QSH effect was obtained in HgTe quantum wells (QWs) [5] by observing a resistance plateau around h/2e 2 in the longitudinal resistance of a mesoscopic Hall bar. Here h is Planck's constant and e is the electron charge. This observation was further confirmed by nonlocal experiments in the ballistic [6] and diffusive [7] transport regime. Conducting edge channels were later probed by scanning SQUID microscopy [8], scanning gate microscopy [9], microwave impedance microscopy [10], and by analyzing supercurrents [11]. The spin polarization of the edge states was investigated so far by electrical means only: by detecting the spin to charge conversion in devices utilizing the inverse spin Hall effect [12] or with ferromagnetic contacts [13].Here we use circularly polarized terahertz radiation to excite selectively spin-up and spin-down electrons circling clockwise and counterclockwise around a sample. We show that the excitation causes an imbalance in the electron distribution between positive and negative wave vectors. This is probed as the associated photogalvanic [14,15] current, which reverses its direction upon switching the helicity.The experiments have been carried out on Hg 0.3 Cd 0.7 Te/HgTe/Hg 0.3 Cd 0.7 Te single QW structures with a well width of 8 nm having inverted band ordering. We used this width to maximize the energy gap to about 25 meV [4,5]. Structures were grown by molecular beam epitaxy o...

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“…In various semiconductor systems, such as lowdimensional structures of GaAs, InAs, SiGe, GaN and ZnO, CPGE has been successfully used as a tool to determine the relative ratio of Rashba and Dresselhaus terms (RD ratio) [23][24][25][26][27][28][29] . Because of the unique SOI property and novel TI phase of HgTe QWs, CPGE in HgTe QWs has also attracted considerable interest [30][31][32] . Experimentally, large CPGE signals in (001)-and (113)-oriented HgTe QWs have been observed in terahertz and mid-infrared regions 30,31 , and have found their application in the fast detection of the infrared-radiation ellipticity 15,16 .…”

Section: Introductionmentioning

confidence: 99%

Enhanced circular photogalvanic effect in HgTe quantum wells in the heavily inverted regime

Yang

Liu

et al. 2017

Phys. Rev. B

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HgTe-based quantum wells (QWs) possess very strong spin-orbit interaction (SOI) and have become an ideal platform for the study of fundamental SOI-dependent phenomena and the topological insulator phase. Circular photogalvanic effect (CPGE) in HgTe QWs is of great interest because it provides an effective optical access to probe the spin-related information of HgTe systems. However, the complex band structure and large spin-splitting of HgTe QWs makes it inadequate to analyze the experimental results of CPGE in HgTe QWs [B. Wittmann et al., Semicond. Sci. Technol. 25, 095005 (2010)] with reduced band models. Here, based on the realistic eight-band k · p Hamiltonian and combined with the density-matrix formalism, we present a detailed theoretical investigation of CPGE in (001)-oriented Hg0.3Cd0.7Te/HgTe/Hg0.3Cd0.7Te QWs. We find the CPGE currents in HgTe QWs in the heavily inverted regime are significantly enhanced due to the strong distortion of band dispersion at a certain range of the energy spectrum. This enhancement effect could offer an experimental certificate that the HgTe QW is in the heavily inverted phase (usually accompanied with the emergence of two-dimensional topological edge states), and could also be utilized in engineering the high efficiency ellipticity detector of infrared and terahertz radiation [S. N. Danilov et al., J. Appl. Phys. 105, 013106 (2009)]. Additionally, within the same theoretical framework, we also investigate the interplay effect of structure inversion asymmetry and bulk inversion asymmetry and the pure spin currents driven by linearly polarized light in HgTe QWs.

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Photogalvanic effect in the HgTe/CdTe topological insulator due to edge-bulk optical transitions

Cited by 38 publications

References 35 publications

Photon drag effect in(Bi1−xSbx)2Te3three-dimensional topological insulators

Photon drag effect in(Bi1−xSbx)2Te3three-dimensional topological insulators

Photogalvanic probing of helical edge channels in two-dimensional HgTe topological insulators

Enhanced circular photogalvanic effect in HgTe quantum wells in the heavily inverted regime

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