Giant photocurrents in a Dirac fermion system at cyclotron resonance

Abstract

We report on the observation of the giant photocurrents in HgTe/HgCdTe quantum well (QW) of critical thickness at which a Dirac spectrum emerges. At an exciting QW of 6.6 nm width by terahertz (THz) radiation and sweeping magnetic field we detected a resonant photocurrent. Remarkably, the position of the resonance can be tuned from negative (−0.4 T) to positive (up to 1.2 T) magnetic fields by means of optical doping. The photocurrent data, accompanied by measurements of radiation transmission as well as Shubnikov-de Haas and quantum Hall effects, prove that the photocurrent is caused by cyclotron resonance in a Dirac fermion system, which allows us to obtain the effective electron velocity v ≈ 7.2 × 10 5 m/s. We develop a microscopic theory of the effect and show that the inherent spin-dependent asymmetry of light-matter coupling in the system of Dirac fermions causes the electric current to flow.

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

“…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.…”

Split Dirac cones in HgTe/CdTe quantum wells due to symmetry-enforced level anticrossing at interfaces

“…Comparing the results of atomistic calculation with the k·p theory we obtain t l-h ≈ 1.5. Extrapolation to HgTe/Cd 0.7 Hg 0.3 Te QWs, the structures commonly used in experiment [9,12,13], gives t l-h ≈ 1.1 and 2|γ| = 10 meV.…”

“…In HgTe/CdTe QWs of critical thickness, the heavyhole subband HH1 switches order with the electron subband E1 [11], the band gap vanishes and elementary excitations behave as massless Dirac 2D fermions [12,13]. The early theoretical description [8] used a model in which the symmetry of the HgTe/CdTe QW was implicitly assumed to contain an inversion center.…”

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

“…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 .…”

“…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 .…”