Circular-Polarization-Dependent Study of the Microwave Photoconductivity in a Two-Dimensional Electron System

Abstract

The polarization dependence of the low field microwave photoconductivity and absorption of a two-dimensional electron system has been investigated in a quasi-optical setup in which linear and any circular polarization can be produced in-situ. The microwave induced resistance oscillations and the zero resistance regions are notedly immune to the sense of circular polarization. This observation is discrepant with a number of proposed theories. Deviations only occur near the cyclotron resonance absorption where an unprecedented large resistance response is observed.PACS numbers: 73.21.-b, 73.43.-f The recent discovery of zero resistance induced by microwaves [1,2,3,4,5,6,7] in ultra-clean twodimensional electron systems (2DES) over extended regions of an applied perpendicular magnetic field B has revived the general interest in microwave photoconductivity and has triggered a remarkably large and diverse body of theoretical works. Original photoconductivity experiments on lower quality samples only revealed the intuitively expected feature due to resonant heating at the cyclotron resonance or more accurately -due to the finite size of the sample -at the combined dimensional plasmon cyclotron resonance frequency [8]. Unanticipated 1/B-periodic oscillations with minima close to the harmonics of the cyclotron resonance first entered the scene [9,10]. They later turned out precursors of the zero resistance regions. The majority of theoretical accounts subdivides the argumentation to explain the zero resistance into two main points. First some mechanism produces an oscillatory photoconductivity contribution that may turn the overall dissipative conductivity negative near the minima. Examples of proposed mechanisms include spatially indirect interLandau-level transitions based on impurity and phonon scattering [11,12,13,14,15,16,17,18,19], the establishement of a non-equilibrium distribution function [3,20,21,22], photon assisted quantum tunneling [23] and non-parabolicity effects [24]. Second, it is argued that negative values of the dissipative conductivity render the initially homogeneous system unstable [25,26] and an inhomogeneous domain structure develops instead [26, 27, 28, 29, 30], which results in zero resistance in experiment. Some theoretical work does not invoke an instability driven formation of domains to explain zero resistance. It relies either on radiation induced gaps in the electronic spectrum [31] or on the microwave driven semi-classical dynamics of electron orbits [32].The sheer multitude of models and their divergence underline that no consensus has been reached on the origin of this non-equilibrium phenomenon. In order to assist in isolating the proper microscopic picture, a detailed polarization dependent study was carried out. In previous work, microwaves were guided to the sample with oversized rectangular waveguides [1,2,3,4,5] or with a coaxial dipole antenna [6,7]. These approaches do not permit control over the polarization state. Rectangular waveguides operated in their fundamental mode...

Nonlinear transport phenomena in a two-subband system

“…The immunity of MIROs and ZRSs to the sense of circular polarization has also been found in Ref. 35 where the authors employed a quasioptical setup in which linear and any circular polarization can be produced in situ.…”

Observation of microwave-induced resistance oscillations in a high-mobility two-dimensional hole gas in a strained Ge/SiGe quantum well

“…One can clearly see that the photoresistance at the minimum is negative indicating that microwave radiation causes a reduction of resistance from its dark value. This negative δR ω is one characteristic feature of MIRO which, in very clean GaAs/AlGaAs-based 2DEG, gives rise to radiation-induced zero-resistance states [4][5][6][7][8][9][10]. Another generic MIRO feature is related to the positions of the maxima and minima relative to the harmonics of the cyclotron resonance.…”

“…Two prime examples of these phenomena are microwave-induced resistance oscillations (MIRO) [2,3] and zero-resistance states [4][5][6][7][8][9][10], which emerge from the MIRO minima in ultrahigh mobility 2DEG [11]. MIRO appear in microwave photoresistance, δR ω , which is the difference between the resistance of irradiated 2DEG and the resistance measured without radiation, R 0 .…”

Radiation-induced resistance oscillations in a 2D hole gas: a demonstration of a universal effect

“…Many experiments have been carried out [4][5][6][7][8][9][10][11][12][13][14][15][16][17] and theoretical explanations [18][19][20][21][22][23][24] have been given to try to explain their physical origin, but to date, it still remains controversial. On the other hand, although these effects have been thoroughly studied, they have been mainly based on GaAs/AlGaAs quantum wells and hardly ever other materials have been used.…”