Analog of microwave-induced resistance oscillations induced in GaAs heterostructures by terahertz radiation

Abstract

We report on the study of terahertz radiation-induced MIRO-like oscillations of magnetoresistivity in GaAs heterostructures. Our experiments provide an answer on two most intriguing questions-effect of radiation helicity and the role of the edges-yielding crucial information for an understanding of the MIRO (microwave-induced resistance oscillations) origin. Moreover, we demonstrate that the range of materials exhibiting radiation-induced magneto-oscillations can be largely extended by using high-frequency radiation. DOI: 10.1103/PhysRevB.94.081301 One of the most interesting phenomena recently observed in two-dimensional electron systems (2DES) is microwave (MW) -induced resistance oscillations (MIRO) and associated zero resistance states (ZRS) [1][2][3][4][5][6][7], reviewed, e.g., in [8]. Like Shubnikov-de Haas oscillations (SdH), MIRO are periodic on a 1/B scale, but occur at lower magnetic fields and show much weaker temperature dependence. Phenomenologically, they are very similar to Weiss oscillations [9], which reflect the commensurability between the cyclotron orbit radius and the period of a periodic potential. MIRO by contrast, reflect the commensurability between the MW photon energy 2π f and the cyclotron energy ω c . In extremely clean samples the minima of the MIRO develop into ZRS [3][4][5], which are explained [10] in terms of an instability of the system and formation of current domains, occurring when the conductivity becomes negative under MW irradiation (see also [8,11,12]).In spite of numerous experiments and significant advances in their theoretical understanding, there is still no commonly accepted microscopic description of the effect [13,14] and the ongoing MIRO investigations remain challenging [15][16][17][18][19][20][21]. Consequently, new materials have been studied [22][23][24][25] and new theoretical models have been put forward [26][27][28][29][30]. To the most pressing issues which need to be clarified experimentally and which might help to differentiate between the different models belong the MIRO polarization dependence [7,8,31] and the "bulk" or "edge" nature of the effect.So far the majority of experimental work has been done in the MW regime (1-350 GHz) and there are only a few reports on MIRO excited at terahertz (THz) frequencies [32][33][34]. Here we report on the observation of pronounced MIRO-like oscillations induced by THz radiation. We exploit the specific advantages of THz laser radiation not present in the MW regime, i.e., the possibility to focus it onto a spot smaller than the sample's size and easy control of the radiation's polarization. The most important features clearly detected on a large variety of samples are (i) a very weak dependence of the oscillations' amplitude on the photon helicity and (ii) the bulk nature of the effect. Furthermore, our study shows that the MIRO oscillations can be excited at THz frequencies even in the samples with low mobility, whereas in the MW range ultrahigh mobility samples are crucially needed for this type of experimen...

Magnetoresistance oscillations induced by high-intensity terahertz radiation

“…The damping parameter τ q = 1.5 ps is taken from similar fitting of the low-intensity data, obtained for I ≃ 0.11 W/cm 2 on the same sample, Ref. 20. Despite almost four orders of magnitude larger intensity, the shape of MIRO including the low-B damping remains precisely the same, such that the only intensity-dependent parameter is the B-independent prefactor A(I).…”

“…2, was taken from our previous work on the same sample, see Ref. 20. There, it was determined both from the cyclotron resonance position in transmission measurements and from the periodicity of MIRO at f = 0.69 THz.…”

“…Concerning the polarization dependence, our previous study 20 of MIRO induced by continuous low-power THz radiation demonstrated that, in the linear regime ∆σ ∝ I, oscillations are insensitive to the radiation helicity. These results, extending similar earlier findings 18 in the microwave range, contradict the expectations based on the semiclassical Drude theory.…”

“…Here, is the reduced Planck constant, f the microwave frequency and ω c the cyclotron frequency. Very recently, it was demonstrated that MIRO can be efficiently excited at substantially higher frequencies of several terahertz 20 . This work gave an experimental answer to two currently most intriguing questions regarding radiation helicity 18 and the role of the contacts/edges 21,22 .…”

Linear response of zero-resistance states

“…Great experimental and theoretical efforts have been made to understand this phenomenon, yielding at present strikingly different explanations. While theories involving pondermotive forces near the contacts [4] or the effect of radiation on edge states [5] seem to be less likely in view of recent measurements [6], other theories, predicting the ZRS to be either homogeneous or inhomogeneous, constitute competing alternatives. The radiation-driven electron orbit model combines semiclassics with an exact solution of a quantum-harmonic-oscillator problem and explains the ZRS in terms wave-packet dynamics and Pauli exclusion principle [7].…”