Abstract

The magneto-transport characteristics of the negative conductivity/resistivity state in the microwave photo-excited two-dimensional electron system (2DES) is examined through a numerical solution of the associated boundary value problem. The results suggest, surprisingly, that a bare negative diagonal conductivity/resistivity state in the 2DES under photo-excitation should yield a positive diagonal resistance along with a sign reversal in the Hall voltage.

Highlights

  • In experiment, the microwave-induced zero-resistance states arise from ”1/4-cycle-shifted” microwave radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs system[1, 4, 33] as these oscillations become larger in amplitude with the reduction of the temperature, T, at a fixed microwave intensity

  • The microwave-radiation-induced zero-resistance state in the high mobility GaAs/AlGaAs 2D electron system is believed to be an example where negative magneto-conductivity/resistivity is responsible for the observed phenomena

  • One feels that the existence of the magnetic field is an important additional feature, and this raises several questions: Could the existence of the magnetic field be sufficiently significant to overcome nominal expectations, based on the zero-magnetic-field analogy, for an instability in a negative magneto-conductivity/resistivity state? If an instability does occur for the negative magnetoconductivity/resistivity state, what is the reason for the instability? Could negative conductivity/resistivity lead to observable negative conductance/resistance at least in some short time-scale transient situation where current domains have not yet formed? one might ask: what are the magneto-transport characteristics of a bare negative conductivity/resistivity state? Remarkably, it turns out that an answer has not yet been formulated for this last question

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Summary

Introduction

The microwave-induced zero-resistance states arise from ”1/4-cycle-shifted” microwave radiation-induced magnetoresistance oscillations in the high mobility GaAs/AlGaAs system[1, 4, 33] as these oscillations become larger in amplitude with the reduction of the temperature, T , at a fixed microwave intensity. Theory identifies a mechanism that helps to realize oscillations in the diagonal magneto-photo-conductivity/resistivity, and provides for the possibility that the minima of the oscillatory diagonal conductivity/resistivity can even take on negative values.[37, 39, 41, 45, 48, 59] The step in the two step approach invokes the theory of Andreev et al.,[38] who suggest that the zero-current-state at negative resistivity (and conductivity) is unstable, and that this favors the appearance of current domains with a non-vanishing current density,[38, 56] followed by the experimentally observed zero-resistance states. The simulations identify an associated, unexpected sign reversal in the Hall voltage under these conditions These features suggest that nominal expectations, based on the zero-magnetic-field analogy, for a negative conductivity/resistivity state in a non-zero magnetic field, need not necessarily follow, and that experimental observations of zero-resistance and a linear Hall effect in the photo-excited GaAs/AlGaAs system could be signatures of vanishing conductivity/resistivity

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