Phase study of oscillatory resistances in microwave-irradiated- and dark- GaAs/AlGaAs devices: Indications of a new class of integral quantum Hall effect

TL;DR

This study explores oscillatory resistances in GaAs/AlGaAs devices under microwave irradiation and darkness, revealing a new class of integral quantum Hall effect characterized by unique phase relations and radiation-induced phenomena.

Contribution

It uncovers a novel class of IQHE with anti-phase oscillations and details the effects of microwave photo-excitation on quantum Hall states in high mobility samples.

Findings

Identification of distinct phase relations in resistances at large filling factors

Observation of quantum Hall plateaus in anti-phase oscillation regimes

Radiation-induced non-monotonic variations in SdH oscillations and Hall plateau widths

Abstract

We report the experimental results from a dark study and a photo-excited study of the high mobility GaAs/AlGaAs system at large filling factors, $\nu$. At large-$\nu$, the dark study indicates several distinct phase relations ("Type-1", "Type-2", and "Type-3") between the oscillatory diagonal- and Hall- resistances, as the canonical Integral Quantum Hall Effect (IQHE) is manifested in the "Type-1" case of approximately orthogonal diagonal- and Hall resistance- oscillations. Surprisingly, the investigation indicates quantum Hall plateaus also in the "Type-3" case characterized by approximately "anti-phase" Hall- and diagonal- resistance oscillations, suggesting a new class of IQHE. Transport studies under microwave photo-excitation exhibit radiation-induced magneto-resistance oscillations in both the diagonal, $R_{xx}$, and off-diagonal, $R_{xy}$, resistances. Further, when the radiation-induced magneto-resistance oscillations extend into the quantum Hall regime, there occurs a radiation-induced non-monotonic variation in the amplitude of Shubnikov-de Haas (SdH) oscillations in $R_{xx}$ \textit{vs}. B, and a non-monotonic variation in the width of the quantum Hall plateaus in $R_{xy}$. The latter effect leads into the vanishing of IQHE at the minima of the radiation-induced $R_{xx}$ oscillations with increased photo-excitation. We reason that the mechanism which is responsible for producing the non-monotonic variation in the amplitude of SdH oscillations in $R_{xx}$ under photo-excitation is also responsible for eliminating, under photo-excitation, the novel "Type-3" IQHE in the high mobility specimen.