Ramesh Mani

Zero-resistance states induced by electromagnetic-wave excitation in GaAs/AlGaAs heterostructures

The observation of vanishing electrical resistance in condensed matter has led to the discovery of new phenomena such as, for example, superconductivity, where a zero-resistance state can be detected in a metal below a transition temperature Tc (ref. 1). More recently, quantum Hall effects were discovered from investigations of zero-resistance states at low temperatures and high magnetic fields in two-dimensional electron systems (2DESs). In quantum Hall systems and superconductors, zero-resistance states often coincide with the appearance of a gap in the energy spectrum. Here we report the observation of zero-resistance states and energy gaps in a surprising setting: ultrahigh-mobility GaAs/AlGaAs heterostructures that contain a 2DES exhibit vanishing diagonal resistance without Hall resistance quantization at low temperatures and low magnetic fields when the specimen is subjected to electromagnetic wave excitation. Zero-resistance-states occur about magnetic fields B = 4/5 Bf and B = 4/9 Bf, where Bf = 2πfm*/e,m* is the electron mass, e is the electron charge, and f is the electromagnetic-wave frequency. Activated transport measurements on the resistance minima also indicate an energy gap at the Fermi level. The results suggest an unexpected radiation-induced, electronic-state-transition in the GaAs/AlGaAs 2DES.

Demonstration of a 1/4-cycle phase shift in the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices.

We examine the phase and the period of the radiation-induced oscillatory magnetoresistance in GaAs/AlGaAs devices utilizing in situ magnetic field calibration by electron spin resonance of diphenyl-picryl-hydrazal. The results confirm a f-independent 1/4-cycle phase shift with respect to the hf=j variant Plancks over 2pi omega(c) condition for j>/=1, and they also suggest a small ( approximately 2%) reduction in the effective mass ratio, m(*)/m, with respect to the standard value for GaAs/AlGaAs devices.

Radiation-induced oscillatory magnetoresistance as a sensitive probe of the zero-field spin-splitting in high-mobilityGaAs/AlxGa1−xAsdevices

We suggest an approach for characterizing the zero-field spin splitting of high mobility two-dimensional electron systems, when beats are not readily observable in the Shubnikov-de Haas effect. The zero-field spin splitting and the effective magnetic field seen in the reference frame of the electron are evaluated from a quantitative study of beats observed in radiation-induced magneto-resistance oscillations.

Radiation-induced oscillatory Hall effect in high-mobility GaAs/Al x Ga 1-x As devices

We examine the radiation induced modification of the Hall effect in high-mobility GaAs/Al x Ga 1 - x As devices that exhibit vanishing resistance under microwave excitation. The modification in the Hall effect upon irradiation is characterized by (a) a small reduction in the slope of the Hall resistance curve with respect to the dark value, (b) a periodic reduction in the magnitude of the Hall resistance R x y that correlates with an increase in the diagonal resistance R x x , and (c) a Hall resistance correction that disappears as the diagonal resistance vanishes.

Radiation-induced oscillatory magnetoresistance in a tilted magnetic field in Ga As ∕ Al x Ga 1 − x As devices

We examine the microwave-photoexcited magnetoresistance oscillations in a tilted magnetic field in the high-mobility two-dimensional electron system (2DES). In analogy to the 2D Shubnikov\char21{}de Haas effect, the characteristic field

Radiation-induced zero-resistance states in GaAs/ AlGaAs heterostructures: Voltage-current characteristics and intensity dependence at the resistance minima

{B}_{f}

Nuclear spin based memory and logic in quantum Hall semiconductor nanostructures for quantum computing applications

and the period of the radiation-induced magnetoresistance oscillations appear dependent upon the component of the applied magnetic field that is perpendicular to the plane of the 2DES. In addition, we find that a parallel component

Hall effect under null current conditions

{B}_{\ensuremath{\Vert}}

TEMPERATURE-INSENSITIVE OFFSET REDUCTION IN A HALL EFFECT DEVICE

in the range of

Magneto-transport characteristics of a 2D electron system driven to negative magneto-conductivity by microwave photoexcitation

0.6l{B}_{\ensuremath{\Vert}}l1.2\phantom{\rule{0.3em}{0ex}}\mathrm{T}