Pritiraj Mohanty

Energy dissipation in suspended micromechanical resonators at low temperatures

We have measured mechanical dissipation in micron-sized single-crystal gallium arsenide torsional resonators. The temperature dependence of the quality factor Q and the shift in resonance frequency can be explained by the presence of two-level systems. The dependence of Q on magnetic eld is compatible with the existence of localized electronic states around material defects. ( 2000 Elsevier Science B.V. All rights reserved.

Measurement of small forces in micron-sized resonators

Abstract We report the measurement of average response of micromechanical resonators to very small driving forces, with a corresponding energy resolution of the order of ℏ ω 0 , the energy quantum of the classical resonator system. The measured coherent excitation is more than an order of magnitude weaker than the random thermal fluctuations.

Notes on decoherence at absolute zero

Abstract The problem of electron decoherence at low-temperature is analyzed from the perspective of recent experiments on decoherence rate measurement and on related localization phenomena in low-dimensional systems. The importance of decoherence at zero temperature, perhaps induced by quantum fluctuations, is put in a broader context.

Persistent current in normal metals

We discuss the recent experiments on persistent current in metallic rings in the backdrop of low temperature decoherence. The observed size of the persistent current, typically on the order of the Thouless energy, e=D, is much larger than the theoretical results, obtained with or without electron interaction. In considering the phenomenology of both decoherence and persistent current, usually observed in similar systems, we argue towards a dynamic role played by decoherence in the generation of a persistent current. A eld-induced phase shift from near-equilibrium high-frequency fluctuations{ which otherwise gives rise to decoherence{under certain conditions of periodicity and asymmetry due to disorder, is argued to induce a steady state diusion current on the order of e=D, comparable to the observed persistent current.

Low Temperature Anomaly in Mesoscopic Kondo Wires

We report the observation of an anomalous magnetoresistance in extremely dilute quasi-one-dimensional AuFe wires at low temperatures, along with a hysteretic background at low fields. The Kondo resistivity does not show the unitarity limit down to the lowest temperature, implying uncompensated spin states. We suggest that the anomalous magnetoresistance may be understood as the interference correction from the accumulation of geometric phase in the conduction electron wave function around the localized impurity spin.

Dephasing of electrons by two-level defects in quantum dots.

The electron dephasing time

Intrinsic dissipation in high-frequency micromechanical resonators

tau_{phi}

Diamagnetic Persistent Current in Diffusive Normal-Metal Rings

in a diffusive quantum dot is calculated by considering the interaction between the electron and dynamical defects, modelled as two-level system. Using the standard tunneling model of glasses, we obtain a linear temperature dependence of

Insulator-Metal Crossover near Optimal Doping in Pr22xCexCuO4: Anomalous Normal-State Low Temperature Resistivity

1/tau_{phi}

Electromagnetic Field Correlation inside a Sonoluminescing Bubble

, consistent with the experimental observation. However, we find that, in order to obtain dephasing times on the order of nanoseconds, the number of two-level defects needs to be substantially larger than the typical concentration in glasses. We also find a finite system-size dependence of