Biomedical subjects

Ashvin Vishwanath

Publications and source records attributed to Ashvin Vishwanath.

3 recordsLinked to original sources

PubMed2005

Dynamic projection on feshbach molecules: a probe of pairing and phase fluctuations.

We describe and justify a simple model for the dynamics associated with rapid sweeps across a Feshbach resonance, from the atomic to the molecular side, in an ultracold Fermi system. The model allows us to relate the observed molecule momentum distribution to equilibrium properties of the initial state. In particular, the dependence of the total molecule number on the sweep rate is found to be a sensitive probe of pairing in the initial state, whether condensed or not. This can be used to establish the presence of a phase fluctuation induced "pseudogap" phase in these systems.

Journal Article↗

PubMed2004

Deconfined quantum critical points.

The theory of second-order phase transitions is one of the foundations of modern statistical mechanics and condensed-matter theory. A central concept is the observable order parameter, whose nonzero average value characterizes one or more phases. At large distances and long times, fluctuations of the order parameter(s) are described by a continuum field theory, and these dominate the physics near such phase transitions. We show that near second-order quantum phase transitions, subtle quantum interference effects can invalidate this paradigm, and we present a theory of quantum critical points in a variety of experimentally relevant two-dimensional antiferromagnets. The critical points separate phases characterized by conventional "confining" order parameters. Nevertheless, the critical theory contains an emergent gauge field and "deconfined" degrees of freedom associated with fractionalization of the order parameters. We propose that this paradigm for quantum criticality may be the key to resolving a number of experimental puzzles in correlated electron systems and offer a new perspective on the properties of complex materials.

Journal Article↗

PubMed2003

Weak-field thermal hall conductivity in the mixed state of d-wave superconductors.

Thermal transport in the mixed state of a d-wave superconductor is considered within the weak-field regime. We express the thermal conductivity, kappa(xx), and the thermal Hall conductivity, kappa(xy), in terms of the cross section for quasiparticle scattering from a single vortex. Solving for the cross section (neglecting the Berry phase contribution and the anisotropy of the gap nodes), we obtain kappa(xx)(H,T) and kappa(xy)(H,T) in surprisingly good agreement with the qualitative features of the experimental results for YBa2Cu3O6.99. In particular, we show that the simple, yet previously unexpected, weak-field behavior, kappa(xy)(H,T) approximately T squareroot [H], is that of thermally excited nodal quasiparticles, scattering primarily from impurities, with a small skew component provided by vortex scattering.

Journal Article↗