Research "highlights" (not so recent)

Vortices and quasiparticles near the "superconductor-insulator" transition in thin films

by V.M. Galitski, G. Refael, M.P.A. Fisher and T. Senthil 

For many years now I have wanted to revisit the magnetic field tuned ``superconductor-insulator" transition in 2d films, and incorporate the effects of the fermionic quasiparticles that were left out in the early work employing the "bosonic only" models (ie. the Bose-Hubbard model)- see Quantum Phase Transition in disordered 2d two-dimensional superconductors by M.P.A. Fisher, Phys. Rev. Lett. 65, 923 (1990). 

While the boson-only approach is reasonable for highly granular films, in amorphous films the normal quasiparticles at the field-induced vortex cores are particularly worrisome. Moreover, a number of experiments on various amorphous films reveal strong deviations from the predicted universality for the sheet resistance at the transition, suggesting the inadequcy of the boson-only approach. In addition, Kapitulnik and co-workers found evidence for a mysterious ``strange metal" phase in amorphous MoGe films at fields below B_c, where the resistance saturates at the lowest temperatures. Motivated by these considerations, we introduced in cond-mat/0504745 a new two-fluid formulation of thin film superconductors in field consisting of fermionized vortices and electrically neutralized Bogoliubov quasiparticles. This approach allowed us to access a novel non-Fermi liquid phase which naturally interpolates between the low B superconductor and the high B normal metal (see Figure). We analyzed the transport, thermodynamic and tunneling properties of the resulting ``vortex metal" phase, and suggested a number of new experiments in such systems.

Atomic quantum simulator for lattice gauge theories 
by H.P. Buchler, M. Hermele, S.D. Huber, M.P.A. Fisher and P. Zoller 

The goal here is to imagine employing the atoms trapped in an optical lattice to "simulate" various models of interest in the field of strongly correlated electrons, specifically models with ring exchange terms (lattice gauge theories in some instances). In this short paper we present the design of a strong coupling Hamiltonian for cold atomic gases subjected to an optical lattice using well understood tools for manipulating and controlling such gases. The Hamiltonian includes a ring exchange interaction describing the correlated hopping of two bosons.