Coulomb phase diagnostics as a function of temperature, interaction range, and disorder.
Physical review letters 110:10 (2013) 107202
Abstract:
The emergent gauge field characteristic of the Coulomb phase of spin ice betrays its existence via pinch points in the spin structure factor S in reciprocal space which takes the form of a transverse projector P at low temperature: S(q) ~ P ~ q perpendicular(2)/q(2). We develop a theory which establishes the fate of the pinch points at low and high temperature, for hard and soft spins, for short- and long-ranged (dipolar) interactions, as well as in the presence of disorder. We find that their detailed shape can be used to read off the relative sizes of entropic and magnetic Coulomb interactions of monopoles in spin ice, and we resolve the question of why pinch points have been experimentally observed for Ho(1.7)Y(0.3)Ti(2)O(7) even at high temperature in the presence of strong disorder.Microscopic model of quasiparticle wave packets in superfluids, superconductors, and paired Hall states.
Physical review letters 109:23 (2012) 237004
Abstract:
We study the structure of Bogoliubov quasiparticles, bogolons, the fermionic excitations of paired superfluids that arise from fermion (BCS) pairing, including neutral superfluids, superconductors, and paired quantum Hall states. The naive construction of a stationary quasiparticle in which the deformation of the pair field is neglected leads to a contradiction: it carries a net electrical current even though it does not move. However, treating the pair field self-consistently resolves this problem: in a neutral superfluid, a dipolar current pattern is associated with the quasiparticle for which the total current vanishes. When Maxwell electrodynamics is included, as appropriate to a superconductor, this pattern is confined over a penetration depth. For paired quantum Hall states of composite fermions, the Maxwell term is replaced by a Chern-Simons term, which leads to a dipolar charge distribution and consequently to a dipolar current pattern.Bionic Coulomb phase on the pyrochlore lattice
Physical Review B American Physical Society (APS) 86:5 (2012) 054411
Fractional Chern insulators and the W ∞ algebra
Physical Review B - Condensed Matter and Materials Physics 85:24 (2012)
Abstract:
A set of recent results indicates that fractionally filled bands of Chern insulators in two dimensions support fractional quantum Hall states analogous to those found in fractionally filled Landau levels. We provide an understanding of these results by examining the algebra of Chern band projected density operators. We find that this algebra closes at long wavelengths and for constant Berry curvature, whereupon it is isomorphic to the W ∞ algebra of lowest Landau level projected densities first identified by Girvin, MacDonald, and Platzman. For Hamiltonians projected to the Chern band this provides a route to replicating lowest Landau level physics on the lattice. © 2012 American Physical Society.Fractional Chern insulators and the W∞ algebra
Physical Review B American Physical Society (APS) 85:24 (2012) 241308