Showing papers by "Shivaji Lal Sondhi published in 2011"
TL;DR: In this article, the properties of the resulting magnetic Coulomb liquid in the framework of Debye-H\"uckel theory are discussed, and the role of bound monopole anti-monopole pairs is discussed.
Abstract: At low temperatures, spin ice is populated by a finite density of magnetic monopoles---pointlike topological defects with a mutual magnetic Coulomb interaction. We discuss the properties of the resulting magnetic Coulomb liquid in the framework of Debye-H\"uckel theory, for which we provide a detailed context-specific account. We discuss both thermodynamical and dynamical signatures and compare Debye-H\"uckel theory to experiment as well as numerics, including data for specific heat and AC susceptibility. We also evaluate the entropic Coulomb interaction that is present in addition to the magnetic one and show that it is quantitatively unimportant in the current compounds. Finally, we address the role of bound monopole anti-monopole pairs and derive an expression for the monopole mobility.
85 citations
TL;DR: The quantum J(1)-J(2) spin model on the honeycomb lattice provides an effective description of the Mott insulating region of the Hubbard model and finds three phases-antiferromagnetic, an unusual Z( 2) SL state, and a dimerized state with spontaneously broken rotational symmetry.
Abstract: Recent numerical work [Z. Y. Meng et al., Nature (London) 464, 847 (2010)] indicates the existence of a spin liquid (SL) phase that intervenes between the antiferromagnetic and semimetallic phases of the half filled Hubbard model on a honeycomb lattice. To better understand the nature of this exotic phase, we study the quantum J(1)-J(2) spin model on the honeycomb lattice, which provides an effective description of the Mott insulating region of the Hubbard model. Employing the variational Monte Carlo approach, we analyze the phase diagram of the model. We find three phases-antiferromagnetic, an unusual Z(2) SL state, and a dimerized state with spontaneously broken rotational symmetry. We identify the Z(2) SL state as the likely candidate for the SL phase of the Hubbard model.
84 citations
TL;DR: In this article, the authors used the gauge/gravity correspondence to compute the full temperature and, generally nonlinear, electric field dependence of the electrical conductivity for some model critical theories, and they also found the full time-dependent response of the system to an arbitrary time dependent external electric field.
Abstract: Transport at a quantum critical point depends sensitively on the relative magnitudes of temperature, frequency and electric field. Here we used the gauge/gravity correspondence to compute the full temperature and, generally nonlinear, electric field dependence of the electrical conductivity for some model critical theories. In the special case of 2 + 1 dimensions we are also able to find the full time-dependent response of the system to an arbitrary time dependent external electric field. The response of the system is instantaneous, implying a frequency independent conductivity. We describe a mechanism that rationalizes the instantaneous response.
41 citations
TL;DR: The Pfaffian phase in the proximity of a half-filled Landau level is understood to be a $p+ip$ superconductor of composite fermions as discussed by the authors.
Abstract: The Pfaffian phase in the proximity of a half-filled Landau level is understood to be a $p+ip$ superconductor of composite fermions. We consider the properties of this paired quantum Hall phase when the pairing energy is small, i.e., in the weak-coupling, BCS limit, where the coherence length is much larger than the charge screening length. We find that, as in a type I superconductor, vortices attract so that, upon varying the magnetic field from its magic value at $\ensuremath{
u}=5/2$, the system exhibits Coulomb frustrated phase separation. We propose that the weakly and strongly coupled Pfaffians exemplify a general dichotomy between type I and type II quantum Hall fluids.
12 citations
TL;DR: In this paper, the authors developed models that exhibit a fractional quantum Hall effect in the absence of an external magnetic field, without the need of external magnetic fields, in the presence of a magnetic field.
Abstract: Researchers develop models that could exhibit a fractional quantum Hall effect in the absence of an external magnetic field.
7 citations