Eivind Smørgrav

Field- and temperature-induced topological phase transitions in the three-dimensional N-component London superconductor

The phase diagram and critical properties of the N-component London superconductor are studied both analytically and through large-scale Monte Carlo simulations in d=2+1 dimensions (components here ...

Observation of a metallic superfluid in a numerical experiment.

We report the observation, in Monte Carlo simulations, of a novel type of quantum ordered state: the metallic superfluid. The metallic superfluid features Ohmic resistance to counterflows of protons and electrons, while featuring dissipationless coflows of electrons and protons. One of the candidates for a physical realization of this remarkable state of matter is hydrogen or its isotopes under high compression. This adds another potential candidate to the presently known quantum dissipationless states, namely, superconductors, superfluid liquids and vapors, and supersolids.

Phase structure of (2+1)-dimensional compact lattice gauge theories and the transition from Mott insulator to fractionalized insulator

Phase structure of (2+1)-dimensional compact lattice gauge theories and the transition from Mott insulator to fractionalized insulator

Criticality in the (2+1)-dimensional compact Higgs model and fractionalized insulators.

We use a novel method of computing the third moment M3 of the action of the (2+1)-dimensional compact Higgs model in the adjoint representation with q=2 to extract correlation length and specific heat exponents nu and alpha without invoking hyperscaling. Finite-size scaling analysis of M3 yields the ratios (1+alpha)/nu and 1/nu separately. We find that alpha and nu vary along the critical line of the theory, which however exhibits a remarkable resilience of Z2 criticality. We propose this novel universality class to be that of the quantum phase transition from a Mott-Hubbard insulator to a charge-fractionalized insulator in two spatial dimensions.

First-Order Phase Transition in Easy-Plane Quantum Antiferromagnets

Quantum phase transitions in Mott insulators do not fit easily into the Landau-Ginzburg-Wilson paradigm. A recently proposed alternative to it is the so-called deconfined quantum criticality scenario, providing a new paradigm for quantum phase transitions. In this context it has recently been proposed that a second-order phase transition would occur in a two-dimensional spin 1/2 quantum antiferromagnet in the deep easy-plane limit. A check of this conjecture is important for understanding the phase structure of Mott insulators. To this end we have performed large-scale Monte Carlo simulations on an effective gauge theory for this system, including a Berry-phase term that projects out the S=1/2 sector. The result is a first-order phase transition, thus contradicting the conjecture.

Critical Properties of the N-Color London Model

The critical properties of the N-color London model are studied in d=2+1 dimensions. The model is dualized to a theory of N vortex fields interacting through a Coulomb and a screened potential. The model with N=2 shows two anomalies in the specific heat. From the critical exponents alpha and nu, the mass of the gauge field, and the vortex correlation functions, we conclude that one anomaly corresponds to an inverted 3Dxy fixed point, while the other corresponds to a 3Dxy fixed point. There are N fixed points, namely, one corresponding to an inverted 3Dxy fixed point, and N-1 corresponding to neutral 3Dxy fixed points. This represents a novel type of quantum fluid, where superfluid modes arise out of charged condensates.

Parallelizing Lattice Gauge Theory Models on Commodity Clusters

This paper addresses fundamental parallel computing issues for efficiently parallelizing 3D Lattice Gauge Theory models (LGT) on distributed memory systems. The long-range application stencil of LGT models put together with the impossibility of updating neighboring lattice sites simultaneously greatly complicates the parallelizing of such simulations. Our algorithms decompose the domain among the processors, and settle a staggered execution with the help of virtual tokens that circulate among the processors, allowing the token holders to update their boundaries. Experimental results show that these algorithms are scalable, and that simple communication trajectories prevail over low surface-to-volume ratios. Rigorous theoretical results are provided under the LogGP model to demonstrate the superiority of our approach over other methods found in the literature

Compact U(1) gauge theories in 2+1 dimensions and the physics of low dimensional insulating materials

Compact abelian gauge theories in d=2+1 dimensions arise often as an effective field-theoretic description of models of quantum insulators. In this paper we review some recent results about the compact abelian Higgs model in d=2+1 in that context. PACS: 11.15.Ha Lattice gauge theory – 11.10.Kk Field theories in dimensions other than four

Phase structure of Abelian Chern-Simons gauge theories

We study the effect of a Chern-Simons (CS) term in the phase structure of two different Abelian gauge theories. For the compact Maxwell-Chern-Simons theory, with the CS term properly defined, we obtain that for values g = n/2π of the CS coupling with n = ±1, ±2, the theory is equivalent to a gas of closed loops with contact interaction, exhibiting a phase transition in the 3dXY universality class. We also employ Monte Carlo simulations to study the noncompact U(1) Abelian Higgs model with a CS term. Finite-size scaling of the third moment of the action yields critical exponents α and ν that vary continuously with the strength of the CS term, and a comparison with available analytical results is made.