Joseph J. Betouras

Publications (6)14.74 Total impact

• Source

  Available from: ArXiv

  Article: Fermionic quantum dimer and fully-packed loop models on the square lattice

  Frank Pollmann, Joseph J. Betouras, Kirill Shtengel, Peter Fulde
  [show abstract] [hide abstract]
  ABSTRACT: We consider fermionic fully-packed loop and quantum dimer models which serve as effective low-energy models for strongly correlated fermions on a checkerboard lattice at half and quarter filling, respectively. We identify a large number of fluctuationless states specific to each case, due to the fermionic statistics. We discuss the symmetries and conserved quantities of the system and show that for a class of fluctuating states in the half-filling case, the fermionic sign problem can be gauged away. This claim is supported by numerical evaluation of the low-lying states and can be understood by means of an algebraic construction. The elimination of the sign problem then allows us to analyze excitations at the Rokhsar-Kivelson point of the models using the relation to the height model and its excitations, within the single-mode approximation. We then discuss a mapping to a U(1) lattice gauge theory which relates the considered low-energy model to the compact quantum electrodynamics in 2+1 dimensions. Furthermore, we point out consequences and open questions in the light of these results.
  01/2011;
• Source

  Available from: Jorge Quintanilla

  Article: Lifshitz transitions and crystallization of fully-polarised dipolar Fermions in an anisotropic 2D lattice

  Sam T. Carr, Jorge Quintanilla, Joseph J. Betouras
  [show abstract] [hide abstract]
  ABSTRACT: We consider a two dimensional model of non-interacting chains of spinless fermions weakly coupled via a small inter-chain hopping and a repulsive inter-chain interaction. The phase diagram of this model has a surprising feature: an abrupt change in the Fermi surface as the interaction is increased. We study in detail this so called meta-nematic transition, and show that the well-known $2 1/2-$order Lifshitz transition is the criticalndpoint of this first order quantum phase transition. Furthermore, in the vicinity of the endpoint, the order parameter has a non-perturbative BCS form. We also study a competing crystallization transition in this model, and derive the full phase diagram. This physics can be demonstrated experimentally in dipolar ultra-cold atomic or molecular gases. In the presence of a harmonic trap, it manifests itself as a sharp jump in the density profile. Comment: 13.5 pages, 9 figures, minor modifications clarifying some points, some references added
  04/2010;
• Source

  Available from: ArXiv

  Article: First-order versus unconventional phase transitions in three-dimensional dimer models.

  Stefanos Papanikolaou, Joseph J Betouras
  [show abstract] [hide abstract]
  ABSTRACT: We study the phase transition between the Coulomb liquid and the columnar crystal in the 3D classical dimer model, which was found to be continuous in the O(3) universality class. In addition to nearest-neighbor interactions which favor parallel dimers, further neighbor interactions are allowed in such a manner that the cubic symmetry of the original system remains intact. We show that the transition in the presence of weak additional, symmetry preserving interactions is first order. However, the universality class of the transition remains continuous when the additional interactions are weakly repulsive. In this way, we verify the existence of a multicritical point near the unperturbed transition, and we identify a critical line of unconventional transitions between the Coulomb liquid phase and the sixfold columnar phase.
  Physical Review Letters 01/2010; 104(4):045701. · 7.37 Impact Factor
• Source

  Available from: Jorge Quintanilla

  Article: Deconfinement and Quantum Liquid Crystalline States of Dipolar Fermions in Optical Lattices

  Sam T Carr, Jorge Quintanilla, Joseph J Betouras
  [show abstract] [hide abstract]
  ABSTRACT: We describe a simple model of fermions in quasi-one dimension that features interaction-induced deconfinement (a phase transition where the effective dimensionality of the system increases as interactions are turned on) and which can be realised using dipolar fermions in an optical lattice1. The model provides a relisation of a "soft quantum matter" phase diagram of strongly-correlated fermions, featuring meta-nematic, smectic and crystalline states, in addition to the normal Fermi liquid. In this paper we review the model and discuss in detail the mechanism behind each of these transitions on the basis of bosonization and detailed analysis of the RPA susceptibility.
  Int J Mod Phys B. 04/2009; 23(20-21):4074-4086.
• Source

  Available from: arxiv.org

  Article: Correlated fermions on a checkerboard lattice.

  Frank Pollmann, Joseph J Betouras, Kirill Shtengel, Peter Fulde
  [show abstract] [hide abstract]
  ABSTRACT: A model of strongly correlated spinless fermions on a checkerboard lattice is mapped onto a quantum fully packed loop model. We identify a large number of fluctuationless states specific to the fermionic case. We also show that for a class of fluctuating states the fermionic sign problem can be gauged away. This claim is supported by numerical evaluation of the low-lying states. Furthermore, we analyze excitations at the Rokhsar-Kivelson point of this model using the relation to the height model and the single-mode approximation.
  Physical Review Letters 11/2006; 97(17):170407. · 7.37 Impact Factor
• Article: Metanematic, smectic, and crystalline phases of dipolar fermions in an optical lattice

  Jorge Quintanilla, Sam T Carr, Joseph J Betouras
  [show abstract] [hide abstract]
  ABSTRACT: It has been suggested that some strongly correlated matter might be understood qualitatively in terms of liquid crystalline phases intervening between the Fermi gas and the Wigner crystal or Mott insulator. We propose a tunable realization of this soft quantum matter physics in an ultracold gas. It uses optical lattices and dipolar interactions to realize a particularly simple model. Our analysis reveals a rich phase diagram featuring a metanematic transition where the Fermi liquid changes dimensionality; a smectic phase (stripes) and a crystalline "checkerboard" phase.
  Phys. Rev. A. 79(3):031601.