arXiv subjects

Jorge Dukelsky

Publications and source records attributed to Jorge Dukelsky.

32 records · Page 2Linked to original sources

arXiv2014

Chiral phases of two-dimensional hard-core bosons with frustrated ring-exchange

We study the zero temperature phase diagram of two-dimensional hard-core bosons on a square lattice with nearest neighbour and plaquette (ring-exchange) hoppings, at arbitrary densities, by means of a hierarchical mean-field theory. In the frustrated regime, where quantum Monte Carlo suffers from a sign problem, we find a rich phase diagram where exotic states with nonzero chirality emerge. Among them, novel insulating phases, characterized by nonzero bond-chirality and plaquette order, are found over a large region of the parameter space. In the unfrustrated regime, the hierarchical mean-field approach improves over the standard mean-field treatment as it is able to capture the transition from a superfluid to a valence bond state upon increasing the strength of the ring-exchange term, in qualitative agreement with quantum Monte Carlo results.

cond-mat.str-el↗

arXiv2013

Density Matrix Embedding from Broken Symmetry Lattice Mean-Fields

Several variants of the recently proposed Density Matrix Embedding Theory (DMET) [G. Knizia and G. K-L. Chan, Phys. Rev. Lett. 109, 186404 (2012)] are formulated and tested. We show that spin symmetry breaking of the lattice mean-field allows precise control of the lattice and fragment filling while providing very good agreement between predicted properties and exact results. We present a rigorous proof that at convergence this method is guaranteed to preserve lattice and fragment filling. Differences arising from fitting the fragment one-particle density matrix alone versus fitting fragment plus bath are scrutinized. We argue that it is important to restrict the density matrix fitting to solely the fragment. Furthermore, in the proposed broken symmetry formalism, it is possible to substantially simplify the embedding procedure without sacrificing its accuracy by resorting to density instead of density matrix fitting. This simplified Density Embedding Theory (DET) greatly improves the convergence properties of the algorithm.

cond-mat.str-el↗

arXiv2013

Repulsive Interactions in Quantum Hall Systems as a Pairing Problem

A subtle relation between Quantum Hall physics and the phenomenon of pairing is unveiled. By use of second quantization, we establish a connection between (i) a broad class of rotationally symmetric two-body interactions within the lowest Landau level and (ii) integrable hyperbolic Richardson-Gaudin type Hamiltonians that arise in (p_{x}+ip_{y}) superconductivity. Specifically, we show that general Haldane pseudopotentials (and their sums) can be expressed as a sum of repulsive non-commuting (p_{x}+ip_{y})-type pairing Hamiltonians. For the Laughlin sequence, it is observed that this problem is frustration free and zero energy ground states lie in the common null space of all of these non-commuting Hamiltonians. This property allows for the use of a new truncated basis of pairing configurations in which to express Laughlin states at general filling factors. We prove separability of arbitrary Haldane pseudopotentials, providing explicit expressions for their second quantized forms, and further show by explicit construction how to exploit the topological equivalence between different geometries (disk, cylinder, and sphere) sharing the same topological genus number, in the second quantized formalism, through similarity transformations. As an application of the second quantized approach, we establish a "squeezing principle" that applies to the zero modes of a general class of Hamiltonians, which includes but is not limited to Haldane pseudopotentials. We also show how one may establish (bounds on) "incompressible filling factors" for those Hamiltonians. By invoking properties of symmetric polynomials, we provide explicit second quantized quasi-hole generators; the generators that we find directly relate to bosonic chiral edge modes and further make aspects of dimensional reduction in the Quantum Hall systems precise.

cond-mat.str-el↗

arXiv2013

Composite Boson Mapping for Lattice Boson Systems

We present a canonical mapping transforming physical boson operators into quadratic products of cluster composite bosons that preserves matrix elements of operators when a physical constraint is enforced. We map the 2D lattice Bose-Hubbard Hamiltonian into $2\times 2$ composite bosons and solve it at mean field. The resulting Mott insulator-superfluid phase diagram reproduces well Quantum Monte Carlo results. The Higgs boson behavior along the particle-hole symmetry line is unraveled and in remarkable agreement with experiment. Results for the properties of the ground and excited states are competitive with other state-of-the-art approaches, but at a fraction of their computational cost. The composite boson mapping here introduced can be readily applied to frustrated many-body systems where most methodologies face significant hurdles.

cond-mat.quant-gas↗

arXiv2010

Quantum phase diagram of the integrable p_x+ip_y fermionic superfluid

We determine the zero temperature quantum phase diagram of a p_x+ip_y pairing model based on the exactly solvable hyperbolic Richardson-Gaudin model. We present analytical and large-scale numerical results for this model. In the continuum limit, the exact solution exhibits a third-order quantum phase transition, separating a strong-pairing from a weak-pairing phase. The mean field solution allows to connect these results to other models with p_x+ip_y pairing order. We define an experimentally accessible characteristic length scale, associated with the size of the Cooper pairs, that diverges at the transition point, indicating that the phase transition is of a confinement-deconfinement type without local order parameter. We show that this phase transition is not limited to the p_x+ip_y pairing model, but can be found in any representation of the hyperbolic Richardson-Gaudin model and is related to a symmetry that is absent in the rational Richardson-Gaudin model.

cond-mat.quant-gas↗

arXiv2008

Breached pairing in trapped three-color atomic Fermi gases

We introduce an exactly solvable model for trapped three-color atom gases. Applications to a cigar-shaped trapped cold fermions reveal a complex structure of breached pairing phases. We find two competing superfluid phases at weak and intermediate couplings, each one with two color pair condensates, that can be distinguished from density profile measurements.

cond-mat.supr-con↗

arXiv2008

Crystallization of trions in SU(3) cold atom gases trapped in optical lattices

Cold Fermionic atoms with three different hyperfine states confined in optical lattices show pronounced Atomic Density Waves (ADWs). These ADWs are pinned due to the confining potential that traps the atoms in the optical lattice and can be considered a crystal of strongly bound trions. We show that the crystalline phase is incompressible and robust against SU(3) symmetry breaking interaction. We also show that it is generic in the presence of the trap due to its incompressible characteristics. A simulation of the time evolution of the fermionic gas after the trapping potential is switch off shows that the formation of the trionic crystal is marked by a freezing of the dynamics in the lattice.

cond-mat.str-el↗

arXiv2007

Commensurability effects for fermionic atoms trapped in 1D optical lattices

Fermionic atoms in two different hyperfine states confined in optical lattices show strong commensurability effects due to the interplay between the atomic density wave (ADW) ordering and the lattice potential. We show that spatially separated regions of commensurable and incommensurable phases can coexist. The commensurability between the harmonic trap and the lattice sites can be used to control the amplitude of the atomic density waves in the central region of the trap.

cond-mat.str-el↗

arXiv2005

BCS-to-BEC crossover from the exact BCS solution

The BCS-to-BEC crossover, as well as the nature of Cooper pairs, in a superconducting and Fermi superfluid medium is studied from the exact ground state wavefunction of the reduced BCS Hamiltonian. As the strength of the interaction increases, the ground state continuously evolves from a mixed-system of quasifree fermions and pair resonances (BCS), to pair resonances and quasibound molecules (pseudogap), and finally to a system of quasibound molecules (BEC). A single unified scenario arises where the Cooper-pair wavefunction has a unique functional form. Several exact analytic expressions, such as the binding energy and condensate fraction, are derived. We compare our results with recent experiments in ultracold atomic Fermi gases.

cond-mat.supr-con↗

arXiv2004

The Density Matrix Renormalization Group for finite Fermi systems

The Density Matrix Renormalization Group (DMRG) was introduced by Steven White in 1992 as a method for accurately describing the properties of one-dimensional quantum lattices. The method, as originally introduced, was based on the iterative inclusion of sites on a real-space lattice. Based on its enormous success in that domain, it was subsequently proposed that the DMRG could be modified for use on finite Fermi systems, through the replacement of real-space lattice sites by an appropriately ordered set of single-particle levels. Since then, there has been an enormous amount of work on the subject, ranging from efforts to clarify the optimal means of implementing the algorithm to extensive applications in a variety of fields. In this article, we review these recent developments. Following a description of the real-space DMRG method, we discuss the key steps that were undertaken to modify it for use on finite Fermi systems and then describe its applications to Quantum Chemistry, ultrasmall superconducting grains, finite nuclei and two-dimensional electron systems. We also describe a recent development which permits symmetries to be taken into account consistently throughout the DMRG algorithm. We close with an outlook for future applications of the method.

cond-mat.mes-hall↗

arXiv2004

Self-Consistent Random Phase Approximation - Application to the Hubbard Model for finite number of sites

Within the 1D Hubbard model linear closed chains with various numbers of sites are considered in Self Consistent Random Phase Approximation (SCRPA). Excellent results with a minimal numerical effort are obtained for 2+4n sites cases, confirming earlier results with this theory for other models. However, the 4n sites cases need further considerations. SCRPA solves the two sites problem exactly. It therefore contains the two electrons and high density Fermi gas limits correctly.

cond-mat.str-el↗

arXiv2003

Solving the Richardson equations for Fermions

Forty years ago Richardson showed that the eigenstates of the pairing Hamiltonian with constant interaction strength can be calculated by solving a set of non-linear coupled equations. However, in the case of Fermions these equations lead to singularities which made them very hard to solve. This letter explains how these singularities can be avoided through a change of variables making the Fermionic pairing problem numerically solvable for arbitrary single particle energies and degeneracies.

nucl-th↗

arXiv2001

Fully Self-consistent RPA description of the many level pairing model

The Self-Consistent RPA (SCRPA) equations in the particle-particle channel are solved without any approximation for the picket fence model. The results are in excellent agreement with the exact solutions found with the Richardson method. Particularly interesting features are that screening corrections reverse the sign of the interaction and that SCRPA yields the exact energies in the case of two levels with two particles.

nucl-th↗

arXiv1997

Valence Bond Mapping of Antiferromagnetic Spin Chains

Boson mapping techniques are developed to describe valence bond correlations in quantum spin chains. Applying the method to the alternating bond hamiltonian for a generic spin chain, we derive an analytic expression for the transition points which gives perfect agreement with existing Density Matrix Renormalization Group (DMRG) and Quantum Monte Carlo (QMC) calculations.

cond-mat↗