Condensed Matter

Displaying 1009 - 1020 of 1258

Gapless spin liquids in frustrated Heisenberg models

Federico Becca SISSA International School for Advanced Studies
May 13, 2014

PIRSA:14050074
Condensed Matter
Bulk-Edge Correspondence in 2+1-Dimensional Abelian Topological Phases

Jennifer Cano University of California, Santa Barbara
May 09, 2014

PIRSA:14050011
Condensed Matter
Scattering of emerging excitations in Matrix Product States

Jutho Haegeman Ghent University
May 06, 2014

PIRSA:14050010
Condensed Matter
Helical edge resistance introduced by charge disorder

Leonid Glazman Yale University
April 29, 2014

PIRSA:14040082
Condensed Matter
Quantum criticality in SU(N) anti-ferromagnets: general strategies to circumvent the sign problem

Ribhu Kaul University of Kentucky
April 22, 2014

PIRSA:14040083
Condensed Matter
The unitary Fermi gas across the superfluid transition

Olga Goulko University of Massachusetts Amherst
April 04, 2014

PIRSA:14040119
Condensed Matter
Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Abolhassan Vaezi Cornell University
April 01, 2014

PIRSA:14040120
Condensed Matter
Are superselection rules fundamental?

Robert Spekkens Perimeter Institute for Theoretical Physics
March 14, 2014

PIRSA:14030114
Condensed Matter
DMRG Analysis of Mobile Impurities and Orbital-selective Mott Phases

Julian (Jose) Rincon Universidad de los Andes
March 12, 2014

PIRSA:14030117
Condensed Matter
Exact holographic mapping and emergent space-time geometry

Xiaoliang Qi Stanford University
March 11, 2014

PIRSA:14030107
Condensed Matter
Numerical detection of symmetry protected and symmetry enriched topological phases

Frank Pollmann Max Planck Institute for Physics, Munich (Werner-Heisenberg-Institut)
February 25, 2014

PIRSA:14020140
Condensed Matter
Quantum Many-body Dynamics with Matrix Product States

Martin Ganahl Sandbox AQ
February 24, 2014

PIRSA:14020156
Astrophysics

Condensed Matter

Gapless spin liquids in frustrated Heisenberg models

Federico Becca SISSA International School for Advanced Studies
May 13, 2014

PIRSA:14050074
Condensed Matter
We present our recent numerical calculations for the Heisenberg model on the square and
Kagome lattices, showing that gapless spin liquids may be stabilized in highly-frustrated
regimes. In particular, we start from Gutzwiller-projected fermionic states that may
describe magnetically disordered phases,[1] and apply few Lanczos steps in order to improve
their accuracy. Thanks to the variance extrapolation technique,[2] accurate estimations of
the energies are possible, for both the ground state and few low-energy excitations.
Our approach suggests that magnetically disordered phases can be described by Abrikosov
fermions coupled to gauge fields.

For the Kagome lattice, we find that a gapless U(1) spin liquid with Dirac cones
is competitive with previously proposed gapped spin liquids when only the nearest-neighbor
antiferromagnetic interaction is present.[3,4] The inclusion of a next-nearest-neighbor term
lead to a Z_2 gapped spin liquid,[5] in agreement with density-matrix renormalization group
calculations.[6] In the Heisenberg model on the square lattice with both nearest- and
next-nearest-neighbor interactions, a Z_2 spin liquid with gapless spinon excitations is
stabilized in the frustrated regime.[7] This results are (partially) in agreement with recent
density-matrix renormalization group on large cylinders.[8]

[1] X.-G. Wen, Phys. Rev. B {\bf 44}, 2664 (1991); Phys. Rev. B {\bf 65}, 165113 (2002).
[2] S. Sorella, Phys. Rev. B {\bf 64}, 024512 (2001).
[3] Y. Iqbal, F. Becca, S. Sorella, and D. Poilblanc, Phys. Rev. B 87, 060405(R) (2013).
[4] Y. Iqbal, D. Poilblanc, and F. Becca, Phys. Rev. B 89, 020407(R) (2014).
[5] W.-J. Hu, Y. Iqbal, F. Becca, D. Poilblanc, and D. Sheng, unpublished.
[6] H.-C. Jiang, Z. Wang, and L. Balents, Nat. Phys. 8, 902 (2012);
S. Yan, D. Huse, and S. White, Science 332, 1173 (2011).
[7] W.-J. Hu, F. Becca, A. Parola, and S. Sorella, Phys. Rev. B 88, 060402(R) (2013).
[8] S.-S. Gong, W.Z., D.N. Sheng, O.I. Motrunich, and M.P.A. Fisher, arXiv:1311.5962 (2013).
Bulk-Edge Correspondence in 2+1-Dimensional Abelian Topological Phases

Jennifer Cano University of California, Santa Barbara
May 09, 2014

PIRSA:14050011
Condensed Matter
The same bulk two-dimensional topological phase can have multiple distinct, fully-chiral edge phases. We show that this can occur in the integer quantum Hall states at fillings 8 and 12 with experimentally-testable consequences. We also show examples for Abelian fractional quantum Hall states, the simplest examples being at filling fractions 8/7, 12/11, 8/15, 16/5. For all examples, we propose experiments that can distinguish distinct edge phases. Our results are summarized by the observation that edge phases correspond to lattices while bulk phases correspond to genera of lattices. Since there are typically multiple lattices in a genus, there are usually many stable fully chiral edge phases corresponding to the same bulk. We show that fermionic systems can have edge phases with only bosonic low-energy excitations and discuss a fermionic generalization of the relation between bulk topological spins and the central charge. The latter follows from our demonstration that every fermionic topological phase can be represented as a bosonic topological phase, together with some number of filled Landau levels. Our analysis also leads to a simple demonstration that all Abelian topological phases can be represented by a Chern-Simons theory parameterized by a K-matrix.
Scattering of emerging excitations in Matrix Product States

Jutho Haegeman Ghent University
May 06, 2014

PIRSA:14050010
Condensed Matter
We review the formalism of matrix product states and one of its recent generalisations which allows to variationally determine the dispersion relation of elementary excitations in generic one-dimensional quantum spin chains. These elementary excitations dominate the low energy effective behaviour of the system. We discuss recent work where we show how we can also describe the effective interaction between these excitations – as mediated by the strongly correlated ground state – and how we can extract the corresponding S matrix. With these two ingredients, we can already build a highly non-trivial low-energy description of any microscopic Hamiltonian by assuming that higher order scattering processes are negligible. This allows to extract accurate information about the behaviour of the system under perturbations or at finite temperature, as we illustrate using the spin 1 Heisenberg model.
Helical edge resistance introduced by charge disorder

Leonid Glazman Yale University
April 29, 2014

PIRSA:14040082
Condensed Matter
Electron puddles created by doping of a 2D topological insulator may violate the ideal helical edge conductance. Because of a long electron dwelling time, even a single puddle may lead to a significant inelastic backscattering. We find the resulting correction to the perfect edge conductance. Generalizing to multiple puddles, we assess the dependence of the helical edge resistance on temperature and on the doping level. Puddles with odd electron number carry a spin and lead to a logarithmically-weak temperature dependence of the resistivity of a long edge. The developed theory provides a framework for analyzing the results of the past and ongoing electron transport experiments with 2D topological insulators
Quantum criticality in SU(N) anti-ferromagnets: general strategies to circumvent the sign problem

Ribhu Kaul University of Kentucky
April 22, 2014

PIRSA:14040083
Condensed Matter
In the first part of the seminar, I will describe a general approach to write down a large family of model SU(N) anti-ferromagnets that do not suffer from the sign problem. In the second half I will show how such Hamiltonians are useful for the study of deconfined quantum critical points and possibly other exotic physics.
The unitary Fermi gas across the superfluid transition

Olga Goulko University of Massachusetts Amherst
April 04, 2014

PIRSA:14040119
Condensed Matter
Quantum Monte Carlo is a versatile tool for studying strongly interacting theories in condensed matter physics from first principles. A prominent example is the unitary Fermi gas: a two-component system of fermions interacting with divergent scattering length. I will present numerical results for different properties of the homogeneous, spin-balanced unitary Fermi gas across the superfluid transition, such as the critical temperature, the equation of state and the temperature dependence of the contact density. Our values show good agreement with recent experimental data.
Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Abolhassan Vaezi Cornell University
April 01, 2014

PIRSA:14040120
Condensed Matter
The possibility of realizing non-Abelian statistics and utilizing it for topological quantum computation (TQC) has generated widespread interest. However, the non-Abelian statistics that can be realized in most accessible proposals is not powerful enough for universal TQC. In this talk, I consider a simple bilayer fractional quantum Hall (FQH) system with the 1/3 Laughlin state in each layer, in the presence of interlayer tunneling. I show that interlayer tunneling can drive a continuous phase transition to an exotic non-Abelian state that contains the famous `Fibonacci' anyon, whose non-Abelian statistics is powerful enough for universal TQC. The analysis that I will present towards this result rests on startling agreements from a variety of distinct methods, including thin torus limits, effective field theories, and coupled wire constructions.

Next, I discuss the experimental aspects of our proposal and potential probes for the Fibonacci phase. I show that the charge gap remains open at the phase transition while the neutral gap closes. This raises the question of whether these exotic phases may have already been realized at nu=2/3 in bilayers, as past experiments may not have definitively ruled them out. Finally, I will discuss about the generalizations to multi-layer states as well as the duality between the interlayer pairing and interlayer tunneling problems.

Reference: arXiv:1403.3383
Are superselection rules fundamental?

Robert Spekkens Perimeter Institute for Theoretical Physics
March 14, 2014

PIRSA:14030114
Condensed Matter
Superselection rules in quantum theory assert the impossibility of preparing coherent superpositions of certain conserved quantities. For instance, it is commonly presumed that there is a superselection rule for charge and for baryon number, as well as a "univalence superselection rule" forbidding a coherent superposition of a fermion and a boson. I will show how many superselection rules can be effectively lifted using a reference frame for the variable that is conjugate to the conserved quantity. I will also discuss subtleties related to the univalence superselection rule.
DMRG Analysis of Mobile Impurities and Orbital-selective Mott Phases

Julian (Jose) Rincon Universidad de los Andes
March 12, 2014

PIRSA:14030117
Condensed Matter
Exact holographic mapping and emergent space-time geometry

Xiaoliang Qi Stanford University
March 11, 2014

PIRSA:14030107
Condensed Matter
Holographic duality is a duality between quantum many-body systems (boundary) and gravity systems with one additional spatial dimension (bulk). In this talk, I will describe a new approach to holographic duality for lattice systems, called the exact holographic mapping. The key idea of this approach can be summarized by two points: 1) The bulk theory is nothing but the boundary theory viewed in a different basis. 2) Space-time geometry is determined by the structure of correlations and quantum entanglement in a quantum state. For free fermion boundary theories, I will show how different bulk geometries including AdS space, black holes and worm-holes emerge. I will also discuss the generalization of this approach in more generic interacting systems.
Numerical detection of symmetry protected and symmetry enriched topological phases

Frank Pollmann Max Planck Institute for Physics, Munich (Werner-Heisenberg-Institut)
February 25, 2014

PIRSA:14020140
Condensed Matter
A topological phase is a phase of matter which cannot be characterized by a local order parameter. We first introduce non-local order parameters that can detect symmetry protected topological (SPT) phases in 1D systems and then show how to generalize the idea to detect symmetry enriched topological (SET) phases in 2D. SET phases are new structures that occur in topologically ordered systems in the presence of symmetries. We introduce simple methods to detect the SET order directly from a complete set of topologically degenerate ground state wave functions. We first show how to directly determine the characteristic symmetry fractionalization of the quasiparticles from the reduced density matrix of the minimally entangled states. Second, we show how a simple generalization of a non-local order parameter can be measured to detect SETs. The usefulness of the proposed approached is demonstrated by examining two concrete model states which exhibit SET: (i) a spin-1 model on the honeycomb lattice and (ii) the resonating valence bond state on a kagome lattice. We conclude that the spin-1 model and the RVB state are in the same SET phases.
Quantum Many-body Dynamics with Matrix Product States

Martin Ganahl Sandbox AQ
February 24, 2014

PIRSA:14020156
Astrophysics

Condensed Matter
The talk is divided into two parts: in the first, I will talk about dynamics of far-from equilibrium initial states in different lattice models. I will present results of quench dynamics of the XXZ-Heisenberg magnet, where interesting physics emerges after quenching the system. Then I will present results for scattering of solitonic objects in different integrable and non-integrable lattice models. In the second part, I will talk about dynamics of impurity systems. There I will talk about how impurity spectral functions can be calculated using the Chebyshev technique, and how MPS can serve as a high resolution impurity solver for Dynamical Mean-Field Theory. Finally, I will show some results for steady-state currents through a quantum dot device.

Title	Speaker(s)	Date	Talk Type	Info link
Gapless spin liquids in frustrated Heisenberg models	Federico Becca	2014-05-13	Scientific Series	View details
Bulk-Edge Correspondence in 2+1-Dimensional Abelian Topological Phases	Jennifer Cano	2014-05-09	Scientific Series	View details
Scattering of emerging excitations in Matrix Product States	Jutho Haegeman	2014-05-06	Scientific Series	View details
Helical edge resistance introduced by charge disorder	Leonid Glazman	2014-04-29	Scientific Series	View details
Quantum criticality in SU(N) anti-ferromagnets: general strategies to circumvent the sign problem	Ribhu Kaul	2014-04-22	Scientific Series	View details
The unitary Fermi gas across the superfluid transition	Olga Goulko	2014-04-04	Scientific Series	View details
Fibonacci Anyons From Abelian Bilayer Quantum Hall States	Abolhassan Vaezi	2014-04-01	Scientific Series	View details
Are superselection rules fundamental?	Robert Spekkens	2014-03-14	Scientific Series	View details
DMRG Analysis of Mobile Impurities and Orbital-selective Mott Phases	Julian (Jose) Rincon	2014-03-12	Scientific Series	View details
Exact holographic mapping and emergent space-time geometry	Xiaoliang Qi	2014-03-11	Scientific Series	View details
Numerical detection of symmetry protected and symmetry enriched topological phases	Frank Pollmann	2014-02-25	Scientific Series	View details
Quantum Many-body Dynamics with Matrix Product States	Martin Ganahl	2014-02-24	Scientific Series	View details

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Gapless spin liquids in frustrated Heisenberg models

Bulk-Edge Correspondence in 2+1-Dimensional Abelian Topological Phases

Scattering of emerging excitations in Matrix Product States

Helical edge resistance introduced by charge disorder

Quantum criticality in SU(N) anti-ferromagnets: general strategies to circumvent the sign problem

The unitary Fermi gas across the superfluid transition

Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Are superselection rules fundamental?

DMRG Analysis of Mobile Impurities and Orbital-selective Mott Phases

Exact holographic mapping and emergent space-time geometry

Numerical detection of symmetry protected and symmetry enriched topological phases

Quantum Many-body Dynamics with Matrix Product States

Gapless spin liquids in frustrated Heisenberg models

Bulk-Edge Correspondence in 2+1-Dimensional Abelian Topological Phases

Scattering of emerging excitations in Matrix Product States

Helical edge resistance introduced by charge disorder

Quantum criticality in SU(N) anti-ferromagnets: general strategies to circumvent the sign problem

The unitary Fermi gas across the superfluid transition

Fibonacci Anyons From Abelian Bilayer Quantum Hall States

Are superselection rules fundamental?

DMRG Analysis of Mobile Impurities and Orbital-selective Mott Phases

Exact holographic mapping and emergent space-time geometry

Numerical detection of symmetry protected and symmetry enriched topological phases

Quantum Many-body Dynamics with Matrix Product States