Condensed Matter

Displaying 913 - 924 of 1172

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Jeremy England Massachusetts Institute of Technology (MIT)
September 17, 2014

PIRSA:14090073
Condensed Matter
Self-assembling tensor networks and holography in disordered spin chains

Andrew Goldsborough Rheinisch-Westfälische Technische Hochschule (RWTH Aachen University)
September 16, 2014

PIRSA:14090029
Condensed Matter
Stripes and pairing in t-J and Hubbard models

Steven White University of California, Irvine
September 11, 2014

PIRSA:14090074
Condensed Matter
Monogamy of entanglement and improved mean-field ansatz for spin lattices

Ralf Schuetzhold Helmholtz-Zentrum Dresden-Rossendorf
September 02, 2014

PIRSA:14090069
Condensed Matter
TBA

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 19, 2014

PIRSA:14080036
Condensed Matter
Reconstructing quantum states from local data

Isaac Kim University of California, Davis
August 12, 2014

PIRSA:14080007
Condensed Matter
Criterion for non-Fermi Liquid behavior in a metal with broken symmetry

Ashvin Vishwanath Harvard University
August 06, 2014

PIRSA:14080004
Condensed Matter
Uni10 Tensor Network Library

Ying-Jer Kao National Taiwan University
August 05, 2014

PIRSA:14080001
Condensed Matter
TBA
July 08, 2014

PIRSA:14070018
Condensed Matter
Designing exotic circuitry with non-Abelian anyons
May 20, 2014

PIRSA:14050029
Condensed Matter
Gapless spin liquids in frustrated Heisenberg models

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

PIRSA:14050074
Condensed Matter

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography
September 19, 2014

PIRSA:14090072
High Energy Physics

Condensed Matter

General Relativity & Quantum Cosmology
We discuss properties of 2-point functions in CFTs in 2+1D at finite temperature. For concreteness, we focus on those involving conserved flavour currents, in particular on the associated conductivity. At frequencies much greater than the temperature, ω >> T, the ω dependence of the conductivity can be computed from the operator product expansion (OPE) between the currents and operators which acquire a non-zero expectation value at T > 0. Such results are found to be in excellent agreement with quantum Monte Carlo studies of the O(2) Wilson-Fisher CFT. Results for the conductivity and other observables are also obtained in vector 1/N expansions. We match these large ω results to the corresponding correlators of holographic representations of the CFT: the holographic approach then allows us to extrapolate to small ω/T. Other holographic studies implicitly only used the OPE between the currents and the energy-momentum tensor, and this yields the correct leading large ω behavior for a large class of CFTs. However, for the Wilson-Fisher CFT a relevant “thermal” operator must also be considered, and then consistency with the Monte Carlo results is obtained without a previously needed ad hoc rescaling of the T value [1]. We also use the OPE to prove sum rules obeyed by the conductivity. **In collaboration with A. Katz, S. Sachdev and E. Sørensen** [1] WWK, E. Sørensen, S. Sachdev, Nat. Phys. 10, 361 (2014)
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Jeremy England Massachusetts Institute of Technology (MIT)
September 17, 2014

PIRSA:14090073
Condensed Matter
In the last few decades, substantial advances have been made in our ability to make general statements about the thermodynamics of systems driven far from thermal equilibrium. In this talk, I will give a brief overview of some the most basic results in this area and explain their connection to classic results in linear response theory. I will then describe how to formally construct the generalization of free energy for macrostates in a far-from-equilibrium system and discuss possible connections to self-organization phenomena in both biological and other contexts.
Self-assembling tensor networks and holography in disordered spin chains

Andrew Goldsborough Rheinisch-Westfälische Technische Hochschule (RWTH Aachen University)
September 16, 2014

PIRSA:14090029
Condensed Matter
We show that the numerical strong disorder renormalization group algorithm (SDRG) of Hikihara et.\ al.\ [{Phys. Rev. B} {\bf 60}, 12116 (1999)] for the one-dimensional disordered Heisenberg model naturally describes a tree tensor network (TTN) with an irregular structure defined by the strength of the couplings. Employing the holographic interpretation of the TTN in Hilbert space, we compute expectation values, correlation functions and the entanglement entropy using the geometrical properties of the TTN. We find that the disorder averaged spin-spin correlation scales with the average path length through the tensor network while the entanglement entropy scales with the minimal surface connecting two regions. Furthermore, the entanglement entropy increases with both disorder and system size, resulting in an area-law violation. Our results demonstrate the usefulness of a self-assembling TTN approach to disordered systems and quantitatively validate the connection between holography and quantum many-body systems.
Stripes and pairing in t-J and Hubbard models

Steven White University of California, Irvine
September 11, 2014

PIRSA:14090074
Condensed Matter
This has been a leading question in condensed matter physics since the discovery of the cuprate superconductors. In this talk I will review some of the DMRG and tensor network results for the ground states of these models. A key question I'll address is the issue of stripes: are the ground states striped? Do stripes compete with or induce d-wave superconductivity? Another question I'll address is: how well does 2D DMRG do in comparison with iPEPS and quantum Monte Carlo. I will also show recent results for a standard 3-band Hubbard model for the cuprates. The asymmetry between hole and electron doped systems which is seen in the cuprates arises naturally from this model.
Monogamy of entanglement and improved mean-field ansatz for spin lattices

Ralf Schuetzhold Helmholtz-Zentrum Dresden-Rossendorf
September 02, 2014

PIRSA:14090069
Condensed Matter
We consider rather general spin-1/2 lattices with large coordination numbers Z.
Based on the monogamy of entanglement and other properties of the concurrence C,
we derive rigorous bounds for the entanglement between neighboring spins,
which show that C decreases for large Z. In addition, the concurrence C measures the deviation from mean-field behavior and can only vanish if the mean-field ansatz yields an exact ground state of the Hamiltonian. Motivated by these findings, we propose an improved mean-field ansatz by adding entanglement
TBA

Senthil Todadri Massachusetts Institute of Technology (MIT) - Department of Physics
August 19, 2014

PIRSA:14080036
Condensed Matter
Reconstructing quantum states from local data

Isaac Kim University of California, Davis
August 12, 2014

PIRSA:14080007
Condensed Matter
We consider the problem of reconstructing global quantum states from local data. Because the reconstruction problem has many solutions in general, we consider the reconstructed state of maximum global entropy consistent with the local data. We show that unique ground states of local Hamiltonians are exactly reconstructed as the maximal entropy state. More generally, we show that if the state in question is a ground state of a local Hamiltonian with a degenerate space of locally indistinguishable ground states, then the maximal entropy state is close to the ground state projector. We also show that local reconstruction is possible for thermal states of local Hamiltonians. Finally, we discuss a procedure to certify that the reconstructed state is close to the true global state. We call the entropy of our reconstructed maximum entropy state the "reconstruction entropy", and we discuss its relation to emergent geometry in the context of holographic duality. This is a joint work with Brian Swingle.
Criterion for non-Fermi Liquid behavior in a metal with broken symmetry

Ashvin Vishwanath Harvard University
August 06, 2014

PIRSA:14080004
Condensed Matter
Uni10 Tensor Network Library

Ying-Jer Kao National Taiwan University
August 05, 2014

PIRSA:14080001
Condensed Matter
TBA
July 08, 2014

PIRSA:14070018
Condensed Matter
Designing exotic circuitry with non-Abelian anyons
May 20, 2014

PIRSA:14050029
Condensed Matter
Non-Abelian anyons are widely sought for the exotic fundamental physics they harbor as well as for their possible applications for quantum information processing. Currently, there are numerous blueprints for stabilizing the simplest type of non-Abelian anyon, a Majorana zero energy mode bound to a vortex or a domain wall. One such candidate system, a so-called "Majorana wire" can be made by judiciously interfacing readily available materials; the experimental evidence for the viability of this approach is presently emerging.
Following this idea, we introduce a device fabricated from conventional fractional quantum Hall states, s-wave superconductors and insulators with strong spin-orbit coupling. Similarly to a Majorana wire, the ends of our “quantum wire” would bind "parafermions", exotic non-Abelian anyons which can be viewed as fractionalised Majorana zero modes.
I will discuss their properties and describe how such parafermions can be used to construct new and potentially useful circuit elements which include current and voltage mirrors, transistors for fractional charge currents and "flux capacitors".
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).

Title	Speaker(s)	Date	Talk Type	Info link
Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography		2014-09-19	Scientific Series	View details
Irreversibility, Entropy Production, and and Self-organization far from Equilibrium	Jeremy England	2014-09-17	Scientific Series	View details
Self-assembling tensor networks and holography in disordered spin chains	Andrew Goldsborough	2014-09-16	Scientific Series	View details
Stripes and pairing in t-J and Hubbard models	Steven White	2014-09-11	Scientific Series	View details
Monogamy of entanglement and improved mean-field ansatz for spin lattices	Ralf Schuetzhold	2014-09-02	Scientific Series	View details
TBA	Senthil Todadri	2014-08-19	Scientific Series	View details
Reconstructing quantum states from local data	Isaac Kim	2014-08-12	Scientific Series	View details
Criterion for non-Fermi Liquid behavior in a metal with broken symmetry	Ashvin Vishwanath	2014-08-06	Scientific Series	View details
Uni10 Tensor Network Library	Ying-Jer Kao	2014-08-05	Other	View details
TBA		2014-07-08	Scientific Series	View details
Designing exotic circuitry with non-Abelian anyons		2014-05-20	Scientific Series	View details
Gapless spin liquids in frustrated Heisenberg models	Federico Becca	2014-05-13	Scientific Series	View details

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Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Self-assembling tensor networks and holography in disordered spin chains

Stripes and pairing in t-J and Hubbard models

Monogamy of entanglement and improved mean-field ansatz for spin lattices

TBA

Reconstructing quantum states from local data

Criterion for non-Fermi Liquid behavior in a metal with broken symmetry

Uni10 Tensor Network Library

TBA

Designing exotic circuitry with non-Abelian anyons

Gapless spin liquids in frustrated Heisenberg models

Conformal field theories at non-zero temperature: operator product expansions, Monte Carlo, and holography

Irreversibility, Entropy Production, and and Self-organization far from Equilibrium

Self-assembling tensor networks and holography in disordered spin chains

Stripes and pairing in t-J and Hubbard models

Monogamy of entanglement and improved mean-field ansatz for spin lattices

TBA

Reconstructing quantum states from local data

Criterion for non-Fermi Liquid behavior in a metal with broken symmetry

Uni10 Tensor Network Library

TBA

Designing exotic circuitry with non-Abelian anyons

Gapless spin liquids in frustrated Heisenberg models