Quantum Matter

434 talks

S021

Collection TypeSeries

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Displaying 349 - 360 of 434

Unconventional Magnetism and Superconductivity in 3 Dimensional Doped Mott Insulators

Baskaran Ganapathy Institute of Mathematical Sciences
April 30, 2013

PIRSA:13040140
Condensed Matter
Quantum transport in one dimension: from integrability to many-body localization and topology

Joel Moore University of California, Berkeley
April 23, 2013

PIRSA:13040125
Condensed Matter
Topological insulator of bosons in 3d via dyon condensation and the statistical Witten effect.

Max Metlitski Massachusetts Institute of Technology (MIT) - Department of Physics
April 10, 2013

PIRSA:13040117
Condensed Matter
S=1 spin liquid with fermionic excitations

Maksym Serbyn Massachusetts Institute of Technology (MIT)
March 28, 2013

PIRSA:13030113
Condensed Matter
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

Michael Hermele University of Colorado Boulder
March 26, 2013

PIRSA:13030116
Condensed Matter
One-photon and two-photon switching in graphene and optical nanomaterials

Mahi Singh Western University
March 08, 2013

PIRSA:13030094
Condensed Matter
Gravitational anomaly and topological phases

Shinsei Ryu University of Illinois at Urbana-Champaign (UIUC)
February 28, 2013

PIRSA:13020148
Condensed Matter
DMRG Studies on the Spin Liquid Ground State of the Kagome Model

Stefan Depenbrock Ludwig-Maximilians-Universitiät München (LMU)
February 26, 2013

PIRSA:13020147
Condensed Matter
A K matrix construction of symmetry enriched phases
February 20, 2013

PIRSA:13020140
Condensed Matter
Fractional Quantum Hall States on an infinite cylinder: characterizing topological order and quasiparticle forces using infinite DMRG.

Michael Zaletel University of California, Berkeley
February 12, 2013

PIRSA:13020129
Condensed Matter
Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter

Unconventional Magnetism and Superconductivity in 3 Dimensional Doped Mott Insulators

Baskaran Ganapathy Institute of Mathematical Sciences
April 30, 2013

PIRSA:13040140
Condensed Matter
Utilizing a variety and also constraints offered by quantum and solid state chemistry, we discuss possibilities of unconventional quantum magnetism and superconductivity in doped 3 dimensional Mott insulators. Some of the possibilities are quantum spin liquid states having pseudo fermi surface coexisting with long range magnetic order, 3 dimensional emergent gauge fields and unconventional superconducting order parameter symmetry. We present a few realistic models to illustrate this and use our theory to understand anomalous behavior of certain double perovskite compounds.
Quantum transport in one dimension: from integrability to many-body localization and topology

Joel Moore University of California, Berkeley
April 23, 2013

PIRSA:13040125
Condensed Matter
Recent advances in analytical theory and numerical methods enable some long-standing questions about transport in one dimension to be answered; these questions are closely related to transport experiments in quasi-1D compounds. The spinless fermion chain with nearest-neighbor interactions at half-filling, or equivalently the XXZ model in zero magnetic field, is an example of an integrable system in which no conventional conserved quantity forces dissipationless transport (Drude weight); we show that there is nevertheless a Drude weight and that at some points its contribution is from a new type of conserved quantity recently constructed by Prosen. Adding an integrability-breaking perturbation leads to a scaling theory of conductivity at low temperature. Adding disorder, we study the question of how Anderson localization is modified by interactions when the system remains fully quantum coherent ("many-body localization"). We find that even weak interactions are a singular perturbation on some quantities: entanglement grows slowly but without limit, suggesting that dynamics in the possible many-body localized phase are glass-like. If time permits, some results on the fractional Luttinger's theorem and the 1D limit of quantum Hall states will be presented.
Topological insulator of bosons in 3d via dyon condensation and the statistical Witten effect.

Max Metlitski Massachusetts Institute of Technology (MIT) - Department of Physics
April 10, 2013

PIRSA:13040117
Condensed Matter
In this talk, I will construct a symmetry protected topological phase of bosons in 3d with particle number conservation and time reversal symmetries, which is the direct bosonic analogue of the familiar electron topological insulator. The construction employs a parton decomposition of bosons, followed by condensation of parton-monopole composites. The surface of the resulting state supports a gapped symmetry respecting phase with intrinsic toric code topological order where both e and m anyons carry charge 1=2. It is well-known that one signature of the 3d electron topological insulator is the Witten eect: if the system is coupled to a compact electromagnetic gauge eld, a monopole in the bulk acquires a half-odd-integer polarization charge. I will discuss the corresponding phenomenon for the constructed topological insulator of bosons: a monopole can remain electrically neutral, but its statistics are transmuted from bosonic to fermionic. This \sta- tistical Witten eect" guarantees that the surface is either gapless, symmetry broken or carries an intrinsic topological order.
S=1 spin liquid with fermionic excitations

Maksym Serbyn Massachusetts Institute of Technology (MIT)
March 28, 2013

PIRSA:13030113
Condensed Matter
In the first part of my talk I describe a search for possible quantum spin liquid ground states for spin S=1 Heisenberg models on the triangular lattice which was motivated by recent experiments on Ba3NiSb2O9. We use representation of spin-1 via three flavors of fermionic spinon operators. The ground state where one gapless flavor of spinons with a Fermi surface coexists with d+id topological pairing of the two other flavors can explain available experimental data. Despite the existence of a Fermi surface, this spin liquid state has fully gapped bulk spin excitations. This results in a linear in-temperature specific heat and constant in-plane spin susceptibility, with an unusually high Wilson ratio. Using variational Monte Carlo technique, we show that proposed spin liquid ground state is realized in an SU(3)-invariant model with sufficiently strong ring-exchange terms. In the second part, I consider the physics of the magnetic s=1/2 impurity embedded in a S=1 spin liquid, where all three flavors of spinons have a Fermi surface. The interplay between non-Fermi-liquid behavior induced by a U(1) gauge field coupled to fermions, and a non-Fermi-liquid fixed point in the overscreened Kondo problem is studied using double expansion. The gauge field changes the physical properties of the system at the overscreened Kondo fixed point. Thus, spin-half impurity in such spin liquid can be used to probe the presence of fermionic spinons coupled to the gauge field. References: arXiv:1108.3070, arXiv:1208.3231 and arXiv:1212.5179
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

Michael Hermele University of Colorado Boulder
March 26, 2013

PIRSA:13030116
Condensed Matter
Quantum number fractionalization is a remarkable property of topologically ordered states of matter, such as fractional quantum Hall liquids, and quantum spin liquids. For a given type of topological order, there are generally many ways to fractionalize the quantum numbers of a given symmetry. What does it mean to have different types of fractionalization? Are different types of fractionalization a universal property that can be used to distinguish phases of matter? In this talk, I will answer these questions, focusing on a simple class of topologically ordered phases, namely two-dimensional gapped Z2 spin liquids, and I will present a symmetry classification of these phases. I will also discuss efforts in progress to find microscopic models realizing different symmetry classes.
One-photon and two-photon switching in graphene and optical nanomaterials

Mahi Singh Western University
March 08, 2013

PIRSA:13030094
Condensed Matter
In this talk we will discuss both the one-photon and two-photon switching mechanisms in hybrid nanomaterials made from two or more semiconductor, metallic and optical nanostructures. The most prominent examples of these nanostructures are graphene, semiconductor quantum dots, metallic nanoparticles, and photonic and polaritonic crystals. Advances in nanoscience have allowed for the construction of these new classes of hybrid nanomaterials. Optical excitations in semiconductor nanostructures are electron-hole pairs (excitons) whereas excitations in metallic nanostructures are surface plasmons which are collective oscillations of electrons. Therefore, the combination of these systems can provide attractive opportunities to modify, design and control optical properties and to observe new phenomena which are based on exciton-plasmon interactions. It is expected that this research will provide a theoretical road map for the development of optical sensing and optical switching.
Gravitational anomaly and topological phases

Shinsei Ryu University of Illinois at Urbana-Champaign (UIUC)
February 28, 2013

PIRSA:13020148
Condensed Matter
Since the quantum Hall effect, the notion of topological phases of matter has been extended to those that are well-defined (or: ``protected'') in the presence of a certain set of symmetries, and that exist in dimensions higher than two. In the (fractional) quantum Hall effects (and in ``chiral'' topological phases in general), Laughlin's thought experiment provides a key insight into their topological characterization; it shows a close connection between topological phases and quantum anomalies. By taking various examples, I will demonstrate that quantum anomalies serve as a useful tool to diagnose (and even define) topological properties of the systems. For chiral topological phases in (2+1) dimensions and (3+1) dimensional topological superconductors, I will discuss topological responses of the system which involve a cross correlation between thermal transport, angular momentum, and entropy. We also argue that gravitational anomaly is useful to study symmetry protected topological phases in (2+1) dimensions.
DMRG Studies on the Spin Liquid Ground State of the Kagome Model

Stefan Depenbrock Ludwig-Maximilians-Universitiät München (LMU)
February 26, 2013

PIRSA:13020147
Condensed Matter
I will present a density-matrix renormalization group (DMRG) study of the S=1/2 Heisenberg antiferromagnet on the kagome lattice to identify the conjectured spin liquid ground state. Exploiting SU(2) spin symmetry, which allows us to keep up to 16,000 DMRG states, we consider cylinders with circumferences up to 17 lattice spacings and find a spin liquid ground state with an estimated per site energy of -0.4386(5), a spin gap of 0.13(1), very short-range decay in spin, dimer and chiral correlation functions and finite topological entanglement consistent with the logarithm of 2, ruling out gapless, chiral or non-topological spin liquids. All this would provide strong evidence for a gapped topological Z_2 spin liquid.
A K matrix construction of symmetry enriched phases
February 20, 2013

PIRSA:13020140
Condensed Matter
We construct in the K matrix formalism concrete examples of symmetry enriched topological phases, namely intrinsically topological phases with global symmetries. We focus on the Abelian and non-chiral topological phases and demonstrate by our examples how the interplay between the global symmetry and the fusion algebra of the anyons of a topologically ordered system determines the existence of gapless edge modes protected by the symmetry and that a (quasi)-group structure can be defined among these phases. Our examples include phases that display charge fractionalization and more exotic non-local anyon exchange under global symmetry that correspond to general group extensions of the global symmetry group.
Fractional Quantum Hall States on an infinite cylinder: characterizing topological order and quasiparticle forces using infinite DMRG.

Michael Zaletel University of California, Berkeley
February 12, 2013

PIRSA:13020129
Condensed Matter
The density matrix renormalization group (DMRG), which has proved so successful in one dimension, has been making the push into higher dimensions, with the fractional quantum Hall (FQH) effect an important target. I'll briefly explain how the infinite DMRG algorithm can be adapted to find the degenerate ground states of a microscopic FQH Hamiltonian on an infinitely long cylinder, then focus on two applications. To characterize the topological order of the phase, I'll show that the bipartite entanglement spectrum of the ground state is sufficient to determine the quasiparticle charges, topological spins, quantum dimensions, chiral central charge, and Hall viscosity of the phase. Then I will show how to introduce localized quasiparticles of fixed topological charge. By pinning a pair of quasiparticles and dragging them into contact, we can directly measure the force curve of their interaction.
Looking for spinon deconfinement in two dimensions

Ying Tang Boston College
February 05, 2013

PIRSA:13020127
Condensed Matter
We have used a recently proposed quantum Monte Carlo algorithm [1] to study spinons (emergent S = 1/2 excitations) in 2D Resonating-Valence-Bond (RVB) spin liquids and in a J-Q model hosting a Neel – Valence Bond Solid (VBS) phase transition at zero temperature [2]. We confirm that spinons are well defined quasi-particles with finite intrinsic size in the RVB spin liquid. The distance distribution between two spinons shows signatures of deconfinement.
However, at the Neel–VBS transition, we found that the size of a single spinon is significantly greater than the bound-state in VBS, which indicates that spinons are “soft” and shrink when bound state is formed. Both spinon size and confinement length diverge as the critical point is approached. We have also compared spinon statistics in J-Q model with bilayer Heisenberg model and 1D spin chain. We conclude that the spinon deconfinement is marginal in the lowest-energy state in the spin-1 sector, due to very weak attractive spinon interactions. Deconfinement in the vicinity of the critical point should occur at higher energies.
A classification of symmetry enriched topological phases with exactly solvable models

Ying Ran Boston College
February 01, 2013

PIRSA:13020122
Condensed Matter
Two types of topological phases have attracted a lot of attention in condensed matter physics: symmetry protected topological(SPT) phases and topologically ordered phases. On the one hand, SPT phases are protected by given global symmetries while there is no topological order in the bulk. On the other hand, topologically ordered phases do not require symmetry and feature topological ground state degeneracy. In this talk, I present a classification of phases with both topological orders and global symmetries, equipped with local bosonic exactly solvable models. This classification, in some sense, organizes previous pieces of understandings on SPT phases, topological orders, symmetry fractionalizations, into a single framework. Solution of the exactly solvable models and measurable consequences will be discussed.

Title	Speaker(s)	Date	Talk Type	Info
Unconventional Magnetism and Superconductivity in 3 Dimensional Doped Mott Insulators	Baskaran Ganapathy	2013-04-30	Scientific Series	View details
Quantum transport in one dimension: from integrability to many-body localization and topology	Joel Moore	2013-04-23	Scientific Series	View details
Topological insulator of bosons in 3d via dyon condensation and the statistical Witten effect.	Max Metlitski	2013-04-10	Scientific Series	View details
S=1 spin liquid with fermionic excitations	Maksym Serbyn	2013-03-28	Scientific Series	View details
Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions	Michael Hermele	2013-03-26	Scientific Series	View details
One-photon and two-photon switching in graphene and optical nanomaterials	Mahi Singh	2013-03-08	Scientific Series	View details
Gravitational anomaly and topological phases	Shinsei Ryu	2013-02-28	Scientific Series	View details
DMRG Studies on the Spin Liquid Ground State of the Kagome Model	Stefan Depenbrock	2013-02-26	Scientific Series	View details
A K matrix construction of symmetry enriched phases		2013-02-20	Scientific Series	View details
Fractional Quantum Hall States on an infinite cylinder: characterizing topological order and quasiparticle forces using infinite DMRG.	Michael Zaletel	2013-02-12	Scientific Series	View details
Looking for spinon deconfinement in two dimensions	Ying Tang	2013-02-05	Scientific Series	View details
A classification of symmetry enriched topological phases with exactly solvable models	Ying Ran	2013-02-01	Scientific Series	View details

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Unconventional Magnetism and Superconductivity in 3 Dimensional Doped Mott Insulators

Quantum transport in one dimension: from integrability to many-body localization and topology

Topological insulator of bosons in 3d via dyon condensation and the statistical Witten effect.

S=1 spin liquid with fermionic excitations

Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

One-photon and two-photon switching in graphene and optical nanomaterials

Gravitational anomaly and topological phases

DMRG Studies on the Spin Liquid Ground State of the Kagome Model

A K matrix construction of symmetry enriched phases

Fractional Quantum Hall States on an infinite cylinder: characterizing topological order and quasiparticle forces using infinite DMRG.

Looking for spinon deconfinement in two dimensions

A classification of symmetry enriched topological phases with exactly solvable models

Unconventional Magnetism and Superconductivity in 3 Dimensional Doped Mott Insulators

Quantum transport in one dimension: from integrability to many-body localization and topology

Topological insulator of bosons in 3d via dyon condensation and the statistical Witten effect.

S=1 spin liquid with fermionic excitations

Classifying fractionalization: symmetry classification of gapped Z2 spin liquids in two dimensions

One-photon and two-photon switching in graphene and optical nanomaterials

Gravitational anomaly and topological phases

DMRG Studies on the Spin Liquid Ground State of the Kagome Model

A K matrix construction of symmetry enriched phases

Fractional Quantum Hall States on an infinite cylinder: characterizing topological order and quasiparticle forces using infinite DMRG.

Looking for spinon deconfinement in two dimensions

A classification of symmetry enriched topological phases with exactly solvable models