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12/13 PSI - Explorations in String Theory Lecture 14

Pedro Vieira Perimeter Institute for Theoretical Physics
April 25, 2013

PIRSA:13040101
Quantum Fields and Strings
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons

Zhihao Hao University of Waterloo
April 25, 2013

PIRSA:13040134
Condensed Matter
12/13 PSI - Explorations in Cosmology Lecture 14

Matthew Johnson York University
April 25, 2013

PIRSA:13040079
Cosmology
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter

Radu Coldea University of Oxford
April 25, 2013

PIRSA:13040133
Condensed Matter
12/13 PSI - Explorations in Condensed Matter Lecture 14
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 25, 2013

PIRSA:13040060
Condensed Matter
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
12/13 PSI - Explorations in String Theory Lecture 13

Pedro Vieira Perimeter Institute for Theoretical Physics
April 24, 2013

PIRSA:13040100
Quantum Fields and Strings
12/13 PSI - Explorations in Cosmology Lecture 13

Matthew Johnson York University
April 24, 2013

PIRSA:13040078
Cosmology
12/13 PSI - Explorations in Condensed Matter Lecture 13
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 24, 2013

PIRSA:13040059
Condensed Matter
12/13 PSI - Explorations in String Theory Lecture 12

Pedro Vieira Perimeter Institute for Theoretical Physics
April 23, 2013

PIRSA:13040099
Quantum Fields and Strings
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
On memory in exponentially expanding spaces

Douglas Stanford Stanford University
April 23, 2013

PIRSA:13040127
Cosmology

12/13 PSI - Explorations in String Theory Lecture 14

Pedro Vieira Perimeter Institute for Theoretical Physics
April 25, 2013

PIRSA:13040101
Quantum Fields and Strings
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons

Zhihao Hao University of Waterloo
April 25, 2013

PIRSA:13040134
Condensed Matter
Motivated by recent numerical and experimental studies of the spin-1/2 Heisenberg antiferromagnet on kagome, we formulate a many-body model for fermionic spinons, which are just uncoupled spins. The spinons interact with an emergent U(1) gauge field and experience strong short-range attraction in the S=0 channel. The ground state of the model is generically a Z(2) liquid. We calculate the edge of the two-spinon continuum and compare the theory to the slave-fermion approach to the Heisenberg model.
12/13 PSI - Explorations in Cosmology Lecture 14

Matthew Johnson York University
April 25, 2013

PIRSA:13040079
Cosmology
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter

Radu Coldea University of Oxford
April 25, 2013

PIRSA:13040133
Condensed Matter
Realizing experimentally continuous phase transitions in the electronic ground state of materials near zero temperature as a function of tuning some external parameter (magnetic field, pressure etc.) offers a unique opportunity to probe the extreme regime (near the transition point) where strong quantum correlations encompass the macroscopic sample as a whole, so called “quantum criticality” [1]. In this regime of strong correlations small perturbations/interactions can stabilize novel forms order or collective fluctuations that otherwise do not exist. One of the theoretically most studied paradigms for quantum criticality is a chain of Ising spins driven by a transverse field to a critical point separating spontaneous magnetic order and paramagnetic phases. We have realized this system experimentally by applying strong magnetic fields to the quasi-one-dimensional Ising ferromagnet CoNb2O6 and have probed via single-crystal inelastic neutron scattering the evolution of the magnetic order and spin excitation spectrum as a function of applied field at mili-Kelvin temperatures [2]. Near the critical point the spin excitations were theoretically predicted nearly two decades ago to have a set of quantum resonances (collective modes of vibration of the interacting spins) with universal ratios between their frequencies reflecting an exceptional mathematical structure of the quantum many-body eigenstates with a “hidden” E8 symmetry governing the physics in the scaling limit. Experiments indeed observed evidence for a spectrum of resonances and the ratio between the frequencies of the two lowest modes approached the "golden ratio" near the critical point, as predicted by field theory. As a second example of novel physics near quantum criticality I will discuss how an amplitude-modulated incommensurate spin-density wave (SDW) order appears near the field-induced critical point in the quasi-1D spin-1/2 XY antiferromagnet Cs2CoCl4. Incommensurate SDWs are very uncommon in magnetic insulators and are not stable zero-temperature ground states at the classical mean-field level, we propose that here such a state is stabilized by the strong quantum fluctuations associated with the proximity to the critical point and the weak frustrated inter-chain couplings.
12/13 PSI - Explorations in Condensed Matter Lecture 14
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 25, 2013

PIRSA:13040060
Condensed Matter
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems
April 24, 2013

PIRSA:13040116
Condensed Matter
In one extreme, where the interactions are sufficiently weak compared to the interactions, electrons form a “Fermi liquid” – the state that accounts for the properties of simple metals. In the other extreme, where the interactions are dominant, the electrons form various “Mott” insulating or “Wigner crystalline” phases, often characterized by broken spatial and/or magnetic symmetries. Corresponding charge and/or magnetically ordered insulating phases are common in nature. Between these two extremes lie highly correlated electronic fluids, and correspondingly a host of interesting and perplexing materials, including such diverse systems as the cuprate and iron-based high temperature superconductors, the failed metamagnet Sr3Ru2O7, and a variety of quantum Hall fluids. Some insight into electron fluids in this rich intermediate coupling regime can be obtained from viewing them as partially melted electron solids, rather than as strongly interacting gases. Here, analogies with the liquid crystalline phases of complex classical fluids provide useful guidance for a new approach to this key problem in condensed matter physics.
12/13 PSI - Explorations in String Theory Lecture 13

Pedro Vieira Perimeter Institute for Theoretical Physics
April 24, 2013

PIRSA:13040100
Quantum Fields and Strings
12/13 PSI - Explorations in Cosmology Lecture 13

Matthew Johnson York University
April 24, 2013

PIRSA:13040078
Cosmology
12/13 PSI - Explorations in Condensed Matter Lecture 13
- Guifre Vidal Alphabet (United States)
- Xiao-Gang Wen Massachusetts Institute of Technology (MIT) - Department of Physics
April 24, 2013

PIRSA:13040059
Condensed Matter
12/13 PSI - Explorations in String Theory Lecture 12

Pedro Vieira Perimeter Institute for Theoretical Physics
April 23, 2013

PIRSA:13040099
Quantum Fields and Strings
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.
On memory in exponentially expanding spaces

Douglas Stanford Stanford University
April 23, 2013

PIRSA:13040127
Cosmology
I will present recent work, done in collaboration with Daniel Roberts, on the global memory of initial conditions that is sometimes, but not always, retained by fluctuating fields on de Sitter space, Euclidean anti de Sitter space, and regular infinite trees. I will discuss applications to the structure of configuration space in de Sitter space and eternal inflation.

Title	Date	Collection	Type	Info
12/13 PSI - Explorations in String Theory Lecture 14	2013‑04‑25	12/13 PSI - Eplorations in String Theory	Course	View details
Spin-1/2 Heisenberg Antiferromagnet on the Kagome Lattice: a Z2 Spin Liquid with Fermionic Spinons	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
12/13 PSI - Explorations in Cosmology Lecture 14	2013‑04‑25	12/13 PSI - Explorations in Cosmology	Course	View details
Reaching Experimentally Quantum Criticality: A Playground to Explore Novel Correlated Quantum States of Matter	2013‑04‑25	4 Corner Southwest Symposium 2013	Conference	View details
12/13 PSI - Explorations in Condensed Matter Lecture 14	2013‑04‑25	12/13 PSI - Explorations in Condensed Matter	Course	View details
Electronic Liquid Crystalline Phases of Highly Correlated Electronic Systems	2013‑04‑24	Colloquium	Scientific Series	View details
12/13 PSI - Explorations in String Theory Lecture 13	2013‑04‑24	12/13 PSI - Eplorations in String Theory	Course	View details
12/13 PSI - Explorations in Cosmology Lecture 13	2013‑04‑24	12/13 PSI - Explorations in Cosmology	Course	View details
12/13 PSI - Explorations in Condensed Matter Lecture 13	2013‑04‑24	12/13 PSI - Explorations in Condensed Matter	Course	View details
12/13 PSI - Explorations in String Theory Lecture 12	2013‑04‑23	12/13 PSI - Eplorations in String Theory	Course	View details
Quantum transport in one dimension: from integrability to many-body localization and topology	2013‑04‑23	Quantum Matter	Scientific Series	View details
On memory in exponentially expanding spaces	2013‑04‑23	Cosmology and Gravitation	Scientific Series	View details

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