Condensed Matter

This series consists of talks in the area of Condensed Matter.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

 

Friday Sep 19, 2014

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.

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Wednesday Sep 17, 2014
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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.

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Tuesday Sep 16, 2014
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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.

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Thursday Sep 11, 2014
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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.

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Tuesday Sep 09, 2014
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Roughly speaking, Many-Body Localization (MBL) refers to the state of a material that fails to thermalize. Though MBL has mostly been studied in quenched disordered systems, several authors have recently proposed that this phase could be realized in clean (translation invariant) systems too. In this talk, I will discuss this idea and ask to which extent an MBL phase can indeed be expected in systems without quenched disorder. Hopefully, the discussion shed also some light on the localization-delocalization transition for more generic many-body systems. From joint work with W.

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Tuesday Sep 02, 2014
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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

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Tuesday Aug 19, 2014
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Tuesday Aug 12, 2014
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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.

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Tuesday Jul 08, 2014
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