Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W19: Holography and Higgs Physics in Condensed Matter |
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Sponsoring Units: DCMP Chair: Philip Phillips, University of Illinois Room: 321 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W19.00001: Spin and holographic metals Victor Alexandrov, Piers Coleman We examine the spin structure of the Green's function of the holographic metal, demonstrating that the excitations of the holographic metal are ``chiral,'' lacking the inversion symmetry of a conventional Fermi surface, with only one spin orientation for each point on the Fermi surface aligned parallel to the momentum. This implies that ferromagnetic spin fluctuations are absent from the holographic metal, leading to a complete absence of Pauli paramagnetism. The talk will discuss a possibility of going to a 3-dimensional holographic metal, where electrons should have both left- and right-handed chiralities.\\[4pt] [1] Phys. Rev. B 86, 125145 (2012) [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W19.00002: The Pauli exclusion principle in semi-local quantum criticality David Ramirez, Richard Anantua, Sean Hartnoll, Victoria Martin A crucial consequence of the Pauli exclusion principle in weakly coupled systems is the presence of low energy degrees of freedom at finite momenta; a natural question is then to what extent does this aspect of Pauli exclusion persist at strong coupling, which may not even admit well-defined quasiparticles? We use holography to address this issue by studying the momentum space structure of low energy current-current correlation functions in finite density field theories exhibiting semi-local criticality. The semi-locally critical theories are characterized by an exponent $\eta$ that determines the low temperature scaling of entropy density to be $s \sim T^\eta$. Despite the fact that spatial momenta do not scale in semi-locally critical theories, we find that operator dimensions can have non-trivial momentum dependence, leading to novel momentum space structure. In particular, for $0 < \eta < 2$, we find sharp discontinuities in the transverse response functions at a non-zero $k_*$, reminiscent of Pauli exclusion-type dynamics. Finally, we comment on the $\eta=1$ geometry, which allowed for analytic expressions for correlation functions at finite temperature as well as interesting phenomenological properties and string theory embeddings. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W19.00003: Superconducting Dome and Anisotropy in Holographic Striped Superconductor Jimmy Hutasoit, Suman Ganguli, Geogre Siopsis, Jason Therrien Using gauge/gravity duality, we study the properties of a strongly coupled striped superconductor with unidirectional charge density wave order. By including the effects of fluctuations, we show that there is a regime in which this holographic model exhibits a superconducting dome. Furthermore, we study the anisotropy of the optical conductivity at temperature below the critical temperature and compare it with the experimental results in cuprate. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W19.00004: Inhomogeneous Phases in Holographic Superfluids Kubra Yeter, Eleftherios Papantonopoulos, George Siopsis We discuss inhomogeneous solutions of a gravitating system consisting of two $U(1)$ gauge fields and a real scalar field. One of the $U(1)$ gauge fields determines the chemical potential, whereas the other one corresponds to a magnetic field interacting with the spin in the boundary theory. We solve the field equations and find a second-order phase transition to an inhomogeneous phase at a critical temperature which we compute. Below the critical temperature, the equations are solved perturbatively, and a spatially dependent charge density is generated. This is compatible with the generation of a charge density wave in condensed matter systems. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W19.00005: Compressible quantum phases from conformal field theories in 2+1 dimensions Subir Sachdev Conformal field theories (CFTs) with a globally conserved U(1) charge $Q$ can be deformed into compressible phases by modifying their Hamiltonian, $H$, by a chemical potential $H \rightarrow H - \mu Q$. We study 2+1 dimensional CFTs upon which an explicit S duality mapping can be performed. We find that this construction leads naturally to compressible phases which are superfluids, solids, or non-Fermi liquids which are more appropriately called `Bose metals' in the present context. The Bose metal preserves all symmetries and has Fermi surfaces of gauge-charged fermions, even in cases where the parent CFT can be expressed solely by bosonic degrees of freedom. Monopole operators are identified as order parameters of the solid, and the product of their magnetic charge and $Q$ determines the area of the unit cell. We discuss implications for holographic theories on asymptotically AdS$_4$ spacetimes: S duality and monopole/dyon fields play important roles in this connection. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W19.00006: Metal-Insulator Transition from Holography Sean Hartnoll, Aristomenis Donos The holographic correspondence allows theoretical control of certain phases of matter that do not admit a quasiparticle description. This approach has proved helpful for the description of quantum critical transport. I will present holographic results for transport away from particle-hole symmetry. This requires explicit inclusion of lattice effects to render the conductivity finite. I will show that the holographic system undergoes a metal-insulator transition as a function of the strength of the lattice. This results implies that holography is capable of describing localization physics in strongly interacting systems. I will present results for the optical conductivity, exibiting a transition from a metallic drude peak to Mott insulating behavior. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 3:54PM |
W19.00007: Multipoint correlators of conformal field theories: implications for quantum critical transport Philipp Strack, Debanjan Chowdhury, Suvrat Raju, Subir Sachdev, Ajay Singh We relate three-point correlators between the stress-energy tensor and conserved currents of conformal field theories (CFTs) in 2+1 dimensions to observables of quantum critical transport. We first compute the correlators in the large-flavor-number expansion of conformal gauge theories and then do the computation using holography. In the holographic approach, the correlators are computed from an effective action on 3+1 dimensional anti-de Sitter space (AdS$_4$), and depend upon the co-efficient, $\gamma$, of a four-derivative term in the action. We find a precise match between the CFT and the holographic results, thus fixing the values of $\gamma$. The CFTs of free fermions and bosons take the values $\gamma=1/12,-1/12$ respectively, and so saturate the bound $|\gamma| \leq 1/12$ obtained earlier from the holographic theory; the correlator of the conserved gauge flux of U(1) gauge theories takes intermediate values of $\gamma$. The value of $\gamma$ also controls the frequency dependence of the conductivity, and other properties of quantum-critical transport at non-zero temperatures. Our results for the values of $\gamma$ lead to an appealing physical interpretation of particle-like or vortex-like transport near quantum phase transitions of interest in condensed matter physics. [Preview Abstract] |
Thursday, March 21, 2013 3:54PM - 4:06PM |
W19.00008: The quasi-normal modes of quantum criticality William Witczak-Krempa, Subir Sachdev We study the general features of charge transport of quantum critical points described by CFTs in 2+1D. We use an effective field theory on an asymptotically AdS spacetime, expanded to fourth order in spatial and temporal gradients. The presence of a horizon at non-zero temperatures implies that this theory has quasi-normal modes with complex frequencies. The quasi-normal modes determine the poles and zeros of the conductivity in the complex frequency plane, and so fully determine its behavior on the real frequency axis, at frequencies both smaller and larger than the temperature. We describe the role of particle-vortex or S-duality on the conductivity, specifically how it maps poles to zeros and vice versa. These analyses motivate two sum rules obeyed by the quantum critical conductivity. Finally, we compare our results with the analytic structure of the O(N) model in the large-N limit, and other CFTs. [Preview Abstract] |
Thursday, March 21, 2013 4:06PM - 4:18PM |
W19.00009: FFLO States in Holographic Superconductors George Siopsis, James Alsup, Eleftherios Papantonopoulos We discuss a novel mechanism to set up a gravity dual of FFLO states in strongly coupled superconductors. The gravitational theory utilizes two $U(1)$ gauge fields and a scalar field coupled to a charged AdS black hole. The first gauge field couples with the scalar sourcing a charge condensate below a critical temperature, and the second gauge field provides a coupling to spin in the boundary theory. The scalar is neutral under the second gauge field. By turning on an interaction between the Einstein tensor and the scalar, it is shown that, in the low temperature limit, an inhomogeneous solution possesses a higher critical temperature than the homogeneous case, giving rise to FFLO states. [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W19.00010: Study of Higgs mode near quantum critical points Yejin Huh, Subir Sachdev We present a study of Higgs excitation mode in different quantum theories in 2 space dimensions. $O(N)$ theory and $CP(N)$ theory near the quantum critical points will be discussed for zero and finite temperature. Electron systems with fermi surfaces will be studied under this framework. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W19.00011: Superconductivity in a model involving transverse gauge bosons Ipsita Mandal, Sudip Chakravarty, Suk Bum Chung It has been known for some time that a system of fermions interacting with transverse gauge bosons does not behave like a Fermi liquid and provides a bona fide model for a non-Fermi liquid. Here we study superconductivity in this model Preliminary calculations show explicitly that a superconducting gap exists only for couplings greater than a threshold. It is hoped that a proper elucidation of this problem would lead to insights that may be useful in developing effective low energy theories of realistic physical problems, such as the normal state of high temperature superconductors, the state of half-filled quantum Hall systems, or the color superconductivity in the quark-gluon system, or even in the effects of disorder in a non-Fermi liquid system that could provide a new paradigm. [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W19.00012: Detection of Higgs mode in D-wave Superconductors Yafis Barlas, Chandra Varma Higgs modes, which are collective excitations of the amplitude of the order parameter, have zero spin and no charge, do not couple directly to experimental probes. They are, however, linearly coupled to excitations which shake the ground state and therefore appear as poles or branch-cuts in their self-energy. In the superconducting state the Higgs modes can be distinguished from other excitations because they can only appear as satellites which steal all their spectral weight from excitations which promote superconductivity. This is an observable effect if such excitations and the Higgs modes are not too far separated in energy. We show that the Higgs mode in the $A_{1g}$ Raman scattering channel appears as a sharp resonance below $2 \Delta$ in the spectral weight of excitations responsible for superconductivity in Cuprates in a class of theories. Comparison is made with existing experiments and further experiments to confirm or rule out the idea are proposed. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W19.00013: Unified Description of Nambu-Goldstone Bosons without Lorentz Invariance Haruki Watanabe, Hitoshi Murayama We address the well-known problem that Nambu-Goldstone's theorem does not correctly predict the number of Nambu-Goldstone bosons in systems without Lorentz invariance. Using the effective Lagrangian approach, we provide a general prescription to predict the number of Nambu-Goldstone bosons and the form of their dispersion relation correctly. We trace the abnormalities in non-Lorentz invariant systems back to Nambu-Goldstone boson pairs becoming canonically conjugate--this reduces the number of Nambu-Goldstone bosons and changes the linear dispersions to quadratic. The generality of our construction clarifies the powerful approach of analyzing quantum many-body systems--including strongly coupled systems--by their symmetry breaking patterns. This will also aid our understanding of recent experiments and theoretical works on spinor BECs and lattices of topological defects. Reference: H. Watanabe, H. Murayama, PRL 108, 251602 (2012) [Preview Abstract] |
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