Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G1: Invited Session: Anderson-Higgs Boson in Condensed Matter Physics |
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Sponsoring Units: DCMP Chair: Subir Sachdev, Harvard University Room: Ballroom I |
Tuesday, March 19, 2013 11:15AM - 11:51AM |
G1.00001: The ``Higgs'' amplitude mode at the two-dimensional superfluid-Mott insulator transition Invited Speaker: Immanuel Bloch Spontaneous symmetry breaking plays a key role in our understanding of nature. In relativistic quantum field theory, a broken continuous symmetry leads to the emergence of two types of fundamental excitation: massless Nambu--Goldstone modes and a massive `Higgs' amplitude mode. An excitation of Higgs type is of crucial importance in the standard model of elementary particle physics, and also appears as a fundamental collective mode in quantum many-body systems. Whether such a mode exists in low-dimensional systems as a resonance-like feature, or whether it becomes overdamped through coupling to Nambu--Goldstone modes, has been a subject of debate. Here we experimentally find and study a Higgs mode in a two-dimensional neutral superfluid close to a quantum phase transition to a Mott insulating phase. We unambiguously identify the mode by observing the expected reduction in frequency of the onset of spectral response when approaching the transition point. In this regime, our system is described by an effective relativistic field theory with a two-component quantum field, which constitutes a minimal model for spontaneous breaking of a continuous symmetry. Additionally, all microscopic parameters of our system are known from first principles and the resolution of our measurement allows us to detect excited states of the many-body system at the level of individual quasiparticles. This allows for an in-depth study of Higgs excitations that also addresses the consequences of the reduced dimensionality and confinement of the system. Our work constitutes a step towards exploring emergent relativistic models with ultracold atomic gases. [Preview Abstract] |
Tuesday, March 19, 2013 11:51AM - 12:27PM |
G1.00002: Higgs Excitations in Dimer Antiferromagnets Invited Speaker: Christian R\"uegg In three-dimensional dimer antiferromagnets a generic quantum critical point (QCP) separates a quantum-disordered ground state with a spin gap from a phase with long-range antiferromagnetic order and finite ordering temperature. While this QCP and related phases have been studied intensely in theoretical and numerical work using among other methods bond-operators and quantum Monte-Carlo, real materials in which they can be explored experimentally are rare. Structurally dimerised antiferromagnets are located on the disordered or ordered side of the QCP and application of pressure offers a way to control the ration of exchange interactions in the material across a critical value, if the compressibility and pressure dependence of the exchange are favourable. In TlCuCl$_{3}$ this QCP was realised for the first time and was studied in great detail by neutron scattering. These experiments provide unprecedented insights into the effects of thermal and quantum fluctuations, and of the elementary excitations near QCPs. A unique phenomena is the emergence of longitudinal modes near the QCP, which are the Higgs exceptions in dimer antiferromagnets proposed by S. Sachdev and coworkers. These Higgs exceptions follow precisely scaling predications and are involved in both the quantum and thermal melting of order in such systems. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 1:03PM |
G1.00003: Higgs Bosons in Superconductors Invited Speaker: Chandra Varma Spurred by some strange experimental observations in some superconductors, the theory of a new collective mode\footnote{P.B. Littlewood and C.M. Varma, Phys. Rev. Lett. {\bf 47}, 811 (1981); Phys. Rev. B {\bf 26}, 4883 (1982). } in superconductors and how it can be experimentally found very easily under certain circumstances was provided in 1981. It was called the ``Amplitude Mode'' to distinguish it from the ``Phase Modes'' which provide Josephson effects and which in homogeneous superconductors are coupled to charge density fluctuations and are at the energies of the plasmons. More generally,\footnote{C.M. Varma, J. Low Temp. Phys., {126}, 901 (2002). } this mode is the amplitude mode of a particle-hole symmetric $U(1)$ field, i.e the model treated by Higgs and others in the1960's whose generalization have played an important role in the standard model of particle physics. Recently the amplitude or Higgs mode for d-wave superconductors have also been discussed,\footnote{Y. Barlas and C.M. Varma, arXiv:1206.0400.} where its various cousins may also be found. I will tell the story of the above and why such modes were missed in the theory of superconductivity for so long and the applications of the ideas to modes for cold bosons and fermions in optical lattices. I will also comment, as a very interested outsider and an enthusiast, on the Higgs in particle physics being discovered at LHC from the point of view of the theory of superconductivity. [Preview Abstract] |
Tuesday, March 19, 2013 1:03PM - 1:39PM |
G1.00004: Fate of the Higgs mode near quantum criticality Invited Speaker: Daniel Podolsky The Higgs mode is a ubiquitous collective excitation in condensed matter systems with broken continuous symmetry. It is expected in antiferromagnets, short coherence length superconductors, charge density waves, and lattice Bose condensates. Its detection is a valuable test of the corresponding field theory, and its mass gap measures the proximity to a quantum critical point. However, since the Higgs mode can decay into low energy Goldstone modes, its experimental visibility has been questioned. Here we show that the visibility of the Higgs mode depends on the symmetry of the measured susceptibility. Furthermore, we investigate the evolution of the Higgs mode upon approach to the Wilson-Fisher fixed point in 2+1 dimensions and demonstrate that the Higgs mode survives as a universal resonance in the scalar susceptibility arbitrarily close to the quantum critical point. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 2:15PM |
G1.00005: The Higgs Mode in Two Dimensional Superfluid Invited Speaker: Nikolay Prokof'ev |
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