IQIM Postdoctoral and Graduate Student Seminar
Andy Mounce started as a Director's Funded Postdoctoral Fellow at Los Alamos National Laboratory in July 2013 studying strongly correlated electron problems of quantum criticality, superconductivity, and magnetism after graduating with his PhD in Physics from Professor Bill Halperin's Condensed Matter NMR group where he studied the high temperature superconducting cuprates. Since then he been awarded a Los Alamos Seaborg Fellowship to search for the nuclear magnetic resonance signature of the Plutonium-239 isotope. In October 2015 he will begin a staff position in the Quantum Information group at Sandia National Laboratory where he will develop resonance techniques for quantum manipulation single Phosphorous nuclei implanted in Silicon.
Abstract: The discovery of f electron superconductivity in CeCu2Si2 [1] and UPt3 [2] revolutionized the way we think about superconductivity, even before the discovery of high temperature superconducting cuprates [3]. The superconducting state in these materials cannot be described by the Bardeen-Cooper-Schrieffer model of phonon mediated superconductivity. [4] Furthermore, the superconducting state is established from a strongly correlated quasiparticle state where correlations between conduction and localized electrons create quasiparticles with mass 100's of times larger than a typical conduction electron. Nuclear magnetic resonance (NMR) is a unique probe in that it is both microscopic, giving information about local properties at the nuclear site, and bulk, averaging these properties over an ensemble of equivalent crystal sites. Through NMR measurements, clues about the superconducting electronic paring symmetry, orbital angular momentum, and magnetic fluctuations are revealed. In this presentation, I will describe unconventional heavy fermion superconductivity and the NMR probe of materials. Building on this foundation, I will demonstrate how NMR has been utilized at Los Alamos to uncover the details of superconductivity in a Uranium superconductor U2PtC2 [5] and the Plutonium superconductor family, the so-called Pu-115's. [6]
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[2] Stewart, G. R. et al. Phys. Rev. Lett. 52, 679 (1984).
[3] Bednorz, J. G. and Muller, K. A. Z. Phys. B. Con. Mat. 64, 189 (1986).
[4] Bardeen, J. Cooper, L. N. and Schrie_er, J. R. Phys. Rev. 106, 162 (1957).
[5] Mounce, A. M. et al. Phys. Rev. Lett. 114, 127001 (2015).
[6] Koutroulakis, G et al. APS Meeting Abstracts 1, 46013 (2014).