Anomalous dynamical line shapes in a quantum magnet at finite temperature

D. A. Tennant, B. Lake, A. J. A. James, F. H. L. Essler, S. Notbohm, H.-J. Mikeska, J. Fielden, P. Kögerler, P. C. Canfield, and M. T. F. Telling
Phys. Rev. B 85, 014402 – Published 4 January 2012

Abstract

The effect of thermal fluctuations on the dynamics of a gapped quantum magnet is studied using inelastic neutron scattering on copper nitrate, a model material for the spin-1/2, one-dimensional (1D) bond alternating Heisenberg chain. A large, highly deuterated, single-crystal sample of copper nitrate is produced using a solution growth method and measurements are made using the high-resolution backscattering spectrometer OSIRIS at the ISIS Facility. Theoretical calculations and numerical analysis are combined to interpret the physical origin of the thermal effects observed in the magnetic spectra. The primary observations are (1) a thermally induced central peak due to intraband scattering, which is similar to Villain scattering familiar from soliton systems in 1D, and (2) the one-magnon quasiparticle pole is seen to develop with temperature into an asymmetric continuum of scattering. We relate this asymmetric line broadening to a thermal strongly correlated state caused by hard-core constraints and quasiparticle interactions. These findings are a counter example to recent assertions of the universality of line broadening in 1D systems and are applicable to a broad range of quantum systems.

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  • Received 20 November 2011

DOI:https://doi.org/10.1103/PhysRevB.85.014402

©2012 American Physical Society

Authors & Affiliations

D. A. Tennant1,2, B. Lake1,2, A. J. A. James3, F. H. L. Essler4, S. Notbohm1,5, H.-J. Mikeska6, J. Fielden7, P. Kögerler7, P. C. Canfield7, and M. T. F. Telling8

  • 1Helmholtz-Zentrum Berlin für Materialien und Energie, Hahn-Meitner Platz 1, 14109 Berlin, Germany
  • 2Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, D-10623 Berlin, Germany
  • 3Department of Condensed Matter Physics and Material Science, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
  • 4Rudolf Peierls Centre for Theoretical Physics, 1 Keble Road, Oxford OX1 3NP, United Kingdom
  • 5School of Physics and Astronomy, North Haugh, St. Andrews, KY15 9SS, United Kingdom
  • 6Department of Theoretical Physics, University of Hannover, D-30167 Hannover, Germany
  • 7Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA
  • 8ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 OQX, United Kingdom

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Vol. 85, Iss. 1 — 1 January 2012

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