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Spin-spin correlations of the spin-ladder compound (C5H12N)2CuBr4 measured by magnetostriction and comparison to quantum Monte Carlo results

Fabrizio Anfuso, Markus Garst, Achim Rosch, Oliver Heyer, Thomas Lorenz, Christian Rüegg, and Karl Krämer
Phys. Rev. B 77, 235113 – Published 18 June 2008

Abstract

Magnetostriction and thermal expansion of the spin-ladder compound piperidinium copper bromide (C5H12N)2CuBr4 are analyzed in detail. We find perfect agreement between experiments and the theory of a two-leg spin-ladder Hamiltonian for more than a decade in temperature and in a wide range of magnetic fields. Relating the magnetostriction along different crystallographic directions to two static spin-spin correlation functions, which we compute with quantum Monte Carlo, allows us to reconstruct the magnetoelastic couplings of (C5H12N)2CuBr4. We especially focus on the quantum critical behavior near the two critical magnetic fields Hc1 and Hc2, which is characterized by strong singularities rooted in the low dimensionality of the critical spin system. Extending our discussion in Lorenz [ et al. Phys. Rev. Lett. 100, 067208 (2008)], we show explicitly that the thermal expansion near the upper critical field Hc2 is quantitatively described by a parameter-free theory of one-dimensional, nonrelativistic fermions. We also point out that there exists a singular quantum critical correction to the elastic moduli. This correction is proportional to the magnetic susceptibility χ, which diverges as χ1/T at the critical fields and thus leads to a strong softening of the crystal.

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  • Received 7 March 2008

DOI:https://doi.org/10.1103/PhysRevB.77.235113

©2008 American Physical Society

Authors & Affiliations

Fabrizio Anfuso, Markus Garst, and Achim Rosch

  • Institut für Theoretische Physik, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany

Oliver Heyer and Thomas Lorenz

  • II. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany

Christian Rüegg

  • London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, London WC1E 6BT, United Kingdom

Karl Krämer

  • Department of Chemistry and Biochemistry, University of Bern, Freiestrasse, CH–3000 Bern 9, Switzerland

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Issue

Vol. 77, Iss. 23 — 15 June 2008

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