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Low-energy excitations and ground-state selection in the quantum breathing pyrochlore antiferromagnet Ba3Yb2Zn5O11

T. Haku, K. Kimura, Y. Matsumoto, M. Soda, M. Sera, D. Yu, R. A. Mole, T. Takeuchi, S. Nakatsuji, Y. Kono, T. Sakakibara, L.-J. Chang, and T. Masuda
Phys. Rev. B 93, 220407(R) – Published 24 June 2016
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    Abstract

    We study low-energy excitations in the quantum breathing pyrochlore antiferromagnet Ba3Yb2Zn5O11 by a combination of inelastic neutron scattering (INS) and thermodynamical property measurements. The INS spectra are quantitatively explained by spin-12 single-tetrahedron model having XXZ anisotropy and Dzyaloshinskii-Moriya interactions. This model has a twofold degeneracy of the lowest-energy state per tetrahedron and well reproduces the magnetization curve at 0.5 K and heat capacity above 1.5 K. At lower temperatures, however, we observe a broad maximum in the heat capacity around 63 mK, demonstrating that a unique quantum ground state is selected due to extra perturbations with an energy scale smaller than the instrumental resolution of INS.

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    • Received 1 March 2016
    • Revised 13 May 2016

    DOI:https://doi.org/10.1103/PhysRevB.93.220407

    ©2016 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Frustrated magnetismSpecific heat
    1. Physical Systems
    Pyrochlores
    1. Techniques
    Inelastic neutron scatteringSpecific heat measurements
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    T. Haku1, K. Kimura2, Y. Matsumoto1, M. Soda1, M. Sera2, D. Yu3, R. A. Mole3, T. Takeuchi4, S. Nakatsuji1, Y. Kono1, T. Sakakibara1, L.-J. Chang5, and T. Masuda1

    • 1Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan
    • 2Division of Materials Physics, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
    • 3Bragg Institute, Australian Nuclear Science and Technology Organization, Lucas Heights, New South Wales 2234, Australia
    • 4Low Temperature Center, Osaka University, Toyonaka, Osaka 560-0043, Japan
    • 5Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan

    See Also

    Anisotropic Exchange within Decoupled Tetrahedra in the Quantum Breathing Pyrochlore Ba3Yb2Zn5O11

    J. G. Rau, L. S. Wu, A. F. May, L. Poudel, B. Winn, V. O. Garlea, A. Huq, P. Whitfield, A. E. Taylor, M. D. Lumsden, M. J. P. Gingras, and A. D. Christianson
    Phys. Rev. Lett. 116, 257204 (2016)

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    Vol. 93, Iss. 22 — 1 June 2016

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    • Figure 1
      Figure 1

      (a)–(d) INS spectra measured at (a) 1.5, (b) 6, (c) 12, and (d) 40 K using setup I. (e) INS spectrum measured at 1.5 K using setup II. (f) Q dependence of the integrated intensity obtained from the spectrum in (e). The red solid curve is the calculation (see text).

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    • Figure 2
      Figure 2

      (a), (b) The ℏω dependences of the neutron intensities at (a) 1.5 and (b) 12 K. (c) Temperature dependences of the intensities of the excitations in (a). (d) Those of the excitations additionally observed in high temperatures in (b). (e) ℏω dependence of the intensity at 1.5 K obtained using setup II. Throughout the panels, red and black solid curves are the calculations using the same parameters in Eqs. (3, 4, 5, 6). (f) Energy level of the S=12 Heisenberg spin tetrahedron model in the previous study [18] and that of the S=12 anisotropic spin tetrahedron in the present study.

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    • Figure 3
      Figure 3

      (a) Heat capacity measured and reported in the previous study [18]. The red solid curve is the calculation. (b) Magnetic field dependence of magnetization at 0.5 K. The red solid curve is the calculation. (c) Solid circles indicate heat capacity. The blue dashed curve is the calculation of the empirical model where the lift of the degeneracy of the ground state is introduced as a single energy gap. The red solid curve is the calculation of the model where the empirical energy gap has distribution. (d) Entropy change estimated from (c). The calculated entropy is shifted so that the calculation has the same value of the data at 0.94 K.

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