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Origin of the Spin-Orbital Liquid State in a Nearly J=0 Iridate Ba3ZnIr2O9

Abhishek Nag, S. Middey, Sayantika Bhowal, S. K. Panda, Roland Mathieu, J. C. Orain, F. Bert, P. Mendels, P. G. Freeman, M. Mansson, H. M. Ronnow, M. Telling, P. K. Biswas, D. Sheptyakov, S. D. Kaushik, Vasudeva Siruguri, Carlo Meneghini, D. D. Sarma, Indra Dasgupta, and Sugata Ray
Phys. Rev. Lett. 116, 097205 – Published 3 March 2016
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    Abstract

    We show using detailed magnetic and thermodynamic studies and theoretical calculations that the ground state of Ba3ZnIr2O9 is a realization of a novel spin-orbital liquid state. Our results reveal that Ba3ZnIr2O9 with Ir5+ (5d4) ions and strong spin-orbit coupling (SOC) arrives very close to the elusive J=0 state but each Ir ion still possesses a weak moment. Ab initio density functional calculations indicate that this moment is developed due to superexchange, mediated by a strong intradimer hopping mechanism. While the Ir spins within the structural Ir2O9 dimer are expected to form a spin-orbit singlet state (SOS) with no resultant moment, substantial frustration arising from interdimer exchange interactions induce quantum fluctuations in these possible SOS states favoring a spin-orbital liquid phase down to at least 100 mK.

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    • Received 16 July 2015

    DOI:https://doi.org/10.1103/PhysRevLett.116.097205

    © 2016 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Spin-orbit coupling
    1. Physical Systems
    IridatesTransition metal alloys
    1. Techniques
    Density functional theoryGGA
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Abhishek Nag1, S. Middey2,‡, Sayantika Bhowal3, S. K. Panda2,§, Roland Mathieu4, J. C. Orain5, F. Bert5, P. Mendels5, P. G. Freeman6,7, M. Mansson6,8, H. M. Ronnow6, M. Telling9, P. K. Biswas10, D. Sheptyakov11, S. D. Kaushik12, Vasudeva Siruguri12, Carlo Meneghini13, D. D. Sarma14, Indra Dasgupta2,3,*, and Sugata Ray1,2,,†

    • 1Department of Materials Science, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
    • 2Centre for Advanced Materials, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
    • 3Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
    • 4Department of Engineering Sciences, Uppsala University, P.O. Box 534, SE-751 21 Uppsala, Sweden
    • 5Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405 Orsay, France
    • 6Laboratory for Quantum Magnetism (LQM), École Polytechnique Fédérale de Lausanne (EPFL), Station 3, CH-1015 Lausanne, Switzerland
    • 7Jeremiah Horrocks Institute for Mathematics, Physics and Astrophysics, University of Central Lancashire, Preston PR1 2HE, United Kingdom
    • 8Department of Materials and Nanophysics, KTH Royal Institute of Technology, Electrum 229, SE-16440 Kista, Sweden
    • 9ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX110QX, United Kingdom
    • 10Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
    • 11Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland
    • 12UGC-DAE-Consortium for Scientific Research Mumbai Centre, R5 Shed, Bhabha Atomic Research Centre, Mumbai 400085, India
    • 13Dipartimento di Scienze, Universitá Roma Tre, Via della Vasca Navale, 84 I-00146 Roma, Italy
    • 14Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India

    • *sspid@iacs.res.in
    • ,†mssr@iacs.res.in
    • ‡Present address: Department of Physics, University of Arkansas, Fayetteville, Arkansas 72701, USA.
    • §Present address: Uppsala University, Uppsala, Sweden.

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    Vol. 116, Iss. 9 — 4 March 2016

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    Images

    • Figure 1
      Figure 1

      (a) The energy states of the low spin 5d t2g4 Ir5+ ion calculated as a function of SOC. (b) The crystal structure of Ba3ZnIr2O9 and the triangular lattice formed by Ir ions in the a−b plane (lower panel). (c) Experimental and refined NPD patterns [13].

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    • Figure 2
      Figure 2

      (a) Valence band photoemission spectra of BZIO. Total DOS obtained within (b) GGA and (c) GGA+SOC+U. Interaction mechanism in the (d) presence and (e) absence of SOC.

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    • Figure 3
      Figure 3

      (a) High resolution NPD recorded at 1.5 K. (b) Time evolution of muon polarization in Ba3ZnIr2O9 in zero external field at different temperatures. (c) Fluctuation rate of the internal fields vs temperature. Inset: The fast initial relaxation of the muon polarization at low temperature.

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    • Figure 4
      Figure 4

      Temperature dependence of (a) specific heat (C), (b) magnetic specific heat (Cm) capacity after subtracting the lattice contribution, and (c) magnetic entropy. (d) FC-ZFC magnetization measured at 5000 Oe magnetic field fitted using the Curie-Weiss law.

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