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Detection of a Disorder-Induced Bose-Einstein Condensate in a Quantum Spin Material at High Magnetic Fields

A. Orlova, H. Mayaffre, S. Krämer, M. Dupont, S. Capponi, N. Laflorencie, A. Paduan-Filho, and M. Horvatić
Phys. Rev. Lett. 121, 177202 – Published 25 October 2018
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    Abstract

    The coupled spin-1 chains material NiCl2−4SC(NH2)2 (DTN) doped with Br impurities is expected to be a perfect candidate for observing many-body localization at high magnetic field: the so-called “Bose glass,” a zero-temperature bosonic fluid, compressible, gapless, incoherent, and short-range correlated. Using nuclear magnetic resonance, we critically address the stability of the Bose glass in doped DTN, and find that it hosts a novel disorder-induced ordered state of matter, where many-body physics leads to an unexpected resurgence of quantum coherence emerging from localized impurity states. An experimental phase diagram of this new “order-from-disorder” phase, established from nuclear magnetic resonance T1−1 relaxation rate data in the 13±1% Br-doped DTN, is found to be in excellent agreement with the theoretical prediction from large-scale quantum Monte Carlo simulations.

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    • Received 2 May 2018

    DOI:https://doi.org/10.1103/PhysRevLett.121.177202

    © 2018 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Quantum phase transitions
    1. Physical Systems
    1-dimensional spin chainsAntiferromagnetsBose-Einstein condensatesDisordered systemsGlasses
    1. Techniques
    Nuclear magnetic resonanceQuantum Monte Carlo
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    A. Orlova1, H. Mayaffre1, S. Krämer1, M. Dupont2, S. Capponi2, N. Laflorencie2,*, A. Paduan-Filho3, and M. Horvatić1,†

    • 1Laboratoire National des Champs Magnétiques Intenses, LNCMI-CNRS (UPR3228), EMFL, UGA, UPS, and INSA, Boîte Postale 166, 38042, Grenoble Cedex 9, France
    • 2Laboratoire de Physique Théorique, IRSAMC, Université de Toulouse, CNRS, UPS, 31062 Toulouse, France
    • 3Instituto de Física, Universidade de São Paulo, 05315-970 São Paulo, Brazil

    • *laflo@irsamc.ups-tlse.fr
    • †mladen.horvatic@lncmi.cnrs.fr

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    Vol. 121, Iss. 17 — 26 October 2018

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    • Figure 1
      Figure 1

      (a) Doping Br to replace Cl atoms modifies locally both the affected bond, J→J′, and the single-ion anisotropy of the nearest spin, D→D′, denoted, respectively, by red bonds and dots in the three-dimensional structure shown in (b). (c) The canted spin polarization in the BEC phase is marginally perturbed by doping. (d) In the BEC* phase, the order is formed among partially polarized doped sites, on a fully polarized background of regular spins. (e) In the Bose-glass regime, the canted polarization at doped sites is uncorrelated and fluctuating. The c-axis direction is horizontal in (a) and vertical in (b)–(e).

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    • Figure 2
      Figure 2

      Sketch of the global phase diagram of (a) pure DTN and (b) 13% doped DTNX, where colors denote the BEC (blue) and BEC* (red) phases, and the Bose-glass (BG, yellow) and gapped (green) regimes. (c) Focus on the main BEC* phase. The Tc determined from QMC simulations for 12.5% doping (blue open diamonds) is compared to Tc estimates from the T1−1 NMR data in a (13±1)% doped sample that are shown in Fig. 3: solid red dots and diamonds denote, respectively, the maximum of T1−1(T) and T1−1(H) dependence, reflecting the maximum of the critical spin fluctuations, while orange squares provide the lowest estimate for the Tc, taken to be the point where the T1−1(T) data turn into their BEC regime (see the text). The gray small dots and diamonds are, respectively, the experimental points and the QMC simulation of the BEC phase boundary in the pure DTN, as reported in [23]. Lines are guide to the eyes.

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    • Figure 3
      Figure 3

      (a) Temperature dependence of T1−1 in 13% doped DTNX at selected field values. The strong decrease of T1−1 at low temperature is a signature of the ordered BEC phase, while the relatively broad maximum corresponds to the critical spin fluctuations at the phase transition into this phase. The error bars are less than the symbol size, except for one point. (b) Magnetic field dependence of T1−1 in the vicinity of the phase transition into the ordered phase. Several positions of the 13% doped DTNX phase diagram (solid dots) are compared to the case of much less, 4% doped DTNX (open squares), to show how strongly is the T1−1 peak broadened by increasing the doping-induced disorder.

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