Bose glass and Mott glass of quasiparticles in a doped quantum magnet

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Abstract

The low-temperature states of bosonic fluids exhibit fundamental quantum effects at the macroscopic scale: the best-known examples are Bose–Einstein condensation and superfluidity, which have been tested experimentally in a variety of different systems. When bosons interact, disorder can destroy condensation, leading to a ‘Bose glass’. This phase has been very elusive in experiments owing to the absence of any broken symmetry and to the simultaneous absence of a finite energy gap in the spectrum. Here we report the observation of a Bose glass of field-induced magnetic quasiparticles in a doped quantum magnet (bromine-doped dichloro-tetrakis-thiourea-nickel, DTN). The physics of DTN in a magnetic field is equivalent to that of a lattice gas of bosons in the grand canonical ensemble; bromine doping introduces disorder into the hopping and interaction strength of the bosons, leading to their localization into a Bose glass down to zero field, where it becomes an incompressible Mott glass. The transition from the Bose glass (corresponding to a gapless spin liquid) to the Bose–Einstein condensate (corresponding to a magnetically ordered phase) is marked by a universal exponent that governs the scaling of the critical temperature with the applied field, in excellent agreement with theoretical predictions. Our study represents a quantitative experimental account of the universal features of disordered bosons in the grand canonical ensemble.

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Figure 1: Sketch of the bosonic phases of DTN and Br-doped DTN.
Figure 2: Thermodynamic properties of the magnetic Bose glass and BEC phases.
Figure 3: Phase diagrams in the field–temperature plane.
Figure 4: Specific heat scaling and Mott glass.
Figure 5: Critical temperature scaling close to the zero-temperature critical fields.

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Acknowledgements

Work at the High Magnetic Field Laboratory at the Physics Institute of the University of São Paulo was supported in part by the Brazilian agencies FAPESP and CNPq. Measurements at the NHMFL High B/T and pulsed field facilities were supported by NSF grant DMR 0654118, by the State of Florida, and by the DOE. Work at LANL was supported by the NSF, and by the DOE's Laboratory Directed Research and Development programme under 20100043DR. C.F.M. acknowledges support by UEFISCDI (project RP-10). The numerical simulations were performed on the computer facilities of the NCCS at the Oak Ridge National Laboratories, and supported by INCITE Award MAT013 of the Office of Science, DOE. Further theory work was supported by the DOE (grant DE-FG03-01ER45908 and DE-FG02-05ER46240), the NSF (grant DMR-1006985) and by the Robert A. Welch Foundation (grant C-1411).

Author information

R.Y., S.H. and T.R. performed the numerical simulations and the theoretical analysis; L.Y., N.S.S., J.S.X. and C.H. performed the susceptibility measurements; A.P.-F. and N.F.O. synthesized the samples and performed the d.c. magnetization measurements; A.S., C.F.M., F.W., R.M., E.-D.M. and V.S.Z. performed the specific heat measurements; and B.L.S. performed the X-ray measurements. V.S.Z. coordinated the experimental efforts and T.R. the theoretical ones. T.R. wrote the manuscript, with the contributions of all the authors.

Correspondence to Tommaso Roscilde.

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Yu, R., Yin, L., Sullivan, N. et al. Bose glass and Mott glass of quasiparticles in a doped quantum magnet. Nature 489, 379–384 (2012) doi:10.1038/nature11406

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