Disorder-induced Revival of the Bose-Einstein Condensation at High Magnetic Fields in Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$)*

We theoretically investigate the high magnetic field regime of the disordered quasi-one-dimensional S=1 antiferromagnetic material Ni(Cl$_{1-x}$Br$_x$)$_2$-4SC(NH$_2$). This compound was believed to provide the first experimental realization of the elusive Bose-glass phase in a quantum magnet [1]. I will review our recent experimental and theoretical works [2-5] in which we discovered that this many-body localized phase is actually undermined by the resurgence of long-range order with a condensation of the underlying impurities degree of freedom, leading to a novel “order-by-disorder” mechanism.

[1] R. Yu et al. Nature 489, 379–384 (2012)
[2] A. Orlova et al. Phys. Rev. Lett. 118, 067203 (2017)
[3] M. Dupont et al. Phys. Rev. Lett. 118, 067204 (2017)
[4] M. Dupont et al. Phys. Rev. B 96, 024442 (2017)
[5] A. Orlova et al. (manuscript in preparation)