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Title: Does LiHo_xY_1-xF4 have a true spin-glass phase and quantum transition?
Plain: LiHoYF4 is a crystal in which magnetic holmium ions are diluted by nonmagnetic yttrium, and a sideways field adds quantum fluctuations. Experiments disagree on whether its low-temperature state is a genuine spin glass, so it is unclear whether it realizes a quantum spin-glass transition.
Precise: In LiHo_xY_1-xF4 with x of about 0.17 to 0.2 (dipolar Ising moments along c, transverse field $H_t$ perpendicular to c), determine whether the nonlinear susceptibility diverges at a finite $T_g(H_t)$ and whether $T_g(H_t)$ ends at a $T = 0$ quantum critical point, given the random longitudinal fields generated by $H_t$ and the hyperfine coupling to Ho nuclei. An answer is a measured phase boundary with critical exponents, or evidence that no thermodynamic glass transition exists.
Settled by: Equilibrium nonlinear ac susceptibility and noise measurements below 0.1 K on samples of controlled x, analyzed by critical scaling and compared with Monte Carlo of the dipolar model including hyperfine terms.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Jonsson et al. (PRL 2007) reported no glass transition at $x = 0.167$ while Ancona-Torres et al. (PRL 2008) reported one; field-induced random fields complicate the transverse-field phase diagram.
Posed since: (empty)