Muons and magnets

Abstract:

Y-kapellasite [ ${\mathrm{Y}}_3{\mathrm{Cu}}_9{(\mathrm{OH})}_{19}{\mathrm{Cl}}_8$ ], which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3,1/3)$ magnetic order [Hering , ], but its magnetic interaction values place it close to a phase boundary to a spin liquid state [Chatterjee , ]. Our $\mathrm{\mu }\mathrm{SR}$ measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at 2.3 GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder.

Abstract:

Hydrogels containing C=O groups and calcium cations show an unexpected paramagnetic effect that may have biomedical applications.

Abstract:

The F-μ-F state provides a unique signature in muon spin rotation data and is observed in many fluorides. It gives rise to a characteristic oscillatory muon polarization that results from entanglement between the spins of the muon and nearby fluorine nuclei. If the muon hops from site to site, then the relaxation of this oscillatory signal can increase. The usual method to treat muon hopping in fluorides assumes the strong-collision approximation, which is then used to dynamicize the standard F-μ-F relaxation function. This approach presupposes Markovian dynamics and so neglects the quantum entanglement between a muon and a neighbouring spin to which it may still be strongly coupled, even after a hopping event. Entanglement that persists between a hopping event becomes even more important to include in the case when a muon subsequently hops back to its initial position. This article demonstrates the effect of including these coherent effects which results in dynamics that depart from those that are calculated using the strong-collision approximation.