title: Pressure-induced quantum phase transition in the spin-liquid TlCuCl3.
abstract: The condensation of magnetic quasiparticles into the nonmagnetic ground state has been used to explain novel magnetic ordering phenomena observed in quantum spin systems. We present neutron scattering results across the pressure-induced quantum phase transition and for the novel ordered phase of the magnetic insulator TlCuCl3, which are consistent with the theoretically predicted two degenerate gapless Goldstone modes, similar to the low-energy spin excitations in the field-induced case. These novel experimental findings complete the field-induced Bose-Einstein condensate picture and support the recently proposed field-pressure phase diagram common for quantum spin systems with an energy gap of singlet-triplet nature.
authors.affiliation: Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institute, 5232 Villigen PSI, Switzerland. christian.rueegg@psi.ch
authors.forename: Ch
authors.initials: Ch
authors.lastname: Rüegg
authors.forename: A
authors.initials: A
authors.lastname: Furrer
authors.forename: D
authors.initials: D
authors.lastname: Sheptyakov
authors.forename: Th
authors.initials: T
authors.lastname: Strässle
authors.forename: K W
authors.initials: KW
authors.lastname: Krämer
authors.forename: H-U
authors.initials: HU
authors.lastname: Güdel
authors.forename: L
authors.initials: L
authors.lastname: Mélési