Micro-eV neutron spectroscopy in Pr₂Zr₂O₇

Low spin pyrochlores where exchange interactions prevail over dipole-dipole interactions can have substantial quantum fluctuations and perhaps realize quantum spin ice [1-2] with emergent electrodynamics [3]. We have conducted ultra-high-resolution neutron scattering experiment to study the low energy excitation in the quantum spin ice candidate Pr₂Zr₂O₇. The floating zone synthesis procedure was optimized to achieve stoichiometric single crystals with high quality. The local (Q-averaged) response function was mapped versus temperature and energy with a resolution of 3.7 μeV. We observed low energy excitations and a gapless spectrum with temperature dependence into the mK regime that links it to the low temperature thermodynamic properties of Pr₂Zr₂O₇. [1] K. A. Ross et al., Phys. Rev. X 1 (2011) 021002. [2] K. Kimura et al., Nat. Commun. 4 (2013) 1934. [3] M. Hermele et al., Phys. Rev. B 69 (2004) 064404.