Spin Waves and Quantum Criticality in the Frustrated

Submitted for the MAR08 Meeting of The American Physical Society Spin Waves and Quantum Criticality in the Frustrated XY Pyrochlore Antiferromagnet Er2Ti2O7 JACOB RUFF, PATRICK CLANCY, BRUCE GAULIN, HANNA DABKOWSKA, MEHMET RAMAZANOGLU, McMaster University, JASON GARDNER, NCNR, ALEX BOURQUE, MARY ANNE WHITE, Dalhousie University, YIMING QIU, JOHN COPLEY, NCNR — We report recent single crystal neutron scattering measurements of the XY pyrochlore antiferromaget Er2Ti2O7, in zero and non-zero magnetic field applied along the (110) direction. Previous results show a magnetically-ordered ground state which is suggested to be stabilized by an unusual order-by-disorder mechanism driven by quantum fluctuations [1]. We present measurements of the low-lying spin excitations of this system, revealing Goldstone modes previously thought to be absent [1]. Also, we explore the response of the ground state to applied magnetic fields, which are shown to induce a quantum phase transition separating the low-field antiferromagnetically ordered phase from the high-field polarized phase. [1] J.D.M. Champion et al. “Er2Ti2O7: Evidence of quantum order by disorder in a frustrated antiferromagnet” PRB 68 (2003) Jacob Ruff McMaster University Date submitted: 01 Dec 2007 Electronic form version 1.4