Singlet-triplet excitations and long range entanglement in the spin-orbital liquid candidate FeSc$_2$S$_4$

ORAL

Abstract

Theoretical models of the spin-orbital liquid (SOL) FeSc$_2$S$_4$ have predicted it to be in close proximity to a quantum critical point separating a spin-orbital liquid phase from a long-range ordered magnetic phase. Here, we examine the magnetic excitations of FeSc$_2$S$_4$ through time-domain terahertz spectroscopy under an applied magnetic field. At low temperatures an excitation emerges that we attribute to a singlet-triplet excitation from the SOL ground state. A three-fold splitting of this excitation is observed as a function of applied magnetic field. Using experimentally obtained parameters we compare to existing theoretical models to determine FeSc$_2$S$_4$'s proximity to the quantum critical point and establish FeSc$_2$S$_4$ as a SOL with long-range entanglement.

*Work at Johns Hopkins was supported by the Gordon and Betty Moore Foundation through Grant GBMF2628, the DOE-BES through DE-FG02-08ER46544, and the ARCS Foundation.

–

Authors

  • N.J. Laurita

    • Institute of Quantum Matter, Johns Hopkins University

  • J. Deisenhofer

    • University of Augsburg

  • LiDong Pan

    • Institute of Quantum Matter, Johns Hopkins University

  • C.M. Morris

    • Institute of Quantum Matter, Johns Hopkins University

  • M. Schmidt

    • University of Augsburg

  • M. Johnsson

    • Stockholm University

  • V. Tsurkan

    • University of Augsburg, Academy of Sciences of Moldova

  • A. Loidl

    • University of Augsburg

  • N.P. Armitage

    • Institute of Quantum Matter, Johns Hopkins University