title: Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality.
abstract: The spinel FeSc_{2}S_{4} has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.|Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Biffin
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.|Department of Quantum Matter Physics, University of Geneva, 1211 Geneva, Switzerland.
authors.forename: Ch
authors.initials: C
authors.lastname: Rüegg
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Embs
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Guidi
authors.affiliation: Laboratory for Neutron Scattering and Imaging, Paul Scherrer Institut, 5232 Villigen, Switzerland.
authors.forename: D
authors.initials: D
authors.lastname: Cheptiakov
authors.affiliation: Experimental Physics 5, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86159 Augsburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Loidl
authors.affiliation: Experimental Physics 5, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, D-86159 Augsburg, Germany.|Institute of Applied Physics, Academy of Sciences of Moldova, MD-2028 Chisinau, Republic of Moldova.
authors.forename: V
authors.initials: V
authors.lastname: Tsurkan
authors.affiliation: Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
authors.forename: R
authors.initials: R
authors.lastname: Coldea