title: Low-energy electrodynamics of novel spin excitations in the quantum spin ice Yb₂Ti₂O₇.
abstract: In condensed matter systems, formation of long-range order (LRO) is often accompanied by new excitations. However, in many geometrically frustrated magnetic systems, conventional LRO is suppressed, while non-trivial spin correlations are still observed. A natural question to ask is then what is the nature of the excitations in this highly correlated state without broken symmetry? Frequently, applying a symmetry breaking field stabilizes excitations whose properties reflect certain aspects of the anomalous state without LRO. Here we report a THz spectroscopy study of novel excitations in quantum spin ice Yb2Ti2O7 under a <001> directed magnetic field. At large positive fields, both right- and left-handed magnon and two-magnon-like excitations are observed. The g-factors of these excitations are dramatically enhanced in the low-field limit, showing a crossover of these states into features consistent with the quantum string-like excitations proposed to exist in quantum spin ice in small <001> fields.
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: LiDong
authors.initials: L
authors.lastname: Pan
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Se Kwon
authors.initials: SK
authors.lastname: Kim
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: A
authors.initials: A
authors.lastname: Ghosh
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Morris
authors.affiliation: 1] Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA [2] NIST Center for Neutron Research, NIST, Gaithersburg, Maryland 20899, USA.
authors.forename: Kate A
authors.initials: KA
authors.lastname: Ross
authors.affiliation: Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1.
authors.forename: Edwin
authors.initials: E
authors.lastname: Kermarrec
authors.affiliation: 1] Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada L8S 4M1 [2] Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada L8S 4M1 [3] Canadian Institute for Advanced Research, 180 Dundas Street W, Toronto, Ontario, Canada M5G 1Z8.
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Gaulin
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: S M
authors.initials: SM
authors.lastname: Koohpayeh
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: Oleg
authors.initials: O
authors.lastname: Tchernyshyov
authors.affiliation: Institute for Quantum Matter, Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
authors.forename: N P
authors.initials: NP
authors.lastname: Armitage