title: Emergence of highly degenerate excited states in the frustrated magnet MgCr2O4.
abstract: High degeneracy in ground states leads to the generation of exotic zero-energy modes, a representative example of which is the formation of molecular spin-liquid-like fluctuations in a frustrated magnet. Here we present single-crystal inelastic neutron scattering results for the frustrated magnet MgCr(2)O(4), which show that a common set of finite-energy molecular spin excitation modes is sustained in both the liquid-like phase above magnetic ordering temperature T(N) and an ordered phase with an extremely complex magnetic structure below T(N). Based on this finding, we propose the concept of high degeneracy in excited states, which promotes local resonant elementary excitations. This concept is expected to have ramifications on our understanding of excitations in many complex systems, including not only spin but also atomic liquids, complex order systems, and amorphous systems.
authors.affiliation: Department of Physics, Tohoku University, Aoba, Sendai 980-8578, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Tomiyasu
authors.affiliation: Department of Physics and Mathematics, Aoyama-Gakuin University, Sagamihara 229-8558, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yokobori
authors.affiliation: Department of Physics and Mathematics, Aoyama-Gakuin University, Sagamihara 229-8558, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Kousaka
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom.
authors.forename: R I
authors.initials: RI
authors.lastname: Bewley
authors.affiliation: ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom.
authors.forename: T
authors.initials: T
authors.lastname: Guidi
authors.affiliation: Department of Physics, College of Science and Technology (CST), Nihon University, Chiyoda, Tokyo 101-8308, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Watanabe
authors.affiliation: Department of Physics and Mathematics, Aoyama-Gakuin University, Sagamihara 229-8558, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Akimitsu
authors.affiliation: Institute of Materials Structure Science, High Energy Accelerator Research Organization, Oho, Tsukuba 305-0801, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Yamada