title: Possible observation of highly itinerant quantum magnetic monopoles in the frustrated pyrochlore Yb2Ti2O7.
abstract: The low-energy elementary excitations in frustrated quantum magnets have fascinated researchers for decades. In frustrated Ising magnets on a pyrochlore lattice possessing macroscopically degenerate spin-ice ground states, the excitations have been discussed in terms of classical magnetic monopoles, which do not contain quantum fluctuations. Here we report unusual behaviours of magneto-thermal conductivity in the disordered spin-liquid regime of pyrochlore Yb2Ti2O7, which hosts frustrated spin-ice correlations with large quantum fluctuations owing to pseudospin-1/2 of Yb ions. The analysis of the temperature and magnetic field dependencies shows the presence of gapped elementary excitations. We find that the gap energy is largely suppressed from that expected in classical monopoles. Moreover, these excitations propagate a long distance without being scattered, in contrast to the diffusive nature of classical monopoles. These results suggests the emergence of highly itinerant quantum magnetic monopole, which is a heavy quasiparticle that propagates coherently in three-dimensional spin liquids.
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.|Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Tokiwa
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamashita
authors.affiliation: Department of Physics, Gakushuin University, Mejiro, Toshima-ku, Tokyo 171-8588, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Udagawa
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
authors.forename: S
authors.initials: S
authors.lastname: Kittaka
authors.affiliation: Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sakakibara
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: D
authors.initials: D
authors.lastname: Terazawa
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Shimoyama
authors.affiliation: Research Center for Low Temperature and Materials Science, Kyoto University, Kyoto 606-8501, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Terashima
authors.affiliation: Department of Physics, School of Science and Technology, Meiji University, Higashi-mita, Tama-ku, Kawasaki 214-8571, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Yasui
authors.affiliation: Department of Advanced Materials Science, University of Tokyo, Kashiwa 277-8561, Japan.
authors.forename: T
authors.identifier: http://orcid.org/0000-0001-5831-4924
authors.initials: T
authors.lastname: Shibauchi
authors.affiliation: Department of Physics, Kyoto University, Kyoto 606-8502, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Matsuda