title: Quantum criticality in an organic spin-liquid insulator κ-(BEDT-TTF)2Cu2(CN)3.
abstract: A quantum spin-liquid state, an exotic state of matter, appears when strong quantum fluctuations enhanced by competing exchange interactions suppress a magnetically ordered state. Generally, when an ordered state is continuously suppressed to 0 K by an external parameter, a quantum phase transition occurs. It exhibits critical scaling behaviour, characterized only by a few basic properties such as dimensions and symmetry. Here we report the low-temperature magnetic torque measurements in an organic triangular-lattice antiferromagnet, κ-(BEDT-TTF)2Cu2(CN)3, where BEDT-TTF stands for bis(ethylenedithio)tetrathiafulvalene. It is found that the magnetic susceptibilities derived from the torque data exhibit a universal critical scaling, indicating the quantum critical point at zero magnetic field, and the critical exponents, γ=0.83(6) and νz=1.0(1). These exponents greatly constrain the theoretical models for the quantum spin liquid, and at present, there is no theory to explain the values, to the best of our knowledge.
authors.affiliation: National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Isono
authors.affiliation: National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan.
authors.forename: Taichi
authors.initials: T
authors.lastname: Terashima
authors.affiliation: Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Miyagawa
authors.affiliation: Department of Applied Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
authors.forename: Kazushi
authors.initials: K
authors.lastname: Kanoda
authors.affiliation: National Institute for Materials Science, Tsukuba, Ibaraki 305-0003, Japan.
authors.forename: Shinya
authors.initials: S
authors.lastname: Uji