title: Nonmonotonic dynamics in a frustrated Ising model with time-dependent transverse field.
abstract: We study how the degree of ordering depends on the strength of the thermal and quantum fluctuations in frustrated systems by investigating the correlation function of the order parameter. Concretely, we compare the equilibrium spin correlation function in a frustrated lattice which exhibits a nonmonotonic temperature dependence (reentrant type dependence) with that in the ground state as a function of the transverse field that causes the quantum fluctuation. We find the correlation function in the ground state also shows a nonmonotonic dependence on the strength of the transverse field. We also study the real-time dynamics of the spin-correlation function under a time-dependent field. After sudden decrease in the temperature, we found nonmonotonic changes of the correlation function reflecting the static temperature dependence, which indicates that an effective temperature of the system changes gradually. For the quantum system, we study the dependence of changes of the correlation function on the sweeping speed of the transverse field. Contrary to the classical case, the correlation function varies little in a rapid change of the field, though it shows a nonmonotonic change when we sweep the field slowly.
authors.affiliation: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa-shi, Chiba 277-8581, Japan. shu-t@alice.math.kindai.ac.jp
authors.forename: Shu
authors.initials: S
authors.lastname: Tanaka
authors.forename: Seiji
authors.initials: S
authors.lastname: Miyashita