Fizika Nizkikh Temperatur: Volume 44, Number 11 (November 2018), p. 1501-1509 ( to contents , go back )
Quantum quench for the biaxial spin system
B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
Max-Planck-Institut für Physik komplexer Systeme, 38 Nöthnitzer Str., D-01187, Dresden, Germany
Received May 14, 2018, published online September 26, 2018
Dynamical non-equilibrium effects after a quantum quench in a quantum spin system, which permits exact analytical solution in both closed and open cases, are studied. The exact analytic results are obtained for the biaxial paramagnet, both for the “easy axis”- and the “easy-plane”-like situations, and for the field directed along both principal axes of the system. Quantum quench of the external magnetic field produces a nonlinear response. For the closed system the average magnetic moment oscillates with time and with the final value of the external field. Such oscillations exist also for the open system, connected to the bath, in the dynamical regime. For the steady-state regime in the open case the oscillations are damped. Non-equilibrium effects yield specific hysteresis phenomena in the considered single spin system.
Key words: quantum quench, biaxial magnetic anisotropy, dynamical hysteresis.