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Fri, 16 Feb 2001 00:00:00 +0100Fri, 16 Feb 2001 00:00:00 +0100Periodic Bounce for Nucleation Rate at Finite Temperature in Minisuperspace Models
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1182
Abstract: The periodic bounce configurations responsible for quantum tunneling are obtained explicitly and are extended to the finite energy case for minisuperspace models of the Universe. As a common feature of the tunneling models at finite energy considered here we observe that the period of the bounce increases with energy monotonically. The periodic bounces do not have bifurcations and make no contribution to the nucleation rate except the one with zero energy. The sharp first order phase transition from quantum tunneling to thermal activation is verified with the general criterions.J.-Q. Liang; H. J. W. Müller-Kirsten; Y.-B. Zhang; A.V. Shurgaia; S.-P Kou; D.K. Parkpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1182Fri, 16 Feb 2001 00:00:00 +0100Macroscopic Quantum Coherence in Small Antiferromagnetic Particle and the Quantum Interference Effects
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1158
Starting from the Hamiltonian operator of the noncompensated two-sublattice model of a small antiferromagnetic particle, we derive the e effective Lagrangian of a biaxial antiferromagnetic particle in an external magnetic field with the help of spin-coherent-state path integrals. Two unequal level-shifts induced by tunneling through two types of barriers are obtained using the instanton method. The energy spectrum is found from Bloch theory regarding the periodic potential as a superlattice. The external magnetic field indeed removes Kramers' degeneracy, however a new quenching of the energy splitting depending on the applied magnetic field is observed for both integer and half-integer spins due to the quantum interference between transitions through two types of barriers.Yi-Hang Nie; Y.-B. Zhang; J.-Q. Liang; H.J.W. Müller-Kirsten; F.-C. Pupreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1158Fri, 09 Feb 2001 00:00:00 +0100Enhancement of Quantum Tunneling for Excited States in Ferromagnetic Particles
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/894
A formula suitable for a quantitative evaluation of the tunneling effect in a ferromagnetic particle is derived with the help of the instanton method. The tunneling between n-th degenerate states of neighboring wells is dominated by a periodic pseudoparticle configuration. The low-lying level-splitting previously obtained with the LSZ method in field theory in which the tunneling is viewed as the transition of n bosons induced by the usual(vacuum) instanton is recovered.The observation made with our new result is that the tunneling effect increases at excited states. The results should be useful in analyzing results of experimental tests of macroscopic quantum coherence in ferromagnetic particles.Jiu-Qing Liang; H. J. W. Müller-Kirsten; F. Zimmerschied; Y.-B. Zhang; Jian-Ge Zhou; F.-C. Pupreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/894Mon, 03 Apr 2000 00:00:00 +0200Quantum-classical phase transition of escape rate in biaxial spin particles
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1069
Y.-B. Zhang; J.-Q. Liang; H.J.W. Müller-Kirsten; F.-C. Pupreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1069Fri, 10 Mar 2000 00:00:00 +0100