Phase Transitions in the Quantum Heisenberg Model

Zero temperature phase transitions in quantum Heisenberg ferromagnets

The purpose of this work is to understand the zero temperature phases, and the phase transitions, of Heisenberg spin systems which can have an extensive, spontaneous magnetic moment; this entails a study of quantum transitions with an order parameter which is also a non-abelian conserved charge. To this end, we introduce and study a new class of lattice models of quantum rotors. We compute thei...

Dynamical quantum phase transitions in the transverse-field Ising model.

A phase transition indicates a sudden change in the properties of a large system. For temperature-driven phase transitions this is related to nonanalytic behavior of the free energy density at the critical temperature: The knowledge of the free energy density in one phase is insufficient to predict the properties of the other phase. In this Letter we show that a close analogue of this behavior ...

Quantum phase transitions in the Bose-Fermi Kondo model

Entanglement in the quantum Heisenberg XY model

We study the entanglement in the quantum Heisenberg XY model in which the so-called W entangled states can be generated for 3 or 4 qubits. By the concept of concurrence, we study the entanglement in the time evolution of the XY model. We investigate the thermal entanglement in the two-qubit isotropic XY model with a magnetic field and in the anisotropic XY model, and find that the thermal entan...

Plaquette Ordered Phase and Quantum Phase Diagram in the Spin-2 J1-J2 Square Heisenberg Model

in the Spin-2 J1-J2 Square Heisenberg Model Shou-Shu Gong, Wei Zhu, D. N. Sheng, Olexei I. Motrunich, and Matthew P. A. Fisher Department of Physics and Astronomy, California State University, Northridge, California 91330, USA Department of Physics, California Institute of Technology, Pasadena, California 91125, USA Department of Physics, University of California, Santa Barbara, California 9310...