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Quantum Phase Transition (quantum + phase_transition)

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Physics and Astronomy	100%

Selected Abstracts

Quantum phase transition between antiferromagnetic and charge order in the Hubbard,Holstein model

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010
Johannes Bauer
Abstract We explore the quantum phase transitions between two ordered states in the infinite dimensional Hubbard,Holstein model at half filling. Our study is based on the dynamical mean field theory (DMFT) combined with the numerical renormalization group (NRG), which allows us to handle both strong electron,electron and strong electron,phonon interactions. The transition line is characterized by an effective electron,electron interaction. Depending on this effective interaction and the phonon frequency ,0 one finds either a continuous transition or discontinuous transition. Here, the analysis focuses on the behavior of the system when the electron,electron repulsion U and the phonon-mediated attraction , are equal. We first discuss the adiabatic and antiadiabatic limiting cases. For finite ,0 we study the differences between the antiferromagnetic (AFM) and charge order, and find that when present the AFM state has a lower energy on the line. [source]

Quantum phase transition in a spin-½ XX chain with three-spin and uniform long-range interactions

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2005
Ping Lou
Abstract A spin-½ XX chain with three-spin and uniform long-range interactions among the z components of the spins is constructed. Based upon the model, using the Jordan,Wigner transformation, the thermodynamic quantities and spin transports of the system are evaluated exactly. The phase diagram together with the key parameters characterizing quantum phase transitions is presented. It is noted that, similarly to classical first-order phase transitions, there are also the metastable states "supercooled" and "superheated" in the first-order quantum phase transitions. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Magnetic-field-driven quantum criticality and thermodynamics in trimerized spin-1/2 isotropic XY chain with three-spin interactions

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2010
L. J. Ding
Abstract The quantum criticality and thermodynamics for the trimerized spin-1/2 isotropic XY chain with three-spin interactions in an external magnetic field are investigated by means of the Green's function theory combined with Jordan,Wigner transformation. The ground-state phase diagrams are explored, in which various phases are identified and described by typical M,h curves. Therein, two cusps emerge for strong three-spin interactions in two gapless phases at low and high fields, respectively. Moreover, the spin correlations and two-site entanglement entropy are calculated for a further understanding of quantum phase transition (QPT). It is also found that the magnetic-field-driven quantum criticality is closely related to the energy spectrum, in which an energy gap responsible for the appearance of 1/3 magnetization plateau can be opened up by three-spin interactions. The critical behavior disappears when the temperature becomes nonzero, yielding only a crossover behavior. In addition, the gapped low-lying excitations are responsible for the observed thermodynamic behaviors, wherein a structure with three peaks in the temperature dependence of specific heat is unveiled. [source]

Quantum criticality of Ce1,xLaxRu2Si2: The magnetically ordered phase

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010
Stéphane Raymond
Abstract We report specific heat and neutron scattering experiments performed on the system Ce1,xLaxRu2Si2 on the magnetic side of its quantum critical phase diagram. The Kondo temperature does not vanish at the quantum phase transition and elastic scattering indicates a gradual localization of the magnetism when x increases in the ordered phase. [source]

Phase diagram of a thin Heisenberg antiferromagnetic film

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 9 2007
J. Cabral Neto
Abstract We investigate the thickness dependence of the Néel temperature of a thin quantum spin-1/2 Heisenberg antiferromagnetic film as a function of the magnetic field on a simple cubic lattice. The Néel temperature TN(H, ,) is obtained by using the framework of the effective-field theory for films consisting of , = 2, 3, 5, 10 and , (bulk) interacting layers. We present the phase diagram of T versus H in the whole range of the magnetic field for several values of ,. A continuous phase-transition line separating the antiferromagnetic and ferromagnetic phases is observed. The critical temperature TN(H, ,) of the film is smaller than the corresponding bulk critical temperature (H) , TN(H, ,) of the infinite system, which has been analyzed recently by Bublitz Filho and de Sousa [Phys. Lett. A 323, 9 (2004)]; as , is increased, TN(H, ,) also increases and approaches (H) for large values of ,. We have, also, studied the quantum phase transition where three critical fields were found: Hc(,) = 6.224 for , , 3 (three-dimensional regime), Hc(, = 2) = 5.210 (intermediate regime) for , = 2 and, finally, the two-dimensional regime at , = 1 with Hc(, = 1) = 4.194. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Short-range ±J interaction Ising spin glass in a transverse field on a Bethe lattice: a quantum-spherical approach

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2006
T. K. Kope
Abstract We consider the short-range interaction disordered quantum Ising model with symmetric binary ±J bond distribution on the Bethe lattice (with coordination number z). The system exhibits quantum phase transition separating the spin glass and disordered phases where the quantum effect are regulated by a param- eter , describing the transverse field. By introducing a mapping of the quantum Hamiltonian of the model onto a soft-spin action we consider it truncated version in a form of the solvable quantized spherical model. Quantum dynamics is examined via various correlation functions on the infinite tree which are evaluated in a closed form. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Quantum phase diagram for homogeneous Bose-Einstein condensate

ANNALEN DER PHYSIK, Issue 4 2005
H. Kleinert
Abstract We calculate the quantum phase transition for a homogeneous Bose gas in the plane of s -wave scattering length as and temperature T. This is done by improving a one-loop result near the interaction-free Bose-Einstein critical temperature Tc(0) with the help of recent high-loop results on the shift of the critical temperature due to a weak atomic repulsion based on variational perturbation theory. The quantum phase diagram shows a nose above Tc(0), so that we predict the existence of a reentrant transition above Tc(0), where an increasing repulsion leads to the formation of a condensate. [source]