相关论文: Critical temperature and the transition from quant…

We have studied the antiferromagnetic order -- disorder transition occurring at $T=0$ in a 2-layer quantum Heisenberg antiferromagnet as the inter-plane coupling is increased. Quantum Monte Carlo results for the staggered structure factor…

We consider quantum Heisenberg ferro- and antiferromagnets on the square lattice with exchange anisotropy of easy-plane or easy-axis type. The thermodynamics and the critical behaviour of the models are studied by the pure-quantum…

Low-temperature thermodynamics of the classical frustrated ferromagnetic spin chain near the ferromagnet-helimagnet transition point is studied by means of mapping to the continuum limit. The calculation of the partition function and spin…

Ferromagnetic transition in three-dimensional double-exchange models is studied by the Monte Carlo method. Critical temperature $T_{\rm c}$ is precisely determined by finite-size scaling analysis. Strong spin fluctuations in this itinerant…

The quantum ferromagnetic transition of itinerant electrons is considered. We give a pedagogical review of recent results which show that zero-temperature soft modes that are commonly neglected, invalidate the standard…

We investigate the critical parameters of an order-disorder quantum phase transitions in the spin-1/2 $J-J'$ Heisenberg and XY antiferromagnets on square lattice. Basing on the excitation gaps calculated by exact diagonalization technique…

We compute the transition temperature $T_c$ and the Ginzburg temperature $T_{\rm G}$ above $T_c$ near a quantum critical point at the boundary of an ordered phase with a broken discrete symmetry in a two-dimensional metallic electron…

The double-layer Heisenberg antiferromagnet with intra- and inter-layer couplings $J$ and $J_\perp$ exhibits a zero temperature quantum phase transition between a quantum disordered dimer phase for $g>g_c$ and a Neel phase with long range…

We consider the finite-temperature phase diagram of the $S = 1/2$ frustrated Heisenberg bilayer. Although this two-dimensional system may show magnetic order only at zero temperature, we demonstrate the presence of a line of…

We analyze the temperature dependence of the entropy of the spin-1/2 Heisenberg model on the three-dimensional simple-cubic lattice, for both the case of antiferromagnetic and ferromagnetic nearest neighbor exchange interactions. Using…

We present the general theory of clean, two-dimensional, quantum Heisenberg antiferromagnets which are close to the zero-temperature quantum transition between ground states with and without long-range N\'{e}el order. For N\'{e}el-ordered…

We demonstrate the presence of an extended critical phase in the transverse field Ising magnet on the triangular lattice, in a regime where both thermal and quantum fluctuations are important. We map out a complete phase diagram by means of…

The nonlinear sigma-model and its generalization on N-component spins, the O(N) model, are considered to describe thermodynamics of a quantum quasi-two-dimensional (quasi-2D) Heisenberg antiferromagnet. A comparison with standard spin-wave…

The scaling of the transition temperature into an ordered phase close to a quantum critical point as well as the order parameter fluctuations inside the quantum critical region provide valuable information about universal properties of the…

We consider the quantum ferromagnetic transition at zero temperature in clean itinerant electron systems. We find that the Landau-Ginzburg-Wilson order parameter field theory breaks down since the electron-electron interaction leads to…

For a system near a quantum critical point (QCP), above its lower critical dimension $d_L$, there is in general a critical line of second order phase transitions that separates the broken symmetry phase at finite temperatures from the…

We study the quantum spin-1/2 Heisenberg model in two dimensions, interacting through a nearest-neighbor antiferromagnetic exchange ($J$) and a ferromagnetic dipolar-like interaction ($J_d$), using double-time Green's function, decoupled…

We study Heisenberg antiferromagnets with nearest- (J1) and third- (J3) neighbor exchange on the square lattice. In the limit of large spin S, there is a zero temperature (T) Lifshitz point at J3 = (1/4) J1, with long-range spiral spin…

We report physical properties of the conductive magnet PdCrO2 consisting of a layered structure with a triangular lattice of Cr3+ ions (S=3/2). We confirmed an antiferromagnetic transition at TN=37.5K by means of specific heat, electrical…

Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown…