A one-loop renormalization group treatment is used to investigate the quantum phase transition and the low-temperature critical properties of a planar Heisenberg ferromagnet in a transverse field. The phase diagram, the free energy density and the relevant critical exponents in the influence...

We investigate the role played by symmetry conserving quenched disorder on quantum criticality of a variety of d-dimensional systems with a continuous symmetry order parameter. We employ a non-standard procedure which combines a preliminary reduction to an effective classical random problem and...

The two-time Green’s function equation of motion method is employed to explore the low-temperature properties and crossovers close to the field-induced quantum critical point of a d-dimensional spin- 1/2 easy-plane ferromagnet with longitudinal uniform interactions. This is performed, on the...

A study of the d-dimensional classical Heisenberg ferromagnetic model in the presence of a magnetic field is performed within the two-time Green function’s framework in classical statistical physics. We extend the well known quantum Callen method to derive analytically a new formula for...

We investigate the low-temperature critical properties of a classical Ising model in a transverse field. This is performed by applying the conventional Wilson renormalization group to the related Ginzburg-Landau functional emerging from a Hubbard-Stratonovich transformation. Results in 4–ε...

The low-temperature properties and crossover phenomena of d-dimensional transverse Ising-like systems within the influence domain of the quantum critical point are investigated solving the appropriate one-loop renormalization group equations. The phase diagram is obtained near and at d=3 and...

Criticality of n-vector quantum systems is studied, via a renormalization group treatment, assuming a pair interaction which decays as a power law involving a characteristics parameter θ. Within a “single”-expansion parameter scheme for finite values of θ, a novel fixed point appears for...

The paper is devoted to a sistematic study of the critical behaviour and quantum regime of a wide class of quantum systems on the basis of the Renormalization Group (RG) approach in the large-n limit. It can be considered as a complement to recent perturbative (RG) investigations for the same...

A method for exploring the destruction of long-range order in pure classical systems with continous symmetry is extended to quantum ferroelectrics in the presence of correlated random fields. This allows us to obtain a reliable estimate of the lower critical dimensionality in terms of the...