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...

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...

A reduction procedure, suggested for classical systems some years ago, is extended to systems with quantum-phase transitions with the aim to generate exactly solvable models capturing fluctuation effects beyond the mean field approximation. For the reduced isotropic m-vector quantum models, an...

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...

The p-spin interaction Ising spin glass model in the presence of a transverse field is studied in the large p-limit by means of a convenient operator extension of the cavity fields method avoiding replicas and the Trotter-Suzuki transformation. The results appear quite consistent with those...

A d-dimensional model of multicomponent interacting bosons with spin S and a magnetic moment in the presence of a magnetic field H is studied by means of a large-n limit treatment and a renormalization group approach, in the spirit of critical phenomena theory. Magnetic phase transitions and a...

The low temperature grand canonical critical properties of a d-dimensional n-vector Bose system in the presence of a random field, which behaves like [h∗khk]av ∽ kθ (θ ⩾ 0), are investigated with the use of replica trick and the Hartree approximation. With a boson free particle spectrum,...