The full Dicke model describes a system of N identical two level-atoms coupled to a single mode quantized bosonic field. The model considers rotating and counter-rotating coupling terms between the atoms and the bosonic field, with coupling constants g1 and g2, for each one of the coupling...

In this work we study two different spin-boson models. Such models are generalizations of the Dicke model, it means they describe systems of N identical two-level atoms coupled to a single-mode quantized bosonic field, assuming the rotating wave approximation. In the first model, we consider the...

In this paper, we investigate quantum correlations (QCs) and quantum phase transition (QPT) in the Ising model with Dzyaloshinskii–Moriya (DM) interaction by employing the quantum renormalization group method. The results show that some quantum correlation measures can effectively exhibit the...

The two-magnon-bound-state mass gap m2 for the two-dimensional quantum Ising model was investigated by means of the numerical diagonalization method; the low-lying spectrum is directly accessible via the numerical diagonalization method. It has been claimed that the ratio m2/m1 (m1: one-magnon...

We have studied the anisotropic two-dimensional nearest-neighbor Ising model with competitive interactions in both uniform longitudinal field H and transverse magnetic field Ω. Using the effective-field theory (EFT) with correlation in cluster with N=1 spin we calculate the thermodynamic...

The quantum phase transitions (QPTs) and magnetization plateau properties, together with magnetocaloric effect (MCE) of the tetrameric chain are investigated by means of Green’s function theory. We reveal the uniform, dimeric and gapped (gapless) tetrameric phases, which are explicitly...

We report on the fact that microscopically enforcing fulfillment of thermodynamics’ third law on a system of fermions automatically yields the values of the external parameter (here coupling strengths in the pertinent Hamiltonian) at which quantum phase transitions take place. Our...

Recent developments of the study on quantum mechanical effects on condensed matter phenomena are overviewed from the viewpoint of numerical investigations. Various phases and phase transitions inherent to quantum mechanical interactions are reviewed. Quantum mechanical dynamics in nanoscale...

The one-dimensional XXZ model (s=12) in a transverse field, with uniform long-range interactions among the transverse components of the spins, is studied. The model is exactly solved by introducing the Jordan–Wigner transformation and the integral Gaussian transformation. The complete critical...

A real-space renormalization-group approach is used to investigate the zero temperature phase diagram of the Kondo necklace (KN) model in the presence of an Ising-like anisotropy parameter (δ). In the full anisotropic case, δ=1, this approach yields a quantum critical point (QCP) separating an...