arXiv subjects

Antônio R. Moura

Publications and source records attributed to Antônio R. Moura.

3 recordsLinked to original sources

arXiv2022

Spin current injection at magnetic insulator/superconductor interfaces

Opposite to the common idea of a magnetic order requirement to obtain spin current propagation, materials with no magnetic ordering have also been revealed to be efficient spin conductors. In this work, we investigate the spin current injection at the interface between a magnetic insulator and a superconductor. We are mainly interested in the paramagnetic insulator/superconductor interface however, our model also describes the ferromagnetic phase. We used the Schwinger bosonic formalism to describe the magnetic insulator and standard BCS theory was applied to treat the superconductor layer. In the normal-metal limit, our results are in agreement with the expected ones. For example, we found the correct spin current behavior $I\approx T^{3/2}$ at low temperature. In addition, our model shows a pronounced peak in the spin current injection at temperatures close to the superconductor transition temperature due to the superconducting quasiparticle coherence. The role of magnetic fields in the spin current injection is also investigated.

cond-mat.supr-con↗

arXiv2013

Phase transitions in the two-dimensional Anisotropic Biquadratic Heisenberg Model

In this paper we study the influence of the single-ion anisotropy in the two-dimensional biquadratic Heisenberg model (ABHM) on the square lattice at zero and finite low temperatures. It is common to represent the bilinear and biquadratic terms by $J_1=J\cosθ$ and $J_2=J\sinθ$, respectively, and it is well documented the many phases present in the model as function of $θ$. However we have adopted a constant value for the bilinear constant ($J_1=1$) and small values of the biquadratic term ($|J_2| D_c$, the excited states are gapped and there is no spin long-range order (LRO) even at zero temperature. Using Schwinger bosonic representation and Self-Consistent Harmonic Approximation (SCHA), we have studied the quantum and thermal phase transitions as a function of the bilinear and biquadratic constants.

cond-mat.str-el↗

arXiv2013

Study of the bilinear biquadratic Heisenberg model on a honeycomb lattice via Schwinger bosons

We analyze the biquadratic bilinear Heisenberg magnet on a honeycomb lattice via Schwinger boson formalism. Due to their vulnerability to quantum fluctuations, non conventional lattices (kagome, triangular and honeycomb for example) have been cited as candidates to support spin liquid states. Such states without long range order at zero temperature are known in one-dimensional spin models but their existence in higher dimensional systems is still under debate. Biquadratic interaction is responsible for various possibilities and phases as it is well-founded for one-dimensional systems. Here we have used a bosonic representation to study the properties at zero and finite low temperatures of the biquadratic term in the two-dimensional hexagonal honeycomb lattice. The results show a ordered state at zero temperature but much more fragile than that of a square lattice; the behavior at finite low temperatures is in accordance with expectations.

cond-mat.str-el↗