Minhas Publicações

Abstract: We perform a comparative study of the electronic structures and electrical resistivity properties of black (A17) and of pressurized gray (A7) phosphorus, showing band-selective Kondoesque electronic reconstruction in these layered p-band phosphorus allotropes. Based on density functional dynamical mean-field theory calculations, we showthat gray phosphorus can host a three-dimensional Kondo semimetal to a Fermi liquid phase crossover under anisotropic compression, which lifts in-layer orbital degeneracy. Therein, the 3p spectrum is almost unaffected both in the semiconducting and semimetallic Kondo phases, however in the Fermi liquid regime strong electronic reconstruction is predicted to exist in the orbital nematic phase of compressed gray phosphorus. These findings contribute to the microscopic understanding of the role played by dynamical multiorbital electronic interactions in the low energy spectrum of correlated semiconductors and topological semimetals.

Abstract: In this paper we have studied the stabilization of the long-range order in (z; x)-plane of two isotropic Heisenberg ferromagnetic monolayers coupled by a short-range exchange interaction (J⊥), by a long range dipole-dipole interactions and a magnetic field. We have applied a magnetic field along of the z-direction to study the thermodynamic properties above the critical temperature. The dispersion relation 𝜔 and the magnetization are given as function of dipolar anisotropy parameter defined as Ed = (g𝜇)2S∕a3J∥ and for other Hamiltonian parameters, and they are calculated by the double-time Zubarev-Tyablikov Green’s functions in the random-phase approximation (RPA). The results show that the system is unstable for values of Ed ≥ 0.012 with external magnetic field ranging between H∕J∥ = 0 and 10−3. The instability appears for Ed larger then Ec d = 0.0158 with H∕J∥ = 10−5, Ecd = 0.02885 with H∕J∥ = 10−4, and Ec d = 0.115 with H∕J∥ = 10−3, i.e., a small magnetic field is sufficient to maintain the magnetic order in a greater range of the dipolar interaction.

Abstract: We investigate anisotropic electronic structure and thermal transport properties of bulk black phosphorus (BP). Using density functional dynamical mean-field theory we first derive a correlation-induced electronic reconstruction, showing band-selective Kondoesque physics in this elemental p-band material. The resulting correlated picture is expected to shed light onto the temperature and doping dependent evolution of resistivity, Seebeck coefficient, and thermal conductivity, as seen in experiments on bulk single crystal BP. Therein, large anisotropic particle-hole excitations are key to consistently understand thermoelectric transport responses of pure and doped BP.

We reveal the emergence of metallicKondo clouds in an atomistic carbon quantum dot, realized as a single-atom junction in a suitably patterned graphene nanoflake. Using density functional dynamical mean-field theory (DFDMFT) we show how correlation effects lead to striking features in the electronic structure of our device, and how those are enhanced by the electron-electron interactions when graphene is patterned at the atomistic scale. Our setup provides a well-controlled environment to understand the principles behind the orbital-selective Kondo physics and the interplay between orbital and spin degrees of freedom in carbon-based anomaterials, which indicate new pathways for spintronics in atomically atterned graphene.

Abstract: Mid-infrared (MIR) sideband generation on a near infrared (NIR) optical carrier is demonstrated within a quantum cascade laser (QCL). By employing an externally injected NIR beam, ENIR, that is resonant with the interband transitions of the quantum wells in the QCL, the nonlinear susceptibility is enhanced, leading to both frequency mixing and sideband generation. A GaAs-based MIR QCL (EQCL = 135 meV) with an aluminumreinforced waveguide was utilized to overlap the NIR and MIR modes with the optical nonlinearity of the active region. The resulting difference sideband (ENIR – EQCL) shows a resonant behavior as a function of NIR pump wavelength and a maximum second order nonlinear susceptibility, χ(2), of ~1 nm/V was obtained. Further, the sideband intensity showed little dependence with the operating temperature of the QCL, allowing sideband generation to be realized at room temperature.

Abstract: We theoretically investigate the electronic transport properties of two closely spaced L-shaped semiconductor quantum wires, for different configurations of the output channel widths as well as the distance between the wires. Within the effective-mass approximation, we solve the time-dependent Schr€ odinger equation using the split-operator technique that allows us to calculate the transmission probability, the total probability current, the conductance, and the wave function scattering between the energy subbands. We determine the maximum distance between the quantum wires below which a relevant non-zero transmission is still found. The transmission probability and the conductance show a strong dependence on the width of the output channel for small distances between the wires.