arXiv subjects

S. Soleimanikahnoj

Publications and source records attributed to S. Soleimanikahnoj.

5 recordsLinked to original sources

arXiv2021

Density-matrix model for photon-driven transport in quantum cascade lasers

We developed a time-dependent density-matrix model to study photon-assisted (PA) electron transport in quantum cascade lasers. The Markovian equation of motion for the density matrix in the presence of an optical field is solved for an arbitrary field amplitude. Level-broadening terms emerge from microscopic Hamiltonians and supplant the need for empirical parameters that are often employed in related approaches. We show that, in quantum cascade lasers with diagonal design, photon resonances have a pronounced impact on electron dynamics around and above the lasing threshold, an effect that stems from the large spatial separation between the upper and lower lasing states. With the inclusion of PA tunneling, the calculated current density and output power are in good agreement with experiment.

cond-mat.mes-hall↗

arXiv2021

Tunable plasmon-enhanced second-order optical nonlinearity in transition metal dichalcogenide nanotriangles

The development of nanomaterials with a large nonlinear susceptibility is essential for nonlinear nanophotonics. We show that transition-metal-dichalcogenide (TMD) nanotriangles have a large effective second-order susceptibility [$χ^{(2)}$] at mid-infrared to near-infrared frequencies owing to their broken centrosymmetry. $χ^{(2)}$ is calculated within the density-matrix formalism that accounts for dissipation and screening. $χ^{(2)}$ peaks in the vicinity of both two-photon resonances (specified by the geometry) and plasmon resonances (tunable via the carrier density). Aligning the resonances yields the values of $χ^{(2)}$ as high as $10^{-6}$ m/V. These findings underscore the potential of TMD nanotriangles for nonlinear nanophotonics, particularly second-harmonic generation.

physics.optics↗

arXiv2020

Numerically efficient density-matrix technique for modeling electronic transport in midinfrared quantum cascade lasers

We present a numerically efficient density-matrix model applicable to midinfrared quantum cascade lasers. The model is based on a Markovian master equation for the density matrix that includes in-plane dynamics, preserves positivity of the density matrix and does not rely on phenomenologically introduced dephasing times. Nonparabolicity in the bandstructure is accounted for with a three-band k.p model, which includes the conduction, light-hole, and spin-orbit split-off bands. We compare the model to experimental results for QCLs based on lattice-matched as well as strain-balanced InGaAs/InAlAs heterostructures grown on InP. We find that our density-matrix model is in quantitative agreement with experiment up to threshold and is capable of reproducing results obtained using the more computationally expensive nonequilibrium Green's function formalism. We compare our density-matrix model to a semiclassical model where off-diagonal elements of the density matrix are ignored. We find that the semiclassical model overestimates the threshold current density by 29% for a 8.5-um QCL based on a lattice-matched heterostructure and 40% for a 4.6-um QCL based on a strain-balanced heterostructure, demonstrating the need to include off diagonal density matrix elements for accurate description of midinfrared QCLs.

cond-mat.mes-hall↗

arXiv2017

Pseudospin Electronics in Phosphorene Nanoribbons

Zigzag phosphorene nanoribbons are metallic owing to the edge states, whose energies are inside the gap and far from the bulk bands. We show that -- through electrical manipulation of edge states -- electron propagation can be restricted to one of the ribbon edges or, in case of bilayer phosphorene nanoribbons, to one of the layers. This finding implies that edge and layer can be regarded as tunable equivalents of the spin-one-half degree of freedom, i.e., the pseudospin. In both layer- and edge-pseudospin schemes, we propose and characterize a pseudospin field-effect transistor, which can generate pseudospin-polarized current. Also, we propose edge- and layer-pseudospin valves that operate analogously to conventional spin valves. The performance of valves in each pseudospin scheme is benchmarked by the pseudomagnetoresistance (PMR) ratio. The edge-pseudospin valve shows a nearly perfect PMR, with remarkable robustness against device parameters and disorder. These results may initiate new developments in pseudospin electronics.

cond-mat.mes-hall↗

arXiv2017

Tunable Electronic Properties of Multilayer Phosphorene and Its Nanoribbons

We study the effects of a vertical electric field on the electronic band structure and transport in multilayer phosphorene and its nanoribbons. In phosphorene, at a critical value of the vertical electric field ($E_c$), the band gap closes and the band structure undergoes a massive-to-massless Dirac fermion transition along the armchair direction. This transition is observable in quantum Hall measurements, as the power-law dependence of the Landau-level energy on the magnetic field $B$ goes from $\sim (n+1/2)B$ below $E_c$, to $\sim [(n+1/2)B]^{2/3}$ at $E_c$, to $\sim [(n+1/2)B]^{1/2}$ above $E_c$. In multilayer phosphorene nanoribbons (PNRs), the vertical electric field can be employed to manipulate the midgap energy bands that are associated with edge states, thereby giving rise to new device functionalities. We propose a dual-edge-gate PNR structure that works as a quantum switch.

cond-mat.mes-hall↗