arXiv subjects

A. Nafis Arafat

Publications and source records attributed to A. Nafis Arafat.

3 recordsLinked to original sources

arXiv2025

Theory of two-component superfluidity of microcavity polaritons

We develop a microscopic mean-field theory describing the coexistence of Bose-Einstein condensates of upper and lower polaritons (UP/LP) in a semiconductor microcavity. Incorporating interbranch scattering within a modified polariton Hamiltonian, we introduce a phenomenological population-split parameter $α$ that quantifies the relative LP/UP occupations. At zero detuning, the critical temperature becomes independent of $α$, converging to a single value that marks the balanced, resonant regime. Away from resonance, variations in $α$ lead to distinctive and experimentally resolvable changes in both the sound velocity $c_s$ and critical temperature $T_c$, relative to the single-component (LP-only) condensate limit. The system under study consists of excitons confined in a transition metal dichalcogenide (TMDC) monolayer, particularly WSe$_2$ embedded within a planar optical microcavity of GaAs where they strongly couple to cavity photons. Our analysis focuses on monolayer WSe$_2$ embdedded in a GaAs microcavity. We present results for GaAs/AlGaAs quantum wells embedded in a GaAs microcavity in the Appendix. While mean-field in scope, the framework provides analytic benchmarks and physical insight for future treatments that include dissipation and fluctuations in nonequilibrium polariton superfluids.

cond-mat.quant-gas↗

arXiv2024

Superfluidity of indirect momentum space dark dipolar excitons in a double layer with massive anisotropic tilted semi-Dirac bands

We have theoretically investigated the spin- and valley-dependent superfluidity properties of indirect momentum space dark dipolar excitons in double layers with massive anisotropic tilted semi-Dirac bands in the presence of circularly polarized irradiation. An external vertical electric field is also applied to the structure and is responsible for tilting and gap opening for the band structure. For our calculations we used the parameters of a double layer of 1T$^\prime$-MoS$_2$. Closed form analytical expressions are presented for the energy spectrum for excitons, their associated wave functions and binding energies. Additionally, we examine the effects which the intensity and frequency of circularly polarized irradiation has for 1T$^\prime$-MoS$_2$ on the effective mass of the excitons since it has been demonstrated that the application of an external high-frequency dressing field tailors the crucial electronic including the exciton binding energy, as well as the critical temperature for superfluidity. We also calculate the sound velocity in the anisotropic weakly-interacting Bose gas of two-component indirect momentum space dark excitons for a double layer of 1T$^\prime$-MoS$_2$. We show that the critical velocity of superfluidity, the spectrum of collective excitations, concentrations of the superfluid and normal component, and mean field critical temperature for superfluidity are anisotropic and formed by a two-component system. The critical temperature for superfluidity is increased when the exciton concentration and interlayer separation are increased. We propose the use of phonon-assisted photoluminescence to experimentally confirm directional superfluidity of indirect momentum space dark excitons in a double layer with massive anisotropic tilted semi-Dirac bands.

cond-mat.mes-hall↗

arXiv2023

Stress control in non-ideal topological Maxwell lattices via geometry

Topological mechanical metamaterials have demonstrated exotic and robust mechanical properties which led to promising engineering applications. One of such properties is the focusing of stress at the interface connecting domains of topological Maxwell lattices of opposite topological polarizations, which protects the bulk of the material against fracturing. Here we generalize this theory to non-ideal Maxwell lattices, incorporate real material features that leads to interactions beyond previous ideal models. By quantitative analysis of stress distributions of topological Maxwell lattices with self-stress interfaces theoretically and computationally, we propose a design rule that minimizes stress in the bulk of the material. This design rule can guide the realization of stress focusing and fracturing protection in real materials.

cond-mat.soft↗