arXiv subjects

Yasufumi Nakano

Publications and source records attributed to Yasufumi Nakano.

3 recordsLinked to original sources

arXiv2026

Coupled-channel approach to scattering of hybrid excitons

We consider the interactions of hybrid excitons in a two-dimensional semiconductor bilayer, where spatially direct and indirect excitons are hybridized by interlayer charge-carrier tunneling. Starting from a microscopic electron-hole description, we construct realistic pseudopotentials for exciton-exciton interactions and use them as inputs to a coupled-channel scattering integral equation. This enables non-perturbative calculations of hybrid-exciton scattering beyond standard perturbative theories, and highlights the importance of energy-dependent scattering and channel mixing. In particular, we show that the interaction strength of hybrid excitons exhibits a rapid growth with increasing energy, which we find is inherited from their indirect-exciton component. We further demonstrate that dielectric screening affects the direct and indirect channels in distinct ways, leading to markedly different interaction strengths across experimentally relevant dielectric environments. Finally, we show that the hybrid-exciton scattering strength can be electrically tuned via the Stark shift, which controls the direct-indirect detuning and hence the hybridization of the two exciton modes.

cond-mat.mes-hall↗

arXiv2026

Light-enhanced dipolar interactions between exciton polaritons

We consider the scenario of excitons in a semiconductor bilayer that are strongly coupled to cavity photons, leading to the formation of dipolar exciton polaritons (dipolaritons). Using a realistic pseudopotential for the dipolar interactions, we exactly determine the scattering between dipolaritons, accounting for the hybridization between interlayer and intralayer excitons. Similar to conventional non-dipolar polaritons, we find that the light-matter coupling enhances the interactions between dipolaritons by forcing excitons to scatter at energies that would otherwise be forbidden in ordinary exciton-exciton collisions. However, we show that this light enhancement is larger for long-range dipolar interactions than for short-range intralayer interactions, and is sensitive to the (non-uniform) dielectric environment of the bilayer. Crucially, we find that the largest dipolariton interactions are achieved for transition metal dichalcogenide bilayers in vacuum. Our results thus reveal the optimal dipolariton setup for realizing strong photon correlations.

cond-mat.mes-hall↗

arXiv2024

Variational approach to the two-dimensional Bose polaron

An impurity particle interacting with a Bose-Einstein condensate (BEC) leads to the formation of a quasiparticle known as the Bose polaron. We investigate the properties of the two-dimensional Bose polaron, applying a variational ansatz that contains up to three Bogoliubov excitations of the BEC. Similar to its three-dimensional counterpart, we observe the existence of two quasiparticle branches, namely the attractive and the repulsive polarons, at different coupling strengths. We find that their energies agree well with recent quantum Monte Carlo calculations. In particular, we observe that the inclusion of three excitations is crucial to capture the attractive polaron energy towards the regime of strong attraction, where the quasiparticle properties are dominated by few-body correlations. We also calculate the attractive polaron effective mass and residue, where we find significant differences between considering a weakly interacting Bose medium and taking the non-interacting limit, signalling enhanced impurity dressing by excitations in the latter case. By contrast, the spectral weight of the metastable repulsive polaron is largely insensitive to the interactions in the BEC and the number of Bogoliubov excitations. Our model may be experimentally realized in dilute atomic vapors and atomically thin semiconductors.

cond-mat.quant-gas↗