arXiv subjects

Kritika Ghosh

Publications and source records attributed to Kritika Ghosh.

4 recordsLinked to original sources

arXiv2025

Anisotropic exciton-polaritons reveal non-Hermitian topology in van der Waals materials

Topological band theory has expanded into various domains in applied physics, offering significant potential for future technologies. Recent developments indicate that unique bulk band topology perceived for electrons can be realized in a system of light-matter quasiparticles with reduced crystal symmetry by utilizing tunable light-matter interaction. In this work we realize topologically non-trivial energy band dispersion of exciton-polaritons confined in two-dimensional anisotropic materials inside an optical microcavity, and show the emergence of exceptional points (EPs) due to non-Hermitian topology arising from excitonic dipole oscillators with finite quasiparticle lifetime. Fourier-plane imaging reveals two pairs of EPs connected by bulk Fermi arcs for each of the transverse electric and magnetic polarized modes. An anisotropic Lorentz oscillator model captures the exact band dispersion observed in our experiment in two-dimensional momentum space. Our findings establish anisotropic two-dimensional materials as a platform for exploring non-Hermitian topological physics, with implications for polarization-controlled optical technologies.

physics.optics↗

arXiv2023

Anisotropic exciton polariton pairs as a platform for PT-symmetric non-Hermitian physics

Non-Hermitian systems with parity-time (PT) symmetry have been realized using optical constructs in the classical domain, leading to a plethora of non-intuitive phenomena. However, PT-symmetry in purely quantum non-Hermitian systems like microcavity exciton-polaritons has not been realized so far. Here we show how a pair of nearly orthogonal sets of anisotropic exciton-polaritons can offer a versatile platform for realizing multiple spectral degeneracies called Exceptional Points (EPs) and propose a roadmap to achieve a PT-symmetric system. Polarization-tunable coupling strength creates one class of EPs, while Voigt EPs are observed for specific orientations where splitting of polariton modes due to birefringence is compensated by Transverse Electric (TE) -Transverse Magnetic (TM) mode splitting. Thus, paired sets of polarized anisotropic microcavity exciton-polaritons can offer a promising platform not only for fundamental research in non-Hermitian quantum physics and topological polaritons, but also, we propose that it will be critical for realizing zero threshold lasers.

cond-mat.mes-hall↗

arXiv2023

Zero-Threshold PT-Symmetric Polariton-Raman Laser

Anisotropy endows topological aspects in optical systems and furnishes a platform to explore non-Hermitian physics, which can be harnessed for the polarization-selective amplification of light. Here, we show a zero-threshold Raman laser can be achieved in an anisotropic optical microcavity via polarization-controlled optical pumping. A loss-gain mechanism between two polarized Stokes modes arises naturally via polarization-dependent stimulated scattering and anisotropic Raman gain of the active layered material inside the microcavity. A Parity-Time (PT) symmetric Hamiltonian has been proposed to explain the emergence of a single polarization mode, essential for achieving a zero-threshold lasing condition. Additionally, intensity correlation measurements of the Stokes modes validate the coherence properties of the emitted light. Our realization of the zero-threshold Raman laser in anisotropic microcavity can open up a new research direction exploring non-Hermitian and topological aspects of light in anisotropic two-dimensional materials.

cond-mat.mes-hall↗

arXiv2021

Interfacial anisotropic exciton-polariton manifolds in ReS$_2$

Light-matter coupling in van der Waal's materials holds significant promise in realizing Bosonic condensation and superfluidity. The underlying semiconductor's crystal asymmetry, if any, can be utilized to form anisotropic half-light half-matter quasiparticles. We demonstrate generation of such highly anisotropic exciton-polaritons at the interface of a biaxial layered semiconductor, stacked on top of a distributed Bragg reflector. The spatially confined photonic mode in this geometry couples with polarized excitons and their Rydberg states, creating a system of highly anisotropic polariton manifolds, displaying Rabi splitting of up to 68 meV. Rotation of the incident beam polarization is used to tune coupling strength and smoothly switch regimes from weak to strong coupling, while also enabling transition from one three-body coupled oscillator system to another. Light-matter coupling is further tunable by varying the number of weakly coupled optically active layers. Our work provides a versatile method of engineering devices for applications in polarization-controlled polaritonics and optoelectronics.

cond-mat.mes-hall↗