arXiv subjects

Tara Shankar Bhattacharya

Publications and source records attributed to Tara Shankar Bhattacharya.

2 recordsLinked to original sources

arXiv2026

Brightening of dark trions in monolayer WS$_2$ via localization of surface plasmons

Among all excitonic complexes in transition-metal dichalcogenides (TMDs), dark and semi-dark trions are poised to play a stellar role in future quantum technologies due to their long lifetimes, about two orders of magnitude greater than those of their bright counterparts. In monolayer (ML) tungsten disulphide (WS$_2$), accessing these states via a suitable brightening mechanism remains challenging, specially, at elevated temperatures. Here, we demonstrate the brightening of dark trions from ML WS$_2$ over the temperature range, 83 K-115 K, enabled by localized surface plasmon modes in a disordered gold substrate. The resulting photoluminescence (PL) spectrum reveals a distinct spectral doublet with the twin peaks of semi-dark and bright trion states, separated by $\sim$ 45 meV. The origin of the semi-dark trion state lies in intervalley electron-electron scatterings, while its visibility in the PL spectrum is made possible by the enhanced out-of-plane electromagnetic field associated with plasmon localization. We also report on the negative degree of circular polarization in ML WS$_2$ at the energy of the semi-dark trion state. Our results establish a scalable plasmonic route to access valley-polarized semi-dark trions, opening new opportunities for quantum and valleytronic applications.

cond-mat.mes-hall↗

arXiv2020

Lattice dynamics of topological Dirac semimetal LaAgSb$_{2}$ with charge density wave ordering

LaAgSb$_{2}$ is a rare material, which offers the opportunity to investigate the complex interplay between charge density wave (CDW) ordering and topology protected electronic band structure. As both of these phenomena are governed by the structural symmetries, a comprehensive study of the lattice dynamics is highly desirable. In this report, we present the results of temperature and pressure dependent Raman spectroscopy and x-ray diffraction in single crystalline LaAgSb$_{2}$. Our results confirm that Raman spectroscopy is a highly sensitive tool to probe CDW ordering phenomenon, particularly the low-temperature second CDW transition in LaAgSb$_{2}$, which appears as a very weak anomaly in most experiments. The crystal orientation-dependent measurements provide the evolution of Raman modes with crystallographic symmetries and can be further studied through group symmetry analysis. The low-temperature x-ray diffraction data show the emergence of structural modulations corresponding to the CDW instability. The combined high-pressure Raman spectroscopy and synchrotron x-ray diffraction reveal multiple structural phase transitions through lowering of crystalline symmetries, which are also expected to lead to electronic topological transitions.

cond-mat.mtrl-sci↗