Research

Research is a systematic process of collecting and analyzing data to generate new knowledge or enhance the understanding of existing concept

Research Interests

Light–matter interactions are fundamental to understanding the intrinsic properties of advanced materials. My research focuses on exploring light-matter interactions in novel layered systems, particularly two-dimensional (2D) transition metal dichalcogenides (TMDCs ), 2D magnetic materials, and Quantum materials.

My work aims to explore the underlying physics of quasiparticle excitations such as phonons, magnons, and excitons, as well as their mutual coupling, interlayer interactions, and thermal behavior in Quantum and 2D materials, which are pivotal to the development of optoelectronic and quantum technologies. I systematically investigate the phenomena/properties associated with the Quantum and 2D materials, as functions of temperature, thickness, excitation energy, and polarization orientation of the incident and scattered light using Raman and photoluminescence (PL) spectroscopic techniques via understanding the dynamics of quasiparticle excitations.

[I] Non-magnetic 2D materials: Transition metal dichalcogenides (TMDCs)

Two-dimensional transition metal dichalcogenides (TMDCs) have emerged as promising materials for future applications due to their unique properties. TMDCs, with the formula MX2 (M = Mo or W; X = S, Se, or Te), consist of a transition metal layer sandwiched between two chalcogen layers, forming a covalently bonded X–M–X structure. In bulk form, these layers are held together by weak van der Waals forces, allowing easy exfoliation into single layers. The properties of TMDCs strongly depend on layer thickness, showing an indirect-to-direct band gap transition in the monolayer limit. Monolayer TMDCs, with their distinctive optical and electronic characteristics, hold great potential for next-generation electronic and optoelectronic devices.

[II] Magnetic 2D materials: Transition-Metal Phosphorus Trichalcogenides (TMPTs)

The discovery of long-range magnetic order in van der Waals (vdW) materials such as CrI3 and Cr2Ge2Te6 has significantly broadened the scope of low-dimensional magnetism and stimulated extensive research on magnetism in the two-dimensional (2D) limit, thereby expanding the family of 2D magnetic materials. Among these, transition-metal phosphorus trichalcogenides (MPX3; M = Mn, Fe, Ni, V, Co; X = S, Se), which form vdW antiferromagnets (AFMs), have emerged as exceptional platforms for exploring exotic and topological phenomena in 2D magnetism. The magnetic exchange interactions, spin-ordering patterns, spin dimensionality, and magnetic anisotropy in these materials are highly sensitive to the specific choice of transition metal and chalcogen atoms, underscoring the tunability of their magnetic properties through chemical substitution. Furthermore, the MPX3 family exhibits a diverse range of quasiparticle excitations including magnetic, excitonic, and lattice excitations and mutual coupling among spin, charge, lattice, and orbital degrees of freedom gives rise to novel bound states, many-body phenomena, hybrid quasiparticles, spin–orbit–entangled excitons, and strong electron correlations.

A short overview of the Raman Spectroscopic Technique

Raman scattering intensity

The Raman spectroscopic technique is a powerful, non-destructive optical technique used to probe the vibrational, rotational, and other quasiparticle excitation, such as magnon excitations, in materials. It is based on the inelastic scattering of monochromatic light. In the quantum mechanical picture, Raman (inelastic) scattering is described as a sequence of photon-electron and electron-phonon interactions that occur during the light-matter interaction process.

When laser light impinges on the system, the electronic state absorbs an incident photon, generating an electron–hole pair and resulting in an electron–photon (radiation) interaction. (ii) The excited electron moves from the ground state to an intermediate (real or virtual) state, where it interacts with the lattice to create a phonon (Stokes process) or annihilation (anti-Stokes), giving rise to electron-phonon coupling and the exchange of energy and momentum between intermediate states. (iii) Finally, the electron relaxes back to the initial ground state and recombines with the hole, emitting a scattered photon in the process-thereby completing the overall electron–photon interaction.

Research Highlights: A few selected works

Spin-entangled (Zhang-Rice) exciton in van der Waals antiferromagnet NiPS3-xSex

In this study, we investigate how anion substitution influences the Zhang-Rice (ZR) exciton in the van der Waals magnet NiPS3, showing that even minimal substitution disrupts and tunes the ZR exciton. Our results reveal a complex interplay between charge transfer, p-orbital disorder, and thermal effects, providing new insights into spin-entangled exciton dynamics and their coupling to magnetic order. npj 2d materials and applications 9, 87 (2025)

Magnetic and lattice excitations and emergent multiple phase transitions in MnPSe3-xSx

In this study, we conducted a detailed Raman spectroscopic analysis of MnPSe3-xSx to investigate the interplay between lattice and magnetic excitations as a function of temperature and composition. Two-magnon excitations show that chalcogen substitution strongly modulates their hybridization with phonon modes. Combined Raman and magnetic susceptibility data reveal three sequential phase transitions: short- and long-range magnetic order, followed by a low-temperature spin-reoriented phase. Further, the results highlight the roles of spin dynamics and Kramers-Anderson superexchange in phonon scattering, demonstrating that chalcogen substitution effectively tunes magnetic–lattice coupling. Physical Review B 112, 144417 (2025)

Thermal effects on Exciton and Trion Dynamics and Valence Band Splitting in VA- and HA-MoS2

In this work, we investigate exciton and trion dynamics and their coupling with phonons and charge carriers in few-layer vertically and horizontally aligned MoS2. Temperature-dependent measurements reveal pronounced interlayer coupling, reflected in valence band splitting. Notably, the valence band splitting decreases by ~22% and 12% for vertical and horizontal MoS2, respectively. Trion signatures is found to persist up to 330 K, with dynamics more strongly affected in the vertical system. Further, trion emission shows stronger thermal quenching than excitons, consistent with its smaller binding energy. Homogeneous linewidth broadening increases with temperature, dominated by acoustic phonons below 100 K and by both acoustic and longitudinal optical phonons at higher temperatures. Journal of Materials Chemistry C 10, 5684 (2022)

Electron-Phonon Coupling, Resonance Effect, and Phonon Dynamics in Mono and Bilayer MoSe2

In this study, we present comprehensive temperature- and polarization-dependent Raman measurements on monolayer and bilayer MoSe2. Phonon modes up to fourth order are observed, including nominally forbidden Raman and infrared-active modes. Their origin is understood in terms of zone-center phonons, multi-phonon scattering from other Brillouin zone regions, and mechanisms such as resonance effects, the Fröhlich exciton–phonon interaction, and the cascade theory of inelastic light scattering. Notably, anomalous temperature-dependent variations in phonon linewidths reveal the significant role of electron–phonon coupling, particularly for the out-of-plane (A1g) and shear (E22g) modes, which is more pronounced in the narrow-gap bilayer compared to the larger-gap monolayer. Phys. Rev. B 105, 085419 (2022)

Davydov Splitting, Resonance Effect, and Phonon Dynamics in CVD-grown Layered MoS2

In this work, we performed temperature-dependent Raman measurements on CVD-grown, horizontally aligned MoS₂ layers under resonant conditions. The phonon frequency shifts and linewidths reveal contributions from three- and four-phonon anharmonic interactions. Davydov splitting of the A1g and E12g modes is observed in trilayer (3L) and few-layer (FL) MoS2, increasing with layer number. The A1g splitting is strongly resolved at low temperatures, indicating enhanced interlayer coupling, while the E12g mode remains split even at room temperature. A nearly sixty-fold enhancement in phonon intensity at low temperature highlights the strong temperature-dependent modulation of resonance effect. Nanotechnology 32, 285705 (2021)

Anisotropic Electron-Photon-Phonon Coupling in Layered MoS2

In this work, we performed comprehensive inelastic light scattering measurements on CVD-grown (horizontally and vertically aligned) and mechanically exfoliated flakes of single-crystal MoS2. The anisotropic optical response was investigated through polarization-dependent Raman spectroscopy as a function of incident photon energy and flake thickness. The polarization-dependent studies reveal strong anisotropy, manifested by the anomalous renormalization of Raman mode intensities with varying thickness, phonon symmetry, and excitation energy. These findings demonstrate pronounced anisotropic light–matter interactions in the highly crystalline layered MoS2 system, particularly for in-plane vibrational modes, providing important insights into their fundamental properties and potential optoelectronic applications. J.Phys.:Condens. Matter 32, 415702 (2020)

Phonon Dynamics in Coexisting Allotropes of Monolayer WS2

In this work, we investigated the thermal properties and multi-phonon Raman scattering in the coexisting 1H, 1T, and 1T′ phases of monolayer WS₂ as a function of temperature. Anomalous behavior in both first- and higher-order modes is observed, arising from resonance detuning and strain due to thermal expansion mismatch with the substrate. Temperature-dependent analysis resolves the ambiguity between the ~297 cm⁻¹ and ~325 cm⁻¹ modes, assigning them to a forbidden first-order (E1g) mode and a combination (A1g + LA(M) mode, respectively. The thermal expansion coefficient was also estimated after isolating substrate effects, revealing distinct temperature-dependent behavior in each phase. J. Phys.: Condens. Matter 31, 505403 (2019)

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