Research/

Molecular Physics, Ion-electron Coincidence Spectroscopy, Coulomb Explosion Imaging, Cluster Physics, Ion-molecule Reactions, Reactive Scattering

We use Terahertz (THz) technology to understand the ultrafast processes and low-energy dynamics in various materials. The integration of THz-spectroscopic and -imaging techniques with the materials of contemporary technological interests such as multiferroics, ferroelectrics and manganites presents opportunities to explore a new range of physical phenomena and appropriate industrial applications. THz-emission via ultrafast, femtosecond-laser-pulse modulated photocurrent density, static and dynamic electric-fields and spin moments can directly probe the ultrafast functionality of the material specific parameters. Using time-resolved THz emission and THz imaging, the ultrafast dynamics of photoexcited carriers, polarization and spin moments can be precisely determined. These studies facilitate understanding of the nondestructive control and the response time of electrical/magnetic memory to the femtosecond laser stimulus. All such features are crucial to design futuristic ultrafast optical and hybrid optoelectric and optomagnetic data storage devices.

The group works in the frontier areas of technological interest, namely, development and applications of optical spectroscopy and imaging techniques to explore non-linear properties and ultrafast photo-control of electronic processes in functional materials. In this area we are employing cutting-edge terahertz technology, nonlinear and time-resolved spectroscopy techniques, etc. These techniques are rapidly evolving and have proven applications and efficacy. Besides the technological aspect, we are also investigating experimentally the physics behind the ultrafast nonlinear optical effects on both the microscopic and macroscopic levels and in the process learning how to control, tailor and enhance them.

We develop nitrogen-vacancy (NV) spin-based diamond magnetometers capable of measuring minute magnetic fields with high sensitivity and spatial resolution. Our aim is to utilize diamond spins as scanning probes to spatially map tiny magnetic fields on the nanoscale. This would allow us to obtain a greater understanding of the magnetic phenomena which are otherwise not discerned by global magnetization measurements due to spatial averaging. Our long-term goals include setting up a cryogenic quantum magnetometer which would open the door for studying a variety of magnetic phenomena in condensed matter nanosystems, together with the possibility of making quantitative measurements. Some of the studies we imagine applying our magnetometer sensitivity and spatial resolution include probing magnetic phase transition in ferritin bioproteins, imaging edge magnetism in graphene, stray-field imaging of vortices in high-temperature superconductors and understanding emergent nanoscale magnetism in oxide heterostructures.

Research is being carried out to study the properties of materials exhibiting superconductivity, magnetism and other unconventional properties. Emphasis is on topological insulators and superconductors which have generated considerable scientific interest in recent years because of their various interesting properties. Three major avenues of research towards this direction are single crystal growth using floating zone, Czochralski, Bridgman, flux and vapor transport methods, measurements of magnetic, muon spectroscopy and neutron scattering (ISIS facility at Rutherford Appleton Laboratory U.K., III Grenoble France and PSI Switzerland) and thermodynamic and transport properties.

The group is working on the study of electronic structure of condensed matter systems having novel properties such as metal insulator transitions, high-temperature superconductivity, unusual magnetism, non-Fermi liquid behaviour, charge and spin density wave state, etc. using high energy and angle resolved photoemission spectroscopy. The photoemission experiments using fixed photon energy are performed with various lab-based x-ray and UV sources, and experiments involving variable photon energies are performed at synchrotron sources such as Elettra, Italy; UVSOR, Japan; AL Sand SRC, USA, etc. In addition to the experimental details, the band structure calculations and model calculations are also performed to get deeper insight and understanding of various ground state properties and solid-state phenomena.

The group is being established to study coherent nonlinear interactions in semiconductor nanostructures. Optical two-dimensional coherent spectroscopy is a powerful tool to study many-body interactions between electronic excitations in semiconductor nanostructures such as quantum dots, monolayer transition metal dichalcogenide, etc. The ultimate aim is to leverage a fundamental understanding of these interactions to design protocols to actively control them for applications in quantum information science.

The group is interested in investigating some of the many-body effects in complex materials which include complex metal oxides and novel 2D materials. The group’s primary focus is to study phonons and their interactions with various other quasiparticles such as, electrons, magnons, orbitons, etc. and try to unravel their role in the novel properties of the complex materials. The group investigates such interactions using Raman spectroscopy in-situ/ex-situ with electron transport and magnetic measurements. Presently, the group is equipped with a micro-Raman spectrometer with a cryo-magnet which is capable of varying sample temperature from 5 to 300 K in combination with a magnetic field of up to 9 T. In addition, a liquid nitrogen-based cryostat is also available to explore these interactions at higher temperatures up to about 870 K.