TeraHertz Time-Domain Spectroscopy

TeraHertz (THz) region of the electromagnetic spectrum lies between the microwave and the infrared part. By illuminating a biased photoconductive antenna (PCA), THz waves can be generated. THz waves can be detected again using a PCA. Time-Domain Spectroscopy (THz-TDS) is a method to study the far infra-red properties of materials. For THz-TDS, the femtosecond laser pulse is split into to two paths, one path reaches the THz emitter and the other path reaches the THz detector. The time delay between the pulses from the two beams can adjusted using a delay stage. The THz pulse is focussed on the sample and detected after passing through the sample. The THz signal reaching the detector is measured using the detector by employing a lock-in technique. From the measured signal the full complex value of the material parameters can be extracted.

Material Systems

TMDC Materials

Transition metal dichalcogenide (TMD or TMDC) monolayers are atomically thin semiconductors of the type MX2, with M a transition metal atom (Mo, W, etc.) and X a chalcogen atom (S, Se, or Te). One layer of M atoms is sandwiched between two layers of X atoms. TMDCs is a group of materials that belong to the family of 2D materials. These materials have emerged as the perfect candidates for applications in optoelectronics, spintronics, valleytronics, etc. What makes them attractive is the layer dependent properties. These materials cover a broad energy range from 1.2 eV to 2.1eV

At present, we are studying the spin and valley properties of semiconducting systems (MoS2, MoSe2, WS2, and WSe2), CDW systems (TaSe2 and SnSe2), and alloy (MoWSe2). We are also interested in studying the excitonic properties of van der Waals heterostructures.

Strongly Correlated Systems

Strongly correlated materials are a wide class of heavy fermion compounds that include insulators and electronic materials, and show unusual (often technologically useful) electronic and magnetic properties, such as metal-insulator transitions, half-metallicity, and spin-charge separation.

In our lab, we are studying Sr₁₄Cu₂₄O₄₁ spin - ladder system using pump - probe and terahertz spectroscopy techniques.