Research Projects

This project aims to explore the rich interplay between light, band topology, and spin degrees of freedom in topological quantum materials (TQMs), particularly topological semimetals (TSMs). TSMs such as Weyl semimetals (WSMs), multi-Weyl semimetals (MSMs), and recently discovered multifold semimetals host gapless quasiparticles with nontrivial topological charges and strong spin-momentum locking (SML). These unique features not only underpin exotic transport and optical responses but also offer potential for next-generation quantum technologies and spintronics. Optical methods, especially circularly polarized light (CPL), provide a symmetry-sensitive probe to manipulate spin textures in these systems. A notable example is the frequency-independent circular optical spin injection (COSI), recently studied in WSMs and MSMs, where it is found to be proportional to the node’s topological charge. However, a complete understanding of its behavior, especially in more complex multifold and altermagnetic semimetals, remains elusive. This project proposes four interconnected theoretical investigations. First, it aims to the study of COSI to topological multifold semimetals, such as triple-point and Rarita-Schwinger-Weyl semimetals, to examine whether COSI remains frequency-independent and sensitive to pseudospin structure. Second, it proposes to study optical spin injection induced by bicircularly polarized light (BCPL), which combines two CPL components with different frequencies and is known to generate novel symmetry-breaking effects. The BCPL-induced spin injection remains unexplored and may offer new optical control mechanisms. Third, the project aims to investigate BCPL-driven Floquet band engineering in TSMs to realize tunable topological phases. Finally, it proposes to examine CPL- and BCPL-induced spin injection in altermagnetic WSMs—a novel magnetic phase combining zero net magnetization with spin-split bands. The overall research plan is structured around key questions addressing each objective, employing density matrix formalism, and Floquet theory and other numerical techniques. The proposed research is motivated by the pressing need to understand and utilize light-induced phenomena in topological systems for future quantum and spintronic devices. Despite extensive studies on CPL-driven responses, the role of BCPL and its capacity to control band topology and spin injection remains largely untapped. Similarly, COSI studies of multifold fermion systems and incorporating altermagnetism offers fertile ground for discovering fundamentally new physics. The research directions are timely and significant, targeting emerging material platforms and theoretical frameworks that align with global efforts, including India’s National Quantum Mission. By clarifying the optical response characteristics and band engineering capabilities of various TSMs, the project aspires to advance both fundamental understanding and practical applications in quantum matter.