Research Projects

4d perovskite niobates have emerged as a potential correlated topological material displaying exceptional transport and optical properties. The strain engineering in epitaxially grown films of these systems results in breaking of structural symmetries and reconstruction of electronic structure, which leads to completely new phases of matter that are not present in their bulk equivalent [1]. For example, strain-tuned ANbO3 is theoretically predicted to exhibit a true 3D Dirac semimetalic phase with the NbO6 octahedral rotation/tilting [2]. In contrast to ordinary semimetals with quadratic bands at the Fermi level in energy-momentum space, Dirac semimetals have a unique topological band structure and can support linear band crossings harbouring massless Dirac fermions. The recent successful realization of strain-modulated 3D Dirac phase in SrNbO3 thin films has been experimentally verified [3]. However, CaNbO3 in this regard remains mostly unexplored. As theoretically predicted [4], in CaNbO3 epitaxial thin films, lattice mismatched single crystalline substrate results in strain-modulated Dirac phase; thus, we aim to study this emergent topological phase and optical properties experimentally. This proposal focuses on the investigation of magneto-transport and optical properties of epitaxially strained ANbO3 (A=Ca, Sr) thin films. Some of the precise problems we aim to pursue are: (i) study of compressive strain induced octahedral rotation and resultant modification of topological band structure in ANbO3 (A=Ca, Sr) epitaxial films. The topological signatures will be probed by measuring temperature-dependent DC conductivity, time-domain terahertz (THz) spectroscopy, and magneto-transport. (ii) ANbO3 (A=Ca, Sr) are transparent conducting oxides (TCOs), which integrate two mutually exclusive properties: high electrical conductivity and optical transparency in the visible spectrum [5]. TCOs are of significant interest in various technological domains, including photovoltaic devices, flat panel displays, and solar cells, to name a few [6]. We aim to enhance the optical transparency of the films by strain modification as well as cation doping. We expect the listed problems in the proposal will lead to quality publications and will pave the path for further investigation of ANbO3 (A=Ca, Sr) films with excellent fundamental and optoelectronic properties. References: [1] A. Paul and T. Birol, Phys. Rev. Mater. 3, 085001 (2019). [2] V. Rosendal et al., Phys. Rev. Mater. 7, 075002 (2023). [3] Ok et al., Sci. Adv. 7, eabf9631 (2021). [4] Mohanta et al., Phys. Rev. B 104, 235121 (2021). [5] Stoner et al., Adv. Funct. Mater. 29, 1808609 (2019). [6] Palakkal et al., Adv. Funct. Mater. 2419990 (2025).