Research Projects

Topological semimetals, including Dirac and Weyl semimetals, represent a frontier in condensed matter physics, where nontrivial topology of the electronic band structure leads to exotic quasiparticle excitations and anomalous transport phenomena. In particular, Weyl semimetals (WSMs) exhibit linear band crossings—Weyl nodes—that act as sources or sinks of Berry curvature in momentum space. These topological monopoles lead to highly unconventional responses to external fields, including anomalous Hall conductivity, nonlinear Hall effects, and negative longitudinal magnetoresistance associated with the chiral anomaly. In this context, Cr₃Te₄, a layered transition metal chalcogenide, has recently emerged as a promising intrinsic magnetic Weyl semimetal. Its broken time-reversal symmetry (TRS) due to ferromagnetism lifts the degeneracy of Weyl nodes and facilitates a net Berry curvature distribution, even in the presence of inversion symmetry. This enables robust topological phenomena to arise without the need for external symmetry breaking—a significant experimental advantage. Contrastingly, NiTe₂ is a nonmagnetic Dirac semimetal that preserves both time-reversal and inversion symmetries. However, theoretical studies suggest that symmetry breaking (e.g., via strain, doping, or hetero-structuring) can induce a transition to a Weyl semimetal phase, making it an ideal material for studying symmetry-tunable topological states. Given these developments, this proposal is driven by the central hypothesis that magnetic Weyl semimetals like Cr₃Te₄ host rich, tunable nonlinear and topological transport signatures that can be manipulated by external perturbations (e.g., doping, disorder, or intercalation), and that comparing these effects with NiTe₂ will help disentangle the role of symmetry, correlations, and topology in transport phenomena. We also hypothesize that higher-order terms in the Hall response, often neglected, play a significant role in these materials due to strong Berry curvature effects. Recent experimental works have demonstrated that Cr₃Te₄ exhibits long-range ferromagnetism at room temperature, with Weyl nodes predicted near the Fermi level. Negative longitudinal magnetoresistance (NLMR) has been observed in several magnetic Weyl materials, indicating the chiral anomaly. Nonlinear Hall effects (NLHE), driven by Berry curvature dipoles, have been experimentally detected in inversion-breaking materials like WTe₂. However, their realization in magnetically ordered Weyl systems remains underexplored. First-principles and tight-binding models predict a finite Berry curvature dipole and strong higher-order nonlinear conductivities in Cr-based tellurides. NiTe₂, although topologically trivial in its pristine form, can transition to a Weyl phase upon symmetry reduction—offering a platform to probe the role of inversion symmetry. Moreover, systematic studies of nonlinear transport phenomena, the role of electron-electron interactions, and the impact of structural modifications in Cr₃Te₄ and NiTe₂ remain limited. The primary objective of this work is to (i) Elucidate the Weyl semi-metallic nature of Cr₃Te₄ through quantum oscillation measurements, and first-principles calculations. (ii) Synthesize high-quality single crystals and thin films of Cr₃Te₄ and NiTe₂ using chemical vapor transport (CVT) and metal-organic chemical vapor deposition (MOCVD). (iii) Investigate the non-linear Hall effect (NLHE), including higher-order contributions due to Berry curvature dipole and skew scattering mechanisms. (iv) Analyse the role of electron-electron interactions and disorder in modifying the Hall coefficient beyond the standard Boltzmann theory. (v) Study the negative longitudinal magnetoresistance (NLMR) as a hallmark of the chiral anomaly and explore its tunability through intercalation and structural engineering.