Sambit Choudhury

The parkerite family of ternary transition-metal chalcogenides, with the general formula A 3 M 2 X 2 , exhibits considerable structural diversity and intriguing electronic properties. Within this family, Ni 3 Bi 2 Se 2 has attracted particular interest due to its rich electronic and transport properties. However, its momentum-resolved electronic structure remains largely unexplored. Here, we present a comprehensive experimental and theoretical investigation of Ni 3 Bi 2 Se 2 to elucidate its electronic structure. Structural and transport measurements confirm the high crystalline quality and multiband semimetallic character of the compound, while x-ray photoelectron spectroscopy establishes the elemental composition and chemical states of its constituent elements. Soft x-ray angle-resolved photoemission spectroscopy measurements reveal anisotropic electron- and hole-like Fermi pockets and band dispersions in good agreement with first-principles calculations. Together, these results provide a comprehensive understanding of the electronic structure of Ni 3 Bi 2 Se 2 and offer new insights into the broader class of parkerite compounds.

The integration of metallic overlayers with topological semimetals provides a promising route to engineer novel quantum heterostructures while preserving nontrivial electronic states. In this work, we investigate the growth and interfacial electronic structure of Sn deposited on Mo 0.3 W 0.7 Te 2 using low-energy electron diffraction, x-ray photoelectron spectroscopy (XPS), and angle-resolved photoemission spectroscopy (ARPES). We find that Sn forms a quasi-van der Waals overlayer with weak interfacial coupling. XPS measurements show no detectable core-level shifts, indicating a chemically abrupt interface with negligible charge transfer. ARPES reveals that the near-Fermi-level band structure, including the Weyl states, remains largely intact upon Sn deposition, with no significant band reconstruction along the Γ ― – Y ― direction. In contrast, modifications are confined to deeper valence band states, particularly along Γ ― – X ― , reflecting weak, energy-dependent hybridization from Sn-derived states. This energy-selective coupling enables the integration of a metallic overlayer while preserving the symmetry-protected topological states of the substrate. Our results establish a viable route for engineering electronically transparent metal-topological semimetal interfaces and exploring proximity-induced quantum phenomena.

Charge density waves (CDWs) are a canonical interaction-driven electronic phenomenon with potential technological applications, such as collective electronic switching and local information storage. Here, we investigate the properties of the CDW in the mixed-chalcogen compound 1T-TaSeTe using bulk- and surface-sensitive diffraction and spectroscopy techniques and transport measurements. Compared to the pristine parent compound 1T-TaSe2, we find that the incommensurate CDW appears to remain incommensurate down to low temperatures. The CDW-induced gapping of the Fermi surface is pronounced and may explain the observed semiconductor-like electrical resistivity behavior in combination with chalcogen disorder. Our results demonstrate that disordered chalcogen substitution doping can modify, yet preserve, the characteristic emergent electronic properties of a transition metal dichalcogenide.

In this study, we have employed a high entropy approach to synthesize a hitherto unexplored tetragonal high entropy spinel with composition (Mn0.2Co0.2Ni0.2Cu0.2Zn0.2)Mn1.8Cr0.2O4. The temperature and field-dependent magnetization studies reveal a complex magnetic behavior characterized by a ferrimagnetic transition occurring at (TC) 85 K, followed by a noncollinear magnetic ground state below 23 K. Remarkably, we have observed the appearance of a large exchange bias effect (exchange bias field HEB = 7.6 kOe at 4 K) below the TC = 85 K in the field cooled mode. The uncompensated magnetic moments in this disordered system create unidirectional anisotropy, leading to the exchange bias effect. The appearance of the large exchange bias effect in a complex high entropy oxide (HEO) indicates that disordered ferrimagnetic HEOs are a promising class to explore systems having potential applications in spintronics.