Keywords

Quantum materials, Topological Insulator, Nodal Line semimetal, Charge density wave, Mott insulator, ARPES, Time resolved ARPES

Abstract

he First Quantum Revolution established quantum mechanics as the foundation of modern physics, enabling transformative technologies such as semiconductors, lasers, and transistors through prin-ciples of quantization, wave-particle duality, and uncertainty. The ongoing Second Quantum Rev-olution harnesses entanglement, superposition, and coherence to advance quantum computation, communication, simulation, and sensing. Central to this endeavor is the study of quantum mate-rials hosting novel electronic structures and emergent phases, including topological insulators and Dirac, Weyl, and nodal-line semimetals. In this thesis, using angle-resolved photoemission spec-troscopy (ARPES), transport measurements, and density functional theory (DFT) calculations, we investigate three classes of materials: (i) magnetic topological semimetals, (ii) charge-density-wave (CDW) materials, and (iii) layer-dimerized Mott insulators. The lanthanide antimony telluride (LnSbTe, Ln = lanthanides) family provides a platform to study the interplay among nonsymmorphic symmetry-protected topology, spin–orbit coupling (SOC), magnetism, and 4 f electron correlations. We identify multiple nodal crossings along the Γ–X and Γ–M high-symmetry directions, forming nodal lines parallel to the X–R bulk direction. A comparative study from PrSbTe to ErSbTe reveals that increasing SOC progressively gaps the unprotected crossings while preserving those enforced by glide-mirror symmetries, establishing a coherent picture of tunable topology across the series. We further investigate the CDW phenomenon in EuTe4, a transition metal chalcogenide exhibiting a complete Fermi surface reconstruction that drives a metal-to-insulator transition. Our ARPES and theoretical studies elucidate the momentum- and temperature-dependent electronic structure evolution underlying CDW formation. Additionally, our study of the breathing kagome materials Nb3X8 (X = Br, Cl, I) reveals a tunable platform for layer-dimerization-driven Mott physics, where geometric frustration, electronic correlations, and interlayer coupling cooperate to produce a correlated insulating ground state. Complementarily, ultrafast time-resolved ARPES captures non-equilibrium electronic dynamics in a Dirac semimetal, extending this thesis beyond equilibrium investigations. Overall, these studies deepen our understanding of the interplay between symmetry, topology, magnetism, and electron correlations in quantum materials.

Completion Date

2026

Semester

Spring

Committee Chair

Neupane, Madhab

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Department of Physics

Document Type

Dissertation/Thesis

Identifier

DP0053262

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