2025 Theses Doctoral

Quantum Localization in Metals

Thinel, Morgan

Localizing electrons is a fundamental pursuit in physics. On one hand, localized electronic states are a promising tool for quantum technologies. On the other hand, localized electrons in flat bands can lead to strong correlations and the emergence of novel quantum phases of matter including unconventional superconductivity. Normally, the precise control of quantum states relies on the localization of quantum energy levels within a spectral vacuum. Single atoms trapped by optical tweezers as well as defect states trapped in the bandgap of insulating materials are two common approaches to the design of qubits. Thus, metallic materials without a bandgap are commonly understood as antithetical to localization.

In this thesis, I will use scanning tunnelling microscopy/spectroscopy and Raman spectroscopy (Chapter 1) to demonstrate and investigate quantum localization in metals. I will present a new approach to the quantum localization of bound states in the continuum via hopping interference in the metallic van der Waals material Pd5AlI2 (Chapter 2).

Next, I will show that Anderson localization from backscattering interference emerges in this material when it is exfoliated to the two-dimensional limit (Chapter 3). I will then discuss charge localization into density waves in the context of my discovery of a quasi-1D charge density wave in electron-doped CrSBr (Chapter 4).

Finally, I will discuss unconventional superconductivity in iron pnictides and the relation of local rotational symmetry breaking dynamics to the observed spatial modulation of the superconducting order parameter in EuRbFe4As4 (Chapter 5).