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Pathak, Vedangi

University of British Columbia

The coexistence of time-reversal symmetry breaking (TRSB) and superconductivity gives rise to exotic phenomena that challenge conventional understanding and hold immense potential for advanced quantum technologies. This thesis explores TRSB in two-dimensional superconducting heterostructures without external magnetic fields, focusing on three distinct platforms where TRSB arises through engineered or spontaneous mechanisms. A major challenge in condensed matter physics is finding platforms that support emergent Majorana quasiparticles - topologically protected states ideal for storing and manipulating quantum information via topological qubits. In the thesis, we first investigate a superconductor-ferromagnet heterostructure where TRSB effects are engineered through a magnetic vortex. Coupled magnetic and superconducting vortices form a stable hybrid vortex hosting robust zero-energy Majorana modes at its core, with a partner mode at the boundary of a disk-shaped topologically non-trivial region. Notably, we propose a novel mechanism for this topological phase formation that relies on the orbital effects of the magnetization field rather than the conventional Zeeman effect. Next, we investigate a twisted bilayer of the high-Tc cuprate Bi₂Sr₂CaCu₂O₈₊ₓ to exhibit a TRSB phase at 45° twist with a topological dx²-y²+ idₓᵧ superconducting order parameter. Using a fully self-consistent microscopic model for this system, we predict the emergence of small but non-vanishing chiral edge currents. Remarkably, we estimate that the magnetic fields generated by these edge currents exceed the detection threshold of state-of-the-art magnetic scanning probe microscopy techniques, demonstrating the realistic potential for detecting topological superconductivity in twisted cuprate bilayers. Finally, we examine a high-Tc cuprate paired with an s-wave superconductor, resulting in a non-topological dₓᵧ± is phase. Here, we predict the occurrence of non-chiral edge currents exhibiting frustration at perpendicular edges, where supercurrents flow in opposing directions, creating spontaneous flux patterns akin to large supercurrent vortices. This unique behavior is characterized using both self-consistent lattice models and a multi-component Ginzburg-Landau formalism, revealing new avenues for understanding and controlling supercurrent flow in unconventional superconductors. By uncovering new mechanisms for topological phase formation and predicting novel superconducting phenomena through TRSB, this thesis offers insights into topological phases, unconventional superconductivity, and potential applications.

Text

2025-04-03

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/90567

Physics

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/