THERMOELECTRICAL TRANSPORT IN TOPOLOGICAL SYSTEMS WITH SUPERCONDUCTING ISLANDS

This thesis studies thermoelectric transport in a magnetic topological insulator strip covered by two superconducting islands. The two islands split the strip into a five-region NSNSN junction. The insulator sits in the quantum anomalous Hall phase, and the proximity-induced pairing places each island in the chiral topological superconductor phase that hosts a single Majorana edge mode.

We compute the linear-response transport with the scattering-matrix (Landauer-Büttiker) formalism. The main quantities are the dimensionless Onsager integrands L11 for for charge and L22 for heat, together with the conductances G and K, as functions of the superconducting phase difference ∆φ and the junction lengths.

The charge and heat integrands oscillate with ∆φ, leading to fluctuating charge and heat conductances. The heat conductance stays small in most cases. However, depending on ∆φ their ratio can be larger or smaller than the Wiedemann-Franz value. The Wiedemann-Franz law breaks down across every geometry studied. The NSNSN junction works as a phase-tunable thermoelectric probe of its topological state.

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