Induced p-wave superconductivity in a dual topological insulator BiTe and unconventional superconductivity in a magnetic topological insulator MnBi2Te4

Abstract

The discovery of topological insulators (TI) and semimetals has led to a whole new world of low-energy electronic devices that enable dissipationless transport through their highly spin-orbit coupled conducting channels. It has been predicted that introducing superconducting correlations into topological surface states of these materials could lead to topological superconductivity, potentially hosting elusive Majorana fermions. These particles may provide a viable route towards fault-tolerant quantum computing via the realization of topologically protected qubits. In this thesis, we study the effect of inducing superconductivity into the surface states of a dual topological insulator BiTe and a magnetic topological insulator MnBi2Te4.

In the first study, we present evidence of p-wave superconductivity at the BiTe/s-wave superconductor (NbSe2) heterojunction through a series of electrical transport measurements. Signatures of superconductivity are observed in magnetoresistance (MR) and resistance vs. temperature (RT) measurements. Four-terminal differential conductance measurements at low temperatures reveal notable features such as a sharp V-shaped zero-bias dip and convex-shaped coherence peaks. Fitting the differential conductance using a multiband 2-D Blonder-Tinkham-Klapwijk (BTK) model uncovers two distinct superconducting gaps with anisotropic p-wave and s-wave characteristics, respectively. Detailed spectra, dependent on out-of-plane magnetic fields, demonstrate that the anisotropic p-wave gap is destroyed at significantly lower fields compared to the s-wave gap. Differential conductance measurements at various magnetic field orientations indicate that the superconductivity in this system is highly sensitive to the direction of the applied magnetic field. The disappearance of superconducting features in the differential conductance spectra above the critical temperature of NbSe2 further supports our findings.

In the second study, we extend the transport analysis of the BiTe/NbSe2 interface to the unproximitized region of BiTe, exploring the impact of the superconducting proximity effect on the DTI BiTe. Detailed electrical transport measurements consistently indicate that the superconducting proximity effect significantly influences the transport properties of BiTe. These findings suggest the presence of an extended superconducting proximity length.

In the third study, we investigate the induced superconductivity in the magnetic topological insulator, MnBi2Te4. The heterojunction of MnBi2Te4/NbSe2 shows signatures of induced superconductivity through magneto-transport measurements. Subsequent differential conductance measurements reveal the unconventional nature of the induced superconductivity through anomalous ripples near the zero-bias dip.