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Symmetry protected Josephson supercurrents in three-dimensional topological insulators
Sungjae Cho1, Brian Dellabetta, Alina Yang
1Department of Physics, Frederick Seitz Materials Research Laboratory, University of Illinois, Urbana, Illinois 61801, USA.
Nature Communications
|April 12, 2013
Summary
Researchers measured Josephson effects in topological insulator-superconductor junctions, confirming surface states carry supercurrents in the true topological regime. This finding is crucial for realizing Majorana quasiparticles.
Area of Science:
- Condensed Matter Physics
- Materials Science
Background:
- Topological insulators (TIs) are materials with conducting surface states and insulating bulk.
- Coupling TIs to superconductors is predicted to host Majorana quasiparticles, essential for topological quantum computing.
- Superconductivity in the depleted surface states of TIs, the true topological regime, remains experimentally elusive.
Purpose of the Study:
- To experimentally investigate superconductivity in the surface states of topological insulators within the true topological regime.
- To clarify the role of surface states in carrying supercurrents in topological insulator-superconductor junctions.
- To determine the robustness of surface-state superconductivity against disorder and magnetic fields.
Main Methods:
- Fabrication of topological insulator-superconductor junctions.
- Measurement of direct current (d.c.) Josephson effects across junctions.
- Tuning the chemical potential through the topological phase transition.
- Comparison with three-dimensional quantum transport simulations.
Main Results:
- Direct observation of d.c. Josephson effects in the true topological regime, where only surface states are conductive.
- Demonstration that supercurrents are predominantly carried by the topological surface states.
- Evidence for the robustness of the surface-state supercurrent against disorder and applied magnetic fields.
- Quantification of bulk/surface state mixing effects.
Conclusions:
- Superconductivity in topological insulator surface states is experimentally confirmed in the regime relevant for Majorana modes.
- Topological surface states are the primary carriers of supercurrent in these junctions, robust against perturbations.
- These findings provide critical insights into the nature of supercurrents in TIs and pave the way for realizing Majorana quasiparticles.
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