Induced superconducting correlations in a quantum anomalous Hall insulator

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Ferromagnetic topological insulators enable the quantum anomalous Hall effect (QAH) without external magnetic fields.
• Inducing Cooper pairing in QAH materials is crucial for realizing topological superconductivity and chiral Majorana edge states.
• Experimental detection of the superconducting proximity effect in these systems is challenging.

Purpose of the Study:

• To demonstrate evidence of the superconducting proximity effect in a quantum anomalous Hall insulator.
• To investigate the crossed Andreev reflection process at the interface between a QAH insulator and a superconductor.
• To explore the potential for realizing topological superconductivity and Majorana physics.

Main Methods:

• Fabrication of thin films of ferromagnetic topological insulator materials.
• Integration of a narrow superconducting Niobium (Nb) electrode in contact with the chiral edge state of the QAH insulator.
• Measurement of the crossed Andreev reflection (CAR) process.

Main Results:

• Successful demonstration of crossed Andreev reflection across the Nb electrode and the chiral edge state of the QAH insulator.
• Observation of CAR as a signature of induced superconducting pair correlation in the chiral edge state.
• Determination that the characteristic length of CAR exceeds the superconducting coherence length of Nb, indicating induced superconductivity on the QAH insulator surface.

Conclusions:

• The study provides compelling evidence for induced superconductivity in a quantum anomalous Hall insulator via the crossed Andreev reflection process.
• The findings suggest a viable platform for future investigations into topological superconductivity and Majorana physics.
• This work opens avenues for the search for non-abelian zero modes in topological systems.