Andreev Reflection in an s-Type Superconductor Proximized 3D Topological Insulator.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Topological insulators (TIs) exhibit unique electronic properties.
• Superconductor-TI interfaces are crucial for novel quantum effects.
• Shot noise analysis reveals charge transport mechanisms.

Purpose of the Study:

• Investigate charge transport and shot noise in normal-metal-3D TI-superconductor contacts.
• Characterize transport regimes and the influence of Andreev reflection.
• Understand the underlying physics of reduced Fano factors in this system.

Main Methods:

• Fabrication of lateral normal-metal-3D TI-superconductor devices using Bismuth-based TIs.
• Measurement of transport properties and shot noise in varying magnetic fields.
• Analysis of Fano factor in normal and Andreev reflection regimes.

Main Results:

• Devices exhibit elastic diffusive transport in the normal state (Fano factor F_N ≈ 1/3).
• Andreev reflection (AR) regime identified in the absence of magnetic field.
• A significantly reduced Fano factor (F_AR ≈ 0.22 ± 0.02) was observed in the AR regime, contrary to expectations.

Conclusions:

• The reduced Fano factor in the AR regime suggests a deviation from standard theories.
• Finite thermal conduction in the superconducting TI, due to residual low-energy states, is proposed as the cause.
• This finding opens new avenues for exploring quantum transport in TI-superconductor hybrid systems.