Effective low-energy theory for superconducting topological insulators

Area of Science:

• Condensed Matter Physics
• Materials Science

Background:

• Superconducting topological insulators can host exotic surface states known as surface Andreev bound states (SABSs), including Majorana fermions.
• The complexity of the two-orbital Bernevig-Hughes-Zhang model hinders a full understanding of low-energy physics and SABSs in these materials.

Purpose of the Study:

• To develop a simplified, intuitive method for constructing low-energy effective models of superconducting topological insulators.
• To elucidate the conditions governing the types and number of SABSs that emerge in these systems.

Main Methods:

• Utilizing an analogy between topological insulators and time-reversal invariant topological superconductors.
• Constructing effective low-energy models based on chemical potential and experimentally relevant parameters.
• Analyzing the impact of surface reflection symmetry on the effective pairing potential.

Main Results:

• Demonstrated that low-energy properties are governed by one or two copies of single-orbital effective models.
• Showed that sign reversal in the effective pairing potential upon surface reflection predicts the appearance of SABSs.
• Analytical calculations using the effective model successfully reproduced numerically confirmed SABS dispersions.

Conclusions:

• The proposed effective model offers a simplified yet accurate approach to understanding the low-energy physics of superconducting topological insulators.
• The findings provide a framework for predicting and identifying Majorana fermions and other SABSs in candidate materials like CuxBi2Se3.