Unusual Dirac fermions on the surface of noncentrosymmetric $\alpha$ - BiPd superconductor

TL;DR

This paper investigates the topological surface states of the noncentrosymmetric superconductor $ ext{BiPd}$, revealing unusual anisotropic Dirac states with variable Fermi velocity and a unique band gap, combining superconductivity and topological properties.

Contribution

It provides the first detailed experimental and theoretical analysis of the unusual Dirac surface states in $ ext{BiPd}$, highlighting their anisotropic and hybridization-induced properties.

Findings

Dirac surface states are strongly anisotropic.

Fermi velocity varies with crystal rotation.

Surface state exhibits a hybridization-induced band gap.

Abstract

Combining multiple emergent correlated properties such as superconductivity and magnetism within the topological matrix can have exceptional consequences in garnering new and exotic physics. Here, we study the topological surface states from a noncentrosymmetric $\alpha$-BiPd superconductor by employing angle-resolved photoemission spectroscopy (ARPES) and first principle calculations. We observe that the Dirac surface states of this system have several interesting and unusual properties, compared to other topological surface states. The surface state is strongly anisotropic and the in-plane Fermi velocity varies rigorously on rotating the crystal about the $y$-axis. Moreover, it acquires an unusual band gap as a function of $k_y$, possibly due to hybridization with bulk bands, detected upon varying the excitation energy. Coexistence of all the functional properties, in addition to the unusual surface state characteristics make this an interesting material.