Polar charge density wave in a superconductor with crystallographic chirality

TL;DR

This study reveals a superconductor, Mo3Al2C, exhibiting both crystallographic polarity and chirality, with a charge density wave phase inducing a symmetry-breaking transition that influences its superconducting properties.

Contribution

It demonstrates the coexistence of polarity, chirality, and superconductivity in a single crystal, a combination not previously studied in detail.

Findings

Identification of a polar charge-density-wave phase in Mo3Al2C.

Observation of a symmetry-breaking transition at T*=155K.

Superconductivity occurs below Tc=8K in a chiral, polar structure.

Abstract

Symmetry plays an important role in determining the physical properties in condensed matter physics, as the symmetry operations of any physical property must include the symmetry operations of the point group of the crystal. As a consequence, crystallographic polarity and chirality are expected to have an impact on the Cooper pairing in a superconductor. While superconductivity with crystallographic polarity and chirality have both been found in a few crystalline phases separately; however, their coexistence and material realizations have not been studied. Here, by utilizing transport, Raman scattering, and transmission electron microscopy, we unveil a unique realization of superconductivity in single-crystalline Mo3Al2C (superconducting Tc=8K) with a polar charge-density-wave phase and well-defined crystallographic chirality. We show that the intriguing charge density wave order leads to a noncentrosymmetric-nonpolar to polar transition below T*=155K via breaking both the translational and rotational symmetries. Superconductivity emerges in this polar and chiral crystal structure below Tc=8K. Our results establish that Mo3Al2C is a superconductor with crystallographic polarity and chirality simultaneously, and motivate future studies of unconventional superconductivity in this category.