Hybrid Nodal Loop Metal: Unconventional Magnetoresponse and Material Realization

TL;DR

This paper introduces hybrid nodal loops combining type-I and type-II points, predicts their realization in Ca2As, and explores their unique magnetic responses and quantum oscillation phenomena.

Contribution

It proposes a new class of hybrid nodal loops, predicts their existence in Ca2As, and analyzes their unconventional magnetic and quantum properties.

Findings

Hybrid nodal loops exist in Ca2As.

Fermi surfaces have coexisting electron and hole pockets.

Unconventional magnetic responses observed in quantum oscillations.

Abstract

A nodal loop is formed by band crossing along a one-dimensional closed manifold, with each point on the loop a linear nodal point in the transverse dimensions and can be classified as type-I or type-II depending on the band dispersion. Here, we propose a class of nodal loops composed of both type-I and type-II points, which are hence termed as hybrid nodal loops. Based on firstprinciples calculations, we predict the realization of such loops in the existing electride material Ca2As. For a hybrid loop, the Fermi surface consists of coexisting electron and hole pockets that touch at isolated points for an extended range of Fermi energies, without the need for fine-tuning. This leads to unconventional magnetic responses, including the zero-field magnetic breakdown and the momentum space Klein tunneling observable in the magnetic quantum oscillations, as well as the peculiar anisotropy in the cyclotron resonance.