# Multiple band-crossings and Fermi surface topology: role of double nonsymmorphic symmetries in MnP-type crystal structures

## TL;DR

This study investigates how double nonsymmorphic symmetries influence multiple band crossings and Fermi surface topology in MnP-type structures, with implications for understanding superconductivity in related materials.

## Contribution

It reveals the role of nonsymmorphic symmetries in creating eight-fold band degeneracies and their impact on Fermi surface topology in MnP-type compounds.

## Key findings

- Eight-fold band degeneracy due to nonsymmorphic symmetries.
- Fermi surface topology changes with Fermi level shifts.
- Spin-orbit interaction splits degenerate bands and Fermi sheets.

## Abstract

We use relativistic ab-initio methods combined with model Hamiltonian approaches to analyze the normal-phase electronic and structural properties of the recently discovered WP superconductor. Remarkably, the outcomes of such study can be employed to set fundamental connections among WP and the CrAs and MnP superconductors belonging to the same space group. One of the key features of the resulting electronic structure is represented by the occurrence of multiple band crossings along specific high symmetry lines of the Brilloiun zone. In particular, we demonstrate that the eight-fold band degeneracy obtained along the SR path at (kx,ky)=(Pi,Pi) is due to inversion-time reversal invariance and a pair of nonsymmorphic symmetries. The presence of multiple degenerate Fermi points along the SR direction constraints the topology of the Fermi surface, which manifests distinctive marks when considering its evolution upon band filling variation. If the Fermi level crosses the bands along the SR line as it happens at the nominal filling of the MnP, these Fermi surfaces are open or closed Fermi pockets. Moving the relative position of the Fermi level away from the eight-fold degenerate bands as for the WP and CrAs compounds, the electronic changeover exhibits a simultaneous modification of the Fermi surface dimensionality and topology. Four two-dimensional (2D) Fermi surface sheets are centered around the SR line with a corrugated profile along the kz direction. Moreover, we show that the spin-orbit interaction determines a selective removal of the band degeneracy and, consequently, a splitting of the quasi 2D Fermi sheets, as it happens in WP. Finally, we comment on the connections between our results and recent experimental and theoretical proposals about the triplet superconductivity in this class of compounds.