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

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 pressure induced superconductors CrAs and MnP compounds 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 an eight-fold band degeneracy is obtained along the S-R path at (kx,ky)=(π,π), due to time reversal invariance and a pair of nonsymmorphic symmetries. The presence of multiple degenerate Fermi points along the S-R direction constraints the topology of the Fermi surface, which manifests distinctive marks when considering its evolution upon band filling variation. We show that, by changing the relative position of the Fermi level with respect to the eight-fold degenerate bands, one can tune the effective dimensionality of the Fermi surface. If the Fermi level does not cross the multifold degenerate bands, as for the WP and CrAs compounds, the degeneracy forces the occurrence of two-dimensional (2D) Fermi surface sheets centered around the S-R line with a corrugated profile along the kz direction. On the contrary, these surfaces are converted into open or closed Fermi pockets, if the bands along the SR line cross the Fermi level, as it happens in MnP. 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.

Dimensionality of the Superconductivity in the Transition Metal Pnictide WP

“…It is well-known that the nonsymmorphic symmetries in the Pnma structure are responsible for exotic topological behaviors like the topological nonsymmorphic crystalline superconductivity [17], 2D Fermi surface topology [9], Dirac topological surface states [44], and topologically-driven linear magnetoresistance [45]. A detailed analysis of the effects of the nonsymmorphic symmetries on the fermiology of this compound and a tight-binding minimal model fitted to the DFT band structure has been reported elsewhere [9]. Here, we provide further investigation using a low-energy tight-binding model in order to calculate the hopping parameters at the Fermi level and give an indication about the dimensionality of the energy spectra.…”

“…Four of the six bonds are inequivalent due to the space group anisotropy [8]. In this compound, the spatial extension of the W-5d orbitals induces a large overlap and a strong coupling with the neighboring p-orbitals, resulting in a distortion of the crystal structure more pronounced compared to that of CrAs and MnP [8,9]. Moreover, the spin-orbit coupling of W-5d electrons is stronger than that of 3d electrons of CrAs and MnP [9].…”

“…In this compound, the spatial extension of the W-5d orbitals induces a large overlap and a strong coupling with the neighboring p-orbitals, resulting in a distortion of the crystal structure more pronounced compared to that of CrAs and MnP [8,9]. Moreover, the spin-orbit coupling of W-5d electrons is stronger than that of 3d electrons of CrAs and MnP [9]. In particular, the 3d materials display strong electron correlations, narrow bandwidths, and robust magnetism.…”

“…Moreover, the relativistic shifts in orbital energies, combined with spin-orbit and bandwidth effects, drive band inversions leading to topological phases and enhanced Rashba splittings. This class of materials exhibits a nonmagnetic phase with no long-range magnetic order with a Fermi surface consisting of hole-like branches with two-dimensional (2D) dispersion, together with electron-like branches with a full three-dimensional (3D) character [9,12]. Therefore, it is legitimate to ask what is the dimensionality of transport in these systems in the superconducting phase.…”

Topological Transition in Pb1-xSnxSe using Meta-GGA Exchange-Correlation Functional

“…Unlike the surfaces states in the conventional Z 2 topological insulators [17], the surface states of TCI are protected by crystalline symmetry, instead of time reversal symmetry. We would like to point out that also the topological crystalline metallic phases have been proposed to be present in orthorhombic structures [18][19][20][21][22].…”