Fermions and bosons in nonsymmorphic PdSb2 with sixfold degeneracy

Abstract

PdSb 2 is a candidate for hosting 6-fold-degenerate exotic fermions (beyond Dirac and Weyl fermions). The nontrivial band crossing protected by the non-symmorphic symmetry plays a crucial role in physical properties. We have for the first time grown high-quality single crystals of PdSb 2 and characterized their physical properties under several stimuli (temperature, magnetic field, and pressure). While it is a diamagnetic Fermi-liquid metal under ambient pressure, PdSb 2 exhibits a large magnetoresistance with continuous increase up to 14 T, which follows the Kohler's scaling law at all temperatures. This implies one-band electrical transport, although multiple bands are predicted by first principles calculations. By applying magnetic field along the [111] direction, de Haas-van Alphen oscillations are observed with frequency of 102 T. The effective mass is nearly zero (0.045m 0 ) with the Berry phase close to , confirming that the band close to the R point has a nontrivial character. Under quasi-hydrostatic pressure (p), evidence for superconductivity is observed in the resistivity below the critical temperature T c . The domeshaped T c versus p is obtained with maximum ~2.9 K. We argue that the formation of Cooper pairs (bosons) is the consequence of the redistribution of the 6-fold-degenerate fermions under pressure.

Sixfold fermion near the Fermi level in cubic PtBi2

“…Indeed, despite the relatively large number of confirmed Weyl and Dirac systems , few show band crossings in close proximity to the Fermi level. For semimetals hosting unconventional fermions the list is smaller still, especially given that to date, few such materials have actually been synthesized and checked experimentally for the presence of nodal fermions [42][43][44][45][46][47][48][49][50].…”

Signatures of Sixfold Degenerate Exotic Fermions in a Superconducting Metal PdSb2

“…The combination of the time reversal symmetry and the inversion symmetry from the crystal structure gives the quadratic nature of the bands at the sixfold crossing point which lacks the net berry curvature and topological surface states. However, the recent quantum oscillation studies under the magnetic field (upon breaking the time reversal symmetry) suggest a nontrivial character of the bands with a π‐Berry phase 34. This can also be a reminiscent of the band inversion between the two pairs of sixfold degenerate points at the R point presented in Note S1 (Supporting Information).…”

“…The carrier compensation thus provided can give rise to parabolic and unsaturated magnetoresistance, which is consistent with the transport properties observed in ref. 34. The nontrivial π‐Berry phase observed in the quantum oscillations studies by Chapai et al34 makes a strong case for a topological phase transition of the sextuple point under strong magnetic field.…”

“…34. The nontrivial π‐Berry phase observed in the quantum oscillations studies by Chapai et al34 makes a strong case for a topological phase transition of the sextuple point under strong magnetic field. This calls for elaborated experimental and theoretical studies on compounds containing sextuple points.…”

“…This calls for elaborated experimental and theoretical studies on compounds containing sextuple points. Furthermore, PdSb 2 is a superconducting pyrite with a d 6 metal configuration 34. We believe that this is the first study to demonstrate the existence of a sextuple point below the Fermi energy in a superconducting pyrite.…”