Nontrivial Topological States in BaSn5 Superconductor Probed by de Haas–van Alphen Quantum Oscillations

We report the nontrivial topological states in an intrinsic type-Ⅱ superconductor BaSn_(5)(T_(c)∼4.4 K)probed by measuring the magnetization,specific heat,de Haas–van Alphen(dHvA)effect,and by performing first-principles calculations.The first-principles calculations reveal a topological nodal ring structure centered at the H point in the k_(z)=πplane of the Brillouin zone,which could be gapped by spin-orbit coupling(SOC),yielding relatively small gaps below and above the Fermi level of about 0.04 eV and 0.14 eV,respectively.The SOC also results in a pair of Dirac points along theΓ–A direction,located at∼0.2 eV above the Fermi level.The analysis of the dHvA quantum oscillations supports the calculations by revealing a nontrivial Berry phase originating from the hole and electron pockets related to the bands forming the Dirac cones.Thus,our study provides an excellent avenue for investigating the interplay between superconductivity and nontrivial topological states.

Photoemission Spectroscopic Evidence of Multiple Dirac Cones in Superconducting BaSn_(3)

Signatures of topological superconductivity(TSC)in superconducting materials with topological nontrivial states prompt intensive researches recently.Utilizing high-resolution angle-resolved photoemission spectroscopy and first-principles calculations,we demonstrate multiple Dirac fermions and surface states in superconductor BaSn_(3) with a critical transition temperature of about 4.4 K.We predict and then unveil the existence of two pairs of type-Ⅰtopological Dirac fermions residing on the rotational axis.Type-ⅡDirac fermions protected by screw axis are confirmed in the same compound.Further calculation for the spin helical texture of the observed surface states originating from the Dirac fermions gives an opportunity for realization of TSC in one single material.Hosting multiple Dirac fermions and topological surface states,the intrinsic superconductor BaSn_(3) is expected to be a new platform for further investigation of topological quantum materials as well as TSC.

de Haas–van Alphen Quantum Oscillations in BaSn3 Superconductor with Multiple Dirac Fermions

Characterization of Fermi surface of the BaSn3 superconductor(Tc~ 4.4K)by de Haas–van Alphen(dHvA)effect measurement reveals its non-trivial topological properties.Analysis of non-zero Berry phase is supported by the ab initio calculations,which reveals a type-II Dirac point setting and tilting along the high symmetric K–H line of the Brillouin zone,about 0.13 eV above the Fermi level,and other two type-I Dirac points on the high symmetric Г–A direction,but slightly far below the Fermi level.The results demonstrate BaSn3 as an excellent example hosting multiple Dirac fermions and an outstanding platform for studying the interplay between nontrivial topological states and superconductivity.