Point-contact Spectroscopy Studies On Several Superconductors And Heavy-fermion Materials

Superconductors and heavy fermions are of great interest in the condense matter communities,where the studies on the superconducting gap structure in superconductors and the hybridization between f and conduction electrons in heavy fermions are crucial to understand their underlying mechanism.We have applied point contact spectroscopy(PCS)measurements to explore the superconducting gap structures of several superconductors,including ?-PdBi2,(PbSe)1.12(TaSe2)and Ca3lr4Sn13,and the behaviors of f electrons in heavy fermions Ce2PdIn8 and Ce3PdIn11 and the Kondo semiconductor CeRu2Alio.(1)The superconductor(3-PdBi2 has been claimed to own nontrivial topological surface states,serving as a promising candidate of topological superconductors.Our PCS measurements,however,show atypical double-peak structure for the conductance curves with the absence of an intrinsic zero-bias conductance peak(ZBCP).The Blonder-Tinkham-Klapwijk(BTK)fitting suggests a fully-opened superconducting gap in ?-PdBi2,following the typical BCS temperature and field behaviors.We would rather note that the existence of topological superconductivity in ?-PdBi2 can't be completely ruled out.(2)The Cl(Br)-doped misfit superconducting compound(PbSe)1.12(TaSe)2 has a natural heterostructure with an alternating stack of single-layer PbSe and TaSe2.A single-layer PbSe is predicted to be topological crystalline insulator from theoretical calculations,and thus Cl(Br)-doped(PbSe)1.12(TaSe2)may be also a candidate of topological superconductors.Our PCS conductance curves show a typical double peak structure,and the BTK fittings suggest a fully open s-wave gap,where its evolution with temperature or magnetic field is consistent with the BCS behavior.Our results show that Cl(Br)-doped(PbSe)1.12(TaSe2)is an s-wave superconductor with a moderate electron-phonon coupling,and its superconductivity may be related with the charge transfer between PbSe and TaSe2 layers.(3)The relationship between the structure transition and superconductivity in Ca3Ir4Sn13 is still in hot debate and the results on its superconducting gap structure are controversial.The extracted gap from a single gap BTK fitting deviates from the BCS temperature dependence,while a two-band BTK fitting gives more reasonable results,yielding ?1=1.25 meV and ?2=0.52 meV.(4)Heavy fermion materials Ce2Pdln8 and Ce3PdIn11 are variants of the classical"115" family but with different ground states.Our point contact measurements show consistent differential conductance curves in an asymmetric Fano spectral shape below the Kondo coherent temperature,which is ascribed to the coherent hybridization between local felectrons and itinerant conduction electrons due to Kondo interactions.(5)Kondo semiconductor CeRu2Al10 exhibits a novel anti ferromagnetic behavior,whose Neel temperature TN is much higher than the expected value due to simple RKKY interactions.Our PCS measurements on different crystal orientations show that an anisotropic charge gap opens near the Fermi level below TN,whose temperature evolution follows the mean field behavior and may be closely related to the antiferromagnetic ordering.Meanwhile,the asymmetric double peaks emerging at low temperatures suggest the formation of a new hybridization gap,corresponding to its heavy fermion behavior.