Single gap superconductivity in beta-Bi2Pd

beta-Bi2Pd compound has been proposed as another example of a multi-gap superconductor [Y. Imai et al., J. Phys. Soc. Jap. 81, 113708 (2012)]. Here, we report on measurements of several important physical quantities capable to show a presence of multiple energy gaps on our superconducting single crystals of beta-Bi2Pd with the critical temperature Tc close to 5 K. The calorimetric study via a sensitive ac technique shows a sharp anomaly at the superconducting transition, however only a single energy gap is detected. Also other characteristics inferred from calorimetric measurements as the field dependence of the Sommerfeld coefficient and the temperature and angular dependence of the upper critical magnetic field point unequivocally to standard single s-wave gap superconductivity. The Hall-probe magnetometry provides the same result from the analysis of the temperature dependence of the lower critical field. A single-gapped BCS density of states is detected by the scanning tunneling spectroscopy measurements. Then, the bulk as well as the surface sensitive probes evidence a standard conventional superconductivity in this system where the topologically protected surface states have been recently detected by ARPES [M. Sakano et al., Nature Comm. 6, 8595 (2015)] .Comment: 7 pages, 4 figures, 1 tabl

Low temperature transition to a superconducting phase in boron-doped silicon films grown on (001)-oriented silicon wafers

We report on a detailed analysis of the superconducting properties of boron-doped silicon films grown along the 001 direction by Gas Immersion Laser Doping. The doping concentration cB has been varied up to approx. 10 at.% by increasing the number of laser shots to 500. No superconductivity could be observed down to 40mK for doping level below 2.5 at.%. The critical temperature Tc then increased steeply to reach 0.6K for cB = 8 at%. No hysteresis was found for the transitions in magnetic field, which is characteristic of a type II superconductor. The corresponding upper critical field Hc2(0) was on the order of 1000 G, much smaller than the value previously reported by Bustarret et al. in Nature (London) 444, 465 (2006).Comment: 4 pages including 4 figures, submitted to PRB-Rapid Communicatio

Pressure effect on the superconducting and the normal state of β- B i2Pd

The pressure effect up to 24.0 kbar on superconducting and normal-state properties of β-Bi2Pd single crystal (Tc≈4.98K at ambient pressure) has been investigated by measurements of the electrical resistivity. In addition, we have performed the heat capacity measurements in the temperature range 0.7-300 K at ambient pressure. The recent calculations of electronic density of states, electron-phonon interaction spectral function, and phonon density of states of β-Bi2Pd [Zheng and Margine, Phys. Rev. B 95, 014512 (2017)10.1103/PhysRevB.95.014512], are used to fit the resistivity and the heat capacity data. In the superconducting state we have focused on the influence of pressure on the superconducting transition temperature Tc and upper critical field Hc2 and a negative effect with dTc/dp=-0.025K/kbar and dHc2/dp=-8mT/kbar is found. A simplified Bloch-Grüneisen model was used to analyze the pressure effect on the temperature dependence of the normal-state resistivity. The obtained results point to a decrease of the electron-phonon coupling parameter λ and to a shift of phonon frequencies to higher values with pressure. Moreover, the temperature dependence of the normal-state resistivity follows a T2 dependence above Tc up to about 25 K. Together with the enhanced value of Sommerfeld coefficient γ=13.23mJmol-1K-2 these results point to a certain role of the electron-electron interaction in the superconducting pairing mechanism in β-Bi2PdThis work was supported by projects VEGA 2/0032/16, VEGA 2/0149/16, APVV-16-0372, EU ERDF Grant No. ITMS26220120047 and by European Microkelvin Platform. Liquid nitrogen for experiments was sponsored by US Steel Košice, s.r.o. E.H. was supported by the Departamento Administrativo de Ciencia, Tecnología e Innovación, COLCIENCIAS (Colombia), programa doctorados en el exterior convocatoria No. 568-2012 and the Universidad Nacional de Colombia, División de Investigación y Extensión sede Bogotá (DIEP) Project No. 356515. H.S. and A. C. by the Spanish Ministry of Economy and Competitiveness (FIS2017-84330-R, MDM-2014-0377), by the Comunidad de Madrid through program Nanofrontmag-CM (S2013/MIT-2850), and by COST CA1621

Unconventional superconductivity in the strong-coupling limit for the heavy fermion system CeCoIn5

We present scanning tunneling spectroscopy measurements of the local quasiparticles' excitation spectra of the heavy fermion CeCoIn5 between 440 mK and 3 K in samples with a bulk Tc=2.25K. The spectral shape of our low-temperature tunneling data, quite textbook nodal-Δ conductance, allow us to confidently fit the spectra with a d-wave density of states considering also a shortening of quasiparticles' lifetime term Γ. The Δ(0) value obtained from the fits yields a BCS ratio 2Δ/kTc=7.73 suggesting that CeCoIn5 is an unconventional superconductor in the strong coupling limit. The fits also reveal that the height of coherence peaks in CeCoIn5 is reduced with respect to a pure BCS spectra and therefore the coupling of quasiparticles with spin excitations should play a relevant role. The tunneling conductance shows a depletion at energies smaller than Δ for temperatures larger than the bulk Tc, giving further support to the existence of a pseudogap phase that in our samples span up to T*∼1.2Tc. The phenomenological scaling of the pseudogap temperature observed in various families of cuprates, 2Δ/kT*∼4.3, is not fulfilled in our measurements. This suggests that in CeCoIn5 the strong magnetic fluctuations might conspire to close the local superconducting gap at a smaller pesudogap temperature-scale than in cuprates.Fil: Fasano, Yanina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Bajas Temperaturas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Szabó, P.. Centre of Low Temperatures Physics; EslovaquiaFil: Kačmarčík, J.. Centre of Low Temperatures Physics; EslovaquiaFil: Pribulová, Z.. Centre of Low Temperatures Physics; EslovaquiaFil: Pedrazzini, Pablo. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Bajas Temperaturas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Samuely, P.. Centre of Low Temperatures Physics; EslovaquiaFil: Correa, Víctor Félix. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Bajas Temperaturas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin