106 research outputs found
Type II superconductivity in SrPd2Ge2
Previous investigations have shown that SrPd2Ge2, a compound isostructural
with "122" iron pnictides but iron- and pnictogen-free, is a conventional
superconductor with a single s-wave energy gap and a strongly three-dimensional
electronic structure. In this work we reveal the Abrikosov vortex lattice
formed in SrPd2Ge2 when exposed to magnetic field by means of scanning
tunneling microscopy and spectroscopy. Moreover, by examining the differential
conductance spectra across a vortex and estimating the upper and lower critical
magnetic fields by tunneling spectroscopy and local magnetization measurements,
we show that SrPd2Ge2 is a strong type II superconductor with \kappa >>
sqrt(2). Also, we compare the differential conductance spectra in various
magnetic fields to the pair breaking model of Maki - de Gennes for dirty limit
type II superconductor in the gapless region. This way we demonstrate that the
type II superconductivity is induced by the sample being in the dirty limit,
while in the clean limit it would be a type I superconductor with \kappa\ <<
sqrt(2), in concordance with our previous study (T. Kim et al., Phys. Rev. B
85, (2012)).Comment: 9 pages, 4 figure
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
Magnetotransport and the upper critical magnetic field in MgB2
Magnetotransport measurements are presented on polycrystalline MgB2 samples.
The resistive upper critical magnetic field reveals a temperature dependence
with a positive curvature from Tc = 39.3 K down to about 20 K, then changes to
a slightly negative curvature reaching 25 T at 1.5 K. The 25- Tesla upper
critical field is much higher than what is known so far on polycrystals of MgB2
but it is in agreement with recent data obtained on epitaxial MgB2 films. The
deviation of Bc2(T) from standard BCS might be due to the proposed two-gap
superconductivity in this compound. The observed quadratic normal-state
magnetoresistance with validity of Kohler's rule can be ascribed to classical
trajectory effects in the low-field limit.Comment: 6 pages, incl. 3 figure
Evidence for conventional superconductivity in SrPd2Ge2
Electronic structure of SrPd2Ge2 single crystals is studied by angle-resolved
photoemission spectroscopy (ARPES), scanning tunneling spectroscopy (STS) and
band-structure calculations within the local-density approximation (LDA). The
STS measurements show single s-wave superconducting energy gap \Delta(0) = 0.5
meV. Photon-energy dependence of the observed Fermi surface reveals a strongly
three-dimensional character of the corresponding electronic bands. By comparing
the experimentally measured and calculated Fermi velocities a renormalization
factor of 0.95 is obtained, which is much smaller than typical values reported
in Fe-based superconductors. We ascribe such an unusually low band
renormalization to the different orbital character of the conduction electrons
and using ARPES and STS data argue that SrPd2Ge2 is likely to be a conventional
superconductor, which makes it clearly distinct from isostructural iron
pnictide superconductors of the "122" family.Comment: submitted to PR
Upper critical field in {BaKBiO}: magnetotransport versus magnetotunneling
Elastic tunneling is used as a powerful direct tool to determine the upper
critical field in the high- oxide BaKBiO. The
temperature dependence of inferred from the tunneling follows the
Werthamer-Helfand-Hohenberg prediction for type-II superconductors. A
comparison will be made with resistively determined critical field data.Comment: 4 pages incl. 5 figure
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