In doped SrTiO3 superconductivity persists down to an exceptionally low concentration of mobile electrons. This restricts the relevant energy window and possible pairing scenarios. We present a study of quantum oscillations and superconducting transition temperature, Tc as the carrier density is tuned from 10 17 to 10 20 cm −3 and identify two critical doping levels corresponding to the filling thresholds of the upper bands. At the first critical doping, which separates the single-band and the two-band superconducting regimes in oxygen-deficient samples, the steady increase of Tc with carrier concentration suddenly stops. Near this doping level, the energy dispersion in the lowest band displays a downward deviation from parabolic behavior. The results impose new constraints for microscopic pairing scenarios.Superconductiviy is induced in insulating SrTiO 3 by introducing n-type charge carriers through chemical doping[1] and survives over three orders of magnitude of carrier concentration. The transition temperature, T c , peaks to 0.45 K around a carrier density of n H ∼ 10 20 cm −3 [2]. A superconducting dome has also been detected in the metallic interfaces of SrTiO 3 [3] when the carrier density is modulated by a gate voltage bias [4]. In unconventional superconductors, such as high-T c cuprates, superconducting domes are often attributed to the proximity of a magnetic order or a Mott insulator. The recent discovery of superconducting dome in gate-tuned MoS 2 [5] in absence of a competing order, however, highlights the limits of our current understanding of the interplay between carrier concentration and superconductivity and motivates a fresh reexamination of superconducting domes. In the specific case of SrTiO 3 , superconductivity occurs in the vicinity of an aborted ferroelectric order[6] and survives deep inside the dilute metallic regime when the Fermi temperature becomes more than one order of magnitude lower than the Debye temperature [7]. This is a second puzzle in addition to the one raised by the drop in T c on the overdoped side. These two questions, raised at the opposite limits of the superconducting dome, remain unsettled.According to band calculations[9-11], doping SrTiO 3 with n-type carriers can fill three bands one after the other. Once the critical threshold for the occupation of a band is attained, a new Fermi surface concentric with the previous one emerges. Previous studies of quantum oscillations in bulk doped SrTiO 3 [7, 12-14] have detected both multiple-frequency [7,13,14] and singlefrequency [7,14] oscillations at different doping levels, but did not determine these critical doping levels. Moreover, according to tunneling experiments, doped SrTiO 3 beyond a carrier density of 10 19 cm −3 is a multi-gap superconductor [8]. The interplay between multi-band occupation in the normal state and multi-gap superconductivity has been a subject of recent theoretical attention [20].We present a systematic study of quantum oscillations and superconducting transition as a function of carrier con...

The thermal conductivity of the heavy fermion superconductor Pr(Os(4)Sb(12) was measured down to T(c)/40 throughout the vortex state. At lowest temperatures and for magnetic fields H approximately 0.07H(c2), already 40% of the normal state thermal conductivity is restored. This behavior (similar to that observed in MgB2) is a clear signature of multiband superconductivity in this compound.

The superconducting state of the heavy fermion PrOs4Sb12 is studied by heat transport measurements on a highly homogeneous single crystal exhibiting only one transition peak in the specific heat. The field and temperature dependence of the thermal conductivity confirm multiband superconductivity and point to fully open gaps on the whole Fermi surface.

We present new measurements of the specific heat of the heavy fermion superconductor PrOs4Sb12, on a sample which exhibits two sharp distinct anomalies at Tc1 = 1.89K and Tc2 = 1.72K. They are used to draw a precise magnetic field-temperature superconducting phase diagram of PrOs4Sb12 down to 350 mK. We discuss the superconducting phase diagram of PrOs4Sb12 and its possible relation with an unconventional superconducting order parameter. We give a detailed analysis of Hc2(T ), which shows paramagnetic limitation (a support for even parity pairing) and multiband effects.

New thermal conductivity experiments on the heavy-fermion superconductor CeCoIn5 down to 10 mK rule out the suggested existence of unpaired electrons. Moreover, they reveal strong multigap effects with a remarkably low "critical" field Hc2S for the small gap band, showing that the complexity of heavy-fermion band structure has a direct impact on their response under magnetic field.

Effect of Co-doping on the resistivity and thermopower of SmFe1-xCoxAsO (0.0≤x≤0.3) AIP Advances 2, 042137 (2012) Critical current reduction in coated conductors when in-plane fields are applied J. Appl. Phys. 112, 073918 (2012) Study of Bi2Sr2CaCu2O8/BiFeO3 nano-composite for electrical transport applications J. Appl. Phys. 112, 053916 (2012) Para-conductivity and critical regime of (Tl1−xCx)Ba2Ca3Cu4O12−δ superconductors J. Appl. Phys. 112, 033912 (2012) The electrical conductivity of bundles of superconducting nanowires produced by laser ablation of metals in superfluid helium

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The first heavy fermion superconductor CeCu 2 Si 2 has not revealed all its striking mysteries yet. At high pressures, superconductivity is supposed to be mediated by valence fluctuations, in contrast to ambient pressure, where spin fluctuations most likely act as pairing glue. We have carried out a multiprobe (electric transport, thermopower, ac specific heat, Hall and Nernst effects) experiment up to 7 GPa on a high-quality CeCu 2 Si 2 single crystal. For the first time, the resistivity data make it possible quantitatively to draw the valence crossover line within the p-T plane and to locate the critical end point at 4.5 ± 0.2 GPa and a slightly negative temperature. In the same pressure region, remarkable features have also been detected in the other physical properties, presumably acting as further signatures of the Ce valence crossover and the associated critical fluctuations: We observe maxima in the Hall and Nernst effects and a sign change and a strong sensitivity on magnetic field in the thermopower signal.