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Register a new userRobust superconductivity with large upper critical field in Nb2PdS5
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We report synthesis, structural details and complete superconducting characterization of very recently discovered Nb2PdS5 new superconductor. The synthesized compound is crystallized in mono-clinic structure. Bulk superconductivity is seen in both magnetic susceptibility and electrical resistivity measurements with superconducting transition temperature (Tc) at 6K. The upper critical field (Hc2), being estimated from high field magneto-transport measure-ments is above 240kOe. The estimated Hc2(0) is clearly above the Pauli paramagnetic limit. Heat capacity measurements show clear transition with well defined peak at Tc, but with lower jump than as expected for a BCS type superconductor. The Sommerfield constant and Debye temperature as determined from low temperature fitting of heat capacity data are 32mJ/moleK2 and 263K respectively. Hall coefficients and resistivity in conjugation with electronic heat capacity indicates multiple gap superconductivity signatures in Nb2PdS5. We also studied the impact of hydrostatic pressure on superconductivity of Nb2PdS5 and found nearly no change in Tc for the given pressure range.
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We determine the upper critical field $mu_0 H_{c2}(T_c)$ of non-centrosymmetric superconductor $Y_2 C_3$ using two distinct methods: the bulk magnetization M(T) and the tunnel-diode oscillator (TDO) based impedance measurements. It is found that the upper critical field reaches a value of 30T at zero temperature which is above the weak-coupling Pauli paramagnetic limit. We argue that the observation of such a large $mu_0 H_{c2}(0)$ in $Y_2 C_3$ could be attributed to the admixture of spin-singlet and spin-triplet pairing states as a result of broken inversion symmetry.
We report specific heat under different magnetic fields for recently discovered quasi-one dimensional Nb2PdS5 superconductor. The studied compound is superconducting below 6 K. Nb2PdS5 is quite robust against magnetic field with dHc/dT of -42 kOe/K. The estimated upper critical field [Hc2(0)] is 190 kOe, clearly surpassing the Pauli-paramagnetic limit of 1.84Tc. Low temperature heat capacity in superconducting state of Nb2PdS5 under different magnetic fields showed s-wave superconductivity with two different gaps. Two quasi-linear slopes in Somerfield-coefficient as a function of applied magnetic field and two band behavior of the electronic heat capacity demonstrate that Nb2PdS5 is a multiband su-perconductor in weak coupling limit with deltagamma/deltaTc=0.9.
We grew single crystals of U6Co by the self-flux method and measured the magnetic susceptibility, resistivity, and specific heat. The magnetic susceptibility shows very small anisotropy and weak temperature dependence, indicating small spin-susceptibility. Superconductivity was clearly observed in the resistivity, susceptibility, and specific heat at Tc~2.3K. The upper critical field was remarkably large, 7.9 and 6.6T for H || [001] and [110], respectively, in the tetragonal structure, indicating that the ellipsoidal Fermi surface is slightly suppressed along the [001] direction according to the effective mass model. The specific heat shows a large jump at Tc with Delta C/gamma Tc = 1.58, and the field dependence of the specific heat at low temperatures shows an almost linear increase. These experimental results are well explained by the BCS model in the dirty limit condition. U6Co is most likely a conventional s-wave superconductor with a full superconducting gap.
The transition temperature Tc of cuprate superconductors falls when the doping p is reduced below a certain optimal value. It is unclear whether this fall is due to strong phase fluctuations or to a decrease in the pairing gap. Different interpretations of photoemission data disagree on the evolution of the pairing gap and different estimates of the upper critical field Hc2 are in sharp contradiction. Here we resolve this contradiction by showing that superconducting fluctuations in the underdoped cuprate Eu-LSCO, measured via the Nernst effect, have a characteristic field scale that falls with underdoping. The critical field Hc2 dips at p = 0.11, showing that superconductivity is weak where stripe order is strong. In the archetypal cuprate superconductor YBCO, Hc2 extracted from other measurements has the same doping dependence, also with a minimum at p = 0.11, again where stripe order is present. We conclude that competing states such as stripe order weaken superconductivity and this, rather than phase fluctuations, causes Tc to fall as cuprates become underdoped.
Resistivity and Hall effect measurements of EuFe$_2$As$_2$ up to 3.2,GPa indicate no divergence of quasiparticle effective mass at the pressure $P_mathrm{c}$ where the magnetic and structural transition disappears. This is corroborated by analysis of the temperature ($T$) dependence of the upper critical field. $T$-linear resistivity is observed at pressures slightly above $P_mathrm{c}$. The scattering rates for both electrons and holes are shown to be approximately $T$-linear. When a field is applied, a $T^2$ dependence is recovered, indicating that the origin of the $T$-linear dependence is spin fluctuations.
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