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Lattice normal modes and electronic properties of the correlated metal LaNiO 3
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Extraction of Normal Electron Self-energy and Pairing Self-energy in the Superconducting State of the Bi2Sr2CaCu2O8 Superconductor via Laser-based Angle-resolved Photoemission
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Substitution of Ni for Fe in superconducting Fe 0.98 Te 0.5 Se 0.5 depresses the normal-state conductivity but not the magnetic spectral weight
We have performed systematic resistivity and inelastic neutron scattering measurements on Fe₀.₉₈₋ z Ni z Te₀.₅Se₀.₅ samples to study the impact of Ni substitution on the transport properties and the low-energy (≤ 12 meV) magnetic excitations. It is found that, with increasing Ni doping, both the conductivity and superconductivity are gradually suppressed; in contrast, the low-energy magnetic spectral weight changes little. Comparing with the impact of Co and Cu substitution, we find that the effects on conductivity and superconductivity for the same degree of substitution grow systematically as the atomic number of the substituent deviates from that of Fe. The impact of the substituents as scattering centers appears to be greater than any contribution to carrier concentration. The fact that low-energy magnetic spectral weight is not reduced by increased electron scattering indicates that the existence of antiferromagnetic correlations does not depend on electronic states close to the Fermi energy.
Visualization of the normal-fluid turbulence in counterflowing superfluid He 4
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Superconducting and normal state properties of the systems La 1 - x M x Pt 4 Ge 12 ( M = Ce , Th )
Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La 1-x M x Pt 4 Ge 12 (M = Ce, Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x > 0.2. Temperature-dependent specific heat data at low temperatures for La 1-x Ce x Pt 4 Ge 12 show a change from power-law to exponential behavior, which may be an indication for multi-band superconductivity in LaPt 4 Ge 12 . A similar crossover was observed in the Pr 1-x Ce x Pt 4 Ge 12 system. However, the suppression rates of the superconducting transition temperatures, T c (x), in the two systems are quite disparate, indicating a difference in the nature of superconductivity, which is conventional in LaPt 4 Ge 12 and unconventional in PrPt 4 Ge 12 . In comparison, a nearly linear and smooth evolution of T c with increasing Th was observed in the La 1-x Th x Pt 4 Ge 12 system, with no change of the superconducting energy gap in the temperature dependence of the specific heat, suggesting similar types of superconductivity in both the LaPt 4 Ge 12 and ThPt 4 Ge 12 compounds.
Effect of proton irradiation on the normal-state low-energy excitations of Ba(Fe 1-x Rh x ) 2 As 2 superconductors
Here, we present a 75 As nuclear magnetic resonance (NMR) and resistivity study of the effect of 5.5 MeV proton irradiation on the optimal electron doped (x = 0.068) and overdoped (x = 0.107) Ba(Fe 1–x Rh x ) 2 As 2 iron based superconductors. While the proton induced defects only mildly suppress the critical temperature and increase residual resistivity in both compositions, sizable broadening of the NMR spectra was observed in all the irradiated samples at low temperature. The effect is significantly stronger in the optimally doped sample where the Curie Weiss temperature dependence of the line width suggests the onset of ferromagnetic correlations coexisting with superconductivity at the nanoscale. 1/T 2 measurements revealed that the energy barrier characterizing the low energy spin fluctuations of these compounds is enhanced upon proton irradiation, suggesting that the defects are likely slowing down the fluctuations between (0,π) and (π,0) nematic ground states.
Pressure-tuned superconductivity and normal-state behavior in Ba ( Fe 0.943 Co 0.057 ) 2 As 2 near the antiferromagnetic boundary
Superconductivity in iron pnictides is unconventional and pairing may be mediated by magnetic fluctuations in the Fe sublattice. Pressure is a clean method to explore superconductivity in iron based superconductors by tuning the ground state continuously without introducing disorder. Here we present a systematic high pressure transport study in Ba (Fe 1 - x Co x ) 2 As 2 single crystals with x = 0.057, which is near the antiferromagnetic instability. Resistivity ρ = ρ 0 + AT n was studied under applied pressure up to 7.90 GPa. The parameter n approaches a minimum value of n ≈ 1 at a critical pressure P c = 3.65 GPa. Near P c , the superconducting transition temperature T c reaches a maximum value of 25.8 K. In addition, the superconducting diamagnetism at 2 K shows a sudden change around the same critical pressure. Finally, these results may be associated with a possible quantum critical point hidden inside the superconducting dome, near optimum T c .
Optical response of Luttinger semimetals in the normal and superconducting states
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