Predominantly Superconducting Origin of Large Energy Gaps in Underdoped Bi2Sr2CaCu2O8-d from Tunneling Spectroscopy

New tunneling data are reported in underdoped Bi2Sr2CaCu2O8-d using superconductor-insulator-superconductor break junctions. Energy gaps, Delta, of 51+2, 54+2 and 57+3 meV are observed for three crystals with Tc=77, 74, and 70 K respectively. These energy gaps are nearly three times larger than for overdoped crystals with similar Tc. Detailed examination of tunneling spectra over a wide doping range from underdoped to overdoped, including the Josephson IcRn product, indicate that these energy gaps are predominantly of superconducting origin.Comment: 10 pages, 4 figures, 1 tabl

Correlation of Tunneling Spectra in Bi2Sr2CaCu2O(8+delta) with the Resonance Spin Excitation

New break-junction tunneling data are reported in Bi2Sr2CaCu2O(8+delta) over a wide range of hole concentration from underdoped (Tc = 74 K) to optimal doped (Tc = 95 K) to overdoped (Tc = 48 K). The conductances exhibit sharp dips at a voltage, Omega/e, measured with respect to the superconducting gap. Clear trends are found such that the dip strength is maximum at optimal doping and that Omega scales as 4.9 kTc over the entire doping range. These features link the dip to the resonance spin excitation and suggest quasiparticle interactions with this mode are important for superconductivity.Comment: 4 pages, 3 figure

Quasiparticle Liquid in the Highly Overdoped Bi2212

We present results from the study of a highly overdoped (OD) Bi2212 with a $T_{c}=51$K using high resolution angle-resolved photoemission spectroscopy. The temperature dependent spectra near the ($\pi,0$) point show the presence of the sharp peak well above $T_{c}$. From the nodal direction, we make comparison of the self-energy with the optimally doped and underdoped cuprates, and the Mo(110) surface state. We show that this OD cuprate appears to have properties that approach that of the Mo. Further analysis shows that the OD has a more $k$-independent lineshape at the Fermi surface than the lower-doped cuprates. This allows for a realistic comparison of the nodal lifetime values to the experimental resistivity measurements via Boltzmann transport formulation. All these observations point to the validity of the quasiparticle picture for the OD even in the normal state within a certain energy and momentum range.Comment: 4 pages, 4 figure

Anisotropic Superconducting Gaps and Boson Mode in FeSe 1−x Sx Single Crystals

Scanning tunneling spectroscopy has been used to investigate the superconducting gaps of FeSe 1−xSx single crystals and to reveal signatures of a bosonic mode in the quasiparticle density of states. We find that both superconducting gaps residing on different pockets of the Fermi surface are anisotropic. Moreover, the bosonic mode appears in the quasiparticle density of states as a redistribution of states at energy Ω/e, measured with respect to the superconducting gap. The energy of the boson mode Ω is found to scale with the superconducting gap, and it can be estimated to be in the range 2.6 ÷ 3.8 meV in agreement with a recent observation of a resonance spin excitation in neutron scattering. This suggests that quasiparticle interactions with this mode are important for superconductivity. © 2016, Springer Science+Business Media New York