N. Tsuda

Tunneling phonon structures and the calculated phonon density of states for Bi2Sr2CaCu2O8

Abstract The spectral function of the electron–phonon interaction, determined by a tunneling experiment, is compared with a calculated phonon density of states. The agreement between them is considerable. For each peak in α 2 F , atomic displacements of the corresponding phonon modes at particular points in the Brillouin zone are shown. Of these, vibrations of oxygen atoms along a c -axis and low-frequency cation vibrations are noteworthy.

Superconducting energy gap of underdoped and overdoped Bi2Sr2CaCu2O8

Abstract The tunneling conductance was measured for a natural-barrier planar tunneling junction of underdoped and overdoped Bi2Sr2CaCu2O8. The temperature dependence of the separation between the gap edge peaks suggests that the amplitude of superconducting gap becomes zero at the superconducting critical temperature.

Tunneling conductance of a Bi2Sr2CaCu2O8-SnO2 junction along the c-axis

Abstractfine structure was observed in the conductance curve of a tunneling junction composed of a single crystalline Bi2212 and an evaporated SnO2 film. It is similar to those of Bi2212-GaAs mechanical junctions and there is a certain correspondence between the structure and the phonon density of states. Thus the previous conclusion that the structure is due to phonons has been complemented by this work. The energy gap 2Δ was 57 meV at 13 K and Tc was 78 K. 2Δ(0)/kBTc is then 8.3. Δ(T) showed the BCS-like temperature dependence.

On the isotope effect in Tc for cuprate superconductors

Abstract The larger isotope effect in T c for underdoped cuprate superconductors is discussed based on our Eliashberg-magnetic pair break model of cuprate superconductivity in which the attractive interaction between electrons is attributed to phonon exchange and T c is reduced by thermally excited magnetic moments above the spin gap at Cu sites. It is claimed that the isotope effect would have been small even for underdoped oxides as found for optimally and overdoped materials if there were no pair break effect.

Electron-phonon spectral function α2F(ω) determined by quasiparticle tunneling spectroscopy for Bi2Sr2CaCu2O8/Au junctions

The electron-phonon spectral function is determined by the tunneling spectroscopy for Bi2Sr2CaCu2O8/Au planar junctions, for which the phonon structures are observed on the second derivative resistance d 2V/dI2 curves though they are obscure on the dI/dV curves. The spectral function is similar to the generalized phonon density of states and gives proper value for the critical temperature in the Eliashberg framework.

Layer number dependence of superconducting critical temperature of cuprates: consequence of a phonon contribution to the pairing

Abstract The layer number dependence of superconducting critical temperature Tc is discussed based on the characteristic feature of the spectral function of an electron–phonon interaction determined by our tunneling experiment. In our model, increase in Tc is attributed to an increase in the density of effective phonon modes with the number of CuO2 layer due to a long-range nature of the interaction.

Phonon contribution to superconductivity of Bi2Sr2CaCu2O8

Abstract Phonon structures were observed in the tunneling conductance of Bi2Sr2CaCu2O8. The spectral function gives proper values for the critical temperature and the energy gap. There is no particular phonon-mode whose contribution to Tc is larger than 12 K. The resistivity and the nuclear-spin relaxation rate were calculated using the spectral function.

Phonon structures in the tunneling conductance of Bi-cuprates

Abstract Reproducibility of phonon structures in the tunneling conductance of Bi-cuprates is demonstrated. Temperature dependence of the gap shows a downward deviation from the BCS relation.

Tunneling study of underdoped and overdoped Bi2Sr2CaCu2O8

Abstract The temperature dependence of the edge peak voltage of a natural-barrier planar tunneling junction of overdoped and underdoped Bi 2 Sr 2 CaCu 2 O 8− x suggests that the superconducting gap closes at the superconducting critical temperature.

Tunneling study of Co-substituted Bi2Sr2CaCu2O8

Abstract Tunneling conductance was measured for Co-substituted Bi2Sr2CaCu2O8/ITO junctions. The results are analyzed by using the spectral function of the electron-phonon interaction for Co-free substance. The magnetic impurity is assumed only to break the pair. For fitting the experimental conductance, an inhomogeneous gap and a temperature-dependent barrier strength must be assumed.