Toshikazu Ekino

SUPERCONDUCTING TUNNELING IN Y-Ba-Cu-O SYSTEM.

Electron tunneling study on high-Tc superconductor Y-Ba-Cu-O system with the onset transition temperature of about 95 K has been carried out. The observed energy gap is slightly larger than that expected from the BCS theory.

Electron Tunneling Study of NbSe3

The two CDW energy gaps of NbSe3 were measured by means of the point contact tunneling technique. The peak to peak values of energy gaps at T=4.2K aretypically 2ΔH180 mV and 2ΔL73 mV from the NbSe3-Au junction, where ΔH and ΔL correspond to the higher CDW transition temperature TH=145K and lower one TL=59K, respectively. From these values, we obtained that 2ΔH/kTH=14.4 and 2ΔL/kTL=14.3, which are much larger than the DCS value.

Superconducting energy gap in BaPb1-xBixO3 determined from point-contact tunneling

Electron tunneling measurements have been performed on single crystals of BaPb 1- x Bi x O 3 with various values of x . The observed density of states in the superconducting state can well be described by the broadened BCS density of states proposed by Dynes et at. The ratio 2 Δ /k T c increases with increasing the Bi concentration of x , suggesting the increase of electron-phonon interactions, and saturates at around x ∼0.2. The values of 2 Δ /k T c in the saturated region coincide with the BCS value.

Electron Tunneling Study on Superconductivity of BaPb1-xBixO3

The electron tunneling measurements have been performed on the single crystal of BaPb1-xBixO3 with various x around x~0.2. The observed density of states can well be described by the broadened BCS density of states proposed by Dynes et al, suggesting the gapless superconductor in BaPb1-xBixO3.

Electron Tunneling into Superconducting Bismuth-Copper Oxide Systems

The energy gaps of the polycrystal1ine Bi-Sr-Ca-Cu-O and Bi-Sr-Cu-O superconductors have been measured by means of the point-contact tunneling technique. We find that the energy gaps at T=OK are 2Δ=76-81meV in Bi2Sr2Ca1Cu2Oy(Tc=76K), 91–100meV in Bi2Sr2Ca2Cu3Oy(Tc=105K) and 3.0–3.5meV in Bi2Sr2Cu1Oy (Tc=6.5K). Temperature variations of these energy gaps are also extracted. The ratios 2Δ/kTc are 11.6–12.4 for Bi2Sr2Ca1Cu2Oy, 10.0–11.0 for Bi2Sr2Ca2Cu3Oy, extremely larger than BCS value. 2Δ/kTc of Bi2Sr2Cu1Oy is 5.4–6.2, larger than those of the usual strong coupling superconductors. These results give the information about the difference of the pairing nature on the superconducting state between these materials which have multiple Cu02 layers or a single CuO2 layer between the SrO layers.