H. Kaneda

Anomalous effect in La2-xSrxCuO4 of doping level x = 1/4n

Anomalous electric response of La 2-x Sr x CuO 4 thin film at Sr doping levels of x 1/4 and 1/16 is observed when charge moves along the c axis. The capacitance C t of the Pd/La 2-x Sr x CuO 4 /SrTiO 3 /Pd structure increases sharply, exceeding the capacitance C STO of the Pd/SrTiO 3 /Pd structure. Oscillatory negative voltage is observed in 4-terminal resistivity measurements of La 2-x Sr x CuO 4 thin film using Pd electrodes at small current. These phenomena are explained by a model of the spatial ordered state in which CuO 2 layers of La 2-x Sr x CuO 4 is replete with O hole pairs.

Macroscopic Quantum Effect Conjugate to Josephson Effect

A new macroscopic quantum effect with conjugate property to Josephson effect is proposed theoretically. Some experiments are given which reveal real existence of the effect.

Anomalous ac dielectric response and carrier state of c-axis oriented La2−xSrxCuO4 films

Abstract In order to study the “fractional Hall effect model” of the carrier state of high temperature superconductors, we measured the x dependence of the capacitance C t of multilayer structure Pd/La 2− x Sr x CuO 4 /(100)SrTiO 3 /Pd. A strong correspondence is found between the x - C t relationship and the filling factor ν dependence of the system energy in the fractional quantum Hall effect.

Synthesis of (Ba,Sr)TiO3 Thin Films by Plasma-Activated Pulsed Laser Deposition Technique

We report the synthesis of (Ba,Sr)TiO3 (BST) thin films using plasma-activated pulsed laser deposition (PA-PLD) in oxygen ambient. In the PA-PLD system, an RF inductive coil was placed between a target and a substrate, to which RF power of about 50 W was supplied. A SiO2 tube was positioned in the coil to confine the plasma particles. The BST films were deposited on SrTiO3 (100) substrates at various temperatures by PA-PLD and the conventional PLD method. X-ray diffraction results show that the films deposited by both methods were highly oriented in the (100) direction, and the crystallinity of conventional PLD films was slightly better than that of PA-PLD films. However, atomic force microcopy observation showed the surface morphology of the PA-PLD films was smoother than that of conventional PLD films. The leakage current characteristics of PA-PLD films were also effectively improved compared to those of conventional PLD.

Phase-quantum tunnel device

Theoretical and Experimental study on granular superconductors shows that (i) they are classified into two groups; fixed-phase superconductor (Θ-superconductor) and fixed-pair-number superconductor (N-superconductor), and that (ii) a new macroscopic quantum device with conjugate property to Josephson effect can be made by use of N-superconductors.

Evidence of strong relationship between carrier states in fractional quantum-Hall effect and in high- temperature superconductivity found in dielectric measurement of La2-xSrxCuO4 film

The capacitance measurement of Pd/La2−xSrxCu04/(100)SrTiO3/Pd multi-layer structure at low ac frequency 40Hz–100kHz shows the increase of its capacitance C t at Sr-doping factor x =1/2k with the decrease at x =1/(2k+1) where k is integer. Strong correspondence is found between the observed x − C t relationship and the v − ΔE relationship known in the fractional quantum Hall effect, where y is the electron filling factor and ΔE is the 2D electron energy. The correspondence exists in the following points. (i) Both x and v are the filling factor of carriers in quantum sites. (ii) Peaks are found when the factors are 1/(even integer). (iii) Sharp valleys are found when the factors are 1/(odd integer). The origin of the correspondence is discussed based on the similarity between the 2D electron state in strong magnetic field and the hole carrier state in the presence of space charge in La2−xSrxCuO4 with periodic block-layer potential.

Anomalous dielectric effect of La/sub 2-x/Sr/sub x/CuO/sub 4/

The dielectric response of c-axis oriented La/sub 2-x/Sr/sub x/CuO/sub 4/ film is experimentally studied using Pd/La/sub 2-x/Sr/sub x/CuO/sub 4//(100)SrTiO/sub 3//Pd multi-layer structure. Anomalous capacitance increase is observed at Sr doping level x/spl ap/1/2/sup n/, where the drop of resistivity in bulk La/sub 2-x/Sr/sub x/CuO/sub 4/ in normal state has been reported.

EXPERIMENT ON PHASE-QUANTUM-TUNNELING DEVICE.

Experimental study is made on the behavior of long-bridge devices made of granular superconductor. The observed result corroborates that the device works on physical principle dual to Josephson effect.

THEORY AND EXPERIMENTAL EVIDENCE FOR PAIR FQHE STATE CAUSED BY ZERO-POINT HARMONIC OSCILLATION IN BLOCK-LAYER POTENTIAL

The zero point oscillation state of hole carriers confined in block layer potential of La2-x Sr x CuO 4 is similar to the zero point state in a Landau gauge, when the effective ”magnetic field” is greater than 103 T. It is shown that a strong effective field and space charge form layered fractional quantum Hall effect (FQHE) state for c-axis oriented La2-x Sr x CuO4 films with localization character, for which there is an anomalous dielectric polarization with negative dielectric constant is expected to appear. Experimental study of the dielectric properties of c-axis oriented La2-x Sr x CuO4 film with oxygen deficiency is made by ”ac method” and ”dc method”. The negativeness of the electric field in La2-x Sr x CuO4 film and of the film capacitance are observed with hysteretic polarization.

Quantum Interference Found in //c Conductance Modulation of La2-xSrxCuO4 Thin Film in CO2 Laser Irradiation

The macroscopic quantum interference of La2-xSrxCuO4 film is studied in 40mW coherent CO2 laser irradiation at room temperature, where are observed conduction modulation and excess-current as the result of new macroscopic quantum effect.