H. F. Lu

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.

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.

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.

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.

Anomalous Hysteretic Dielectric Polarization in C-Axis-Oriented La2-xSrxCuO4 Film

The dependence of polarization of c-axis oriented La2-x Sr x CuO4 film on dc voltage is measured by “ac method” and “dc method”. When the film has surface charging, the field inside the film is found to have sense reverse to the applied field. Hysteretic polarization of the film is observed in “dc method”.

Anomalous electric characteristic of La2−xSrxCuO4 at x=1/4n

The resistivity of LSCO materials drops sharply at χ≈4-n from, low up to room temperature. Anomalous dielectric response of LSCO film at χ≈4-n and χ≈2x4-n is found along c axis. The capacitanceC t of multi-layer structure Pd/LSCO/STO/Pd increases at thex values exceeding the capacitanceCsto of Pd/STO/Pd structure from low to room temperature, where effective dielectric constant of the conductive normal state is consideed to be negative. TheC-V measurement reveals the existence of “critical voltage” in the anomalous dielectric property.