Electric field effects in high-Tccuprates

Abstract

Dependences of ${T}_{c}$ on hole concentration in ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}y}$ (Y-123) and ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+x}$ (Bi-2212) cuprates have been calculated in the transverse electric field $\stackrel{\ensuremath{\rightarrow}}{E}$ in the framework of the two-band model. The phase space for the pair-transfer scattering between the overlapping bands is determined by the position of the chemical potential. The dependence of ${T}_{c}$ on the hole concentration ${n}_{h}$ has a maximum. The calculated ${T}_{c}{(n}_{h})$ agree in $\stackrel{\ensuremath{\rightarrow}}{E}=0$ with the experiment in Bi-2212 and Y-123 cuprates. The electric-field effects in cuprates are considered with the use of ${T}_{c}{(n}_{h}).$ In metal-insulator-superconductor structures, the electric field induces changes in the carrier concentration and in the position of chemical potential. The field-induced shifts of ${T}_{c}$ depend on the strength and polarity of the electric field. For maximum field effect, the superconductor has to be away from optimal doping, i.e., maximum ${T}_{c},$ ${\mathrm{dT}}_{c}{/dn}_{h}=0,$ and has to be closer to the maximum of the slope ${\mathrm{dT}}_{c}{/dn}_{h}.$ The asymmetry $|\ensuremath{\Delta}{T}_{c}(\stackrel{\ensuremath{\rightarrow}}{E})|\ensuremath{\ne}|\ensuremath{\Delta}{T}_{c}(\ensuremath{-}\stackrel{\ensuremath{\rightarrow}}{E})|$ changes with $\stackrel{\ensuremath{\rightarrow}}{E}.$ In agreement with experiment, the shifts $|\ensuremath{\Delta}{T}_{c}(\stackrel{\ensuremath{\rightarrow}}{E})|$ decrease when the film thickness increases. The field effects in both systems are similar, but in Bi-2212 they are stronger. The theory agrees qualitatively and, in some cases, quantitatively with experiment. The dependence of the ratio of surface and bulk conductivities on the film thickness $(d)$ allows us to obtain quantitative agreement between the calculated $d$ dependence of $|\ensuremath{\Delta}{T}_{c}(\stackrel{\ensuremath{\rightarrow}}{E})|$ and the experimental data in Y-123 and Bi-2212. The influence of the photodoping on ${T}_{c}$ of cuprates and photoinduced superconductivity are discussed.