V.I. Kudinov

Photoinduced superconductivity in YBaCuO films

Abstract The phenomenon of persistent photoconductivity in YBa2Cu3O6+x (x ≈ 0.4) films near the semiconductor-metal transition has been studied. Transport and magnetic measurements of the illuminated films were performed. The transition to the metallic state and photoinduced superconductivity have been observed. The mechanism of persistent photoconductivity in reduced YBa2Cu3O6+x films is also discussed.

Interaction of the moving domain wall with phonons

Abstract The interaction between the moving domain wall (DW) and acoustic phonons in the weak ferromagnet YFeO 3 has been investigated by means of Brillouin-Mandelstam spectroscopy method for the first time. The light scattering by the moving DW with the frequency shift due to the Doppler effect has been observed. The DW velocity and the intensity of the scattered light were determined from the spectra as a function of pulsed magnetic field at different temperatures. It was determined that as the DW velocity approaches that of transverse of longitudinal sound extra phonons, or sound soliton, are generated. The light scattering from the excited phonons was observed directly. The space and time evolution of this sound soliton was investigated at T =2 K. Nonstationary supersound DW motion has been observed. Nonlinear excitation of longitudinal sound was discovered. The temperature dependence of the DW mobility was also measured. The general picture of the DW motion at v ≈ s was discussed.

Metastable photoinduced superconductivity in YBaCuO films close to metal-semiconductor transition

The paper gives a brief overview of experiments concerned with the metastable photoinduced superconductivity phenomenon that have been recently discovered. As evidenced, illuminating the YBa2Cu3O6.4 films by visible light to enhancement of metal properties and occurrence of a superconducting transition at low temperatures. Both the temperature of the onset of a superconducting transition and the superconducting phase space in the films rise with the increase of exposure dose. The phenomena discovered are due to photoexcitation of extra mobile holes in the CuO2 plane allowing a new metastable superconducting phase to be initiated (photodoping). Also discussed are microscopic mechanisms of photoinduced superconductivity.

Dependence of photoinduced superconductivity on illumination dose in YBa2Cu3O6.4 films

Abstract Photoinduced superconductivity has been investigated in YBa 2 Cu 3 O 6.4 films near to the semiconductor-metal transition. Light-induced changes in the resistance and growth of the diamagnetic moment were observed. The data revealed a dependence between the photoinduced reduction of the normal state resistance and the increase of the onset temperature of superconductivity in the films. Prolonged irradiation led to a seemingly complete loss of resistivity below 5 K. These phenomena are attributed to photogeneration of additional mobile holes in CuO 2 layers resulting in superconductivity.

Photo induced superconductivity in YBa2Cu3O6.4 films

Abstract Photoinduced superconductivity has been investigated in YBa2Cu3O6.4 films near to the semiconductor-metal transition. Light induced changes in the resistance and growth of a diamagnetic moment were observed. The data revealed a dependence between photoinduced reduction of normal state resistance and the increase of the onset temperature of superconductivity in the films. Prolonged irradiation leaded to a seemingly complete loss of resistivity below 5 K. These phenomena were attributed to photo generation of additional mobile holes in CuO2 layers resulting to superconductivity.

Observation of new inelastic light scattering mechanism in antiferromagnet in AFMR studies

Abstract A new mechanism of inelastic light scattering due to the s-f exchange is discovered in AFMR studies in EuTe. This mechanism leads to inelastic scattering in a canted antiferromagnet when it has modes with longitudinal vibration of magnetization.

Interaction between the moving domain wall and acoustic phonons

Abstract The interaction between the moving domain wall (DW) and acoustic phonons in YFeO 3 was investigated by means of the inelastic light scattering method. It was determined that as the DW velocity approaches that of sound, extra phonons are generated. The light scattering by the excited phonons was observed directly. The space and time resolution of the formed sound wave were investigated. Nonlinear excitation of longitudinal sound was discovered.

FMR and phase diagram of easy plane 2D ferromagnets

We have measured FMR of 2D ferromagnets K 2 CuF 4 and (CH 3 NH 3 ) 2 CuCl 4 , and have determined H-T phase diagrams when the magnetic field is perpendicular to the easy plane. On the basis of the Berezinskii, Kosterlitz and Thouless (BKT) theory success has been achieved in quantitatively describing the measured phase diagrams.

Persistent photoconductivity in YBaCuO films

Abstract The phenomenon of the persistent photoconductivity (PPC) in YBa2Cu306+x films near the semiconductor-metal transition, x=0.4, has been investigated. Under exposure of semiconducting films to visible light the resistance was found to reduce drastically. After interrupting the irradiation no change of the resistance could be observed with time. Resistance temperature dependencies evidence that with increasing of cumulative light doses a semiconductor like behavior progressively changes to that of a metal. The state of PPC is practically retained up to room temperature at which it decays approximately in a period of 20 hours. Microscopic mechanisms of the PPC phenomenon in the reduced YBaCuO films are also discussed.

Inelastic Light Scattering by Magnons in Antiferromagnetic EuTe

The Brillouin-Mandel’stam scattering (BMS) of light is one of a few experimental methods which makes it possible to study excitations in magnetic solids directly.