LABORATORY FOR ADVANCED MATERIALS PHYSICS

The investigation of high-temperature superconductors with radiospectroscopy techniques:

Heterogeneity in electronic properties of yttrium-barium superconductors has been established   by means of  EPR;

Analyzing the linewidth of the EPR signal of spin probes an empiric relationship between the state density of charge carriers and the critical temperature of lanthanum-strontium superconductors has been derived;

An anomalous slowing down of two-dimensional magnetic fluctuations in the low-temperature tetragonal phase of the lanthanum cuprates has been established; a strong pinning of the stripe phase, due to the commensuration effects, has been revealed and the amplitude of modulation of the charge density as well as the magnitude of copper magnetic moments in strip antiferromagnetic domains have been estimated.

A scanning spin-probe method for investigating the distribution of the magnetic flow in the critical state of type II superconductors has been elaborated and the phase diagram of the vortex lattice in Bi₂Sr₂CaCu₂O₈ has been examined for various pinning regimes.

The investigation of strongly correlated electronic systems:

The appearance of local magnetic moments when nonmagnetic dopants are introduced into the copper-oxygen planes of the metaloxides has been experimentally observed and theoretically interpreted;

The amplification of antiferromagnetic correlations in the proximity of nonmagnetic and magnetic impurities in high-temperature superconducting materials has been theoretically substantiated; it has been predicted that, as the temperature decreases, this will lead to the anomalous increase of the Knight shift and the magnetic resonance linewidth ;

A theory accounting for the anomalous magnon spectrum degradation in manganates has been suggested, a theory of orbital dynamics and the metal-isolator transition in manganates has been developed.

The investigation of multilayered systems:

Research of  the proximity effect in thin-film layer systems of the superconductor-ferromagnet type has revealed that the critical temperature of the superconducting layer nonmonotonously depends on the thickness of the ferromagnetic layer;

Along with the strong suppression of the superconducting transition  temperature, in the Nb/Fe system with the Fe layer sufficiently thin, a magnetic structure rearrangement due to the superconductivity effect also occurs ;

The transmission coefficient of the superconductor-ferromagnet interface for Cooper pairs in the Pb/Fe system is considerably limited due to the exchange splitting of the Fe conduction band and the absence of the hybridization of the Fe and Pb conduction bands.      

• Institute of Crystallography of RAS, Moscow.
• A.F. Ioffe Physical Technical Institute, Saint-Petersburg.
• Institute of Solid State Physics of RAS, Chernogolovka.
• Ruhr University, Bochum, Germany.
• Köln University, Köln, Germany.
• University of Mainz, Mainz, Germany.
• Max-Planck Institute, Stuttgart, Germany.
• Institute for Solid State Physics, Jülich, Germany.
• University of Groningen, Groningen, The Netherlands.
• University of Kanagawa, Kanagawa, Japan.

1. Muehge Th., Garif'yanov N.N., Goryunov Yu.V., Khaliullin G.G., Tagirov L.R., Westerholt K., Garifullin I.A., Zabel H.: Possible Origin for Oscillatory Superconducting Transition Temperature in Superconductor/Ferromagnet Multilayers. Phys. Rev. Lett. 77, 1857-1860 (1996)
2. Khasanov R.I., Talanov Yu.I., Assmus W., Teitel'baum G.B.: Crossover from Bulk Pinning to Geometrical Barrier in a BiSrCaCuO Single Crystal as Revealed by a Scanning ESR-Probe Method. Phys. Rev. B 54, 13339 (1996)
3. Kataev V., Rameev B., Buechner B., Huecker M., Borowski R.: Slow Antiferromagnetic Dynamics in the Low-Temperature Tetragonal Phase of La_2-xSr_xCuO₄ as Revealed by ESR of Gd Spin Probes. Phys. Rev. B 55, R3394 (1997)
4. Kataev V., Rameev B., Validov A., Buechner B., Huecker M., Borowski R.: Magnetic Properties of Eu-Doped La_2-xSr_xCuO₄ Studied by ESR. Phys. Rev. B 58, R11876 (1998)
5. Kilian R., Khaliullin G.: Orbital Dynamics: The Origin of the Anomalous Optical Spectra in Ferromagnetic Manganites. Phys. Rev. B 58, R11841 (1998)
6. Kilian R., Krivenko S., Khaliulin G., Fulde P.: Impurity-Induced Spin Polarization and NMR Line Broadening in Underdoped Cuprates. Phys. Rev. B 59, 14432 (1999)
7. Lazar L., Westerholt K., Zabel H., Tagirov L.R., Goryunov Yu.V., Garif'yanov N.N., Garifullin I.A.: Superconductor/Ferromagnet Proximity Effect in Fe/Pb/Fe Trilayers. Phys. Rev. B 61, 3711 (2000)
8. Teitel'baum G.B., Buechner B., de Gronckel H.: Cu NQR Study of the Stripe Phase Local Structure in the Lanthanum Cuprates. Phys. Rev. Lett. 84, 2949 (2000)