Nonuniform superconducting states and Umklapp processes in ferromagnet–superconductor nanostructures (in Russian)
Abstract
For the layered ferromagnetic metal/superconductor (FM/S) structures new boundary-value problem, which takes into account a competition between the one-dimensional (1D) and three-dimensional (3D) realizations of the Larkin-Ovchinnikov-Fulde-Ferrell states, is derived. Superconductivity in the FM/S structures proves to be a superposition of the BCS pairing with zero total momentum in the S layers and the FFLO paring with nonzero pair momentum k in the FM layers. It is shown that processes of transition and mutual transformation of the BCS and FFLO pairs at the FM/S boundary occur as the Umklapp processes during which the coherent pair momentum k is conserved with exactness up to the reciprocal LOFF lattice vector G . These Umklapp processes can occur both in normal (1D states) and in the tangent (3D states) directions with respect to the FM/S interface. It is found that nonmonotonic behavior of the critical temperature Tc in the FM/S billayers is caused by the oscillations of the Cooper pairs flux through the S/FM boundary due to 3D-1D-3D phase transition cascade and switching between normal and tangent Umklapp processes. For the FM/S superlattices the existence of new π-magnetic 0π and ππ LOFF states, which at certain conditions can have a much higher Tc than earlier known 0-magnetic 00 and π0 LOFF states, is discovered. The Tc nonmonotony in the FM/S superlattices may be due to the 3D(0π)-1D(ππ)-3D(ππ) phase transitions cascade at small S interlayer thickness or due to another chain of the 3D(00)-1D(π0)-3D(π0) transitions at larger S interlayer thickness.
Supporting agencies: Работа частично поддержана фондами РФФИ ( 04-0216761 ) и CRDF (REC-007).
About the Author
M. G. Khusainov
Kazan state university; Kazan state technical university
Russian Federation
Russian Federation
Kazan; branch "Vostok", Chistopol'
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Review
For citations:
Khusainov M.G. Nonuniform superconducting states and Umklapp processes in ferromagnet–superconductor nanostructures (in Russian). Magnetic Resonance in Solids. 2004;6(1):103-118.
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