Non-equilibrium Spin Waves in Paramagnetic Metals

We theoretically study the effect of exchange interaction on the non-equilibrium spin waves in disordered paramagnetic metals under the spin injection condition. We show that the gapless spectrum of spin waves, describing the spin precession in the absence of the applied magnetic field, changes sign to negative on the paramagnetic side near the ferromagnet - paramagnet phase transition. The damping of spin waves is small in the limit when electron-electron exchange energy is larger than the inverse electron mean free time, while in the opposite limit the propagation of spin waves is strongly suppressed. We discuss the amplification of the electromagnetic field by the non-equilibrium spin waves.Comment: 6 pages, 3 figure

Superconductivity from incoherent Cooper pairs in strong-coupling regime

We propose a scenario for superconductivity at strong electron-electron attractive interaction, in the situation when the increase of interaction strength promotes the nucleation of the local Cooper pairs and forms a state with a spatially phase incoherent Cooper pair order parameter. We show that this state can be characterized by a pseudogap and a scattering rate, which are determined by the self-energy due to electron scattering on phase fluctuations. At low temperatures, however, long-range correlations between the regions with different phases become important and establish global phase coherence hence superconductivity in the system. We develop a mean-field theory to describe a phase transition between the preformed Cooper pair and superconducting states. This scenario of superconductivity applies not only to conductors with parabolic bands but also to the flat-band systems in which flat and dispersive bands coexist and responsible for the Cooper pair formation as well as their phase synchronization.Comment: 9 pages, 1 figur

Spin injection dependent metamagnetic transition

We define the metamagnetic phase transition of itinerant electrons controlled by the spin injection mechanism. The current flow between a ferromagnetic metal and a metamagnetic metal produces the non-equilibrium shift of chemical potential for spin up and spin down electrons that acts as an effective magnetic field driving the metamagnetic transition.Comment: 6 pages, 3 figure

Transport spectroscopy of Kondo quantum dots coupled by RKKY interaction

We develop the theory of conductance of a quantum dot which carries a spin and is coupled via RKKY interaction to another spin-carrying quantum dot. The found dependence of the differential conductance on bias and magnetic field at fixed RKKY interaction strength may allow one to distinguish between the possible ground states of the system. Transitions between the ground states are achieved by tuning the RKKY interaction, and the nature of these transitions can be extracted from the temperature dependence of the linear conductance. The feasibility of the corresponding measurements is evidenced by recent experiments by Craig et al. [cond-mat/0404213].Comment: published version: minor changes, references adde