We consider a problem of persistent magnetization precession in a single-domain ferromagnetic nanoparticle under the driving by the spin-transfer torque. We find that the adjustment of the electronic distribution function in the particle renders this state unstable. Instead, abrupt switching of the spin orientation is predicted upon increase of the spin-transfer torque current. On the technical level, we derive an effective action of the type of Ambegaokar-Eckern-Schön action for the coupled dynamics of magnetization [gauge group SU(2)] and voltage [gauge group U(1)].
We demonstrate that in sufficiently long diffusive superconducting-normal-superconducting (SNS) junctions dc Josephson current is exponentially suppressed by electron-electron interactions down to zero temperature. This suppression is caused by the effect of Cooper pair dephasing which occurs in the normal metal and defines a new fundamental length scale Lφ in the problem. This length is fully consistent with that derived earlier from the analysis of dissipative electron transport across NS interfaces at subgap energies. Provided the temperature length exceeds Lφ this dephasing length can be conveniently extracted from equilibrium measurements of the Josephson current.
We study a one-dimensional anisotropic XXZ Heisenberg spin-12 chain with weak random fields hizSiz by means of Jordan-Wigner transformation to spinless Luttinger liquid with disorder and bosonization technique. First, we reinvestigate the phase diagram of the system in terms of dimensionless disorder γ=h2/J2≪1 and anisotropy parameter Δ=Jz/Jxy, we find the range of these parameters where disorder is irrelevant in the infrared limit and spin-spin correlations are described by power laws, and compare it with previously obtained numerical and analytical results. Then we use the diagram technique in terms of plasmon excitations to study the low-temperature (T≪J) behavior of heat conductivity κ and spin conductivity σ in this power-law phase. The obtained Lorentz number L≡κ/σT differs from the value derived earlier by means of the memory function method. We argue also that in the studied region inelastic scattering is strong enough to suppress quantum interference in the low-temperature limit.