On Transverse Effects in Transport in Semi- and Superconductors

Abstract

In this dissertation, the results obtained during my PhD work are presented. As an introduction, the brief review of the theory of superconducting fluctuations and a short discussion of experimental situation in the field of spin caloritronics are presented. Next, the original study of two important transport transverse effects is reported. The first one is the Hall effect in metallic films, enhanced by super-conducting fluctuations. We develop an appropriate technique, based on solution of Usadel equation in the presense of classical and quantum noise and including leading contributions due to electron-hole asymmetry. This allows us to extend the previously known results for Cooper interaction-dominated transverse conductivity to a broader range of temperatures and magnetic fields, including the vicinity of the magnetic field induced quantum critical point. The second effect under study is Transverse Spin Seebeck Effect (TSSE). The TSSE remains one of the most puzzling of the recently discovered spin-dependent thermoelectric effects merging spin, charge, and thermal physics. We build a theory, which allows to quantitatively interpret the recent experimental results in terms of magnetized electrons, dragged but low-energy out-of-equilibrium phonons. The theory explains the manifestly non-local nature of the TSSE from the fact that phonons that store the energy (thermal) and the phonons that transfer it (subthermal) are located in different parts of the spectrum and have different kinetics. This gives rise to a spectral phonon distribution that deviates from local equilibrium along the substrate and is sensitive to boundary conditions. The theory also predicts a non-magnon origin of the effect in ferromagnetic metals in agreement with observations in recent experiments.