Origin of the high Neel temperature in SrTcO3

We investigate the origin of the high Neel temperature recently found in Tc perovskites. The electronic structure in the magnetic state of SrTcO3 and its 3d analogue SrMnO3 is calculated within a framework combining band-structure and many-body methods. In agreement with experiment, the Neel temperature of SrTcO3 is found to be four times larger than that of SrMnO3. We show that this is because the Tc-compound lies on the verge of the itinerant-to-localized transition, and also has a larger bandwidth, while the Mn-compound lies deeper into the localized side. For SrTcO3 we predict that the Neel temperature depends weakly on applied pressure, in clear violation of Bloch's rule, signaling the complete breakdown of the localized picture.Comment: 4+ pages, 3 figures, published versio

Spin Seebeck coefficient and spin-thermal diffusion in the two-dimensional Hubbard model

We investigate the spin Seebeck coefficient $S_s$ in the square lattice Hubbard model at high temperatures of relevance to cold-atom measurements. We solve the model with the finite-temperature Lanczos and with the dynamical mean-field theory methods and find they give similar results in the considered regime. $S_s$ exceeds the atomic 'Heikes' estimates and the Kelvin entropic estimates drastically. We analyze the behavior in terms of a mapping onto the problem of a doped attractive model and derive an approximate expression that allows relating the enhancement of $S_s$ to distinct scattering of the spin-majority and the spin-minority excitations. Our analysis reveals the limitations of entropic interpretations of Seebeck coefficient even in the high-temperature regime. Large values of $S_s$ could be observed on optical lattices. We also calculate the full diffusion matrix. We quantify the spin-thermal diffusion, that is, the extent of the mixing between the spin and the thermal diffusion and discuss the results in the context of recent measurements of the spin-diffusion constant in cold atoms.Comment: 7 pages, 4 figure