61 research outputs found
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 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. 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 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 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
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