Common Fermi-liquid origin ofT2resistivity and superconductivity inn-type SrTiO3

Abstract

A detailed analysis is given of the T 2 term in the resistivity observed in electron-doped SrTiO3. Novel bandstructure data are presented, which provide values for the bare mass, density of states, and plasma frequency of the quasiparticles as a function of doping. It is shown that these values are renormalized by approximately a factor 2 due to electron-phonon interaction. It is argued that the quasiparticles are in the anti-adiabatic limit with respect to electron-phonon interaction. The condition of anti-adiabatic coupling renders the interaction mediated through phonons effectively non-retarded. We apply Fermi-liquid theory developed in the 70's for the T 2 term in the resistivity of common metals, and combine this with expressions for Tc and with the Brinkman-Platzman-Rice (BPR) sum-rule to obtain Landau parameters of n-type SrTiO3. These parameters are comparable to those of liquid 3 He, indicating interesting parallels between these Fermi-liquids despite the differences between the composite fermions from which they are formed. PACS numbers:arXiv:1109.3050v1 [cond-mat.str-el]

Theory of spin-orbit coupling at LaAlO3/SrTiO3interfaces and SrTiO3surfaces

“…Thus SOC lifts orbital and spin degeneracies. For a cubic perovskite such as STO, the six initially degenerate t 2g orbitals at the Γ point are indeed split by SOC [10][11][12][13], but Kramers degeneracy (time reversal symmetry) is preserved. Because bulk STO has both crystal inversion symmetry ε( k, ↑) = ε(− k, ↑) and time reversal symmetry ε( k, ↑) = ε(− k, ↓), the energy ε at wave vector k is still spin-degenerate.…”

“…In contrast, the zx and xy orbitals have the same, large energy dispersion and a light effective mass of 0.41m e . Including the SOC, the six-fold degenerate orbitals are split into a doubly and a four-fold degenerate level with an orbital splitting of ∆ O = 29 meV [13], see Fig.1. The energy dispersion of the resulting orbitals is now considerably different from the initial orbitals.…”

Superconductivity on a Charge Diet

“…Let us compare these findings with the conclusions of recent ab initio band calculations [30]. As the insulator is doped by n-type carriers, the first available band to be filled is a threefold degenerate one associated with a Ti 3d orbital.…”

“…Note, however, that the latter measurements are performed at higher concentrations, where several bands with possibly different masses are present. The cyclotron mass obtained here is 2.5 times larger than the band mass (0:7m e [30,31]). The mass enhancement is presumably due to a combination of electron-phonon and electron-electron interactions.…”

“…Filling these bands successively generates three interpenetrating ellipsoids at the center of the Brillouin zone. According to these calculations, at a critical doping of x c1 ¼ 4 Â 10 À5 carriers per formula unit [30], the second band starts to be filled. The corresponding carrier density is n c1 ¼ 6:8 Â 10 17 cm À3 , slightly larger than our most dilute sample.…”