Effective Hamiltonians for cuprate, cobaltate and topological superconductors

ALIGIA, A.A.; CAMJAYI, A.; MANUEL, L. O.; VON OPPEN, F.; HAMAD, I. J.; ARRACHEA, L.

Foz de Iguazú

Congreso; Autumn Meeting of the Brazilian Physical Society; 2018

The Brazilian Physical Society

We discuss three cases for the construction of low-energy effective models to describe the electronic structure of superconductors. The first concerns the controversy of the validity of the description based on Zhang-Rice singlets for the cuprates, which was recently extended to Tetragonal CuO (T-CuO). We rigorously derive an effective one-band generalized t−J model for T-CuO. By means of the self-consistent Born approximation, we evaluate the quasiparticle dispersion for a single hole doped in antiferromagnetically ordered half-filled T-CuO,obtaining very good agreement with angle-resolved photoemission spectra (ARPES). Next we discuss a three-band model for effective t2g orbitals in Nax CoO2. An important role is played by the splitting ∆ as the local symmetry around a Co ion is reduced from Oh to D3d . A controversy of the value of ∆ exist between ab initio and cluster calculations including correlations. Only the latter are consistent with ARPES experiments. We find that ∆ is very sensitive to a Coulomb parameter which controls the Hund coupling and charge distribution among the d orbitals.Finally, we show that an effective low-enery model can be used to interpret continuous-time Monte-Carlo simulations for the Josephson current through a quamtum dot between two time reversal invariant topologicalsuperconducting wires. The expected 0-to-π transition is quenched via formation of a spin singlet from the quantum dot spin and the fractional spins associated with the two adjacent topological superconductors.