Pavel E. Dolgirev — Page 3

arXiv2018

Current-phase relation and flux-dependent thermoelectricity in Andreev interferometers

We predict a novel $(I_0,ϕ_0)$-junction state of multi-terminal Andreev interferometers that emerges from an interplay between long-range quantum coherence and non-equilibrium effects. Under non-zero bias $V$ the current-phase relation $I_S(ϕ)$ resembles that of a $ϕ_0$-junction differing from the latter due to a non-zero average $I_0(V) = \left< I_S(ϕ)\right>_ϕ$. The flux-dependent thermopower ${\mathcal S}(Φ)$ of the system exhibits features similar to those of a $(I_0,ϕ_0)$-junction and in certain limits it can reduce to either odd or even function of $Φ$ in the agreement with a number of experimental observations.

cond-mat.supr-con↗

arXiv2017

Pseudogap and Fermi surface in the presence of spin-vortex checkerboard for 1/8-doped lanthanum cuprates

Lanthanum family of high-temperature cuprate superconductors is known to exhibit both spin and charge electronic modulations around doping level 1/8. We assume that these modulations have the character of two-dimensional spin-vortex checkerboard and investigate whether this assumption is consistent with the Fermi surface and the pseudogap measured by angle-resolved photo-emission spectroscopy. We also explore the possibility of observing quantum oscillations of transport coefficients in such a background. These investigations are based on a model of non-interacting spin-1/2 fermions hopping on a square lattice and coupled through spins to a magnetic field imitating spin-vortex checkerboard. The main results of this article include (i) calculation of Fermi surface containing Fermi arcs at the positions in the Brillouin zone largely consistent with experiments; (ii) identification of factors complicating the observations of quantum oscillations in the presence of spin modulations; and (iii) investigation of the symmetries of the resulting electronic energy bands, which, in particular, indicates that each band is double-degenerate and, in addition, has at least one conical point, where it touches another double-degenerate band. We discuss possible implications these cones may have for the transport properties and the pseudogap.

cond-mat.str-el↗