London penetration depth in the ensemble of spin polarons of cuprate superconductors

Dzebisashvili, Dmitry M.; Komarov, Konstantin K. Source: EUROPEAN PHYSICAL JOURNAL B, 91 (11):10.1140/epjb/e2018-90266-6 NOV 13 2018

Within the spin-polaron concept for hole-doped cuprates superconductors the temperature and doping dependence of the London penetration depth λ is studied. To calculate λ we developed a novel approach which (i) does not suppose the analytical expression for the quasiparticle spectrum to be known in advance, and (ii) allows to take into account the strong coupling between a spin localized on the copper ion and a hole residing on the four nearest oxygen ions rigorously. Within this approach the expression for supercurrent density j⃗ is obtained in the long-wavelength limit for external magnetic field vector potential. It is shown that j⃗ is mainly due to the spin-polaron quasiparticles rather then bare oxygen holes. Temperature dependence of λ−2 at various doping is calculated and compared with available experimental data. It is argued that the inflection point revealed experimentally in the temperature behavior of λ−2 in La1.83Sr0.17CuO4 may be considered as a manifestation of the spin-polaron nature of quasiparticles in cuprates.