ANNEY, E. A.; http://lattes.cnpq.br/5576146059828349; ANNEY, Elijah Anertey.
Resumo:
Superconductivity is defined by the ability of certain materials to conduct electric current with no
resistance. This capacity produces interesting and potential useful effects. One of the most notable effects of
superconductivity (SC) is the Meissner effect. It occurs due to screening currents near the surface that produce a
magnetic field to cancel the field inside the material when this is cooled to lower than the critical temperature
Tc. In that case an applied magnetic field lower than the critical field Hc would not be able to penetrate the
interior of the superconductor. Although the Meissner effect is known since 1933, its physical
mechanism is still not fully understood today. One possible explanation was recently postulated by Jorge
Eduardo Hirsch [1], which in the absence of an applied magnetic field the orbital expansion for the angular
momentum in the presence of an ionic electric field would generate through spin-orbit interaction a spin
current near the surface of the superconductor. This spin-Meissner effect would therefore exist in all
superconductors and be at the root of the Meissner effect. It was also recently postulated [2] that x-ray beams
carrying orbital angular momentum (OAM) could induce strong dichroic effects. However, the production of
such x-ray orbital polarization requires nanofocalized beam, which has thwarted attempts to experimentally
probe this effect. Here we propose a dynamical method to probe the spin and the conventional Meissner effect in
type I and type II superconductors using the spin-orbit interactions and the possibility to probe both
orbital and angular momentum in an experiment analogous to X-ray magnetic circular dichroism (XMCD). In
this work we used Ta (type I superconductor) and IrZr2 (type II superconductor) samples as prototypical
compounds to validate this methodology. XMCD spectra collected in the superconducting state of Tametal
and IrZr2 indicate a small but clear signal arising from the coupling between the orbital moment of the
screening currents and the orbital moment of the photoelectron. Tantalum metal samples differing in their
granularity and morphological shape where used. The maximum signal correlated to Meissner effect was
observed considering the coherence length and the penetration depth of all the samples [3-5].