Spin polarized and degenerate tunneling spectra in intrinsic Josephson junctions of Bi2212

Abstract

PACS 74.50.+r, 74.81.Fa Tunneling characteristics of HgBr2 intercalated superconducting Bi2212 single crystals have been obtained by using 10x10 µm 2 intrinsic Josephson junction stacks, so called mesa structures. The spin degenerate current is driven along the c-axis with Au layer using point contact tunneling assembly at 4.2 K. The spin polarized current is also driven along the c-axis of crystals with Au/Co/Au multilayer. In order to understand the role of ferromagnetic layer (Co), quasiparticle branches are examined with and without magnetic field. The magnetic field evolution of switching currents are obtained for gaining further insight about the spin injection through the stack. In this study, the tunneling spectra of a regular mesa-IJJ stack (58 nm) with a Au layer and a ferromagnetic mesa-IJJ stack (73 nm) with Au/Co/Au multilayer on HgBr 2 intercalated Bi2212 single crystals are reported with and without magnetic field application. Insets of Figs. 1 (a) and (b) show schematic side view of the fabricated structures. In the latter configuration, ferromagnetic metal, Co is used as a source of spin polarized carriers injected into Bi2212 crystal. The aim of this study is to investigate the effect of the spin transfer from ferromagnetic metal through the Bi2212 stack and to obtain the influence of such kind of effect on the c-axis tunneling characteristics. For this reason, two sets of samples were prepared; in one set, freshly cleaved Bi2212 crystals have been deposited with Au while the other set has ferromagnetic multilayer (Au = 15 nm/Co = 80 nm /Au= 156 nm) on the crystal. Using photolithography and Ar ion beam etching techniques described elsewhere [12], 10x10 µm 2 mesa structures were fabricated on HgBr 2 intercalated crystals with T

Emission of the THz waves from large area mesas of superconducting Bi2Sr2CaCu2O8+δ by the injection of spin polarized current

“…The Josephson critical current density, J c , is 120 A/cm 2 at 22 K which is 2-3 times smaller than as-grown Bi2212 crystals due to injection of spin polarized current and it is comparable to other THz emitting mesas [9]. Decrement in J c due to the spin injection was also demonstrated by previous works in our group by comparing spin degenerate and spin polarized cases [46]. At high bias voltages, when I-V curve shows backbending, the bolometer detects the heating of the mesa in the form of unpolarized black body radiation.…”

“…This nonequilibrium state leads to spin accumulation in superconductor and suppression of superconductivity due to pair breaking effect in CuO 2 layers as a result of excess magnetic moments and quasiparticle redistribution [38][39][40]. Many times, it was experimentally verified that the injection of spin polarized carriers into high-T c superconductor is led to reduction of the critical current [38][39][40][41][42][43][44][45][46][47][48].…”