Determination of spin polarization using an unconventional iron superconductor

Abstract

An unconventional iron superconductor, SmO0.7F0.3FeAs, has been utilized to determine the spin polarization and temperature dependence of a highly spin-polarized material, La0.67Sr0.33MnO3, with Andreev reflection spectroscopy. The polarization value obtained is the same as that determined using a conventional superconductor Pb but the temperature dependence of the spin polarization can be measured up to 52 K, a temperature range, which is several times wider than that using a typical conventional superconductor. The result excludes spin-parallel triplet pairing in the iron superconductor.

Singlet superconductivity in a single-crystal NiBi3 superconductor

“…If there is any spin-parallel triplet pairing with Sz = 1 in the NiBi3 SC, the P value will be zero because AR of a triplet SC is not suppressed by a spin-polarized current. The P = 0.81 is the same as that obtained using a singlet SC [38], suggesting that all spin states in the NiBi3 sample is antiparallel, the same as that of a singlet SC.…”

“…After the determination of the gap value and its symmetry with an unpolarized current, next we utilize a highly spin-polarized current to determine the spin states of the Cooper pairs in NiBi 3 . The polarized current is injected from LSMO, which has a spin polarization over 80% determined by singlet SC Pb [38]. Some representative ARS spectra from NiBi 3 /LSMO contact are shown in figures 3(a)-(e).…”

“…The gap () and P values are extracted by fitting the whole ARS spectrum to the modified BTK model. Spin polarization of many magnetic materials [26][27][28][29][30][31][32][33][34][35][36][37][38] including some highly spin-polarized [28][29][30][31][32][33][34][35] and half-metallic materials [28][29] has been determined by ARS using a known singlet SC. Similarly, superconducting gap of many SCs, including two band MgB2 [39], and iron SCs [38,40] has been studied by ARS using metals with known P value.…”

Discovery of a magnetic conductive interface in PbZr0.2Ti0.8O3 /SrTiO3 heterostructures

“…To confirm this local metallic behavior, Andreev reflection spectroscopy (ARS) was employed to study the STO/PZT interface of STO (10 nm)/PZT/DSO heterostructure 21 – 23 . As schematically drawn in the inset of Fig.…”

“…The metallic behavior with a resistance ( R ) of about 1 kΩ was found for all contacts, indicating the presence of 2DEG in the sample. Very interestingly, by analyzing the spectra G ( V ) using the modified Blonder–Tinkham–Klapwijk (BTK) model 21 – 23 , we obtained a large spin polarization ( P ) value for each contact. The best fits are shown in Fig.…”