Spin polarization of charge carriers and Andreev reflection in (LaCa)MnO/superconductor point contacts

Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)

“…Contribution of such a small region to the contact's resistance is less than 1%. That is indeed observed for the most part of the samples [15,[22][23][24][25][26][27][28][29][49][50][51][52][53][54][55]. However, for some of the cases, the measured contact's spectra revealed very distinct features which were interpreted as manifestation of an unconventional proximity effect.…”

“…For the first time direct experimental evidence of half-metallic density of states in ferromagnetic La 0.7 Ca 0.3 MnO 3 was obtained by scanning tunneling spectroscopy by Wei et al [44]. These results were then confirmed by optical [5,[45][46][47][48] and transport measurements [15,[22][23][24][25][26][27][28][29][49][50][51][52][53][54][55]. However, it should be taken into account that different experiments yield quite different value of spin polarization (see Table 1).…”

“…(For more details see original reports [14,27,56,57,61,63,64], textbook [12] and recent review [13]. )…”

“…(2)- (4), where now all the amplitudes, A N (ε,Z), B N (ε,Z), A P (ε,Z), and B P (ε,Z), must be accordingly generalized. We will not write out here the extended expressions referring the reader to reports [13,18,24,27].…”

“…Since then, this technique has been used to measure spin polarization in a broad range of ferromagnetic materials, including the transition metal elements Fe, Ni, and Co [15,17], metallic alloys of transition metals such as permalloy [15,18], Heusler alloys such as NiMnSb [15,19], halfmetals such as CrO 2 [15,[19][20][21], doped manganites [15,19,[22][23][24][25][26][27][28][29], and other ferromagnetic metals and semiconductors. The foregoing may lead to a conclusion that the PCAR technique is indeed a robust and universal way for measuring spin polarization applicable to all magnetic compounds.…”