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Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)
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10.1063/1.4795172
/content/aip/journal/ltp/39/3/10.1063/1.4795172
http://aip.metastore.ingenta.com/content/aip/journal/ltp/39/3/10.1063/1.4795172

Figures

Image of FIG. 1.
FIG. 1.

The current-voltage dependence of the Pb/La0.65Sr0.35MnO3 contact without visible superconducting proximity effect; T = 4.2 K. Top inset: the temperature dependence of the contact's resistance R(T); arrow indicates TC Pb = 7.2 K. Bottom inset: the contact's Andreev-reflection spectra; T = 4.2 K; arrows indicate superconducting gap of Pb. Adopted from Ref. 29 .

Image of FIG. 2.
FIG. 2.

Temperature dependence of a resistance of Pb/La0.67Ca0.33MnO3 contact. Inset: Andreev-reflection spectra. Adopted from Ref. 28 .

Image of FIG. 3.
FIG. 3.

Normalized conductivity (dI/dV)/(I/V) of MgB2/La0.65Ca0.35MnO3 (1) Pb/La0.7Sr0.3MnO3 (2), and Pb/La0.65Ca0.35MnO3 (3) PCs (the graphs are shifted along the vertical axis for clarity). In case (3), the contact is in the thermal regime (theory is solid line, experiment is symbols). The degree of the spin polarization of charge carriers obtained by fitting are PC  ≈ 83%, 78%, and 65%, respectively. T = 4.2 K. Adopted from Ref. 27 .

Image of FIG. 4.
FIG. 4.

The current-voltage dependence of the proximity affected Pb/La0.7Sr0.3MnO3 contact; T = 4.2 K. Top inset: the temperature dependence of the contact's resistance R(T). Bottom inset: the contact's Andreev-reflection spectra at T = 4.2 K. Reproduced from Ref. 29 .

Image of FIG. 5.
FIG. 5.

The current-voltage dependence of the proximity affected Pb/La0.7Sr0.3MnO3 contact; T = 4.2 K. Top inset: the evolution of the proximity induced quasiparticle gap Δtr with temperature. Bottom inset: the temperature dependence of the contact's Andreev-reflection spectra. The curves are shifted for clarity. Reproduced from Ref. 29 .

Image of FIG. 6.
FIG. 6.

Normalized conductance spectra for proximity affected Pb/La0.65Ca0.35MnO3 point contacts (CP#2 and CP#4), and MgB2/La0.65Ca0.35MnO3 contact (CMg#7). The curves are shifted for clarity. The arrows indicate the energies of the subharmonic gap resonances for CP#2 contact. See Table II for classification of the resonances; Δtr is the apparent proximity induced single-particle gap of the La0.65Ca0.35MnO3. Reproduced from Ref. 28 .

Image of FIG. 7.
FIG. 7.

Those as in Fig. 6 for proximity affected Pb/La0.7Sr0.3MnO3 point contact at 4.2 K. Reproduced from Ref. 29 .

Image of FIG. 8.
FIG. 8.

Pair correlation functions in the ferromagnet of a ballistic s-wave superconductor–weak spin-polarized ferromagnet junction. Adopted from Ref. 92 .

Image of FIG. 9.
FIG. 9.

Spatial structure of the current through the proximity affected sSC/half-metallic manganite contact. The x axis is directed perpendicular to the sSC/HMF interface that is at x = 0; the HMF is placed in the region x > 0, while the sSC is located at x < 0. Proximity affected region LPE is much longer than the superconducting coherence length ξ T  = (DF /2πT)1/2 and LPE  ≫  ξ T . Reproduced from Ref. 28 .

Image of FIG. 10.
FIG. 10.

Semiconductor picture of proximity affected sSC/half-metallic manganite contact. Weak link here is a region where both singlet and triplet pairing interactions are suppressed (a). Trajectory of a quasiparticle that is accelerated out of the condensate by the electric field suffering multiple Andreev reflections. In the case of singlet and triplet superconducting electrodes every Andreev reflection is foregone with a spin-flip scattering. Spin-flip Andreev-reflection processes are illustrated by lines with stars (a). Reproduced from Ref. 29 .

Tables

Generic image for table
Table I.

Degree of spin polarization deduced for doped manganites. Technique: SPT—spin-polarized tunneling; SPPh—spinpolarized photoemission; BC—band calculation; PCAR—pointcontact Andreev reflection; STS—scanning tunneling spectroscopy; ARPES—angle-resolved photoemission spectroscopy.

Generic image for table
Table II.

The voltage corresponding to the SGS in Figs. 6 and 7 , point contacts Pb–(La,Ca)MnO3 and Pb–(La,Sr)MnO3, respectively; here ΔPb ≈ 1.4 meV, Δtr ≈ ΔLCMO  ≈ ΔLSMO  ≈ 18–20 meV.

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/content/aip/journal/ltp/39/3/10.1063/1.4795172
2013-03-27
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Point-contact Andreev-reflection spectroscopy of doped manganites: Charge carrier spin-polarization and proximity effects (Review Article)
http://aip.metastore.ingenta.com/content/aip/journal/ltp/39/3/10.1063/1.4795172
10.1063/1.4795172
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