Andreev-spectroscopy study of unconventional superconductivity in MgB₂:(La,Sr)MnO₃ nanocomposite

• Main Authors: Krivoruchko, V.N., D’yachenko, A.I., Tarenkov, V.Yu.
• Format: Article
• Language: Russian
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2014
• Series: Физика низких температур
• Subjects: III Международный семинар по микроконтактной спектроскопии
• Online Access: http://dspace.nbuv.gov.ua/handle/123456789/119669

Unconventional high-temperature superconductivity in MgB₂:La₀:₆₅Sr₀:₃₅MnO₃ (MgB:LSMO) nanocomposite has been found recently [Phys. Rev. B 86, 10502 (2012)]. In this report, the symmetry of the nanocomposite superconducting order parameter and plausible pairing mechanisms have been studied by the point-contact Andreev-reflection (PCAR) spectroscopy. To clarify the experimental results obtained, we consider a model of a ferromagnetic superconductor, which assumes a coexistence of itinerant ferromagnetism and mixed-parity superconductivity. The Balian–Werthamer state, with quasiparticle gap topology of the same form as that of the ordinary s-wave state, fits the experimental data reasonably well. Utilizing the extended Eliashberg formalizm, we calculated the contribution of MgB₂ in the total composite’s conductivity and estimated the magnitude of the electron–phonon effects originated from MgB₂ in I–V characteristics of the composite at above-gap energies. It was found that distinctive features observed in the PC spectra of the MgB:LSMO samples and conventionally attributed to the electron–phonon interaction cannot be related to the MgB₂ phonons. It is argued that the detected singularities may be a manifestation of the electron-spectrum renormalizations due to strong magnetoelastic (magnon–phonon) interaction in LSMO.