M. V. Sudakova

Evidence for a two-band behavior of MgB2 from point-contact and tunneling spectroscopy

Ya. G. Ponomarev, S. A. Kuzmichev, M. G. Mikheev, M. V. Sudakova, S. N. Tchesnokov, N. Z. Timergaleev, A. V. Yarigin, M. V. Lomonosov Moscow State University, Department of Physics, 119899 Moscow, Russia, E. G. Maksimov, S. I. Krasnosvobodtsev and A. V. Varlashkin, P. N. Lebedev Physics Institute, RAS, Moscow, Russia, M. A. Hein, G. Müller, H. Piel, Bergische Universität Wuppertal, Fachbereich Physik, D-42097 Wuppertal, Germany, L. G. Sevastyanova, O. V. Kravchenko, K. P. Burdina, B. M. Bulychev, M. V. Lomonosov Moscow State University, Department of Chemistry, 119899 Moscow, Russia.

Multiple Andreev Reflections Spectroscopy of Two-Gap 1111- and 11 Fe-Based Superconductors

Using the “break-junction” technique, we prepared and studied superconductor–constriction–superconductor (ScS) nanocontacts in polycrystalline samples of Fe-based superconductors CeO0.88F0.12FeAs (Ce-1111;

Investigation of a superconducting Mg1−xAlxB2 system by tunneling and microjunction (Andreev) spectroscopies

T_{C}^{\mathrm{bulk}} = 41 \pm1~\mathrm{K}

Leggett’s mode in Mg1−x AlxB2

), LaO0.9F0.1FeAs (La-1111;

Quasiparticle tunneling in the c-direction in stacks of Bi2Sr2CaCu2O8+δ S–I–S junctions and the symmetry of the superconducting order parameter

T_{C}^{\mathrm{bulk}} = 28 \pm1~\mathrm {K}

Inelastic tunneling of Cooper pairs in c-direction in BSCCO single Josephson junctions and stacks

), and FeSe (

Fine Structure in the Tunneling Characteristis of Bi-Sr-Ca-Cu-O:Pb

T_{C}^{\mathrm{bulk}} = 12 \pm1~\mathrm{K}

Single Crystal Break Junctions

). We detected two subharmonic gap structures related with multiple Andreev reflections, indicating the presence of two superconducting gaps with the BCS-ratios 2ΔL/kBTC=4.2÷5.9 and 2ΔS/kBTC∼1≪3.52, respectively. Temperature dependences of the two gaps ΔL,S(T) in FeSe indicate a k-space proximity effect between two superconducting condensates. For the studied iron-based superconductors, we found a linear relation between the gap ΔL and magnetic resonance energy, Eres≈2ΔL.

Terahertz phonon spectroscopy of doped superconducting cuprates

A detailed investigation of multiband superconductivity in the Mg 1−xAlxB2 system was carried out by the methods of tunneling and Andreev spectroscopy. Temperature dependences of the superconducting gaps and their variation upon an increase in the degree of disorder and the Al concentration were studied. It is shown that the experimentally observed dependences cannot be explained in detail within the framework of the presently available microscopic theories.

Single-particle tunneling and Josephson effect in Bi-Sr-Ca-Cu-O:Pb and Tl-Ba-Ca-Cu-O compounds

A detailed investigation of multiband superconductivity and Leggett’s mode in the Mg1−xAlxB2 (0 ≤ x ≤ 0.45) system was carried out using tunneling and Andreev spectroscopy. Temperature dependences of superconducting gaps Δσ and Δπ and their variation upon the degree of disorder and the Al concentration were studied. The dependence of the Leggett’s mode energy ε0 upon the values of the gaps Δσ and Δπ has been derived.