[超导基础理论和实验技术系列讲座（七十五）] μSR studies of unconventional Fe and Cr-based superconductors

[超导基础理论和实验技术系列讲座（七十四）] 实用化超导量子干涉器件SQUID及其在地球物理探测领域的应用

[超导基础理论和实验技术系列讲座（七十三）] 非常规超导体的输运性质

[超导基础理论和实验技术系列讲座（七十二）] 高温超导电性机理研究进展

[超导基础理论和实验技术系列讲座（六十九）] Vortices in superconductors: All the physics in a single grip

We discuss physics of Abrikosov vortices in type II superconductors. Abrikosov vortices, which are the topological excitations of the superconducting order parameter, exhibit a wealth of fascinating properties and phenomena. An interplay of vortex-vortex interactions, thermal fluctuations, and disorder leads to a rich phase diagram and novel phases: Bose and vortex glasses and vortex Mott state. In a glassy state, vortices exhibit nonlinear glassy dynamics, vortex creep. The correspondence between the quantum mechanics and statistical physics makes vortex systems a perfect and unique laboratory for studying many-body quantum strongly correlated systems, in particular out-of-equilibrium Mott transition which is hardly available by other means. In two dimensions vortices mediate Berezinskii-Kosterlitz-Thouless transition bringing a new paradigm, topological phase transition. The duality between vortices and Cooper pairs in two dimensions results in novel superinsulating and Bose-metal states. Finally, vortices became a platform for new development in physics: a non-Hermitian Hamiltonian theory of out of equilibrium phase transitions.

[超导国家重点实验室学术报告] Resonant Inelastic X-ray Scattering study of Magnetic Excitations in high-Tc cuprate superconductors

Resonant Inelastic X-ray Scattering (RIXS) is a photon-in and photon-out technique which becomes popular in recent years due to the fast progress in the instrumentation and by importanttheoretical achievements. RIXS can be used in a very effective way to study the charge and spin excitations in strongly correlated 3d transition-metal systems.

[超导国家重点实验室学术报告] Thin film deposition and high-field transport properties of Fe-based superconductors

The Fe-based superconductors (FBS) are very interesting materials both for basic research as well as in view of potential applications. FBS are unconventional, anisotropic, partially quantum-critical, multi-band superconductors, and all of these characteristics reflect to some extend in the electrical transport properties. They usually show very high upper critical fields and concurrent high irreversibility fields at low temperatures. This opens the possibility of high in-field critical current densities Jc, interesting especially for high-field applications.

[超导国家重点实验室学术报告] Thermoelectric Materials and Fast Ionic Conductors with Structural Instabilities

Copper selenide attracted interest due to high ionic conductivity and efficient thermoelectric properties. I will present results of neutron scattering investigation of the crystal structure, diffuse scattering, quasi-elastic neutron scattering and BWS calculations in the Cu-Se superionic compounds.

[超导国家重点实验室学术报告]Current-induced crossover between two distinct quantum coherence effects in superconducting Nb nano-ring

   I will report on our new magnetoresistance measurements in a granular Nb nano-ring revealing current-induced crossover between two distinct quantum coherence effects. At low bias currents, Cooper-pairs coherence is manifested by Little-Parks oscillations with flux periodicity of h/2e. At high bias currents, magnetoresistance oscillations with flux period of h/e are observed and interpreted as Aharonov-Bohm oscillations, reflecting phase coherence of individual quasi-particles. The model explaining these data views the ring as a chain of superconducting grains weakly coupled by tunnel junctions. Low bias currents allow coherent tunneling of Cooper pairs between the grains. Increasing the current above the critical current of all the junctions creates a quasi-particles conduction channel along the ring, allowing for quantum interference of quasi-particles.

[超导国家重点实验室学术报告] Combining superconductors and ferromagnets :  from p-junctions to spin-triplets

  The study of superconductor (S) / ferromagnet (F) hybrids is a by now a well-established field. One of the early interests was formed by the realization that a thin F layer in an SFS structure could lead to a phase change of π between the condensates in the two S contacts. Such π-junctions are still investigated for use in devices such as superconducting memory elements. More recently it became clear that also spin triplet pair correlations can be induced in ferromagnets and lead to long-range supercurrents. These triplets are the centrepiece of the newly emerging field of superconducting spintronics. They are generated by engineering magnetic inhomogeneities at the S/F interface, for instance by using a sandwich of different layers, in order to mix the two spin channels and rotate the quantization axis. Using ferromagnets also allows control over the supercurrents, and two examples will be discussed. One concerns CrO2, which is a fully spin-polarized ferromagnet, in which it is possible to induce supercurrents with very high current density (above 109 A/m2) over distances approaching a micron. The other example demonstrates a device which also allows control over the supercurrent distribution based on a disk-shaped Josephson junction with a Co layer containing a magnetic vortex. With a magnetic field  we can change the position of the vortex, and thereby the supercurrent pathways. This device exemplifies a novel platform where adaptable supercurrent paths can be customized for a given application.