First-Order Reorientation of the Flux-Line Lattice in CaAlSi

The flux line lattice in CaAlSi has been studied by small angle neutron scattering. A well defined hexagonal flux line lattice is seen just above Hc1 in an applied field of only 54 Oe. A 30 degree reorientation of this vortex lattice has been observed in a very low field of 200 Oe. This reorientation transition appears to be of first-order and could be explained by non-local effects. The magnetic field dependence of the form factor is well described by a single penetration depth of 1496(1) angstroms and a single coherence length of 307(1) angstroms at 2 K. At 1.5 K the penetration depth anisotropy is 2.7(1) with the field applied perpendicular to the c axis and agrees with the coherence length anisotropy determined from critical field measurements.Comment: 5 pages including 6 figures, to appear in Physical Review Letter

Direct observation of the quantum critical point in heavy fermion CeRhSi3_3

We report on muon spin rotation studies of the noncentrosymmetric heavy fermion antiferromagnet CeRhSi$_3$. A drastic and monotonic suppression of the internal fields, at the lowest measured temperature, was observed upon an increase of external pressure. Our data suggest that the ordered moments are gradually quenched with increasing pressure, in a manner different from the pressure dependence of the N\'eel temperature. At \unit{23.6}{kbar}, the ordered magnetic moments are fully suppressed via a second-order phase transition, and $T_{\rm{N}}$ is zero. Thus, we directly observed the quantum critical point at \unit{23.6}{kbar} hidden inside the superconducting phase of CeRhSi$_3$

Magnetic-field-induced nonlocal effects on the vortex interactions in twin-free YBa2Cu3O7

The vortex lattice (VL) in the high-kappa superconductor YBa2Cu3O7, at 2 K and with the magnetic field parallel to the crystal c-axis, undergoes a sequence of transitions between different structures as a function of applied magnetic field. However, from structural studies alone, it is not possible to determine precisely the system anisotropy that governs the transitions between different structures. To address this question, here we report new small-angle neutron scattering measurements of both the VL structure at higher temperatures, and the field- and temperature-dependence of the VL form factor. Our measurements demonstrate how the influence of anisotropy on the VL, which in theory can be parameterized as nonlocal corrections, becomes progressively important with increasing magnetic field, and suppressed by increasing the temperature towards Tc. The data indicate that nonlocality due to different anisotropies play important roles in determining the VL properties.Comment: To appear in Phys. Rev.

Switching of magnetic domains reveals evidence for spatially inhomogeneous superconductivity

The interplay of magnetic and charge fluctuations can lead to quantum phases with exceptional electronic properties. A case in point is magnetically-driven superconductivity, where magnetic correlations fundamentally affect the underlying symmetry and generate new physical properties. The superconducting wave-function in most known magnetic superconductors does not break translational symmetry. However, it has been predicted that modulated triplet p-wave superconductivity occurs in singlet d-wave superconductors with spin-density wave (SDW) order. Here we report evidence for the presence of a spatially inhomogeneous p-wave Cooper pair-density wave (PDW) in CeCoIn5. We show that the SDW domains can be switched completely by a tiny change of the magnetic field direction, which is naturally explained by the presence of triplet superconductivity. Further, the Q-phase emerges in a common magneto-superconducting quantum critical point. The Q-phase of CeCoIn5 thus represents an example where spatially modulated superconductivity is associated with SDW order

Adult Education and Work Contexts: International Perspectives and Challenges

Il volume, un collettaneo, presenta differenti prospettive nel campo dell'employability in education analizzando in particolare: 1. Lifelong Learning Policies Targeting Employment Contexts 2. Trasnational Perspectives and Lifelong Learning Policies 3. Employment Perspectives and Professionalization in Adult Education. I contributi raccolti sono stati sottopposti a peer review doppio ceco

Reflecting Teams als Seminarmethode

http://methodenpool.uni-koeln.de/download/reflectingteam.pd