arXiv subjects

L. DeBeer-Schmitt

Publications and source records attributed to L. DeBeer-Schmitt.

24 records · Page 2Linked to original sources

arXiv2012

Metastable Vortex Lattice Phases in Superconducting MgB2

The vortex lattice (VL) symmetry and orientation in clean type-II superconductors depends sensitively on the host material anisotropy, vortex density and temperature, frequently leading to rich phase diagrams. Typically, a well-ordered VL is taken to imply a ground state configuration for the vortex-vortex interaction. Using neutron scattering we studied the VL in MgB2 for a number of field-temperature histories, discovering an unprecedented degree of metastability in connection with a known, second-order rotation transition. This allows, for the first time, structural studies of a well-ordered, non-equilibrium VL. While the mechanism responsible for the longevity of the metastable states is not resolved, we speculate it is due to a jamming of VL domains, preventing a rotation to the ground state orientation.

cond-mat.supr-con↗

arXiv2010

Observations of Pauli Paramagnetic Effects on the Flux Line Lattice in CeCoIn5

From small-angle neutron scattering studies of the flux line lattice (FLL) in CeCoIn5, with magnetic field applied parallel to the crystal c-axis, we obtain the field- and temperature-dependence of the FLL form factor, which is a measure of the spatial variation of the field in the mixed state. We extend our earlier work [A.D. Bianchi et al. 2008 Science 319, 177] to temperatures up to 1250 mK. Over the entire temperature range, paramagnetism in the flux line cores results in an increase of the form factor with field. Near H_c2 the form factor decreases again, and our results indicate that this fall-off extends outside the proposed FFLO region. Instead, we attribute the decrease to a paramagnetic suppression of Cooper pairing. At higher temperatures, a gradual crossover towards more conventional mixed state behavior is observed.

cond-mat.supr-con↗

arXiv2009

Small-angle neutron scattering study of the vortex lattice in superconducting LuNi2B2C

We present studies of the magnetic field distribution around the vortices in LuNi2B2C. Small-angle neutron scattering measurements of the vortex lattice (VL) in this material were extended to unprecedentedly large values of the scattering vector q, obtained both by using high magnetic fields to decrease the VL spacing and by using higher order reflections. A square VL, oriented with the nearest neighbor direction along the crystalline [110] direction, was observed up to the highest measured field. The first-order VL form factor, |F(q10)|, was found to decrease exponentially with increasing magnetic field. Measurements of the higher order form factors, |F(qhk)|, reveal a significant in-plane anisotropy and also allow for a real-space reconstruction of the VL field distribution.

cond-mat.supr-con↗

arXiv2007

Pauli Paramagnetic Effects on Vortices in Superconducting TmNi2B2C

The magnetic field distribution around the vortices in TmNi2B2C in the paramagnetic phase was studied experimentally as well as theoretically. The vortex form factor, measured by small-angle neutron scattering, is found to be field independent up to 0.6 Hc2 followed by a sharp decrease at higher fields. The data are fitted well by solutions to the Eilenberger equations when paramagnetic effects due to the exchange interaction with the localized 4f Tm moments are included. The induced paramagnetic moments around the vortex cores act to maintain the field contrast probed by the form factor.

cond-mat.supr-con↗

arXiv2006

Field Dependent Coherence Length in the Superclean, High-Kappa Superconductor CeCoIn5

Using small-angle neutron scattering, we have studied the flux-line lattice (FLL) in superconducting CeCoIn5. The FLL is found to undergo a first-order symmetry and reorientation transition at ~0.55 T at 50 mK. The FLL form factor in this material is found to be independent of the applied magnetic field, in striking contrast to the exponential decrease usually observed in superconductors. This result is consistent with a strongly field-dependent coherence length in CeCoIn5, in agreement with recent theoretical predictions for superclean, high-kappa superconductors.

cond-mat.supr-con↗

arXiv2006

Measuring the Penetration Depth Anisotropy in MgB$_2$ using Small-Angle Neutron Scattering

Using small-angle neutron scattering we have measured the misalignment between an applied field of 4 kOe and the flux-line lattice in MgB$_2$, as the field is rotated away from the c axis by an angle $θ$. The measurements, performed at 4.9 K, showed the vortices canting towards the c axis for all field orientations. Using a two-band/two-gap model to calculate the magnetization we are able to fit our results yielding a penetration depth anisotropy, $\glam = 1.1 \pm 0.1$.

cond-mat.supr-con↗