arXiv subjects

M. R. Eskildsen

Publications and source records attributed to M. R. Eskildsen.

41 records · Page 3Linked to original sources

arXiv2002

Hexagonal and Square Flux Line Lattices in CeCoIn5

Using small-angle neutron scattering, we have imaged the magnetic flux line lattice (FLL) in the d-wave heavy-fermion superconductor CeCoIn5. At low fields we find a hexagonal FLL. Around 0.6 T this undergoes what is very likely a first-order transition to square symmetry, with the nearest neighbors oriented along the gap node directions. This orientation of the square FLL is consistent with theoretical predictions based on the d-wave order parameter symmetry.

cond-mat.supr-con↗

arXiv2002

Scanning Tunneling Spectroscopy on Single Crystal MgB2

We report on the results of scanning tunneling spectroscopy measurements on single crystals of Mg2. Tunneling was performed both parallel and perpendicular to the crystalline c-axis. In the first case, a single superconducting gap (Delta_pi = 2.2 meV) associated with the pi-band is observed. Tunneling parallel to the ab-plane reveals an additional, larger gap (Delta_sigma ~ 7 meV) originating in the highly two-dimensional sigma-band. Vortex imaging in the pi-band was performed with the field and tunnel current parallel to the c-axis. The vortices have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. A comparison to specific heat measurements is performed.

cond-mat.supr-con↗

arXiv2002

Vortex Imaging in the pi-Band of Magnesium Diboride

We report scanning tunneling spectroscopy imaging of the vortex lattice in single crystalline MgB2. By tunneling parallel to the c-axis, a single superconducting gap (Delta = 2.2 meV) associated with the pi-band is observed. The vortices in the pi-band have a large core size compared to estimates based on Hc2, and show an absence of localized states in the core. Furthermore, superconductivity between the vortices is rapidly suppressed by an applied field. These results suggest that superconductivity in the pi-band is, at least partially, induced by the intrinsically superconducting sigma-band.

cond-mat.supr-con↗

arXiv2001

Temperature Dependence of the Flux Line Lattice Transition into Square Symmetry in Superconducting LuNi$_2$B$_2$C

We have investigated the temperature dependence of the H || c flux line lattice structural phase transition from square to hexagonal symmetry, in the tetragonal superconductor LuNi_2B_2C (T_c = 16.6 K). At temperatures below 10 K the transition onset field, H_2(T), is only weakly temperature dependent. Above 10 K, H_2(T) rises sharply, bending away from the upper critical field. This contradicts theoretical predictions of H_2(T) merging with the upper critical field, and suggests that just below the H_c2(T)-curve the flux line lattice might be hexagonal.

cond-mat.supr-con↗

arXiv1999

Interdependence of magnetism and superconductivity in the borocarbide TmNi2B2C

We have discovered a new antiferromagnetic phase in TmNi2B2C by neutron diffraction. The ordering vector is Q_A = (0.48,0,0) and the phase appears above a critical in-plane magnetic field of 0.9 T. The field was applied in order to test the assumption that the zero-field magnetic structure at Q_F = (0.094,0.094,0) would change into a c-axis ferromagnet if superconductivity were destroyed. We present theoretical calculations which show that two effects are important: A suppression of the ferromagnetic component of the RKKY exchange interaction in the superconducting phase, and a reduction of the superconducting condensation energy due to the periodic modulation of the moments at the wave vector Q_A.

cond-mat↗