arXiv subjects

M. Jourdan

Publications and source records attributed to M. Jourdan.

22 records · Page 2Linked to original sources

arXiv2004

Magnetic tunneling junctions with the Heusler compound Co_2Cr_{0.6}Fe_{0.4}Al

The Heusler alloy is used as an electrode of magnetic tunneling junctions. The junctions are deposited by magnetron dc sputtering using shadow mask techniques with AlO_{x} as a barrier and cobalt as counter electrode. Measurements of the magnetoresistive differential conductivity in a temperature range between 4K and 300K are shown. An analysis of the barrier properties applying the Simmons model to the bias dependent junction conductivity is performed. VSM measurements were carried out to examine the magnetic properties of the samples.

cond-mat.other↗

arXiv2003

Superconductivity of SrTiO_{3-δ}

Superconducting SrTiO_{3-δ} was obtained by annealing single crystalline SrTiO_3 samples in ultra high vacuum. An analysis of the V(I) characteristics revealed very small critical currents I_c which can be traced back to a unavoidable doping inhomogeneity. R(T) curves were measured for a range of magnetic fields B at I<<I_c, thereby probing only the sample regions with the highest doping level. The resulting curves B_{c2}(T) show upward curvature, both at small and strong doping. These results are discussed in the context of bipolaronic and conventional superconductivity with Fermi surface anisotropy. We conclude that the special superconducting properties of SrTiO_{3-δ} can be related to its Fermi surface and compare this finding with properties of the recently discovered superconductor MgB_2.

cond-mat.supr-con↗

arXiv2002

Correlation gap in the heavy-fermion antiferromagnet UPd_2Al_3

The optical properties of the heavy-fermion compound UPd$_2$Al$_3$ have been measured in the frequency range from 0.04 meV to 5 meV (0.3 to 40 cm$^{-1}$) at temperatures $2 {\rm K}<T< 300$ K. Below the coherence temperature $T^*\approx 50$ K, the hybridization gap opens around 10 meV. As the temperature decreases further ($T\leq 20$ K), a well pronounced pseudogap of approximately 0.2 meV develops in the optical response; we relate this to the antiferromagnetic ordering which occurs below $T_N\approx 14$ K. The frequency dependent mass and scattering rate give evidence that the enhancement of the effective mass mainly occurs below the energy which is associated to the magnetic correlations between the itinerant and localized 5f electrons. In addition to this correlation gap, we observe a narrow zero-frequency conductivity peak which at 2 K is less than 0.1 meV wide, and which contains only a fraction of the delocalized carriers. The analysis of the spectral weight infers a loss of kinetic energy associated with the superconducting transition.

cond-mat.str-el↗

arXiv2000

c-Axis tunneling in YBa2Cu3O7-δ/PrBa2Cu3O7-δsuperlattices

In this work we report c-axis conductance measurements done on a superlattice based on a stack of 2 layers YBa2Cu3O{7-δ} and 7 layers PrBa2Cu3O{7-δ} (2:7). We find that these quasi-2D structures show no clear superconducting coupling along the c-axis. Instead, we observe tunneling with a gap of Δ_c=5.0\pm 0.5 meV for the direction perpendicular to the superconducting planes. The conductance spectrum show well defined quasi-periodic structures which are attributed to the superlattice structure. From this data we deduce a low temperature c-axis coherence length of ξ_c=0.24\pm 0.03 nm.

cond-mat.supr-con↗