arXiv subjects

R. Jansen

Publications and source records attributed to R. Jansen.

22 records · Page 2Linked to original sources

arXiv2001

Observation of band structure and density of states effects in Co-based magnetic tunnel junctions

Utilizing Co/Al$_2$O$_3$/Co magnetic tunnel junctions (MTJs) with Co electrodes of different crystalline phases, a clear relationship between electrode structure and junction transport properties is presented. For junctions with one fcc(111) textured and one polycrystalline (poly-phase and poly-directional) Co electrode, a strong asymmetry is observed in the magnetotransport properties, while when both electrodes are polycrystalline the magnetotransport is essentially symmetric. These observations are successfully explained within a model based on ballistic tunneling between the calculated band structures (DOS) of fcc-Co and hcp-Co.

cond-mat.mtrl-sci↗

arXiv2001

A stochastic rainbow caustic observed with cold atoms

We report the direct observation of a novel type of rainbow caustic. In contrast to known examples, this caustic originates from a dissipative, stochastic process. We have observed this using cold ^{87}Rb atoms bouncing inelastically on an evanescent-wave atom mirror. The caustic appears as a sharp peak at the lower edge of the asymmetric velocity distribution of the bouncing atoms. The stochastic process is a spontaneous Raman transition due to photon scattering during the bounce. The results are in good agreement with a classical calculation.

physics.atom-ph↗

arXiv2000

Elastic and Inelastic Evanescent-Wave Mirrors for Cold Atoms

We report on experiments on an evanescent-wave mirror for cold $^{87}$Rb atoms. Measurements of the bouncing fraction show the importance of the Van der Waals attraction to the surface. We have directly observed radiation pressure parallel to the surface, exerted on the atoms by the evanescent-wave mirror. We analyze the radiation pressure by imaging the motion of the atom cloud after the bounce. The number of photon recoils ranges from 2 to 31. This is independent of laser power, inversely proportional to the detuning and proportional to the evanescent-wave decay length. By operating the mirror on an open transition, we have also observed atoms that bounce inelastically due to a spontaneous Raman transition. The observed distributions consist of a dense peak at the minimum velocity and a long tail of faster atoms, showing that the transition is a stochastic process with a strong preference to occur near the turning point of the bounce.

physics.atom-ph↗

arXiv2000

Observation of radiation pressure exerted by evanescent waves

We report a direct observation of radiation pressure, exerted on cold rubidium atoms while bouncing on an evanescent-wave atom mirror. We analyze the radiation pressure by imaging the motion of the atoms after the bounce. The number of absorbed photons is measured for laser detunings ranging from {190 MHz} to {1.4 GHz} and for angles from {0.9 mrad} to {24 mrad} above the critical angle of total internal reflection. Depending on these settings, we find velocity changes parallel with the mirror surface, ranging from 1 to {18 cm/s}. This corresponds to 2 to 31 photon recoils per atom. These results are independent of the evanescent-wave optical power.

quant-ph↗