700 research outputs found
Experimental Evidence for Crossed Andreev Reflection
We report on electronic transport properties of mesoscopic
superconductor-ferromagnet spin-valve structures. Two ferromagnetic iron leads
form planar tunnel contacts to a superconducting aluminum wire, where the
distance of the two contacts is of the order of the coherence length of the
aluminum. We observe a negative non-local resistance which can be explained by
crossed Andreev reflection, a process where an electron incident from one of
the leads gets reflected as a hole into the other, thereby creating a pair of
spatially separated, entangled particles.Comment: LT24 conference proceeding, 2 pages, 2 figure
Two-dimensional simulations of temperature and current-density distribution in electromigrated structures
We report on the application of a feedback-controlled electromigration
technique for the formation of nanometer-sized gaps in mesoscopic gold wires
and rings. The effect of current density and temperature, linked via Joule
heating, on the resulting gap size is investigated. Experimentally, a good
thermal coupling to the substrate turned out to be crucial to reach electrode
spacings below 10 nm and to avoid overall melting of the nanostructures. This
finding is supported by numerical calculations of the current-density and
temperature profiles for structure layouts subjected to electromigration. The
numerical method can be used for optimizing the layout so as to predetermine
the location where electromigation leads to the formation of a gap.Comment: 9 pages, 6 figure
Multidimensional entropy landscape of quantum criticality
The Third Law of Thermodynamics states that the entropy of any system in
equilibrium has to vanish at absolute zero temperature. At nonzero
temperatures, on the other hand, matter is expected to accumulate entropy near
a quantum critical point (QCP), where it undergoes a continuous transition from
one ground state to another. Here, we determine, based on general thermodynamic
principles, the spatial-dimensional profile of the entropy S near a QCP and its
steepest descent in the corresponding multidimensional stress space. We
demonstrate this approach for the canonical quantum critical compound
CeCu6-xAux near its onset of antiferromagnetic order. We are able to link the
directional stress dependence of S to the previously determined geometry of
quantum critical fluctuations. Our demonstration of the multidimensional
entropy landscape provides the foundation to understand how quantum criticality
nucleates novel phases such as high-temperature superconductivity.Comment: 14 pages, 4 figure
A mechanism for the non-Fermi-liquid behavior in CeCu_{6-x}Au_x
We propose an explanation for the recently observed non-Fermi-liquid behavior
of metallic alloys CeCu_{6-x}Au_x: near x=0.1, the specific heat c is
proportional to T \ln (T_0/T) and the resistivity increases linearly with
temperature T over a wide range of T. These features follow from a model in
which three-dimensional conduction electrons are coupled to two-dimensional
critical ferromagnetic fluctuations near the quantum critical point, x_{c}=0.1.
This picture is motivated by the neutron scattering data in the ordered phase
(x=0.2) and is consistent with the observed phase diagram.Comment: 4 pages, LaTeX, 3 figure
Low temperature magnetization of the quantum critical heavy fermion superconductor -YbAlB
-YbAlB is the first Yb-based heavy fermion superconductor with
mK. We measured low temperature magnetization of high-purity
single crystals down to 25 mK. The measurements have revealed a
considerable amount of volume fractions of the superconductivity and the upper
critical field curve under field along the c axis, consistent with the
previous results. In the normal state, the previously observed divergent
behavior in the temperature dependence of the magnetization has been confirmed
using higher quality samples and under a low field of 22 mT. In addition, the
measurements have revealed a power law behavior, namely, , which has a slightly higher exponent than the previous results.Comment: 3 pages, 4 figures, a proceedings paper of QCNP 200
- âŠ