9,233 research outputs found
Patterned Irradiation of YBa_2Cu_3O_(7-x) Thin Films
We present a new experiment on YBa_2Cu_3O_{7-x} (YBCO) thin films using
spatially resolved heavy ion irradiation. Structures consisting of a periodic
array of strong and weak pinning channels were created with the help of metal
masks. The channels formed an angle of +/-45 Deg with respect to the symmetry
axis of the photolithographically patterned structures. Investigations of the
anisotropic transport properties of these structures were performed. We found
striking resemblance to guided vortex motion as it was observed in YBCO single
crystals containing an array of unidirected twin boundaries. The use of two
additional test bridges allowed to determine in parallel the resistivities of
the irradiated and unirradiated parts as well as the respective current-voltage
characteristics. These measurements provided the input parameters for a
numerical simulation of the potential distribution of the Hall patterning. In
contrast to the unidirected twin boundaries in our experiment both strong and
weak pinning regions are spatially extended. The interfaces between
unirradiated and irradiated regions therefore form a Bose-glass contact. The
experimentally observed magnetic field dependence of the transverse voltage
vanishes faster than expected from the numerical simulation and we interpret
this as a hydrodynamical interaction between a Bose-glass phase and a vortex
liquid.Comment: 7 pages, 8 Eps figures included. Submitted to PR
Emission Noise and High Frequency Cut-Off of the Kondo Effect in a Quantum Dot
By coupling on chip a carbon nanotube to a quantum noise detector, a
superconductor-insulator-superconductor junction, via a resonant circuit, we
measure the emission noise of a carbon nanotube quantum dot in the Kondo
regime. The signature of the Kondo effect in the current noise is measured for
different ratios of the Kondo temperature over the measured frequency and for
different asymmetries of the coupling to the contacts, and compared to finite
frequency quantum noise calculations. Our results point towards the existence
of a high frequency cut-off of the electronic emission noise associated with
the Kondo resonance. This cut-off frequency is of the order of a few times the
Kondo temperature when the electronic system is close to equilibrium, which is
the case for a strongly asymmetric coupling. On the other hand, this cut-off is
shifted to lower frequency in a symmetric coupling situation, where the bias
voltage drives the Kondo state out-of-equilibrium. We then attribute the low
frequency cut-off to voltage induced spin relaxation.Comment: 5 pages, 3 figures and appendi
- …