Theoretical analysis of the transmission phase shift of a quantum dot in the presence of Kondo correlations

We study the effects of Kondo correlations on the transmission phase shift of a quantum dot coupled to two leads in comparison with the experimental determinations made by Aharonov-Bohm (AB) quantum interferometry. We propose here a theoretical interpretation of these results based on scattering theory combined with Bethe ansatz calculations. We show that there is a factor of 2 difference between the phase of the S-matrix responsible for the shift in the AB oscillations, and the one controlling the conductance. Quantitative agreement is obtained with experimental results for two different values of the coupling to the leads.Comment: 4 pages, 4 figures, accepted for publication in Physical Review Letter

Noisy Kondo impurities

The anti-ferromagnetic coupling of a magnetic impurity carrying a spin with the conduction electrons spins of a host metal is the basic mechanism responsible for the increase of the resistance of an alloy such as Cu${}_{0.998}$Fe${}_{0.002}$ at low temperature, as originally suggested by Kondo . This coupling has emerged as a very generic property of localized electronic states coupled to a continuum . The possibility to design artificial controllable magnetic impurities in nanoscopic conductors has opened a path to study this many body phenomenon in unusual situations as compared to the initial one and, in particular, in out of equilibrium situations. So far, measurements have focused on the average current. Here, we report on \textit{current fluctuations} (noise) measurements in artificial Kondo impurities made in carbon nanotube devices. We find a striking enhancement of the current noise within the Kondo resonance, in contradiction with simple non-interacting theories. Our findings provide a test bench for one of the most important many-body theories of condensed matter in out of equilibrium situations and shed light on the noise properties of highly conductive molecular devices.Comment: minor differences with published versio

Bistable Thin-Film Shape Memory Actuators for Applications in Tactile Displays

Bistable shape memory actuators were fabricated by microsystem technology processes and characterized with regard to their use in tactile graphic displays. The actuators were realized as sputter-deposited buckled metallic thin-film carriers, having structured Ti-Ni-Cu and Ti-Ni-Hf shape memory alloys on the top and at the bottom, respectively. They were sputtered on wavy-structured substrate and had lateral dimensions ranging from 2.2 to 3.5 min in width and from I to 3 mm in length. The actuators were switched with voltages in the range of 0.2 to 0.8 V and with currents in the range of 0.2 to 0.8 A. A force of 2.2 mN with a displacement of 0.7 mm was reached. To improve the performance further, a special test setup was developed. The bistable actuators in it were sputtered on a planar substrate with lateral dimensions ranging from 6 to 8 mm in width and from 3 to 6 min in length. These actuators were switched with actuation voltages in the range of 0.6 to 1.6 V and with currents in the range of 0.6 to 1.8 A. Thus, a force of 16 mN with a displacement of 1.2 min was reached. [2007-0261