Volume 34, Issue 8, August 2008
Index of content:
- SUPERCONDUCTIVITY, INCLUDING HIGH-TEMPERATURE SUPERCONDUCTIVITY
Influence of combined deformation and heat treatment on the superconducting properties of a niobium-titanium alloy34(2008); http://dx.doi.org/10.1063/1.2966714View Description Hide Description
The influence of combined deformation, including equal-channel multiangle pressing (ECMAP), and heat treatment on the critical current density of a superconducting wire made from the alloy Ti is investigated. It is found that the combined deformation, including ECMAP, can increase the critical current density by up to two times. The relationship between the character of the structural inhomogeneities and the pinning force is estimated. The pinning efficiency is linked to the nanostructural state of the alloy.
34(2008); http://dx.doi.org/10.1063/1.2967504View Description Hide Description
In this paper we discuss solid-state nanoelectronic realizations of Josephson flux qubits with large tunneling amplitude between the two macroscopic states. The latter can be controlled via the height and form of the potential barrier, which is determined by quantum-state engineering of the flux qubit circuit. The simplest circuit of the flux qubit is a superconducting loop interrupted by a Josephson nanoscale tunnel junction. The tunneling amplitude between two macroscopically different states can be increased substantially by engineering of the qubit circuit if the tunnel junction is replaced by a ScS contact. However, only Josephson tunnel junctions are particularly suitable for large-scale integration circuits and quantum detectors with present-day technology. To overcome this difficulty we consider here a flux qubit with high energy-level separation between the “ground” and “excited” states, consisting of a superconducting loop with two low-capacitance Josephson tunnel junctions in series. We demonstrate that for real parameters of resonant superposition between the two macroscopic states the tunneling amplitude can reach values greater than . Analytical results for the tunneling amplitude obtained within the semiclassical approximation by the instanton technique show good correlation with a numerical solution.
34(2008); http://dx.doi.org/10.1063/1.2967505View Description Hide Description
The effect of an amorphousSbcoating on the resistivity of amorphous and crystalline V, Yb, and Bi films is investigated. The values of decrease for both phase states of V and Bi and increase for Yb. The effect of a coating on is limited by the thickness of the coating, depending on the type and phase state of the base metal. Increasing the coating thickness to does not change further. The observed changes in are attributed to electron flow from amorphousantimony into Bi and V and from amorphous and crystalline Yb films into amorphousantimony with a contact potential difference forming between the metal and semiconductor layers. In the process the density of states of the conduction electrons in the metal changes, and this is responsible for the change in .