166 research outputs found
Fabrication and properties of sub-micrometric YBCO biepitaxial junctions
No full textWe report on the fabrication procedure and the transport properties of submicron grain boundary biepitaxial YBCO Josephson junctions. These first results are very encouraging and justify further expectations on improved performances for such types of devices. A reduced and more controlled faceting along the grain boundary interface, for instance, will better preserve intrinsic d-wave effects, and favour the study of fluxons dynamics
Dynamics of d-wave YBa2Cu3O7−x dc SQUIDs
No full textThe predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current - phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current - phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current - phase relation, with a pronounced second harmonic sin( 2 phi) term. This fact has to be taken into account when designing d- wave SQUIDs for quantum circuitry
Dynamics of d-wave YBa2Cu3O7-x
No full textThe predominant d-wave pairing symmetry in high temperature superconductors leads to an unconventional current phase relation in Josephson junctions. This circumstance may induce new effects in the dynamics of dc SQUIDs. In this contribution we report on the measurements of the dependence of the SQUID Josephson current on the external magnetic field taken at very low temperatures, down to 20 mK. Different grain boundaries have been fabricated by using the biepitaxial and the bicrystal technique. Some of the effects which are induced by a nonsinusoidal current phase relation can be clearly identified in the dynamics of the SQUIDs. The experimental data are also compared with theoretical simulations taking into account the inductance of the loop. The data show that, in specific conditions, a non-negligible inductance of the loop can induce effects similar to an unconventional current phase relation, with a pronounced second harmonic sin(2) term. This fact has to be taken into account when designing d-wave SQUIDs for quantum circuitry
Quantum properties of d-wave YBaCaO Josephson junction
No full textWe have measured the transport properties of YBa2Cu3O7d (YBCO) dc SQUIDs with Josephson junctions characterized by a combination
of 45 [00 1] tilt and a [100] tilt grain boundary with a = 0, ±10 and 45. By increasing the component of transport in the
YBCO c-axis direction (increasing values of a), the SQUIDs showed an enhanced quality factor. At the same time, for all the devices
the response under an external magnetic field presented the main features of an unconventional Josephson current phase relation with
a pronounced sin2u component. Switching current measurements at low temperature (10th of mK) also revealed that the dynamics of
grain boundary junction resulting from a combination of 45 [00 1] and 45 [100] tilt is dominated by macroscopic quantum tunnelling of
the superconductive phase. The features are quite encouraging for applications of d-wave junctions in quantum circuitry
Fabrication and properties of sub-micrometric YBCO biepitaxial junctions
No full textWe report on the fabrication procedure and the transport properties of submicron grain boundary biepitaxial YBCO Josephson junctions. These first results are very encouraging and justify further expectations on improved performances for such types of devices. A reduced and more controlled faceting along the grain boundary interface, for instance, will better preserve intrinsic d-wave effects, and favour the study of fluxons dynamics
Dynamics of a LC Shunted YBa2Cu3O7-δ Josephson Junction
No full textWe have measured the energy level separation from the ground state to the first excited state in a high critical temperature superconductor d-wave Josephson junction. We observe that the bias current dependence of the energy level separation is strongly affected by the large shunt capacitance and inductance of the junction electrodes. In order to describe the effect of a shunt capacitance and shunt inductance on the junction dynamics we derive the equation of motion of the total system. In general such a circuit displays two resonance frequencies corresponding to two different energy scales. We discuss various limits for the values of the shunt inductor and capacitor
Resonant phase dynamics in 0-π Sine–Gordon facets
No full textAlocally phase-shifted Sine–Gordon modelwell accounts for the phenomenology of unconventional
Josephson junctions. The phase dynamics shows resonant modes similar to Fiske modes that appear both in
the presence and in the absence of the external magnetic field in standard junctions. In the latter case, they
are also in competition with zero field propagation of Sine–Gordon solitons, i.e., fluxons, which give rise
to the so-called zero field steps in the current–voltage (I–V) of the junction. We numerically study the I–V
characteristics and the resonances magnetic field patterns for some different faceting configurations, in various
dissipative regimes, as a function of temperature. The simulated dynamics of the phase is analyzed for lowerorder
resonances.We give evidence of a nontrivial dynamics due to the interaction of propagating fluxons with
localized semifluxons. Numerical results are compared with experimental outcomes obtained on high-quality
high-Tc grain boundary YBCO junctions
Sub-Micron YBa2Cu3O7-x Biepitaxial Junctions
No full textWe report on the fabrication and properties of sub-micron YBa2Cu3O7-x off-axis biepitaxial junctions. The vision behind this work is to set up a reliable nanotechnology processing to improve junctions' performances and reproducibility through the reduction of their size. We will illustrate the fabrication procedure employed and show the results obtained on samples where the transport parameters were tuned in a predictable way. Also, proofs of a clean barrier structure with few facets and low disorder were obtained
Underlying physical aspects of fluctuations in YBa 2 Cu 3 O 7- grain boundary Josephson junctions
No full textHigh quality YBa2Cu3O7d biepitaxial grain boundary junctions allowed one of the first evidences of macroscopic quantum behavior
and mesoscopic transport in high critical temperature superconductors (HTS) systems. Both these studies touch delicate issues on fluctuations
and give important feedback on the understanding of coherent transport of quasiparticles and of the dissipation mechanisms in
HTS
Energy level quantization in a YBaCuO Josephson Junction
No full textWe have observed energy level quantization in an all high critical temperature superconductor d-wave Josephson junction. From the measurements we have also extracted the quality factor Q of the junction which is of the order of 40. These results indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for the class of solid state "quiet" quantum bit with longer coherence time
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