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Conditioning of Superconductive Properties in Graph-Shaped Reticles
Authors:
M. Lucci,
D. Cassi,
V. Merlo,
R. Russo,
G. Salina,
M. Cirillo
Abstract:
We report on phenomena observed in planar integrated networks obtained connecting superconducting island by Josephson tunnel junctions. These networks, identifiable as tree-like graphs, have branches consisting of series arrays of Josephson junctions which can be individually current biased and characterized. Both Josephson supercurrents and gap parameters of the arrays embedded in the graph struc…
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We report on phenomena observed in planar integrated networks obtained connecting superconducting island by Josephson tunnel junctions. These networks, identifiable as tree-like graphs, have branches consisting of series arrays of Josephson junctions which can be individually current biased and characterized. Both Josephson supercurrents and gap parameters of the arrays embedded in the graph structures display properties significantly different from those of reference arrays fabricated on the same chips and having identical geometrical shape. The temperature and magnetic field dependencies of the Josephson current of the embedded arrays both show a singular behavior when a critical value is reached by the Josephson characteristic energy. The gap parameter of the junctions generating the embedded arrays is higher than that of the junctions forming the reference geometrical arrays.
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Submitted 22 March, 2020; v1 submitted 27 January, 2020;
originally announced January 2020.
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Characterization of Anomalous Pair Currents in Josephson Junction Networks
Authors:
I. Ottaviani,
M. Lucci,
R. Menditto,
V. Merlo,
M. Salvato,
M. Cirillo F. Mueller,
T. Weimann,
M. G. Castellano,
F. Chiarello,
G. Torrioli,
R. Russo
Abstract:
Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependencies of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of a theo…
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Measurements performed on superconductive networks shaped in the form of planar graphs display anomalously large currents when specific branches are biased. The temperature dependencies of these currents evidence that their origin is due to Cooper pair hopping through the Josephson junctions connecting the superconductive islands of the array. The experimental data are discussed in terms of a theoretical model which predicts, for the system under consideration, an inhomogeneous Cooper pair distribution on the superconductive islands of the network.
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Submitted 11 September, 2013;
originally announced September 2013.
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Superconducting flux-flow type ultra-low-noise magnetic sensors - An alternative to dc-SQUIDs
Authors:
Roberto Monaco,
Carmine Granata,
Roberto Russo,
antonio Vettoliere
Abstract:
A superconducting magnetometers based on the magnetic field dependence of the Eck step voltage in long Josephson tunnel junctions (LJTJs) is demonstrated. The field to be measured is applied perpendicular to a continuous superconducting pickup loop. Wherever the loop has a narrow constriction, the density of the flux-restoring circulating currents will become relatively high and will locally creat…
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A superconducting magnetometers based on the magnetic field dependence of the Eck step voltage in long Josephson tunnel junctions (LJTJs) is demonstrated. The field to be measured is applied perpendicular to a continuous superconducting pickup loop. Wherever the loop has a narrow constriction, the density of the flux-restoring circulating currents will become relatively high and will locally create a magnetic field large enough to bring a biased LJTJ in the flux-flow state, i.e., at a finite voltage proportional to the field strength. This method allows the realization of a novel family of robust and general-purpose superconducting devices which, despite their simplicity, function as ultra-low-noise, wide-band and high-dynamics magnetometers. The performances of low-T$_c$ sensor prototypes, among which a highly linear voltage responsivity and a magnetic spectral density $S_B^{1/2}< 3\,fT/Hz^{1/2}$, promise to be competitive with those of the best superconducting quantum interference devices.
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Submitted 16 June, 2013; v1 submitted 21 April, 2013;
originally announced April 2013.
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Current Noise Investigation in Josephson Devices by Switching Current Measurements
Authors:
C. Granata,
A. Vettoliere,
R. Russo,
M. Russo,
B. Ruggiero
Abstract:
An experimental investigation of the critical current noise in underdamped niobium based Josephson junctions by a technique based on the switching current measurements is reported. By sweeping the junction with a current ramp we measure the critical current switching using the standard time of flight technique and analyze the data to extract the current noise. The experimental results show a linea…
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An experimental investigation of the critical current noise in underdamped niobium based Josephson junctions by a technique based on the switching current measurements is reported. By sweeping the junction with a current ramp we measure the critical current switching using the standard time of flight technique and analyze the data to extract the current noise. The experimental results show a linear behavior of the current white noise from both the junction area and the temperature. These measurement provide very useful information about the intrinsic noise of Josephson devices involving SQUIDs and qubits.
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Submitted 9 July, 2010;
originally announced July 2010.
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Inhomogeneous Superconductivity in Comb-Shaped Josephson Junction Networks
Authors:
P. Sodano,
A. Trombettoni,
P. Silvestrini,
R. Russo,
B. Ruggiero
Abstract:
We show that some of the Josephson couplings of junctions arranged to form an inhomogeneous network undergo a non-perturbative renormalization provided that the network's connectivity is pertinently chosen. As a result, the zero-voltage Josephson critical currents $I_c$ turn out to be enhanced along directions selected by the network's topology. This renormalization effect is possible only on gr…
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We show that some of the Josephson couplings of junctions arranged to form an inhomogeneous network undergo a non-perturbative renormalization provided that the network's connectivity is pertinently chosen. As a result, the zero-voltage Josephson critical currents $I_c$ turn out to be enhanced along directions selected by the network's topology. This renormalization effect is possible only on graphs whose adjacency matrix admits an hidden spectrum (i.e. a set of localized states disappearing in the thermodynamic limit). We provide a theoretical and experimental study of this effect by comparing the superconducting behavior of a comb-shaped Josephson junction network and a linear chain made with the same junctions: we show that the Josephson critical currents of the junctions located on the comb's backbone are bigger than the ones of the junctions located on the chain. Our theoretical analysis, based on a discrete version of the Bogoliubov-de Gennes equation, leads to results which are in good quantitative agreement with experimental results.
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Submitted 25 September, 2006;
originally announced September 2006.
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Topology-Induced Critical Current Enhancement in Josephson Networks
Authors:
P. Silvestrini,
R. Russo,
V. Corato,
B. Ruggiero,
C. Granata,
S. Rombetto,
M. Russo,
M. Cirillo,
A. Trombettoni,
P. Sodano
Abstract:
We investigate the properties of Josephson junction networks with inhomogeneous architecture. The networks are shaped as "quare comb" planar lattices on which Josephson junctions link superconducting islands arranged in the plane to generate the pertinent topology. Compared to the behavior of reference linear arrays, the temperature dependencies of the Josephson currents of the branches of the n…
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We investigate the properties of Josephson junction networks with inhomogeneous architecture. The networks are shaped as "quare comb" planar lattices on which Josephson junctions link superconducting islands arranged in the plane to generate the pertinent topology. Compared to the behavior of reference linear arrays, the temperature dependencies of the Josephson currents of the branches of the network exhibit relevant differences. The observed phenomena evidence new and surprising behavior of superconducting Josephson arrays as well as remarkable similarities with bosonic junction arrays.
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Submitted 28 September, 2006; v1 submitted 19 December, 2005;
originally announced December 2005.
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Anomalous thermal escape in Josephson systems perturbed by microwaves
Authors:
N. Grønbech-Jensen,
M. G. Castellano,
F. Chiarello,
M. Cirillo,
C. Cosmelli,
V. Merlo,
R. Russo,
G. Torrioli
Abstract:
We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multi-valued temperature ranges both below and above the the classical to quantum crossover temperature. Switching current d…
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We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multi-valued temperature ranges both below and above the the classical to quantum crossover temperature. Switching current distributions are obtained both experimentally and numerically at temperatures both near and far above the quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with a simple anharmonic theory for Josephson resonance frequency as a function of bias current. Throughout, experimental results and direct numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement.
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Submitted 26 December, 2004;
originally announced December 2004.
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High quality superconducting niobium films produced by Ultra High Vacuum Cathodic Arc
Authors:
R. Russo,
L. Catani,
A. Cianchi,
S. Tazzari,
J. Langner
Abstract:
The vacuum arc is a well-known technique to produce coating with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapor pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a Cathodic Arc system working…
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The vacuum arc is a well-known technique to produce coating with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapor pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a Cathodic Arc system working under Ultra High Vacuum conditions (UHVCA). UHVCA has been used to produce ultra-pure niobium films with excellent structural and electrical properties at a deposition temperature lower than 100oC. The UHVCA technique therefore opens new perspectives for all applications requiring ultra-pure films or, as in the case of Plasma Immersion Ion Implantation, ultra-pure plasmas.
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Submitted 10 September, 2004;
originally announced September 2004.
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Microwave-induced thermal escape in Josephson junctions
Authors:
N. Gronbech-Jensen,
M. G. Castellano,
F. Chiarello,
G. Torrioli,
M. Cirillo,
L. Filippenko,
R. Russo,
C. Cosmelli
Abstract:
We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multi-valued in a temperature range far exceeding the classical to quantum crossover temperature. Plots of the switching cur…
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We investigate, by experiments and numerical simulations, thermal activation processes of Josephson tunnel junctions in the presence of microwave radiation. When the applied signal resonates with the Josephson plasma frequency oscillations, the switching current may become multi-valued in a temperature range far exceeding the classical to quantum crossover temperature. Plots of the switching currents traced as a function of the applied signal frequency show very good agreement with the functional forms expected from Josephson plasma frequency dependencies on the bias current. Throughout, numerical simulations of the corresponding thermally driven classical Josephson junction model show very good agreement with the experimental data.
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Submitted 9 March, 2004;
originally announced March 2004.
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Irreversibility Line in Nb/CuMn Multilayers with a Regular Array of Antidots
Authors:
C. Attanasio,
T. Di Luccio,
L. V. Mercaldo,
S. L. Prischepa,
R. Russo,
M. Salvato,
L. Maritato,
S. Barbanera,
A. Tuissi
Abstract:
The transport properties of Nb/CuMn multilayers with a regular array of electron beam lithography obtained antidots have been measured at different temperatures in the presence of external perpendicular magnetic fields. Hysteretical I-V characteristics have been observed which disappear when approaching the upper critical magnetic field curve H_{c2}(T). Comparing these data with other results (A…
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The transport properties of Nb/CuMn multilayers with a regular array of electron beam lithography obtained antidots have been measured at different temperatures in the presence of external perpendicular magnetic fields. Hysteretical I-V characteristics have been observed which disappear when approaching the upper critical magnetic field curve H_{c2}(T). Comparing these data with other results (Arrhenius plots of resistive transition curves, logV-logI characteristics) we have been able to relate the onset of the hysteresis to the presence of an irreversibility line. We discuss several possible mechanisms to clarify the nature of this line. Among them the most plausible seems to be the vortex melting mainly induced by quantum fluctuations.
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Submitted 14 January, 2000;
originally announced January 2000.