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Hydrogen (H) plays a key role in the near-to-room temperature superconductivity of hydrides at megabar pressures. This suggests that H doping could have similar effects on the electronic and phononic spectra of materials at ambient pressure as well. Here, we demonstrate the non-volatile control of the electronic ground state of titanium diselenide (1T-TiSe2) via ionic liquid gating-driven H intercalation. This protonation induces a superconducting phase, observed together with a charge-density wave through most of the phase diagram, with nearly doping-independent transition temperatures. The H-induced superconducting phase is possibly gapless-like and multi-band in nature, in contrast with those induced in TiSe2 via copper, lithium, and electrostatic doping. This unique behavior is supported by ab initio calculations showing that high concentrations of H dopants induce a full reconstruction of the bandstructure, although with little coupling between electrons and high-frequency H phonons. Our findings provide a promising approach for engineering the ground state of transition metal dichalcogenides and other layered materials via gate-controlled protonation. The key role played by hydrogen (H) in the near-to-room temperature superconductivity of hydrides at megabar pressures suggests that H doping could produce similar effects in materials at ambient pressure. Here the authors show that ionic gate-driven H intercalation in the layered compound TiSe2 induces a superconducting phase with features distinct from those obtained through other doping techniques. [ABSTRACT FROM AUTHOR]

Analyzing the electrodynamic response of MgB2 films in the microwave region showing that this material is promising for microwave applications in view of the small values of R(sub s) and the low sensitivity to the r.f. field levels is described. In view of possible device applications, the microwave response is studied in detail.

In this paper we report a detailed µ+SR and 19F NMR study of the La0.7Y0.3FeAsO1− xF x class of materials. Here, the diamagnetic La1− yY y substitution increases chemical pressure and, accordingly, sizeably enhances the optimal superconducting transition temperature. We investigate the magnetic-superconducting phase transition by keeping the Y content constant ( y = 0.3) and by varying the F content in the range $0.025\leq x\leq 0.15$. Our results show how magnetism and superconductivity coexist for x = 0.065. Such coexistence is due to segregation of the two phases in macroscopic regions, resembling what was observed in LaFeAsO1− xF x materials under applied hydrostatic pressure. This scenario is qualitatively different from the nanoscopic coexistence of the two order parameters observed when La is fully substituted by magnetic rare-earth ions like Sm or Ce. [ABSTRACT FROM AUTHOR]

We present a systematic study of the superconducting properties of high quality V3Si thin films, grown by high vacuum pulsed laser deposition from a stoichiometric target, a technique never reported in literature for this compound. By changing both the substrate (crystal structure and orientation) and the deposition conditions (substrate temperature, target-substrate distance, laser frequency and pulse energy) the critical temperature and the resistivity values of the samples have been finely tuned. Best results (TC - 16.1 K and Residual Resistivity Ratio RRR = 8.5) are obtained for deposition temperatures higher than 12000 C on both LaAlO3 and MgO substrates. All the samples are polycrystalline, that however does not affect the good quality of the transport properties. The possibility of multiband superconductivity in this com- pound is investigated, probing as a function of temperature: (i) the critical field up to 28 T using voltamperometric measurements, and (ii) the superfluid density via magnetic penetration depth measurements with a single coil inductive technique operating in the MHz region. [ABSTRACT FROM AUTHOR]

Niobium thin film coated copper RF cavities are an interesting alternative to niobium bulk cavities for the development of high performance superconducting accelerators. The main limiting factor in their use is the degradation of the quality factor Q with increasing accelerating field (the "Q-Slope"). To try and overcome this limitation, we have developed an alternative coating technique based on a Cathodic Arc system working under UHV conditions (UHVCA). High quality Nb samples have been synthesized under different deposition angles and their characteristics are presented. The UHVCA technique has been used to deposit 1.3 GHz TESLA-type single cell cavities. To further improve cavity performance the first critical field has to be enhanced. The use of multilayers consisting of alternating insulating and superconducting layers may produce the desired enhancement providing that the superconducting layer thickness is smaller than the London penetration depth. To this aim, we present also the experimental characterization of the superconducting properties (Tc, Bc1) of Nb/AlOx/Nb multilayers. [ABSTRACT FROM AUTHOR]

High-quality c-axis oriented MgB[sub 2] superconducting thin films were grown on MgO and Al[sub 2]O[sub 3] single crystal substrates by a d.c. planar magnetron sputtering technique. The films were obtained starting by Mg rich Mg-B precursor films, subsequently annealed in situ at 800°C for 10 min in a In sealed Nb box in the presence of saturated Mg vapor. The process is highly reproducible and can be easily scaled to produce large area films. Resistive transition of the 1 µm thick resulting films showed a maximum critical temperature T[sub c] of 35 K and a transition width lower than 0.5 K. The residual resistivity ratio was 1.6 for the best samples. The films were characterized by a variety of structural and electronic techniques including profilometry, XRD, EDS, and STM-AFM analyses, critical current, upper critical field and penetration depth measurements. In view of possible device applications, the microwave response has been studied in detail. The measured dependence of the surface impedance from temperature and r.f. field amplitude at 20 GHz via a dielectric resonator technique is reported and discussed. [ABSTRACT FROM AUTHOR]

Describes a high-Josephson-current density NbN junction developed on R-plane sapphire substrates. Characterization of NbN layers on R-plane sapphire; Sputtering of NbN layers on sapphire; Superconductivity of NbN junction electrode lines.

Hydrogen (H) plays a key role in the near-to-room temperature superconductivity of hydrides at megabar pressures. This suggests that H doping could have similar effects on the electronic and phononic spectra of materials at ambient pressure as well. Here, we demonstrate the non-volatile control of the electronic ground state of titanium diselenide (1T-TiSe2) via ionic liquid gating-driven H intercalation. This protonation induces a superconducting phase, observed together with a charge-density wave through most of the phase diagram, with nearly doping-independent transition temperatures. The H-induced superconducting phase is possibly gapless-like and multi-band in nature, in contrast with those induced in TiSe2 via copper, lithium, and electrostatic doping. This unique behavior is supported by ab initio calculations showing that high concentrations of H dopants induce a full reconstruction of the bandstructure, although with little coupling between electrons and high-frequency H phonons. Our findings provide a promising approach for engineering the ground state of transition metal dichalcogenides and other layered materials via gate-controlled protonation. The key role played by hydrogen (H) in the near-to-room temperature superconductivity of hydrides at megabar pressures suggests that H doping could produce similar effects in materials at ambient pressure. Here the authors show that ionic gate-driven H intercalation in the layered compound TiSe2 induces a superconducting phase with features distinct from those obtained through other doping techniques. [ABSTRACT FROM AUTHOR]

In this paper we report a detailed µ+SR and 19F NMR study of the La0.7Y0.3FeAsO1− xF x class of materials. Here, the diamagnetic La1− yY y substitution increases chemical pressure and, accordingly, sizeably enhances the optimal superconducting transition temperature. We investigate the magnetic-superconducting phase transition by keeping the Y content constant ( y = 0.3) and by varying the F content in the range $0.025\leq x\leq 0.15$. Our results show how magnetism and superconductivity coexist for x = 0.065. Such coexistence is due to segregation of the two phases in macroscopic regions, resembling what was observed in LaFeAsO1− xF x materials under applied hydrostatic pressure. This scenario is qualitatively different from the nanoscopic coexistence of the two order parameters observed when La is fully substituted by magnetic rare-earth ions like Sm or Ce. [ABSTRACT FROM AUTHOR]

The effect of isoelectronic substitutions on the microscopic properties of LaFe1-xRux AsO, for 0 ≤ x≤ 0.8, has been investigated by means of μSR and 139La NMR. It was found that Ru substitution causes a progressive reduction of the Néel temperature (TN) and of the magnetic order parameter without leading to the onset of superconductivity. The temperature dependence of 139La nuclear spin-lattice relaxation rate 1/T1 can be suitably described within a two-band model. One band giving rise to the metallic antiferromagnetic ground state, while the other one is characterized by weakly correlated electrons. Ru for Fe substitution yields a progressive decrease of the density of states at the Fermi level close to the one derived from band structure calculations. The reduction of TN with increasing Ru content follows the predictions of the J1-J2 model on a square lattice, which appears to be an effective framework to describe the magnetic properties of the magnetic ground state. [ABSTRACT FROM AUTHOR]