Abstract. Manufacturing superconducting circuits out of ultrathin films is a challenging task when it comes to pattern complex compounds, which are likely to be deteriorated by the patterning process. With the purpose of developing high-Tc superconducting photon detectors, we designed a novel route to pattern ultrathin YBCO films down to the nanometric scale. We believe that our method, based on a specific use of a focused ion beam, consists in locally implanting Ga 3+ ions and/or defects instead of etching the film. This protocol could be of interest to engineer high-Tc superconducting devices (SQUIDS, SIS/SIN junctions, Josephson junctions), as well as to treat other sensitive compounds.PACS numbers: 85.25. Am, 81.16.Nd, 74.78.Bz, 81.15.Cd, 85.25.Pb Patterning of ultrathin YBCO nanowires using a new focused-ion-beam process 2

In this work we map tunnel conductance curves with nanometric spatial resolution, tracking polaronic quasiparticle excitations when cooling across the insulator-to-metal transition in La0.7Ca0.3MnO3 films. In the insulating phase the spectral signature of polarons, a depletion of conductance at low bias flanked by peaks, is detected all over the scanned surface. These features are still observed at the transition and persist on cooling into the metallic phase. Polaron-binding-energy maps reveal that polarons are not confined to regions embedded in a highly-conducting matrix but are present over the whole field of view both above and below the transition temperature. 71.30.+h, 68.37.Ef In manganite compounds such as La 1−x Ca x MnO 3 (0.2 < x < 0.5), the coupling between lattice, magnetism and transport leads to a transition from metallic (dρ/dT > 0) to insulating (dρ/dT > 0) behavior in tune with the suppression of ferromagnetic order at a temperature T MI [1,2]. Understanding the transport properties of the insulating phase required the consideration of the electron-phonon coupling mechanism in addition to double-exchange interactions [3,4]. In the strong coupling limit electrons are bound by a surrounding lattice distortion forming polaronic quasiparticles [3,4]. In the insulating phase, polaron hopping is the dominant transport mechanism and gives rise to the measured thermally-activated resistivity [5,6,7]. Although in these context theoretical predictions [3,4] state that on cooling below T MI spin order leads to electron delocalization, evidence from numerous experimental techniques [8,9,10,11,12,13] suggests the presence of polarons also at T < T MI . Optical reflectivity [14] and structural [15,16] investigations propose a crossover from a large to small-polaron regime on warming across the MIT and a coexistence of both polaronic phases at T ∼ T MI . Therefore, the existence of polarons in the metallic phase and the relevance of nanoscale inhomogeneities [2] to the metal-to-insulator transition (MIT) remain active subjects of debate. Insight into this problem can be gained from scanning tunnelling spectroscopy (STS) studies as the one presented here which probes local electronic properties at the atomic scale.Although the phase separation scenario has gained popularity in recent years, it is mostly supported by results from macroscopic techniques [2]. Local spectroscopy studies in La 1−x Ca x MnO 3 claim electronic phase separation [17,18,19,20], but a strong influence of chemical and structural disorder present in the samples cannot be ruled out. In contrast, a recent study in a fullyrelaxed film reports homogeneous conductance maps [21]. * Electronic address: silvia.seiro@physics.unige.ch However, conductance maps at a fixed energy do not provide enough information on the eventual presence, spectroscopic characteristics and spatial distribution of polaronic quasiparticles. Therefore, in this work we measure tunnel current vs. voltage maps with nanometric spatial resolution in La 0.7 Ca 0.3 MnO 3 (LC...

We have investigated the resistive response of high-T c thin films submitted to a high density of current. For this purpose, current pulses were applied into bridges made of Nd 1.15 Ba 1.85 Cu 3 O 7Ϫ␦ and Bi 2 Sr 2 CaCu 2 O 8ϩ␦ . By recording the time-dependent voltage, we observe that at a certain critical current j*, a highly dissipative domain develops somewhere along the bridge. The successive formation of these domains produces stepped I-V characteristics. We present evidence that these domains are not regions with a temperature above T c , as for hot spots. In fact this phenomenon appears to be analog to the nucleation of phase-slip centers observed in conventional superconductors near T c , but here in contrast they appear in a wide temperature range. Under some conditions, these domains will propagate and destroy the superconductivity within the whole sample. We have measured the temperature dependence of j* and found a similar behavior in the two investigated compounds. This temperature dependence is just the one expected for the depairing current, but the amplitude is about 100 times smaller.

X-ray diffraction and transport measurements on a series of La0.67Ca0.33MnO3 films grown on (110)-cut NdGaO3 substrates are presented. Contrary to widespread belief assuming strain-free growth, this work shows the presence of strain in a 42nm film. On increasing thickness structural relaxation occurs, reaching a bulklike state for 500nm. No evidence of coexistence of strained and relaxed regions is found. The evolution of lattice parameters toward bulk values is accompanied by an increase of the metal-to-insulator transition temperature and a decrease of the polaron activation energy. Therefore, strain effects cannot always be neglected in La0.67Ca0.33MnO3 films grown on small-mismatch NdGaO3.

We present a low-energy muon-spin-rotation study of the magnetic and superconducting properties of YBa2Cu3O7−/PrBa2Cu3O7− trilayer and bilayer heterostructures. By determining the magnetic-field profiles throughout these structures, we show that a finite superfluid density can be induced in otherwise semiconducting PrBa2Cu3O7− layers when juxtaposed to YBa2Cu3O7− "electrodes," while the intrinsic antiferromagnetic order is unaffected. ©2012 American Physical Society We present a low-energy muon-spin-rotation study of the magnetic and superconducting properties of YBa2Cu3O 7−δ /PrBa2Cu3O 7−δ trilayer and bilayer heterostructures. By determining the magnetic-field profiles throughout these structures we show that a finite superfluid density can be induced in otherwise semiconducting PrBa2Cu3O 7−δ layers when juxtaposed to YBa2Cu3O 7−δ "electrodes" while the intrinsic antiferromagnetic order is unaffected.