Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet

The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La_0.7Sr_0.3MnO₃ combined with the superconducting cuprate YBa₂Cu₃O₇. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing.

Large intrinsic anomalous Hall effect in SrIrO3 induced by magnetic proximity effect

The anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, by skew or side-jump scattering due to chiral features of the disorder scattering, or by an intrinsic contribution directly linked to the topological properties of the Bloch states. Here we show that the AHE can be artificially engineered in materials in which it is originally absent by combining the effects of symmetry breaking, spin orbit interaction and proximity-induced magnetism. In particular, we find a strikingly large AHE that emerges at the interface between a ferromagnetic manganite (La_0.7Sr_0.3MnO₃) and a semimetallic iridate (SrIrO₃). It is intrinsic and originates in the proximity-induced magnetism present in the narrow bands of strong spin-orbit coupling material SrIrO₃, which yields values of anomalous Hall conductivity and Hall angle as high as those observed in bulk transition-metal ferromagnets. These results demonstrate the interplay between correlated electron physics and topological phenomena at interfaces between 3d ferromagnets and strong spin-orbit coupling 5d oxides and trace an exciting path towards future topological spintronics at oxide interfaces.

Controlled Sign Reversal of Electroresistance in Oxide Tunnel Junctions by Electrochemical-Ferroelectric Coupling

The persistence of ferroelectricity in ultrathin layers relies critically on screening or compensation of polarization charges which otherwise destabilize the ferroelectric state. At surfaces, charged defects play a crucial role in the screening mechanism triggering novel mixed electrochemical-ferroelectric states. At interfaces, however, the coupling between ferroelectric and electrochemical states has remained unexplored. Here, we make use of the dynamic formation of the oxygen vacancy profile in the nanometer-thick barrier of a ferroelectric tunnel junction to demonstrate the interplay between electrochemical and ferroelectric degrees of freedom at an oxide interface. We fabricate ferroelectric tunnel junctions with a La_{0.7}Sr_{0.3}MnO_{3} bottom electrode and BaTiO_{3} ferroelectric barrier. We use poling strategies to promote the generation and transport of oxygen vacancies at the metallic top electrode. Generated oxygen vacancies control the stability of the ferroelectric polarization and modify its coercive fields. The ferroelectric polarization, in turn, controls the ionization of oxygen vacancies well above the limits of thermodynamic equilibrium, triggering the build up of a Schottky barrier at the interface which can be turned on and off with ferroelectric switching. This interplay between electronic and electrochemical degrees of freedom yields very large values of the electroresistance (more than 10^{6}% at low temperatures) and enables a controlled switching between clockwise and counterclockwise switching modes in the same junction (and consequently, a change of the sign of the electroresistance). The strong coupling found between electrochemical and electronic degrees of freedom sheds light on the growing debate between resistive and ferroelectric switching in ferroelectric tunnel junctions, and moreover, can be the source of novel concepts in memory devices and neuromorphic computing.

Ferroelectric Control of Interface Spin Filtering in Multiferroic Tunnel Junctions

The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a La_{0.7}Sr_{0.3}MnO_{3}/BaTiO_{3}/La_{0.7}Sr_{0.3}MnO_{3} multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics.

Phase separation enhanced magneto-electric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films

We study the origin of the magnetoelectric coupling in manganite films on ferroelectric substrates. We find large magnetoelectric coupling in La0.7Ca0.3MnO3/BaTiO3 ultra-thin films in experiments based on the converse magnetoelectric effect. The magnetization changes by around 30-40% upon applying electric fields on the order of 1 kV/cm to the BaTiO3 substrate, corresponding to magnetoelectric coupling constants on the order of α = (2-5) · 10(-7) s/m. Magnetic anisotropy is also affected by the electric field induced strain, resulting in a considerable reduction of coercive fields. We compare the magnetoelectric effect in pre-poled and unpoled BaTiO3 substrates. Polarized neutron reflectometry reveals a two-layer behavior with a depressed magnetic layer of around 30 Å at the interface. Magnetic force microscopy (MFM) shows a granular magnetic structure of the La0.7Ca0.3MnO3. The magnetic granularity of the La0.7Ca0.3MnO3 film and the robust magnetoelastic coupling at the La0.7Ca0.3MnO3/BaTiO3 interface are at the origin of the large magnetoelectric coupling, which is enhanced by phase separation in the manganite.

Insight into spin transport in oxide heterostructures from interface-resolved magnetic mapping

At interfaces between complex oxides, electronic, orbital and magnetic reconstructions may produce states of matter absent from the materials involved, offering novel possibilities for electronic and spintronic devices. Here we show that magnetic reconstruction has a strong influence on the interfacial spin selectivity, a key parameter controlling spin transport in magnetic tunnel junctions. In epitaxial heterostructures combining layers of antiferromagnetic LaFeO(3) (LFO) and ferromagnetic La(0.7)Sr(0.3)MnO(3) (LSMO), we find that a net magnetic moment is induced in the first few unit planes of LFO near the interface with LSMO. Using X-ray photoemission electron microscopy, we show that the ferromagnetic domain structure of the manganite electrodes is imprinted into the antiferromagnetic tunnel barrier, endowing it with spin selectivity. Finally, we find that the spin arrangement resulting from coexisting ferromagnetic and antiferromagnetic interactions strongly influences the tunnel magnetoresistance of LSMO/LFO/LSMO junctions through competing spin-polarization and spin-filtering effects.

Effect of interface-induced exchange fields on cuprate-manganite spin switches

We examine the anomalous inverse spin switch behavior in La0.7Ca0.3MnO3(LCMO)/YBa2Cu3O7-δ (YBCO)/LCMO trilayers by combined transport studies and polarized neutron reflectometry. Measuring magnetization profiles and magnetoresistance in an in-plane rotating magnetic field, we prove that, contrary to many accepted theoretical scenarios, the relative orientation between the two LCMO's magnetizations is not sufficient to determine the magnetoresistance. Rather the field dependence of magnetoresistance is explained by the interplay between the applied magnetic field and the (exponential tail of the) induced exchange field in YBCO, the latter originating from the electronic reconstruction at the LCMO/YBCO interfaces.

Single-mode, optical-fiber sensors and tunable wavelength filters based on the resonant excitation of metal-clad modes

The resonant excitation of metal-clad modes, including fundamental and higher-order modes, in a multilayer structure deposited on the polished cladding of a single-mode optical fiber is theoretically analyzed and experimentally demonstrated. The excitation of metal-clad modes is shown as a resonant power transfer from the fiber to the metal-clad mode that takes place for an external refractive-index value such that the effective index of the metal-clad mode reaches the cladding level. The observed attenuation on the TM polarization provides a suitable transducing mechanism for refractive-index sensor devices as well as the principle for developing tunable wavelength-polarized filters with a wide range of optical performance characteristics.

Comparison between intensity correlation and Fourier transform of the time interval probability techniques applied to laser Doppler velocimetry

In this paper we study the improvement in a laser Doppler velocimetry experiment when the Fourier transform of the time interval probability is measured instead of the intensity correlation function. The errors involved in determination of the velocity are found to be greatly improved for low scattered intensities.

[Mixed essential cryoglobulinemia. Report of five cases (author's transl)]

Cryoglobulins are serum immunoglobulins which precipitate in the cold and redissolve on warming at 37 degrees C. According to its immunochemical composition three different types have been described. Cryoglobulins have been reported associated with hematologic disorders, systemic diseases, infectious conditions, and diseases of the liver and kidneys. There is also an idiopathic variant called essential cryoglobulinemia. Five patients (four males) with mixed essential cryoglobulinemia are reported. Common clinical manifestations included fever, articular symptoms, purpura, glomerulonephritis, Raynaud's phenomenon, erythematomacular cutaneous eruption, polyneuritis and abdominal pain. Serum activity of rheumatoid factor has been detected in three cases; in other three decreased levels of serum complement have been found. Serum HBsAg was negative in four cases (passive hemagglutination technique). It is possible that all cases of mixed essential cryoglobulinemia may correspond to bacterial, viral or fungal occult infections.

[Cryoglobulins and liver disease. Study of 34 cases (author's transl)]

Cryoglobulins are immunoglobulins characterized by precipitating when serum is cooled and redissolving when serum is heated. There is strong evidence to consider mixed cryoglobulins as circulating immunocomplexes, and various investigators have applied the precipitating physical property as a method to isolate immunocomplexes. In the recent years some authors have reported the presence of cryoglobulins in acute and chronic liver diseases of diverse etiology. This study investigates the presence of cryoglobulins in 34 patients with different liver diseases. Mixed cryoglobulins were detected in eight patients (23.5 percent), but only three of them had clinical symptoms attributable to the existence of cryoglobulins. In relation to the etiology of the liver disease, the highest frequency has been found among patients with hepatopathies of undetermined origin.

[Cryoglobulins in systemic and rheumatological diseases. Report of 70 cases (author's transl)]

Cryoglobulins are immunoglobulins characterized by precipitating when serum is cooled and redissolving when serum is heated. There is strong evidence to consider mixed cryoglobulins as circulating immunocomplexes. Cryoglobulins have been demonstrated in association to hematologic, hepatic, lymphoproliferative, autoimmune and infectious conditions. There is also an essential or idiopathic variant. The present report studies a series of 70 patients with several rheumatic and systemic diseases, and a group of ten patients with cutaneous vasculitis. Significant levels of cryoglobulins have been detected in nine cases (overall incidence 12.8 percent). The diagnoses corresponding to these patients were as follows: systemic lupus erythematosus in three cases, dermatopolymyositis in three cases, Sjögren's syndrome in two cases, and Wegener's granulomatosis in one case. Cryoglobulins could not be demonstrated in patients with rheumatoid artritis, sclerodermia, periarteritis nodosa, cutaneous vasculitis, Reiter's syndrome, ankylosing spondilitis and acute articular rheumatism. Among patients with systemic lupus erythematosus a good correlation has been observed between the presence of serum cryoglobulins, the activity and severity of the diseases and the decrease of serum complement levels.

Treatment of respiratory infections with fosfomycin

Results are presented for a series of 29 patients, 14 males and 15 females, with serious respiratory infections, in which fosfomycin proved effective. In all cases the study was completed by bacteriological, clinical, radiological and analytical controls. The average dose was 6 g/day (3 g orally and 3 g intramuscularly) for 1 or 2 weeks. The four isolated were P. aeruginosa, E. coli, Klebsiella-Enterobacter and D. pneumoniae. Overall sensitivity percentages were best for fosfomycin, gentamicin and colistin. Of the 29 germs isolated, only one strain of P. aeruginosa became resistant: this represents 3% resistance development. No side effects of intolerance or signs of hepatorenal insufficiency were observed during the treatment. Of the 29 patients treated, 22 were clinically cured, denoting 76% success.

Pericarditis, pleural effusion, and pneumonitis with transient mitochondrial antibodies

Four women with fever, arthromyalgias, pericarditis, pleural effusion, high erythrocyte sedimentation rates, and lymphopenia had mitochondrial antibodies in the serum in the absence of antinuclear antibody. Their illness lasted 5-12 weeks and the antibody test results became negative on remission. Absence of specific bacteriological findings, normal antistreptolysin O titres, resistance to antibiotics, and good response to steroids suggested that these cases represented a milder and less persistent form of the syndrome resembling systemic lupus erythematosus described by German authors.

The liver in boutonneuse fever

Hepatic lesions were studied for the first time in 13 cases of boutonneuse fever (Mediterranean exanthematous fever). The glutamic-oxalacetic transaminases were raised in eight patients, the glutamic-pyruvic transaminases showed an increase in 10 patients, alkaline phosphatases in seven of the 10 patients investigated, and conjugate bilirubin showed moderate increases in three patients. Five patients were studied histologically; this study showed lesions of a granulomatous type, similar to those described in Q fever, in three patients, fatty degeneration with marked alcoholism in another patient, and a normal liver in the last patient. Two of the three patients with granulomatous lesions showed a moderate increase in alkaline phosphatases. After this report boutonneuse fever must be included among the infectious conditions that can produce granulomas within the liver.