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Navarro, H.; Sirena, M.; Kim, J.; Haberkorn, N. |
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Title |
Josephson coupling in high-Tc superconducting junctions using ultra-thin BaTiO3 barriers |
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Journal Article |
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Year |
2020 |
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Materials Science and Engineering: B |
Abbreviated Journal |
Mater. Sci. Eng. B |
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262 |
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114714 |
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Josephson junctionsHigh-Tc superconductorsThin films |
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We study the electrical transport of vertically-stacked Josephson tunnel junctions using GdBa2Cu3O7−δ electrodes and a BaTiO3 barrier with thicknesses between 1 nm and 3 nm. Current-voltage measurements at low temperatures show a Josephson coupling for junctions with BaTiO3 barriers of 1 nm and 2 nm. Reducing the barrier thickness bellow a critical thickness seems to suppress the ferroelectric nature of the BaTiO3. The Josephson coupling temperature reduces as the barrier thicknesses increases. The Josephson energies at 12 K are of ≈ 1.5 mV and ≈ 7.5 mV for BaTiO3 barriers of 1 nm and 2 nm, respectively. Fraunhofer patterns are consistent with fluctuations in the critical current due to structural inhomogeneities in the barriers. Our results are promising for the development of Josephson junctions using high-Tc electrodes with energy gaps much higher than those usually present in conventional low-temperature superconductors. |
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0921-5107 |
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BT @ pedrazp @ |
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858 |
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Ale Crivillero, M.V.; Amigó, M.L.; Haberkorn, N.; Nieva, G.; Guimpel, J. |
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Title |
Microstructural control of the transport properties of β-FeSe films grown by sputtering |
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Journal Article |
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Year |
2019 |
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Journal of Applied Physics |
Abbreviated Journal |
Journal of Applied Physics |
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126 |
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11 |
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115303 |
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American Institute of Physics |
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0021-8979 |
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doi: 10.1063/1.5094131 |
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BT @ gnieva @ |
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847 |
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Hofer, J.A.; Ginzburg, M.; Bengio, S.; Haberkorn, N. |
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Title |
Nanocrystalline superconducting γ-Mo2N ultra-thin films for single photon detectors |
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Journal Article |
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Year |
2022 |
Publication |
Materials Science and Engineering: B |
Abbreviated Journal |
Materials Science and Engineering: B |
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275 |
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115499 |
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We analyze the influence of the surface passivation produced by oxides on the superconducting properties of γ-Mo2N ultra-thin films. The superconducting critical temperature of thin films grown directly on Si (100) with those using a buffer and a capping layer of AlN are compared. The results show that the cover layer avoids the presence of surface oxides, maximizing the superconducting critical temperature for films with thicknesses of a few nanometers. We characterize the flux-flow instability measuring current-voltage curves in a 6.4 nm thick Mo2N film with a superconducting critical temperature of 6.4 K. The data is analyzed using the Larkin and Ovchinnikov model. Considering self-heating effects due to finite heat removal from the substrate, we determine a fast quasiparticle relaxation time ≈ 45 ps. This value is promising for its applications in single-photon detectors. |
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0921-5107 |
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BT @ pedrazp @ |
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871 |
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Hofer, J.A.; Bengio, S.; Rozas, G.; Pérez, P.D.; Sirena, M.; Suárez, S.; Haberkorn, N. |
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Title |
Compositional effects on the electrical properties of extremely disordered molybdenum oxynitrides thin films |
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Journal Article |
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Year |
2020 |
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Materials Chemistry and Physics |
Abbreviated Journal |
Mater. Chem. Phys. |
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242 |
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122075 |
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Keywords |
Molybdenum; Oxynitrides; Thin films; Sputtering; Electrical transport |
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Molybdenum oxynitride (MoNxOy) thin films were grown by reactive sputtering on Si (100) substrates at room temperature. The partial pressure of Ar was fixed at 90%, and the remaining 10% was adjusted with mixtures N2:O2 (varying from pure N2 to pure O2). The electrical properties of the films depend on the chemical composition. Thin films grown using mixtures up to 2% O2 have γ-Mo2N phase and display superconductivity. The superconducting critical temperature Tc reduces from ∼6.8 K to below 3.0 K as the oxygen increases. On the other hand, the films are mostly amorphous for gas mixtures above 2% O2. The electrical conductivity shows a semiconductor-like behavior well described by variable-range hopping conduction. The analysis of the optical properties reveals that the samples do not have a defined semiconductor bandgap, indicating that the high structural disorder produces electron excitation for a wide range of energies. |
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0254-0584 |
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BT @ pedrazp @ |
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860 |
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Haberkorn, N.; Zhang, Y.Y.; Bi, Z.X.; Park, B.H.; Civale, L.; Jia, Q.X |
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Title |
Effect of Co2N impurity on the superconducting properties of δ-MoN thin films grown by polymer assisted deposition |
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Journal Article |
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Year |
2021 |
Publication |
Materials Chemistry and Physics |
Abbreviated Journal |
Materials Chemistry and Physics |
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Volume |
259 |
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124184 |
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We report the effect of Co2N impurity on the superconducting properties of δ-MoN thin films grown by polymer-assisted deposition on c-cut sapphire (Al2O3). The films show a superconducting transition temperature of 10.4 K and an upper critical field Hc2(0) perpendicular to the film surface around 3 T. The latter corresponds to a relatively large coherence length ξ, which enhances the two-dimensional limit when the magnetic field is applied parallel to the film surface. In comparison with pure δ-MoN films, the inclusion of Co2N impurity in the δ-MoN films could significantly modify the critical current density at the vortex-free state. The ability to tune the superconducting properties of metal-nitride superconductors by introducing chemically and structurally compatible impurity may find potential applications for superconducting single-photon detectors. |
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0254-0584 |
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BT @ pedrazp @ |
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873 |
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Haberkorn, N.; Jeehoon, Kim; Suárez, S; Lee, Jae-Hun; Moon, S.H. |
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Title |
Influence of random point defects introduced by proton irradiation on the flux creep rates and magnetic field dependence of the critical current density J c of co-evaporated GdBa 2 Cu 3 O 7− δ coated conductors |
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Journal Article |
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Year |
2015 |
Publication |
Superconductor Science and Technology |
Abbreviated Journal |
Supercond. Sci. Technol. |
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28 |
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12 |
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125007 |
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We report the influence of random point defects introduced by 3 MeV proton irradiation (doses of 0.5 × 10 16 , 1 × 10 16 , 2 × 10 16 and 6 × 10 16 cm −2 ) on the vortex dynamics of co-evaporated 1.3 μ m thick, GdBa 2 Cu 3 O 7− δ coated conductors. Our results indicate that the inclusion of additional random point defects reduces the low field and enhances the in-field critical current densities J c . The main in-field J c enhancement takes place below 40 K, which is in agreement with the expectations for pinning by random point defects. In addition, our data show a slight though clear increase in flux creep rates as a function of irradiation fluence. Maley analysis indicates that this increment can be associated with a reduction in the exponent μ characterizing the glassy behavior. |
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0953-2048 |
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BT @ pedrazp @ |
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725 |
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Author |
Amigó, M.L.; Haberkorn, N.; Pérez, P.; Suárez, S.; Nieva, G. |
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Title |
Vortex dynamics in β -FeSe single crystals: effects of proton irradiation and small inhomogeneous stress |
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Journal Article |
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2017 |
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Superconductor Science and Technology |
Abbreviated Journal |
Supercond. Sci. Technol. |
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30 |
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12 |
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125017 |
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We report on the critical current density J c and the vortex dynamics of pristine and 3 MeV proton irradiated (cumulative dose equal to ##IMG## [http://ej.iop.org/images/0953-2048/30/12/125017/sustaa9518ieqn1.gif] {$2\times {10}^{16}$} cm −2 ) β -FeSe single crystals. We also analyze a remarkable dependence of the superconducting critical temperature T c , J c and the flux creep rate S on the sample mounting method. Free-standing crystals present T c = 8.4(1) K, which increases to 10.5(1) K when they are fixed to the sample holder by embedding them with GE-7031 varnish. On the other hand, the irradiation has a marginal effect on T c . The pinning scenario can be ascribed to twin boundaries and random point defects. We find that the main effect of irradiation is to increase the density of random point defects, while the embedding mainly reduces the density of twin boundaries. Pristine and irradiated crystals present two outstanding features in the temperature dependence of the flux creep rate: ##IMG## [http://ej.iop.org/images/0953-2048/30/12/125017/sustaa9518ieqn2.gif] {$S(T)$} presents large values at low temperatures, which can be attributed to small pinning energies, and a plateau at intermediate temperatures, which can be associated with glassy relaxation. From Maley analysis, we observe that the characteristic glassy exponent μ changes from ∼1.7 to 1.35–1.4 after proton irradiation. |
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0953-2048 |
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BT @ pedrazp @ |
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770 |
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Hofer, J.A.; Haberkorn, N. |
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Flux flow velocity instability and quasiparticle relaxation time in nanocrystalline β-W thin films |
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Journal Article |
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2021 |
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Thin Solid Films |
Abbreviated Journal |
Thin Solid Films |
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730 |
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138690 |
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Thin films; Electrical transport; Vortex velocities |
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We characterized the superconducting properties of a micropatterned 23 nm thick β-W film using electrical transport measurements in magnetic fields. The film is nanocrystalline and displays a smooth surface. The superconducting critical temperature is 4.6 K. The critical current densities display a fast drop with the magnetic field, indicating weak vortex pinning. From the analysis of the instability in the vortex motion at low magnetic fields in the flux-flow state, we observe vortex velocities up 800 m/s. An inelastic lifetime of quasiparticles around 0.6 ns is estimated at low temperatures. Together with high uniformity in thickness and simplicity in the fabrication process, the superconducting properties make β-W films promising for applications in fast single-photon detectors. |
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0040-6090 |
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BT @ pedrazp @ |
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870 |
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Sutter, J.G.; Chávez, A.S.; Soria, S.; Granada, M.; Neñer, L.; Bengió, S.; Granell, P.; Golmar, F.; Haberkorn, N.; Leyva, A.G.; Sirena, M. |
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Tuning the magneto-electrical properties of multiferroic multilayers through interface strain and disorder |
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Journal Article |
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2020 |
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Journal of Alloys and Compounds |
Abbreviated Journal |
J. Alloys Compd. |
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157820 |
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multiferroic; superlattices; manganites; magnetism; disorder |
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Artificially engineered superlattices were designed and fabricated to induce different growth mechanisms and structural characteristics. DC sputtering was used to grow ferromagnetic (La0.8Ba0.2MnO3)/ferroelectric (Ba0.25Sr0.75TiO3 or BaTiO3) superlattices. We systematically modified the thickness of the ferromagnetic layer to analyze dimensional and structural disorder effects on the superlattices with different structural characteristics. The crystalline structure was characterized by X-ray diffraction and transmission electron microscopy. The magnetic and electronic properties were investigated by SQUID magnetometry and resistance measurements. The results show that both strain and structural disorder can significantly affect the physical properties of the systems. Ba0.25Sr0.75TiO3 based superlattices with a low thickness of the ferromagnetic layers (4 nm.) present compressive strain that decreases the ferromagnetic transition temperature from 250 K corresponding to the unstressed samples to 230 K. In these samples, the localization energy of the charge carrier through the electron-phonon interaction decreases at low temperatures (∼100 meV). Ba0.25Sr0.75TiO3 based superlattices with thicknesses of the ferromagnetic layers higher than 12 nm present tensile strain that reduces the charge carrier localization energy at low temperatures (∼1 meV), increasing the ferromagnetic transition temperature (Tc∼265K). Structural defects in BaTiO3 based superlattices have a stronger influence on the magnetic properties than on the transport properties. Nevertheless, disorder blocks the ferromagnetic transition for highly disordered samples (thickness of the ferromagnetic layer < 3 nm). These results help to further understand the role of strain and interface effects in the magnetic and transport properties of manganite based multiferroic systems. |
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0925-8388 |
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BT @ pedrazp @ |
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861 |
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Sutter, J.G.; Sarmiento Chávez, A.; Soria, S.; Granada, M.; Neñer, L.; Bengió, S.; Granell, P.; Golmar, F.; Haberkorn, N.; Leyva, A.G.; Sirena, M. |
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Tuning the magneto-electrical properties of multiferroic multilayers through interface strain and disorder |
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Journal Article |
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2021 |
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Journal of Alloys and Compounds |
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J. Alloys Compd. |
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859 |
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157820 |
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Artificially engineered superlattices were designed and fabricated to induce different growth mechanisms and structural characteristics. DC sputtering was used to grow ferromagnetic (La0.8Ba0.2MnO3)/ferroelectric (Ba0.25Sr0.75TiO3 or BaTiO3) superlattices. We systematically modified the thickness of the ferromagnetic layer to analyze dimensional and structural disorder effects on the superlattices with different structural characteristics. The crystalline structure was characterized by X-ray diffraction and transmission electron microscopy. The magnetic and electronic properties were investigated by SQUID magnetometry and resistance measurements. The results show that both strain and structural disorder can significantly affect the physical properties of the systems. Ba0.25Sr0.75TiO3 based superlattices with a low thickness of the ferromagnetic layers (4 nm) present compressive strain that decreases the ferromagnetic transition temperature from 250 K corresponding to the unstressed samples to 230 K. In these samples, the localization energy of the charge carrier through the electron-phonon interaction decreases at low temperatures (∼100 meV). Ba0.25Sr0.75TiO3 based superlattices with thicknesses of the ferromagnetic layers higher than 12 nm present tensile strain that reduces the charge carrier localization energy at low temperatures (∼1 meV), increasing the ferromagnetic transition temperature (Tc∼265 K). Structural defects in BaTiO3 based superlattices have a stronger influence on the magnetic properties than on the transport properties. Nevertheless, disorder blocks the ferromagnetic transition for highly disordered samples (thickness of the ferromagnetic layer < 3 nm). These results help to further understand the role of strain and interface effects in the magnetic and transport properties of manganite based multiferroic systems. |
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BT @ pedrazp @ |
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