8 results on '"Heera, V."'
Search Results
2. Negative Magneto- and Electroresistance of Silicon Films with Superconducting Nanoprecipitates: The Role of Inelastic Cotunneling.
- Author
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Heera, V., Fiedler, J., Schmidt, B., Hübner, R., Voelskow, M., Skrotzki, R., and Skorupa, W.
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ELECTRIC resistance , *SILICON films , *SUPERCONDUCTORS , *CHARGE transfer , *TEMPERATURE effect , *MAGNETIC fields - Abstract
The electronic transport properties of insulating Si:Ga films with superconducting, Ga-rich nanoprecipitates are investigated in dependence on temperature, current, and magnetic field. The large negative magnetoresistance, observed below the critical temperature can be explained by Cooper pair breaking and subsequent tunneling of the fermionic quasiparticles. Localization due to quantum interferences of bosons or fermions, as recently discussed, seems not to be the reason for the insulating state and the large magnetoresistance. Cooper pair tunneling is blocked by the high Coulomb barrier. The quasiparticles can overcome the barrier by inelastic cotunneling that results in nonlinear current-voltage characteristics and negative electroresistance. Since the experimental results obtained for the Si:Ga film resemble that of many other films with superconducting nanoprecipitates the conclusions drawn here could be quite general. [ABSTRACT FROM AUTHOR]
- Published
- 2015
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- View/download PDF
3. Depth-resolved transport measurements and atom-probe tomography of heterogeneous, superconducting Ge:Ga films.
- Author
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Heera, V, Fiedler, J, Naumann, M, Skrotzki, R, Kölling, S, Wilde, L, Herrmannsdörfer, T, Skorupa, W, Wosnitza, J, and Helm, M
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ATOM-probe tomography , *SUPERCONDUCTORS , *THIN films , *ION implantation , *MACROSCOPIC kinetics - Abstract
Ge films with a mean Ga content of about 8 and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change in the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters of up to 10 000 atoms. Since no percolating Ga clusters exist, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect. [ABSTRACT FROM AUTHOR]
- Published
- 2014
- Full Text
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4. Silicon films with gallium-rich nanoinclusions: from superconductor to insulator.
- Author
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Heera, V., Fiedler, J., Hübner, R., Schmidt, B., Voelskow, M., Skorupa, W., Skrotzki, R., Herrmannsdörfer, T., Wosnitza, J., and Helm, M.
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SILICON films , *GALLIUM , *RAPID thermal processing , *SUPERCONDUCTORS , *ELECTRIC insulators & insulation , *ELECTRIC conductivity - Abstract
Si films sputter deposited on thermally oxidized Si are enriched with Ga by ion implantation through a SiO2 capping layer. The morphology and the electrical transport properties of these films are investigated after rapid thermal annealing. Amorphous, Ga-rich nanoinclusions are embedded in a nanocrystalline Si matrix. The metallic nanoinclusions become superconducting below 7 K. They form a random network of junctions to heavily doped Si crystallites. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. Ga-rich Si films show a wealth of low-temperature transport phenomena, which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance. The possibility to prepare and modify Ga-rich Si films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
5. Superconducting Ga-overdoped Ge layers capped with SÍO2: Structural and transport investigations.
- Author
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Fiedler, J., Heera, V., Skrotzki, R., Herrmannsdörfer, T., Voelskow, M., Mücklich, A., Facsko, S., Reuther, H., Perego, M., Heinig, K.-H., Schmidt, B., Skorupa, W., Gobsch, G., and Helm, M.
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SUPERCONDUCTORS , *GALLIUM compounds , *MOLECULAR structure , *GERMANIUM , *SILICA , *ANNEALING of metals , *TEMPERATURE effect - Abstract
Superconducting Ga-rich layers in Ge are fabricated by Ga implantation through a thin Si02 cover layer. After annealing in a certain temperature window, Ga accumulation at the SiC/Ge interface is observed. However, no Ga-containing crystalline phases are identified. Thus it is suggested that the volatile Ga is stabilized in an amorphous mixture of all elements available at the interface. Electrical transport measurements reveal p-type metallic conductivity and superconducting transition. The superconducting properties of the samples with high Ga concentration at the interface change dramatically with etching the amorphous surface layer. A critical temperature of 6 K is measured before, whereas after etching it drops below 1 K. Therefore, one can conclude that the superconducting transport is based on two different layers: a Ga-rich amorphous phase at the interface and a heavily Ga-doped Ge layer. Finally, the comparison of the transport properties of Ga-rich Ge with those of Si demonstrates distinct differences between the interface layers and even the deeper-lying doped regions. [ABSTRACT FROM AUTHOR]
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- 2012
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6. Superconducting films fabricated by high-fluence Ga implantation in Si.
- Author
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Fiedler, J., Heera, V., Skrotzki, R., Herrmannsdörfer, T., Voelskow, M., Mücklich, A., Oswald, S., Schmidt, B., Skorupa, W., Gobsch, G., Wosnitza, J., and Helm, M.
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SUPERCONDUCTORS , *GALLIUM , *THIN films , *SILICON , *SCATTERING (Physics) , *ELECTRON microscopy - Abstract
Ga-rich layers in Si were fabricated by 80 keV Ga implantation through a 30 nm SiO2 cover layer and subsequent rapid thermal annealing for 60 s in a temperature range between 500 °C and 1000 °C. Fluences of 2x1016 cm-2 and 4x1016 cm-2, leading to Ga peak concentrations of 8 at. % and 16 at. %, are chosen. Residual damage in the implanted layers and the Ga distribution were investigated by Rutherford-backscattering spectrometry in combination with ion channeling, cross-sectional electron microscopy, and x-ray photoelectron spectroscopy. Temperature-dependent Hall-effect measurements were carried out in order to determine the electrical properties of the implanted layers. It is shown that annealing at temperatures up to 800 °C leads to the formation of polycrystalline layers containing random distributed amorphous clusters. At the Si/SiO2 interface a dense and narrow band of Ga-rich clusters is observed. For 4 x 1016 cm-2 the amount of mobile Ga is higher than for 2x1016 cm-2 and an increase of the cluster density at the Si/SiO2 interface was found. Due to the higher cluster density for 4x1016 cm-2 this interface layer can become superconducting below 7 K with critical fields exceeding 9 T at optimized annealing conditions. Critical currents are above 1 kA/cm² and therefore this seems to be a possible material system for future microelectronic applications. After annealing at 900 °C and above, the implanted layers are single crystalline and no amorphous precipitates were detected. [ABSTRACT FROM AUTHOR]
- Published
- 2011
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7. Superconductor-insulator transition controlled by annealing in Ga implanted Si.
- Author
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Heera, V., Fiedler, J., Voelskow, M., Mücklich, A., Skrotzki, R., Herrmannsdörfer, T., and Skorupa, W.
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SUPERCONDUCTORS , *ANNEALING of semiconductors , *METAL-insulator transitions , *NANOSTRUCTURES , *QUANTUM phase transitions , *HOLES (Electron deficiencies) , *SILICON , *GALLIUM - Abstract
Heavily Ga implanted Si nanolayers covered with a thin SiO2 layer exhibit a superconductor-insulator transition in dependence on annealing conditions. The transition characteristics resemble those of ultrathin quench-condensed metal films although the implanted layer differs clearly in composition, width, and nanostructure. This implies a general physical mechanism for the superconductor-insulator transition in thin, disordered layers which is supposed to be a quantum phase transition between dual states-the superconducting and the superinsulating one. There is a resistance criterion for the phase transition closely associated with a critical hole concentration. [ABSTRACT FROM AUTHOR]
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- 2012
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8. Optical study of superconducting Ga-rich layers in silicon.
- Author
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Fischer, T., Pronin, A. V., Skrotzki, R., Herrmannsdörfer, T., Wosnitza, J., Fiedler, J., Heera, V., Helm, M., and Schachinger, E.
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SILICON , *SUPERCONDUCTORS , *AMORPHOUS substances , *ELECTRONS , *PHONONS , *PHYSICS - Abstract
We performed phase-sensitive terahertz (0.12-1.2 THz) transmission measurements of Ga-enriched layers in silicon. Below the superconducting transition Tcmiddle = 6.7 K we find clear signatures of the formation of a superconducting condensate and of the opening of an energy gap in the optical spectra. The London penetration depth λ(T) and the condensate density ns = λ2(0)/λ²(T) as functions of temperature demonstrate behavior typical for conventional superconductors with λ(0) = 1.8 μm. The terahertz spectra can be well described within the framework of Eliashberg theory with strong electron-phonon coupling: the zero-temperature energy gap is 2Δ(0) = 2.64 meV and 2Δ(0)/kB Tc = 4.6, consistent with the amorphous state of Ga. At temperatures just above Tc, the optical spectra demonstrate Drude behavior. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
- View/download PDF
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