Excess currents larger than the point contact limit in normal-metal/superconducting junctions |
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| Institution: | 1. Laboratorio de Bajas Temperaturas, Departamento de Física de la Materia Condensada, Instituto de Ciencia de Materiales Nicolás Cabrera, Condensed Matter Physics Center (IFIMAC), Facultad de Ciencias, Universidad Autónoma de Madrid, E-28049 Madrid, Spain;2. Departamento de Ciencias Naturales, Facultad de ingeniería y Ciencias Básicas, Universidad Central, Bogotá, Colombia;3. National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA;4. Unidad Asociada de Altos Campos Magnéticos y Bajas Temperaturas, UAM, CSIC, Madrid, Spain |
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| Abstract: | In a point contact NS junction, perfect Andreev reflection occurs over a range of voltages equal to the superconducting energy gap, producing an excess current of Iexc = (4 / 3)(2 eΔ / h). If the superconductor has a finite width, rather than the infinite width of the point contact, one cannot neglect superfluid flow inside the superconducting contact. The energy range available for perfect Andreev reflections then becomes larger than the superconducting gap, since superfluid flow alters the dispersion relation inside the finite width superconductor. We find a maximum excess current of approximately (7 / 3)(2 eΔ / h) when the width of the superconductor is approximately 7 / 3 times the width of the normal metal. |
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