Current–voltage characteristics of Nb–carbon–Nb junctions

• Veröffentlicht in: Физика низких температур
• Datum: 2014
• ISSN: 0132-6414
• Hauptverfasser: Nevirkovets, I.P., Shafranjuk, S.E., Chernyashevskyy, O., Masilamani, N., Ketterson, J.B.
• Format: Artikel
• Sprache: Englisch
• Veröffentlicht: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2014
• Schlagworte: Свеpхпpоводимость, в том числе высокотемпеpатуpная
• Online Zugang: https://nasplib.isofts.kiev.ua/handle/123456789/119426
• Назва журналу: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Zitieren: Current–voltage characteristics of Nb–carbon–Nb junctions / I.P. Nevirkovets, S.E. Shafranjuk, O. Chernyashevskyy, N. Masilamani, J.B. Ketterson // Физика низких температур. — 2014. — Т. 40, № 3. — С. 250-258. — Бібліогр.: 18 назв. — англ.

We report on properties of Nb(/Ti)–carbon–(Ti/)Nb junctions fabricated on graphite flakes using e-beam lithography. The devices were characterized at temperatures above 1.8 K where a Josephson current was not observed, but the differential conductivity revealed features below the critical temperature of Nb, and overall metallic conductivity, in spite of a high-junctions resistance. Since the conductivity of graphite along the planes is
 essentially two-dimensional (2D), we use a theoretical model developed for metal/graphene junctions for interpretation of the results. The model involves two very different graphene “access” lengths. The shorter length
 characterizes ordinary tunneling between the three-dimensional Nb(/Ti) electrode and 2D graphene, while
 the second, much longer length, is associated with the Andreev reflections (AR) inside the junction and involves
 also “reflectionless” AR processes. The relevant transmission factors are small in the first case and much larger
 in the second, which explains the apparent contradiction of the observed behaviors