Size dependence of the Josephson critical behavior in pyrolytic graphite TEM lamellae

Abstract

We have studied the transport properties of TEM lamellae obtained from a pyrolytic graphite sample with electrical contacts at the edges of the embedded interfaces. The temperature dependence of the resistance as well as the current-voltage characteristic curves are compatible with the existence of Josephson coupled superconducting regions. The transition temperature at which the Josephson behavior sets in, decreases with the interface width and vanishes for width below 200 nm. This unexpected behavior is apparently due to the influence of weak localization effects on the superconducting critical temperature.

Evidence for room temperature superconductivity at graphite interfaces

“…6(c,d). -The more disordered the graphite structure or the smaller the size or length of the interfaces the lower is the temperature where superconducting-like behavior is observed [41,42]. -Finally, the I −V curves measured at different temperatures [37] are compatible with the behavior expected for Josephson junctions under the influence of thermal activation [43].…”

On the low-field Hall coefficient of graphite

“…Note that effective critical temperature depends on the size or area of the interfaces according to recently published experimental results. 41 The crossover to a negative Hall coefficient at large enough fields and temperatures observed in Refs. 1,8,14, and 15 can be understood in a similar way as shown in sections III B 2 and III C. In Ref.…”

“…37 Furthermore, calculations indicate that high-temperature surface superconductivity survives throughout the bulk due to the proximity effect between ABC/ABA interfaces where the order parameter is enhanced. 37 Following experimental results that indicate the existence of granular superconductivity at certain interfaces in bulk HOPG samples of high grade, 27,28,41 it is then appealing to take the contribution of the interfaces in the behavior of the Hall effect into account. Doing this we are able to interpret several results from literature as well as the Hall coefficient obtained from three, micrometer small graphite flakes described below.…”

“…Doing this we are able to interpret several results from literature as well as the Hall coefficient obtained from three, micrometer small graphite flakes described below. The characteristics of the embedded interfaces, as for example their size or area 41 or the twist angle between the two Bernal graphite blocks 29 can have a direct influence on the temperature and magnetic field dependence of the Hall coefficient of a graphite sample with interfaces. Furthermore, the alignment dependence reported earlier 13 can be understood arguing that the interfaces are created or get larger in area the higher the alignment of the grains.…”

Electrical properties of in-plane-implanted graphite nanoribbons

“…For example, in refs. [11,12,17], RT resistivities of HOPG ribbons vary between 10 4 µΩ.cm and 10 6 µΩ.cm. Such devices have shown the same insulating-like R(T) behavior found here when excited with electrical currents above few nano-Amperes.…”