Experimental Evidence for the Existence of Interfaces in Graphite and Their Relation to the Observed Metallic and Superconducting Behavior

Evidence for room temperature superconductivity at graphite interfaces

“…The high fields increase of the TH is not compatible with any known magnetic order in carbon-based ferromagnetic Finally, magnetization measurements done on bulk highly oriented pyrolytic graphite samples of high grade with interfaces, see Section III, show similar behavior as for the water-treated graphite powder, in contrast to a bulk HOPG sample without or less density of interfaces [8]. Several others experimental studies partially reviewed in [17,18] indicate that superconductivity is embedded in certain interfaces of the graphite structure. Structural evidence for the existence of interfaces is presented in the next section.…”

“…This field driven MIT in graphite was speculated in the past to be related to superconductivity [45,46]. Nowadays we know that the MIT in graphite as well as the metalliclike behavior of its resistance are not intrinsic but are due to the contribution of certain interfaces in parallel to the graphene layers of the graphite structure [18,20,21]. If one measures the resistance with care, see [19] for more details, one can identify an anomaly at T ∼ 350 K for that sample.…”

“…Several electrical resistance measurements of graphite samples of different thickness published in the last years suggest that graphite samples are not homogeneous and that the temperature as well as the absolute value of the electrical resistivity and Hall effect are not unique but thickness- [18,[20][21][22] and sample-length dependent [23,24]. Whereas the last dependence is due to the increasing contribution of ballistic transport to the total resistance the smaller the sample length, the thickness dependence observed in the transport properties is mainly due to the existence of interfaces between the two stacking orders, hexagonal or Bernal (2H) and rhombohedral (3R), see Fig.…”

Ordered Defects: A Path to High-Temperature Superconductivity and Magnetic Order

“…More patterns in the electronic spectrum measured by STM due to misoriented graphene layers of the graphite structure were found already in 1990, at the surface of a graphite HOPG bulk sample [18,19]. Their influence on the measured conductivity was not, however, realized till 2008 [20,21]. There are two more 2D interfaces that can appear parallel to the graphene planes in real graphite samples, namely: a.…”

Influence of surface band bending on a narrow band gap semiconductor: Tunneling atomic force studies of graphite with Bernal and rhombohedral stacking orders

“…[16] Kelvin force microscopy studies of the surface of well-oriented graphite samples, done in air as well as in inert atmosphere, revealed the coexistence of insulatingand conducting-like regions, [17] whose origin can also be related to the presence of ideal graphite and regions with SF at or near the surface, respectively. These highly conducting 2D SF are the origin for the metallic-like behavior in the temperature dependence of the resistance [2,11], for the low temperature Shubnikov-de Haas and de Haasvan Alphen quantum oscillations [10,11], and also for the huge diamagnetism of graphite [18] at fields applied parallel to the c−axis [19]. In other words, the proposed Fermi surface [3] does not correspond to ideal graphite, in contradiction to the semimetal picture proposed more than 60 years ago.…”