International Nanotechnology Conference & Expo
April 04-06, 2016 | Baltimore, USA
Superconductivity and unusual magnetic behavior in nano amorphous carbon
Racah Institute of Physics, The Hebrew University, Israel
Traces of superconductivity (SC) up to 65 K were observed by magnetic measurements in three different inhomogeneous sulfur doped amorphous carbon (a-C) systems: (i) commercial, and (ii) synthesized powders and in (iii) a-C thin films. (i) Studies performed on commercial (a-C) powder which contains 0.21% sulfur, revealed traces of twonon-percolated superconducting phases around Tc34 and 65 K. The SC volume fraction is enhanced by the sulfur doping. (ii) Another a-C powder obtained by pyrolytic decomposition of sucrose, did not show any sign for SC above 5 K. However, mixing of this powder with sulfur and synthesize of the mixture at 400 °C (a-CS), yields an inhomogeneous products which showstraces of SC phases at TC= 17 and 42 K.(iii) Non-superconducting a-C thin films were grown by electron-beam induced deposition. SC emerged at Tc = 34.4 K only after heat treatment with sulfur.
Other partsof the same commercial a-C and pyrolytic a-CS powders, show unusual magnetic features. (1) Pronounced irreversible peaks around 55-75 K appear in the first zero-field-cooled (ZFC) sweep only and they aretotally suppressed in the second ZFC runsmeasured a few minutes later. Their origin is not known. (2) Around the peak position the field-cooled (FC) curves cross the ZFC plots (ZFC>FC). These peculiar magnetic observations are connected to each other. All SC and magnetic phenomena observed are intrinsic properties of the a-CS materials.
It is proposed that the a-CS systems behave similarly to the high TCcurates and/or pnictides in which SC emerges from magnetic states. In addition, the a-CS system resembles the sulfur hydrides (H3S) material which becomes SC at TC = 203 K under high pressure (>200 GPa). SCinH3S is explained by the interaction between the electrons and the high frequencies hydrogen vibrations. This model may also be applied to a-CS. The relatively light nonmetallic carbon atoms and their high vibration frequencies as simple harmonicoscillatorsinduce SC even atambientpressurewithTCashig has 67K. Alternatively, it is possible that the a-Cand a-CS powders contains mall amount of hydrogen and that the observed SC states arepressedH3S embedded or adsorbed in thea-C matrix.
Israel Felner has completed his PhD at the Hebrew University (HU) of Jerusalem, Israel and his postdoctoral studies at UCSD, San-Diego, California, USA (1979). Since then he works at the “Racah” Institute of Physics at the HU. He became a full professor in 1995. During 2003-2006 he served as the chairman of physics studies at the HU. He has published more than 480 papers in reputed journals and serves as an editorialboard member of three prestige scientific journals.