  In 1986, a cuprate superconductor (Ba-La-Cu-O system) having a critical
temperature which goes over the BCS limit (~30 K) was discovered and then a
cuprate superconductor (Y-Ba-Cu-O system) with a critical temperature higher
than 77 K was discovered. Furthermore, a Hg-based cuprate with a critical
temperature of 133 K was found. The 133 K is still the highest critical
temperature of conventional superconductors under atmospheric pressure.
  We have shown that materials obtained by bringing n-alkanes into contact with
graphite are capable of conducting electricity with almost no energy loss at
room temperature. We here report that the sudden jump in resistance showing a
phase transition is observed in the materials during heating by two-probe
resistance measurement. The measured critical temperatures of the materials
consisting of pitch-based graphite fibers and n-alkanes having 7-16 carbon
atoms range from 363.08 to 504.24 K and the transition widths range between
0.15 and 3.01 K. We also demonstrate that superconductors with critical
temperatures beyond 504 K are obtained by alkanes with 16 or more carbon atoms.
