Such a strange property may be expected to occur in conductors operating at cryogenic temperatures, but a team of researchers led by the Lawrence Berkeley National Laboratory claims to have discovered this unique property in vanadium dioxide at temperatures of around 67 °C (153 °F).
Of all the metals found on Earth, most are both good conductors of heat and electricity. This is because classic physics dictates that their electrons are responsible for both the movement of electrical current and the transfer of heat. This correlation between electrical and thermal conductivity is dictated by the Wiedemann-Franz Law, which basically says that metals that conduct electricity well are also good conductors of heat.
However, metallic vanadium dioxide (VO2) seems to be different. When the researchers passed an electrical current through nanoscale rods of single-crystal VO2, and thermal conductivity was measured, the heat produced by electron movement was actually ten times less than that predicted by calculations of the Wiedemann-Franz Law.