2-CHANNEL KONDO SCALING IN CONDUCTANCE SIGNALS FROM 2-LEVEL TUNNELINGSYSTEMS

The temperature (T) and voltage (V) dependence of conductance signals in metal point contacts, previously asserted to be due to 2-channel Ko ndo scattering from atomic 2-level tunnelling systems, collapse onto a universal scaling curve dependent on eV/k(B)T, for all T and eV/k(B) below a characteristic Kondo scale. Measurements determine a conductan ce exponent of 1/2, as expected from conformal field theory solution o f the 2-channel Kondo model. The magnetic field (H) dependence at low T is nonanalytic at H = 0 (proportional to\H\) in contrast to Fermi-Li quid theory but in agreement with conformal field theory.