Universal peak conductivities at the transition between insulating and integer quantum Hall states

Experimental data available in the literature for the peak values, View the MathML source, of the diagonal conductivity at the transition between the insulating state and the lowest integer quantum Hall states are compared with the universal values of View the MathML source and 1 (in units e2/h). A good agreement is found for different two-dimensional charge-carrier systems by taking account for the presence of electronic valley or spin degeneracy in the appropriate cases.