Mean field theory of electron spin resonance g-factors in β-YbAlB4

We present a mean-field theory of the conduction electron spin resonance g-factors in β-YbAlB4. The temperature-dependent shift in the g-factors is attributed to an isotropic exchange interaction between the spin of the conduction electrons and the spin of the Yb3+ ion. In the mean field approximation, the difference between the parallel and perpendicular g-factors is proportional to the difference between the parallel and perpendicular susceptibilities. Using experimental values for the susceptibilities, and fitting the data at 4.2 K, we predict the temperature dependence of the g-shifts at higher temperatures. (fast track communication)