$$T_K \sim D \exp\left(-\frac1J\rho(\epsilon_F)\right)$$
$$\rho(T) = \rho_0 \left[ 1 + 2 J \rho(\epsilon_F) \ln\left(\fracDT\right) + \dots \right]$$ $dj/d\ln D = -2j^2 <
For small $j>0$, $dj/d\ln D = -2j^2 < 0$ → as we lower the cutoff $D$ (i.e., lower temperature), $j$ increases . This is the opposite of asymptotic freedom in QCD; it is infrared slavery . The flow diverges at a scale $D \sim T_K$, signaling a new fixed point. signaling a new fixed point.