We show how the collapse of an energy scale in a quantum critical metal can lead to physics beyond the weak-field limit usually used to compute transport quantities. For a density-wave transition we show that the presence of a finite magnetic field at the critical point leads to discontinuities in the transport coefficients as temperature tends to zero. The origin of these discontinuities lies in the breakdown of the weak-field Jones-Zener expansion which has previously been used to argue that magnetotransport coefficients are continuous at simple quantum critical points. The presence of potential scattering and magnetic breakdown rounds the discontinuities over a window determined by $\tau \Delta <1$ where $\Delta$ is the order parameter and $\tau$ is the quasiparticle elastic lifetime.

• Received 27 July 2005

DOI:https://doi.org/10.1103/PhysRevLett.95.247201