We analyze a two-dimensional Pomeranchuk-nematic instability, trigger by the Landau parameter $F_2<0$, in the presence of a small magnetic field. Using Landau Fermi-liquid theory in the isotropic phase, we analyze the collective modes near the quantum critical point $F_2=-1,{\omega }_c=0$ (where ${\omega }_c$ is the cyclotron frequency). We focus on the effects of parity symmetry breaking on the Fermi-surface deformation. We show that the linear response approximation of the Landau-Silin equation is not sufficient to study the critical regime and it is necessary to compute corrections at least of order ${\omega }_c^2$. Identifying the slowest oscillation mode in the disordered phase, we compute the phase diagram for the isotropic/nematic phase transition in terms of $F_2$ and ${\omega }_c$.

• Received 10 October 2012

DOI:https://doi.org/10.1103/PhysRevB.87.075147