Ferromagnetic Quantum Critical Point in Noncentrosymmetric Systems

Ferromagnetic quantum criticality in clean metals has proven elusive due to fermionic soft modes that drive the transition first order. We show that noncentrosymmetric metals with a strong spin-orbit interaction provide a promising class of materials for realizing a ferromagnetic quantum critical point in clean systems. The spin-orbit interaction renders massive the soft modes that interfere with quantum criticality in most materials, while the absence of spatial inversion symmetry precludes the existence of new classes of soft modes that could have the same effect.

Figure 1

Phase diagram in the space spanned by $t$, $r$, and $\nu$ based on Eq. (1). Shown are a flat surface of second-order transitions at $r=0$ (solid blue area), a curved surface of first-order transitions (meshed green area), and a line of tricritical points delineating the two (red curve). In a given material, $\nu$ will be fixed. For a given $\nu$, $r$ will be a complicated function of pressure and temperature.