Generic non-Fermi-liquid behavior of the resistivity in magnets with ferromagnetic, helical, or skyrmionic order

Abstract

The electrical resistivity of several relatively clean metallic ferromagnets, as well as the helimagnet MnSi, is commonly observed to exhibit non-Fermi-liquid behavior at low temperatures. This behavior, which is found in both ordered and disordered phases, and both near and away from the magnetic transition, remains a major unsolved problem. We derive and discuss three novel mechanisms underlying such behavior that are based on electron scattering mediated by the exchange of (1) ferromagnons or (2) skyrmionic fluctuations, both in conjunction with weak disorder, or (3) helimagnons in clean systems. Since the magnetic transition in weakly disordered sytems is generically discontinuous, static droplets of the ordered phase can exist within the disordered phase, making the mechanisms viable there as well. We compare our theoretical results with existing experimental ones and suggest additional experiments.

Anomalous Transport Behavior in Quantum Magnets

“…Parameter values appropriate for ZrZn 2 have been estimated in Ref. [9]. The result is a prefactor A FM 3/2 ≈ 0.01µΩcm/K 3/2 , which is very close to what is observed in this material, see the discussion in Secs.…”

“…From Ref. [9]. Right panel: Magnetic field -temperature phase diagram of MnSi, showing various phases.…”

“…[38][39][40][41]. Recently, electron scattering from Goldstone modes in both ferromagnets and helimagnets has been reconsidered, and several new mechanism for anomalous transport behavior have been discussed [9]. In this section we give a summary of the current state of the theory.…”

“…We focus on three mechanisms that yield a resistivity exponent s = 3/2 at least in some temperature regime, for more complete results see Ref. [9]. For completeness, and to clarify some common misconceptions, we also briefly discuss the effects of non-generic critical fluctuations, and the extent to which they exist.…”

“…The lower limit on the temperature window is dictated by the constraints on the ballistic disorder regime [9]. For lower temperatures, the electron dynamics are diffusive.…”