Theory of helimagnons in itinerant quantum systems. II. Nonanalytic corrections to Fermi-liquid behavior

A recent theory for the ordered phase of helical or chiral magnets such as $\mathrm{MnSi}$ is used to calculate observable consequences of the helical Goldstone modes or helimagnons. In systems with no quenched disorder, the helimagnon contribution to the specific heat coefficient is shown to have a linear temperature dependence, while the quasiparticle inelastic scattering rate is anisotropic in momentum space and depends on the electronic dispersion relation. For cubic lattices the generic temperature dependence is given by a non-Fermi-liquid $T^{3∕2}$ behavior. The contribution to the temperature dependence of the resistivity is shown to be $T^{5∕2}$ in a Boltzmann approximation. The helimagnon thus leads to nonanalytic corrections to Fermi-liquid behavior. Implications for experiments, and for transport theories beyond the Boltzmann level, are discussed.

Figure 1

The lowest-order electronic self-energy $\Sigma$ in terms of the potential $V$ (dashed line) and the electronic Green’s function (solid line).

Figure 2

Diagrammatic representation of the bare spin-triplet interaction $A$ and the reference ensemble Green function $G$.

Figure 3

Effective spin-triplet interaction resulting from a ladder resummation.

Figure 4

The direct (a) and exchange (b) contributions to the single-particle self-energy.

Figure 5

Consistent approximation for the self-energy $\Sigma$ and the vertex function $\mathit{\Gamma }$.