Theory of helimagnons in itinerant quantum systems. III. Quasiparticle description

Abstract

In two previous papers we studied the problem of electronic properties in a system with longranged helimagnetic order caused by itinerant electrons. A standard many-fermion formalism was used. The calculations were quite tedious because different spin projections were coupled in the action, and because of the inhomogeneous nature of a system with long-ranged helimagnetic order. Here we introduce a canonical transformation that diagonalizes the action in spin space, and maps the problem onto a homogeneous fermion problem. This transformation to quasiparticle degrees of freedom greatly simplifies the calculations. We use the quasiparticle action to calculate singleparticle properties, in particular the single-particle relaxation rate. We first reproduce our previous results for clean systems in a simpler fashion, and then study the much more complicated problem of three-dimensional itinerant helimagnets in the presence of an elastic relaxation rate 1/τ due to nonmagnetic quenched disorder. Our most important result involves the temperature dependence of the single-particle relaxation rate in the ballistic limit, τ 2 T ǫF > 1, for which we find a linear temperature dependence. We show how this result is related to a similar result found in nonmagnetic two-dimensional disordered metals.

Electronic relaxation rates in metallic ferromagnets

“…[6][7][8] In antiferromagnets, the corresponding contribution is known to be proportional to T 3 . 9 These results all hold for three-dimensional systems, which is the only physical dimension in which longrange magnetic order exists.…”

Non-Fermi Liquid Regimes and Superconductivity in the Low Temperature Phase Diagrams of Strongly Correlated d- and f-Electron Materials

“…The results demonstrate that the helimagnon contribution would be negligible compared to the Fermi-liquid contribution [184]. Therefore, the good agreement between theory and experiment for the helimagnons at ambient pressure indicates that the helimagnons are most likely not the source for the NFL behavior of the resistivity above P c .…”

“…For a more realistic scenario, including weak disorder effects as expected near to the phase transition, the leading term in the resistivity caused by helimagnons is linear in temperature [184], in contrast to the observed T 1.5 dependence. Before our study, no experimental results about the nature of the helimagnetic Goldstone modes were available, partly because the experimental conditions are extremely challenging.…”

Soft modes in electronic stripe phases and their consequences for thermodynamics and transport

“…The leading temperature dependence of the electrical resistivity 1/σ is weaker than that of 1/τ by one power of T in clean systems, and the same as that of 1/τ in weakly disordered ones, respectively. Qualititively, all of these results also hold for the exchange of helimagnons between electrons in helical magnets, 22,38 and they are summarized in Table I. We conclude with some speculations pertaining to the electrical conductivity.…”

“…In the weak-disorder regime, 30,34 T ≫ λ/(ǫ F τ el ) 2 , the calculation proceeds in analogy to Ref. …”