Breakdown of Hydrodynamic Transport Theory in the Ordered Phase of Helimagnets

TL;DR

This paper demonstrates that strong fluctuations in helimagnets at finite temperature invalidate hydrodynamic transport descriptions, leading to nonlocal behavior and divergent transport coefficients, with implications for neutron scattering experiments.

Contribution

It reveals the breakdown of hydrodynamic transport theory in helimagnets due to fluctuations, highlighting the nonlocal nature of the macroscopic description.

Findings

Hydrodynamics breaks down in helimagnets at T>0 due to fluctuations.

Transport coefficients undergo infinite renormalizations.

At T=0, effects are finite and observable in neutron scattering.

Abstract

It is shown that strong fluctuations preclude a hydrodynamic description of transport phenomena in helimagnets, such as MnSi, at T>0. This breakdown of hydrodynamics is analogous to the one in chiral liquid crystals. Mode-mode coupling effects lead to infinite renormalizations of various transport coefficients, and the actual macroscopic description is nonlocal. At T=0 these effects are weakened due to the fluctuation-dissipation theorem, and the renormalizations remain finite. Observable consequences of these results, as manifested in the neutron scattering cross-section, are discussed