Chiral Paramagnetic Skyrmion-like Phase in MnSi

We present a comprehensive study of chiral fluctuations in the reference helimagnet MnSi by polarized neutron scattering and neutron spin echo spectroscopy, which reveals the existence of a completely left-handed and dynamically disordered phase. This phase may be identified as a spontaneous Skyrmion phase: it appears in a limited temperature range just above the helical transition $T_C$ and coexists with the helical phase at $T_C$.

Figure 1

Polarized neutron small angle scattering patterns measured by 12 (a) slightly below ($T_C-0.1\mathrm{K}$) and (b) above ($T_C+0.2\mathrm{K}$) the helimagnetic transition of MnSi. The vectors $P_0$ mark the polarization of the incoming neutron beam.

Figure 2

Intensity at the position of the ${\overrightarrow{\tau }}_{111}$ helical peak (a), chiral fraction of the dominant left-handed domain (b), and characteristic time $t_0$ of the fluctuations at ${\overrightarrow{\tau }}_{111}$ and ${\overrightarrow{\tau }}_{110}$ (c). In (b) the red circles are deduced from the extinction [${\mathbb{P}}_{x,x}$ Eq. (1)], the blue squares from the nondiagonal terms ${\mathbb{P}}_{y,x}$ and ${\mathbb{P}}_{z,x}$ and the green dotted line is calculated from ${\xi }_{111}$ and Eq. (4). The error bars are calculated from the counting rates and do not include systematic errors. For the sake of comparison between different cryogenic setups the data are plotted against $T-T_C$. The lines are guides for the eyes.

Figure 3

Dynamic correlations at the position of one of the helical Bragg peaks ${\overrightarrow{\tau }}_{111}$ measured by polarimetric NSE for the ${\mathbb{P}}_{z,x}$ term of the polarization matrix (Table ).