查看文章

Noncoplanar spin structures, eg, skyrmion crystals, have drawn a lot of attention for their peculiar transport phenomena and a wide variety of potential applications [1]. In these systems, the spin scalar chirality, which is defined by the triple product of three spins, plays an essential role as it gives rise to an effective magnetic field for electrons via the spin Berry phase mechanism. In fact, there have been many studies in spin-charge coupled systems, focusing on a ferroic spin scalar chiral ordering [2, 3, 4, 5]. Recently, a spatially-modulated spin scalar chiral ordering has also drawn considerable interest, as it might lead to a rich variety of novel electronic structures and transport phenomena [6].

In this study, in order to explore the possibility of spatially-modulated chiral orders, we focus on multiple-Q orderings anticipated from the instability of Fermi surface [4, 7, 8]. Multiple-Q orderings are characterized by more than a single wave vector, which can be the origin of the spin scalar chiral ordering. For this purpose, we consider the Kondo lattice model and investigate the energies for single-Q and multiple-Q states in the weak spin-charge coupling region. By considering dominant contributions from the Fermi surface instability, we evaluate both energy gain and loss for multiple-Q states relative to single-Q states. As a result, we find that a double-Q ordered state, which forms a meron (half-skyrmion) crystal with spin scalar chiral stripes becomes more stable than the single-Q states irrespective of the shape of the Fermi surface. We discuss the results in comparison with the numerical results in the previous talk.