Seminarium Fizyki Materii Skondensowanej

Helical arrangements of spins are common among magnetic phases ofmatter. The first material to harbour a corkscrew pattern of electrondensity on the other hand, was discovered only relatively recently.This difference can be directly attributed to the nature of theinvolved order parameters: whereas rotating a magnetic vector around apropagation direction trivially yields a helical pattern, the purelyscalar charge density cannot straightforwardly support a chiral state.Here, I will show that spiral charge distributions can nonethelessspontaneously form in certain materials, as long as they areaccompanied by a simultaneous emergence of orbital order. Theapplication of this generic theory to two specific materials classeswill be discussed. I will also point out some of its unusualconsequences, like the presence of a nonlocal Hall effect, and thepossibility of an order-out-of-disorder transition.References:[1] J. Ishioka et al., Phys. Rev. Lett., 105, 176401 (2010).[2] J. van Wezel, Europhys. Lett., 96, 67011 (2011).[3] J.P. Castellan et al., Phys. Rev. Lett. 110, 196404 (2013).[4] H. Fukutome, Prog. Theor. Phys. 71, 1 (1984).[5] M. Gradhand et al., Phys. Rev. B, 92, 041111 (2015).