# SciPost Commentary Page

### Original publication:

 Title: Chirality and orbital order in charge density waves Author(s): Jasper van Wezel As Contributors: Jasper van Wezel Journal ref.: EPL (Europhysics Letters) 96, 67011 DOI: http://dx.doi.org/10.1209/0295-5075/96/67011 Date: 2011-12-01

### Abstract:

Helical arrangements of spins are common among magnetic materials. The ﬁrst material to harbor a corkscrew pattern of charge density, on the other hand, was discovered only very recently. The nature of the order parameter is of key relevance, since rotating a magnetic vector around any propagation vector trivially yields a helical pattern. In contrast, the purely scalar charge density cannot straightforwardly support a chiral state. Here we use a Landau order parameter analysis to resolve this paradox, and show that the chiral charge order may be understood as a form of orbital ordering. We discuss the microscopic mechanism driving the transition and show it to be of a general form, thus allowing for a broad class of materials to display this novel type of orbital-ordered chiral charge density wave.

Please note that the atomic structure of the chiral phase in $1T$-TiSe$_2$ actually has the (base-centred) space group C2, rather than the (primitive) space group P2 mentioned in the paper.