Aspects of unconventional density waves

TL;DR

This paper discusses the concept of unconventional density waves, including their properties, differences from conventional density waves, and evidence for their existence in various complex materials and phases.

Contribution

It provides an overview of unconventional density waves and discusses evidence for their presence in several complex condensed matter systems.

Findings

Unconventional density waves have gapless quasiparticle spectra.

Many candidate materials exhibit properties consistent with UDW.

Evidence suggests UDW plays a role in various complex phases.

Abstract

Recently many people discuss unconventional density waves (i.e. unconventional charge density waves (UCDW) and unconventional spin density waves (USDW)). Unlike in conventional density waves, the quasiparticle spectrum in these systems is gapless. Also these systems remain metallic. Indeed it appears that there are many candidates for UDW. The low temperature phase of alpha-(BEDT-TTF)_2KHg(SCN)_4, the antiferromagnetic phase in URu_2Si_2, the CDW in transition metal dichalcogenite NbSe_2, the pseudogap phase in high T_c cuprate superconductors, the glassy phase in organic superconductor kappa-(BEDT-TTF)_2Cu[N(CN)_2]Br. After a brief introduction on UCDW and USDW, we shall discuss some of the above systems, where we believe we have evidence for unconventional density waves.