X-ray evidence of charge density wave modulations in the magnetic phases of (TMTSF) 2PF 6 and (TMTTF) 2Br

Abstract

We have performed X-ray scattering investigations of (TMTSF) 2PF 6 and (TMTTF) 2 Br in their magnetic ground states. Very weak 2k F and 4k F satellite reflections are observed in the spin density wave (SDW) ground state of (TMTSF) 2PF 6. They are probably the signature of a purely electronic charge density wave (CDW) modulation of about one tenth of electron per molecule. Our X-ray results together with magnetic measurements show that the ground state of (TMTSF) 2PF 6 will exhibit an unprecedented 2k F mixed CDW-SDW modulation. 4k F satellite reflections are observed in the antiferromagnetic (AF) ground state of (TMTTF) 2Br. In this salt the 4k F CDW modulation is probably set by magnetoelastic coupling of the lattice degrees of freedom with the AF modulation.