X-ray evidence of charge density wave modulations in the magnetic phases of (TMTSF)2PF6 and (TMTTF)2Br

We have performed X-ray scattering investigations of (TMTSF)2PF6 and (TMTTF)2 Br in their magnetic ground states. Very weak 2kF and 4kF satellite reflections are observed in the spin density wave (SDW) ground state of (TMTSF)2PF6. 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)2PF6 will exhibit an unprecedented 2kF mixed CDW-SDW modulation. 4kF satellite reflections are observed in the antiferromagnetic (AF) ground state of (TMTTF)2Br. In this salt the 4kF CDW modulation is probably set by magnetoelastic coupling of the lattice degrees of freedom with the AF modulation.