EVIDENCE FOR A 1-Q TO 3-Q TRANSITION AND 3-Q SOLITON LATTICE IN INCOMMENSURATE PROUSTITE

As-75 nuclear quadrupole resonance line shape data demonstrate the exi stence of a transition from a single-q state, consisting of a superpos ition of one dimensionally modulated incommensurate domains, to a genu ine triple-q modulated incommensurate state with three independent non coplanar modulation waves in the high temperature part of the incommen surate phase of proustite. The NMR spectra are consistent with the exi stence of a triple-q modulated multisoliton lattice in the low tempera ture part of the incommensurate phase. The temperature dependence of t he soliton density has been determined.