Magnetic phase transitions in bechgaard salts and related compounds: Electronic localisation and interchain couplings

Abstract

The physical properties of Bechgaard salts and related compounds are quickly described when an electronic localisation is present. In this case, the low-temperature ground state results in a competition between two instabilities: a Spin-Peierls distortion and an antiferromagnetic ordering. 1D theory results are compared with experimental data to show that the electronic localisation is not the only relevant parameter which drives this competition. The need for a quasi-1D theory is demonstrated with the introduction of relevant interchain couplings. The nature of these couplings is discussed to show that the Spin-Peierls ground state does not appear frequently, in agreement with experiment.

Structural Aspects of the Bechgaard and Fabre Salts: An Update

“…However there is the possibility for the Bechgaard salts, and as previously suggested for the Fabre salts [57], of conflicting interchain coupling mechanisms if Coulomb interactions, g 1┴ , and FS nesting tend to promote different b* transverse periodicities: g 1┴ (possibly mediated by the anion shift-see below) favoring q b = 1/2b*, as observed for the AO and SP modulations (see Sections 7 and 6), while the nesting of the FS favoring q b ~ 1/4b* as discussed above.…”

NMR in Commensurate and Incommensurate Spin Density Waves

“…NMR, on the other hand, is unaffected by this charge localization, due to the one-dimensional spin-charge decoupling [6]. Moreover, it has already been extensively used in the study of incommensurate systems like distorsive crystals [7], CDW[81, and SDW [9-111, providing data on the incommensurability through lineshape analysis and on the dynamics through nuclear spin lattice relaxation (NSLR) measurements.…”