Electronic states in the spin-density wave phase of organic conductors: roles of the coexisting 2kF and 4kF charge–density waves

From charge- and spin-ordering to superconductivity in the organic charge-transfer solids

“…Convincing proof of this coupling was obtained from direct X-ray measurements by Pouget and Ravy [169,183] and Kagoshima et al [193,194], which we briefly discuss below. Yet another subject of interest is the nature of the very low temperature phase below 4 K [187,[193][194][195][196][197][198], which has only recently shown from 13 C-NMR to be commensurate SDW [199]. The pressure-induced transition to SC is therefore a commensurate BCSDW-SC transition, making it even more likely that the mechanisms of the superconducting transition in the so-called quasi-1D compounds and the strongly 2D ET and [Pd(dmit) 2 ] 2 compounds (see Section 5) are related.…”

“…Of greater relevance to the present review are however indications for the coupling between the lattice, charge and spin degrees of freedom that is not expected within a simple nesting mechanism for the SDW instability, but that were indicated over the years by a variety of experiments [188][189][190][191][192]. Convincing proof of this coupling was obtained from direct X-ray measurements by Pouget and Ravy [169,183] and Kagoshima et al [193,194], which we briefly discuss below. Yet another subject of interest is the nature of the very low temperature phase below 4 K [187,[193][194][195][196][197][198], which has only recently shown from 13 C-NMR to be commensurate SDW [199].…”

“…The lowest temperature at which Pouget and Ravy saw the 2k F and 4k F scatterings was 10.7 K. The intensities of the satellite reflections were weaker than the usual 2k F and 4k F reflections by 2 to 3 orders of magnitude. Kagoshima et al observed that below 4 K, there was remarkable decrease in the intensities with decreasing temperature, and the satellites were completely absent at 1.6 K [193,194]. Kagoshima et al's experiment gave strong evidence for the existence of a SDW subphase below 4 K that was presumably different from the high temperature phase, as had been conjectured already from other experiments [187,[195][196][197][198].…”

“…The pressure-induced transition to SC is therefore a commensurate BCSDW-SC transition, making it even more likely that the mechanisms of the superconducting transition in the so-called quasi-1D compounds and the strongly 2D ET and [Pd(dmit) 2 ] 2 compounds (see Section 5) are related. X-ray scattering experiments have directly demonstrated the mixed CDW-SDW nature of the broken symmetry below T SDW in (TMTSF) 2 PF 6 [169,183,193,194]. Pouget and Ravy observed satellites with wave vector components a * /2 (2k F ) as well as a * (4k F ), thus confirming that the CDW and SDW periodicities were identical.…”