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About commensurability effects in quasi 1d conductors (CROSBI ID 523235)

Prilog sa skupa u zborniku | sažetak izlaganja sa skupa | međunarodna recenzija

Barišić, Slaven About commensurability effects in quasi 1d conductors // RECENT DEVELOPMENTS IN LOW DIMENSIONAL CHARGE DENSITY WAVE CONDUCTORS / Biljaković, Katica ; Dumas, Jean ; Starešinić, Damir (ur.). Zagreb: Institut za fiziku, 2006. str. 3-x

Podaci o odgovornosti

Barišić, Slaven

engleski

About commensurability effects in quasi 1d conductors

The phase diagram of the Bechgaard and Fabre organic conductors is revisited. A special care is devoted to the commensurability effects associated with bond and site dimerization on the conducting organic chains which appear essential in the theoretical description of the observed phase diagram and of the physical behaviors associated with various phases. The bond dimerization effects are relevant in the paramagnetic insulating (MI) phase, in the (AF) phase with the tetramerized spin order, in the spin-Peierls (SP) phase with lattice tetramerization added to the (AF) spin order while the bond/site charge dimerization is relevant in the (CO) phase. The relevance of dimerizations is experimentally observed by the enhancement of the dimerization of distances between the adjacent organic molecules in the MI, AF and SP phases and by the apparition of the homogeneous shift of the counter ion lattice along the direction of the molecular chains in the CO phase. This ferroelectric shift is driven by the the charge disproportiation between adjacent organic molecular sites. In contrast to that, the dimerization of the intermolecular distances and/or the homogeneous shift of the counter ions is absent in the superconducting phase, strongly indicating that the latter is stable only when the dimerization is irrelevant. Those observations are traditionally related to the behavior of the dominant fluctuations in the purely 1d weak coupling model with forward and backward scatterings g2 and g1 of comparable magnitude and an Umklapp scattering g3 induced by dimerization, which is relatively small. The &#8220; phase diagram&#8221; of the 1d model is carefully reconsidered with the emphasis on the behavior in the region of (g2 - g1/2) &#8776; -| g3 |. For (g2 - g1/2) close above -| g3 | the Mott gap &#916; &#961; is finite but extremely small. For larger (g2 - g1/2) it remains small due to the relative smallness of | g3 |. The dominant 1d fluctuations below &#916; &#961; are of the AF type (spin tetramerization). It is emphasized that in the range -| g3 |<(g2 - g1/2)<0 the dominant fluctuations in the sizeable temperature range above &#916; &#961; are of the SDW type, somewhat stronger than those of the CDW/BOW (bond density wave) type. At even higher temperatures the superconducting singlet (SS) or triplet (TS) 1d fluctuations prevail. The strengths of the interchain hopping t&#9524; , the interchain backward Coulomb scattering and the coupling to phonons then determine the scales related to the true critical temperatures of the observed phase transitions. In this respect a special role is played by t&#9524; . For temperatures below t&#9524; the tendency of all correlations towards the Luttinger liquid behaviors is arrested and replaced by the appropriate Fermi liquid behaviors with pseudogaps and gaps. Below t&#9524; the temperature behaviors of all relevant correlation functions, including the single electron propagator, can be approximately described by the ladder theories. In particular the singular correlation functions define the appropriate order parameters and give the corresponding mean field transition temperatures related to pseudogaps, assuming that they are lower than t&#9524; . These mean field temperatures appear to be consistent with the observed phase diagram, and its evolution with pressure, assuming that the pressure decreases the relative role of |g3|. The transition temperatures associated with the long range orders in the phases of the order parameters can be reasonably estimated by the appropriate generalization of the ladder theories, the simplest of which is through Landau expansions in terms of the critical order parameters.

charge density waves; organic conductors

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Podaci o prilogu

3-x.

2006.

objavljeno

Podaci o matičnoj publikaciji

RECENT DEVELOPMENTS IN LOW DIMENSIONAL CHARGE DENSITY WAVE CONDUCTORS

Biljaković, Katica ; Dumas, Jean ; Starešinić, Damir

Zagreb: Institut za fiziku

Podaci o skupu

Workshop &#8222 ; ; ; ; ; Recent developments in low dimensional charge density wave conductors&#8220 ; ; ; ; ; Skradin, Croatia June 29.-July 3. 2006.

pozvano predavanje

29.06.2006-03.07.2006

Skradin, Hrvatska

Povezanost rada

Fizika