Charge incommensurate

Kawamoto T, Mori T, Konoike T, Enomoto K, Terashima T, Uji S, Kitagawa H, Takimiya K, Otsubo T (2006) Charge transfer degree and superconductivity of the incommensurate organic superconductor (MDT-TSF)(l3)o.422- Phys Rev B 73 094513/1-8... 

Figure 2.27 STM image of incommensurate charge density wave (CDW) state in Nbo.04Tao.96S2. Black lines highlight the insertion of extra rows of CDW maxima in the lattice (From Dai Lieber, 1993).

In conducting solids, the conduction electron density is spatially modulated, forming charge density waves (CDW) the periodic distortion accompanying the CDW (due to interaction between the conduction electron and the lattice) is responsible for the incommensurate phase (Overhauser, 1962 Di Salvo Rice, 1979 Riste, 1977). The occurrence of CDW and the periodic distortion can be understood in terms of the model proposed by Peierls and Frdhlich for one-dimensional metals. Let us consider a row of uniformly spaced chain of ions (spacing = a) associated with conduction electrons of energy E k) and a wave vector k. At 0 K, all the states are filled up to the Fermi energy, = E(kp). If the electron density is sinusoidally modulated as in Fig. 4.15 such that... 

Abstract Electronic correlation effects in La2.ISrINi04 lead to spontaneous phase separation into microscopic spin/charge stripes with commensurate or incommensurate order. Raman scattering experiments on such single crystalline materials show a rich phenomenology of phonon and magnon anomalies due to the new, self-organized periodicities. These effects are observable as function of temperature. 

The Peierls169 metal-to-semiconductor phase transition in TTFP TCNQ p was detected in an oscillation camera these streaks became bona fide X-ray spots only below the phase transition temperature of 55 K this transition is incommensurate with the room-temperature crystal structure, due to its partial ionicity p 0.59, and the "freezing" of the concomitant itinerant charge density waves (this effect was missed by four-circle diffractometer experiments, which had been set to interrogate only the intense Bragg peaks of either the commensurate room-temperature metallic structure, or the commensurate low-temperature semiconducting structure). 

Commensurability. Incommensurate lattice distortions and commensurate-incommensurate phase transitions are often observed in these materials. The incommensurability comes either from an incommensurate Fermi wave vector (2A F, 4kF scattering in charge-transfer salts) or from the counterion stacks (e.g., triiodide-containing materials). 

When the band filling is irrational, the CDW reflections at wavelength are incommensurate with the background lattice of periodicity d, and the charge transfer p is ... 

The marked effects of disorder in pseudo-ID systems have been clarified by both experiment and theory. These include (a) transport in the absence of collective effects (INV 1, INV 13), (b) the role of impurities in pinning incommensurate CDW s and the effect on charge transport (F3), and (c) the relative effect of impurities on the Peierls and superconducting transition temperature. 

Fig. 9.6. (a) Calculated image with only the incident beam and the four superstructure spots of type 011 inside the objective aperture (b) a similar experimental image where disorder of the image features caused by charge modulation is present, both incommensurability and out of phase boundaries. 

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