Pauli susceptibility correlations

The low value of U in (TMTSF)2X salts in view of their filled electron band (or the hole band) is in striking contrast to the high Us in -filled M(TCNQ)2 conductors, which often have a susceptibility enhancement over the Pauli susceptibility of factors of 10-30, suggesting that C//4i 1. As pointed out by Mazumdar and Bloch (100), U is an effective parameter which is magnified at the band filling of . This makes it much easier to understand why M(TCNQ)2 and (TMTTF)2X salts show strong correlation effects and why in (TMTSF)2X salts U is so low. 

The larger N E ) and smaller density of uncorrelated spins for PPy(PFg) correlates with the larger fraction of the sample having 3D order [173], i.e., crystallinity stabilizes a metallic density of states. Similar to doped PAN, where the metallic Pauli susceptibility is associated with the 3D-ordered regions [14,63], a large finite N( p) is present in PPy when there are large 3D-ordered (crystalline) regions. In more disordered materials, localized polarons or bipolarons predominate. 

Where strong-correlation fluctuations are present in an itinerant-electron matrix, the magnetic susceptibility may be interpreted as a coexistence of Curie-Weiss and mass-enhanced Pauli paramagnetism. 

In the metallic regime, the susceptibility has usually been analyzed within the limit of weak correlations [Eq. (15)] (Pauli enhanced). 

On the other hand, in the case of a Pauli paramagnet the magnetic susceptibility is proportional to the density of states at the Fermi level. The change of the electronic properties by alloying leads to a variation of the susceptibility. Weiqi et al. (1992) and Jianhui et al. (1992) have measured the susceptibility to observe changes in the electronic properties of Pd in Pd R/AI2O3 catalysts and to correlate them with their catalytic properties. 

If, though, one uses these two pair potentials independently, one finds the same ordering of solutions as with the umklapp method. This occurs because the two pair potentials (corresponding to an acoustic and optic branch) are essentially a foldback of the susceptibility into the first zone. Thus, the peak in % at the reciprocal lattice vector 2 = (0,0,1) corresponds to a peak in the optic branch at = 0, and so one obtains again odd parity solutions with Ai the highest and Ej the next highest. An additional feature of these calculations occurs if one takes into account the anisotropy of the susceptibility (i.e. the He form of the pair potential, Fs-i, is replaeed by F s.sy where s are Pauli matrices, and ij are cartesian indices). Since the AF correlations are only present in the x x Xyy eomponents of the susceptibility, it turns out that the order parameter d vector is locked to the c axis since and F drops... 

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