Pseudogap phase

As is explained above, even the assignment of major peaks in the optical conductivity is unsettled even today. This fact seems to indicate that we need the transport theory that goes beyond the conventional one. Actually, there a number of other anomalous behaviors in the pseudogap phase that strongly suggest the need for a new transport theory. In the following, we list the four most important anomalous behaviors ... 

Conventional CDW and SDW states are ubiqiutous in metals with the commensurate SDW or antiferromagnetic (AF) order being the most common. Compounds with confirmed unconventional density waves sofar are rather scarce and with certainty have only been found in organic metals and perhaps in manimn HF compounds and the pseudogap phase of underdoped cuprates. This may in part be due to the difficulty detecting such hidden order parameters which leave no signature in standard neutron or X-ray diffraction experiments. 

Varma, C.M. (1999) Pseudogap phase and the quantum-aitical point in copper-oxide metals. Phys. Rev. Lett., 83, 3538-3541. 

As we saw in Section 3.2, in the absence of disorder (A(x)=Ao), the electron spectrum has a gap between the energies =-Aq and e=+Ao- Disorder gives rise to the appearance of electron states inside the gap, although for weak disorder a pseudogap still exists. Using the phase formalism [471, Ovchinnikov and Erikhman derived a losed expression for the integrated average density of states (J of the... 

Shortly after, we recognized that ScCu4Ga2 (Im3) [70] might also be tuned to a QC, but the correct stoichiometry and reaction conditions were not achieved in our limited experiments. Recently, Honma and Ishimasa [71] have reported that i-QC phase forms almost exclusively from a rapidly quenched ScisCu48Ga34 composition, emphasizing a very narrow phase width and its thermodynamic metastability at room temperature. However, the failure turned us to other Ga intermetallics, which led to the pseudogap tuning concepts that follow. 

Fig. 16 DOS calculated by LMTO for the known Ca-Au-In 1/1 AC (e/a = 1.73). The pseudogap shown at eja = 2.00 is close to the composition of i-QC phase, with eja = 1.98. (Reproduced with permission from [79], Copyright 2005 American Chemical Society)...

Abstract Existing data on 63Cu-nuclear spin relaxation reveal two independent relaxation processes the one that is temperature independent we link to incommensurate peaks seen by neutrons, while the "universal temperature dependent contribution coincides with 1/6371 (1/ ) for two-chain YBCO 124. We argue that this new result substitutes for a "pseudogap regime in a broad class of high-Tc cuprates and stems from the 1st order phase transition that starts well above the superconductivity Tc but becomes frustrated because of broken electroneutrality in the CuC>2 plane. 

Mean-field calculations [19] on the general model give a phase diagram similar to fig. (3), with a QCP at xc and an unusual time-reversal violating phase for the pseudogap region. 

The vast array of experiments in the cuprates narrows the possible theories for the phenomena. One can be certain that the theories should have a QCP with a phase with a pseudogap ending at it. One can also be certain that in the long wavelength limit, the fluctuations about the QCP must have the form of Eq. (2) because that is what is observed [29],... 

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