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We propose that the nonequilibrium current measured in the a-b plane of an underdoped cuprate (in either the strange metal or pseudogap regime) in contact with either an overdoped cuprate or a standard Fermi liquid can be used to diagnose how different the pseudogap and strange metals are from a Fermi liquid. Naively, one expects the strange metal to be more different from a Fermi liquid than the pseudogap is. We compute the expected nonequilibrium transport signal with the three Green's functions that are available in the literature: (1) marginal Fermi-liquid theory, (2) the phenomenological ansatz for the pseudogap regime, and (3) the Wilsonian reduction of the Hubbard model which contains both the strange metal and pseudogap. All three give linear 7-V curves at low bias voltages. Significant deviations from linearity at higher voltages obtain only in the marginal Fermi-liquid approach. The key finding, however, is that I-V curves for the strange metal/Fermi-liquid contact exceed that of the pseudogap/Fermi-l iquid system. If this is borne out experimentally, this implies that the strange metal is less orthogonal to a Fermi liquid than the pseudogap is. Within the Wilsonian reduction of the Hubbard model, this result is explained in terms of a composite-particle picture. Namely, the pseudogap corresponds to a confinement transition of the charge degrees of freedom present in the strange metal. In the strange metal the composite excitations break up and electron quasiparticles scatter off bosons. The bosons here, however, do not arise from phonons but from the charge degrees of freedom responsible for dynamical spectral weight transfer. [ABSTRACT FROM AUTHOR]

We study thermoelectric transport at low temperatures in correlated Kondo insulators, motivated by the recent observation of a high thermoelectric figure of merit (ZT) in FeSb2 at T∼10K [ A. Bentien et al. Eur. Phys. Lett. 80 17008 (2007)]. Even at room temperature, correlations have the potential to lead to high ZT, as in YbAl3, one of the most widely used thermoelectric metals. At low temperature correlation effects are especially worthy of study because fixed band structures are unlikely to give rise to the very small energy gaps Eg∼5 kT necessary for a weakly correlated material to function efficiently at low temperature. We explore the possibility of improving the thermoelectric properties of correlated Kondo insulators through tuning of crystal-field and spin-orbit coupling and present a framework to design more efficient low-temperature thermoelectrics based on our results. [ABSTRACT FROM AUTHOR]

Two remarkable features emerge from the exact Wilsonian procedure for integrating out the high-energy scale in the Hubbard model. At low energies, the number of excitations mat couple minimally to the electromagnetic gauge is less than the conserved charge, thereby implying a breakdown of Fermi liquid theory. In addition, two charge e excitations emerge in the lower band, the standard projected electron and a composite entity (comprised of a hole and a charge 2e bosonic field), which give rise to poles and zeros of the single-particle Green function, respectively. The poles generate spectral weight along an arc centered at (π/2,π/2), while the zeros kill the spectral intensity on the back side of the arc. The result is the Fermi arc structure intrinsic to cuprate phenomenology. The presence of composite excitations also produces a broad incoherent pseudogap feature at the (π,Ο) region of the Brillouin zone, thereby providing a mechanism for the nodal/antinodal dichotomy seen in the cuprates. [ABSTRACT FROM AUTHOR]