Hidden charge-2eboson: Experimental consequences for doped Mott insulators

Abstract

We show here that many of the normal state properties of the cuprates can result from the new charge 2e bosonic field which we have recently ͓Phys. Rev. Lett. 99, 046404 ͑2007͒; Phys. Rev. B 77, 014512 ͑2007͔͒ shown to exist in the exact low-energy theory of a doped Mott insulator. In particular, the ͑1͒ midinfrared band including the nonvanishing of the restricted f-sum rule in the Mott insulator, ͑2͒ T 2 contribution to the thermal conductivity, ͑3͒ pseudogap, ͑4͒ bifurcation of the electron spectrum below the chemical potential, as recently seen in angle-resolved photoemission, ͑5͒ insulating behavior away from half-filling, ͑6͒ high-and low-energy kinks in the electron dispersion, and ͑7͒ T-linear resistivity all derive from the charge 2e bosonic field. We also calculate the inverse dielectric function and show that it possesses a sharp quasiparticle peak and a broad particle-hole continuum. The sharp peak is mediated by a new charge e composite excitation formed from the binding of a charge 2e boson and a hole and represents a distinctly new prediction of this theory. It is this feature that is responsible for the dynamical part of the spectral weight transferred across the Mott gap. We propose that electron-energy loss spectroscopy at finite momentum and frequency can be used to probe the existence of such a sharp feature.

Spectral kinks and mid-infrared optical conductivity of doped Mott insulators from strong electron correlations

“…Our result that the mid-IR is caused by a single state ͑of the 256 plaquette states͒ that has d x 2 −y 2 symmetry is striking and indicates that the mid-IR is likely to be caused by the same physics that underlies the pseudogap as optics experiments seem to indicate. 14 Further, the mechanism identified here, which is identical to that mediated by the charge 2e boson in the exact low-energy theory of the Hubbard model [28][29][30] ͑Fig. 6͒, could explain why an extrapolated nonzero intercept of the restricted f-sum rule might be a generic feature of doped Mott insulators, in contrast to recent claims.…”

“…Consequently, the kink we have found here does not have a simple interpretation in terms of spin fluctuations as such a scenario would not require the explicitly doubly occupied sector. A kink arising from an explicit mixing between singly and doubly occupied sectors with S = 1 is consistent, however, with the physics mediated by the charge 2e boson [28][29][30] that appears in the exact low-energy theory of a doped Mott insulator modeled by the Hubbard model. Excitation of the boson, which mediates mixing with all the doubly occupied sectors, occurs on the energy scale t 2 / U.…”

“…In a series of recent papers [28][29][30] we formulated the exact low-energy theory of a doped Mott insulator and showed that another excitation emerges at low energies. The excitation is a charge 2e boson which is not made out of elemental excitations.…”

Two-fluid model of the pseudogap of high-temperature cuprate superconductors based on charge-2ebosons

“…By contrast, our explanation of the two fluids relies entirely on the strong correlations of a doped Mott insulator, that is, Mottness. Here we show that the exact low-energy theory of a doped Mott insulator [14][15][16] described by the Hubbard model naturally resolves the two-component conundrum in the cuprates. The propagating degrees of freedom that constitute the two fluids are the standard projected electron in the lower Hubbard band and a bound composite excitation composed of a charge-2e boson and a hole.…”

Preparation of Existing and Novel Superconductors using a Spatial Composition Spread Approach

“…Independent measurements of the hole concentration can be obtained by measuring the intensity of a feature located 2 eV below the O Kedge (530 eV) by X-ray absorption spectroscopy (XAS) (Kuiper et al, 1988). These measurements would not only allow us to evaluate whether this unexpected result is a truly novel feature and not simply a consequence of oxygen non-stoichiometry and/or film strain, it would also test a theory that predicts the existence of charge 2e bosons in the PG state (Leigh et al, 2007;Choy et al, 2008).…”