Metal-insulator (fermion-boson)-crossover origin of pseudogap phase of cuprates I: anomalous heat conductivity, insulator resistivity boundary, nonlinear entropy

Abstract

Among all the experimental observations of cuprate physics, the metal-insulator-crossover (MIC), seen in the pseudogap (PG) region of the temperature-doping phase diagram of copper-oxides under a strong magnetic field when the superconductivity is suppressed, is most likely the most intriguing one. Since it was expected that the PG-normal state for these materials, as for conventional superconductors, is conducting. This MIC, revealed in such phenomena as heat conductivity downturn, anomalous Lorentz ratio, insulator resistivity boundary, nonlinear entropy, resistivity temperature upturn, insulating ground state, nematicity-and stripe-phases and Fermi pockets, unambiguously indicates on the insulating normal state, from which high-temperature superconductivity (HTS) appears. In the present work (article I), we discuss the MIC phenomena mentioned in the title of article. The second work (article II) will be devoted to discussion of other listed above MIC phenomena and also to interpretation of the recent observations in the hidden magnetic order and scanning tunneling microscopy (STM) experiments spin and charge fluctuations as the intra PG and HTS pair ones. We find that all these MIC (called in the literature as non-Fermi liquid) phenomena can be obtained within the Coulomb single boson and single fermion two liquid model, which we recently developed, and the MIC is a crossover of single fermions into those of single bosons. We show that this MIC originates from bosons of Coulomb two liquid model and fermions, whose origin is these bosons. At an increase of doping up to critical value or temperature up to PG boundary temperature, the boson system undegoes bosonic insulator -bosonic metal -fermionic metal transitions.Keywords: high critical temperature superconductivity, cuprate, metal-insulator-crossover, temperature-doping phase diagram, anomalous heat conductivity, insulator resistivity boundary, nonlinear entropy.

Normal state pair nematicity and hidden magnetic order and metal-insulator (fermionboson) crossover origin of pseudogap phase of cuprates II

“…[6]) we have shown that these non-Landau Fermi liquid behaviors of the low-T heat conductivity and Lorentz ratio are results of the MIC property of the cuprate PG regions, in which the IGS originates from a plasmon gas of 2D charged single bosons, pinned by a ferroelectric field of parent compound atoms (see also previous section). In this section, we show that the downturn T dependence carries the important information on the low-T scale of the MIC charge conductivity or resistivity.…”

“…Then, the bosonic insulator -bosonic metal transition can experimentally be observed at a point for this frequency when it goes to zero. Physically, this transition corresponds to the changing of the charged boson gas elementary excitation spectrum from a plasmon part into a free particle one [6].…”

“…This behavior, called in the literature as downturn, has also been observed in the other hole-doped copper-oxides (see for references Refs. [6,7]). The measurement of κ was performed in these hole-doped copper-oxides likewise after suppression of the HTS by a strong magnetic field.…”

“…For the HTS cuprates (copper-oxides), the normal PG state exhibits highly non-Fermi liquid properties (see, for example, our papers: I [6] and [7], for a comprehensive list of references) and it is unclear whether QPs defined in the momentum space are essential for the PG physics or not. However, as it will be shown in this paper, the real space PG pairs mentioned above and observed in the STM experiment are essential for an understanding of this physics.…”

“…In our first paper I [6] we gained an understanding of the following observed MIC phenomena: heat conductivity downturn, anomalous Lorentz ratio, insulator resistivity boundary, and nonlinear entropy. In the present paper (II), we will try to understand of other observed MIC phenomena: IGS, nematicity-and stripe-phases, Fermi pockets evolution, and resistivity temperature upturn.…”