332 research outputs found
Direct Connection between Mott Insulator and d-Wave High-Temperature Superconductor Revealed by Continuous Evolution of Self-Energy Poles
The high-temperature superconductivity in copper oxides emerges when carriers
are doped into the parent Mott insulator. This well-established fact has,
however, eluded a microscopic explanation. Here we show that the missing link
is the self-energy pole in the energy-momentum space. Its continuous evolution
with doping directly connects the Mott insulator and high-temperature
superconductivity. We show this by numerically studying the extremely small
doping region close to the Mott insulating phase in a standard model for
cuprates, the two-dimensional Hubbard model. We first identify two relevant
self-energy structures in the Mott insulator; the pole generating the Mott gap
and a relatively broad peak generating the so-called waterfall structure, which
is another consequence of strong correlations present in the Mott insulator. We
next reveal that either the Mott-gap pole or the waterfall structure (the
feature at the energy closer to the Fermi level) directly transforms itself
into another self-energy pole at the same energy and momentum when the system
is doped with carriers. The anomalous self-energy yielding the
superconductivity is simultaneously born exactly at this energy-momentum point.
Thus created self-energy pole, interpreted as arising from a hidden fermionic
excitation, continuously evolves upon further doping and considerably enhances
the superconductivity. Above the critical temperature, the same self-energy
pole generates a pseudogap in the normal state. We thus elucidate a unified
Mott-physics mechanism, where the self-energy structure inherent to the Mott
insulator directly gives birth to both the high-temperature superconductivity
and pseudogap.Comment: 14 pages, 18 figure
Doped high-Tc cuprate superconductors elucidated in the light of zeros and poles of electronic Green's function
We study electronic structure of hole- and electron-doped Mott insulators in
the two-dimensional Hubbard model to reach a unified picture for the normal
state of cuprate high-Tc superconductors. By using a cluster extension of the
dynamical mean-field theory, we demonstrate that structure of coexisting zeros
and poles of the single-particle Green's function holds the key to understand
Mott physics in the underdoped region. We show evidence for the emergence of
non-Fermi-liquid phase caused by the topological quantum phase transition of
Fermi surface by analyzing low-energy charge dynamics. The spectra calculated
in a wide range of energy and momentum reproduce various anomalous properties
observed in experiments for the high-Tc cuprates. Our results reveal that the
pseudogap in hole-doped cuprates has a d-wave-like structure only below the
Fermi level, while it retains non-d-wave structure with a fully opened gap
above the Fermi energy even in the nodal direction due to a zero surface
extending over the entire Brillouin zone. In addition to the non-d-wave
pseudogap, the present comprehensive identifications of the spectral asymmetry
as to the Fermi energy, the Fermi arc, and the back-bending behavior of the
dispersion, waterfall, and low-energy kink, in agreement with the experimental
anomalies of the cuprates, do not support that these originate from (the
precursors of) symmetry breakings such as the preformed pairing and the
d-density wave fluctuations, but support that they are direct consequences of
the proximity to the Mott insulator. Several possible experiments are further
proposed to prove or disprove our zero mechanism.Comment: 17 pages, 15 figure
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