Article

# Particle–hole symmetry breaking in the pseudogap state of Bi2201

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(Impact Factor: 20.15). 06/2010; 6(6). DOI: 10.1038/nphys1632
Source: arXiv

ABSTRACT In conventional superconductors, a gap exists in the energy absorption
spectrum only below the transition temperature (Tc), corresponding to
the price to pay in energy for breaking a Cooper pair of electrons and
creating two excited states. In high-Tc cuprate superconductors above Tc
but below a temperature T*, an energy gap called the
pseudogap exists, and is controversially attributed either to pre-formed
superconducting pairs, which would show particle-hole symmetry, or to
competing phases that would typically break it. Scanning tunnelling
microscopy (STM) studies suggest that the pseudogap stems from lattice
translational symmetry breaking and is associated with a different
characteristic spectrum for adding or removing electrons (particle-hole
asymmetry; refs 2, 3). However, no signature of either energy or spatial
symmetry breaking of the pseudogap has previously been observed by
angle-resolved photoemission spectroscopy (ARPES). Here we report ARPES
data from Bi2201, which reveal both particle-hole symmetry breaking and
pronounced spectral broadening-indicative of spatial symmetry breaking
without long-range order at the opening of the pseudogap. Our finding
supports the STM proposal that the pseudogap state is a broken-symmetry
state that is distinct from homogeneous superconductivity.

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Available from: Zahid Hussain, Sep 29, 2015
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• "Our routine sets the in-gap points of Σ eff (ω) to zero and computes the transformation by Fast Fourier transform assuming electronhole symmetry. We have verified by simulations that a possible violation of electron-hole symmetry [16] should not significantly alter the findings here. We note that Eq. 1 is a conventional definition of Σ eff . "
##### Article: Large momentum-dependence of the main dispersion "kink" in the high-Tc superconductor Bi2Sr2CaCu2O8+{\delta}
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ABSTRACT: Ultrahigh resolution angle-resolved photoemission spectroscopy with low-energy photons is used to study the detailed momentum dependence of the well-known nodal "kink" dispersion anomaly of Bi2Sr2CaCu2O8+{\delta}. We find that the kink's location transitions smoothly from a maximum binding energy of about 65 meV at the node of the d-wave superconducting gap to 55 meV roughly one-third of the way to the antinode. Meanwhile, the self-energy spectrum corresponding to the kink dramatically sharpens and intensifies beyond a critical point in momentum space. We discuss the possible bosonic spectrum in energy and momentum space that can couple to the k-space dispersion of the electronic kinks.
• ##### Article: Can Magnetic Moments Due to Orbital Currents Exist in an Electron-Lattice Model of Cuprate Superconductors?
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ABSTRACT: The recent discovery of unusual magnetic modes in the CuO2 planes of high-temperature superconducting cuprates HgBa2CuO4+δ in the pseudogap phase, if confirmed, suggests the existence of a new phase of condensed matter. The present situation is controversial since recent measurements of the magnetic environment of barium atoms in YBa2Cu4O8 obtained negative results. The theoretical situation is also controversial since several theoretical studies of the same three-band Hubbard model gave conflicting results. However, the important experimental evidence of ubiquitous strong electron-lattice interaction remains to be understood and we investigate the question of whether orbital currents can exist in an electron-lattice model. We show in a simple physical picture that if a predominant mode of vibration of the oxygens is an unusual planar non-linear mode, orbital currents can be generated. Simple order of magnitude estimates of the magnetic fields generated are remarkably in agreement with an experimental measurement.
Journal of Superconductivity and Novel Magnetism 12/2014; 25(4). DOI:10.1007/s10948-011-1369-0 · 0.91 Impact Factor
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##### Article: Modeling a striped pseudogap state
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ABSTRACT: We study the electronic structure within a system of phase-decoupled one-dimensional superconductors coexisting with stripe spin and charge density wave order. This system has a nodal Fermi surface (Fermi arc) in the form of a hole pocket and an antinodal pseudogap. The spectral function in the antinodes is approximately particle-hole symmetric contrary to the gapped regions just outside the pocket. We find that states at the Fermi energy are extended whereas states near the pseudogap energy have localization lengths as short as the inter-stripe spacing. We consider pairing which has either local d-wave or s-wave symmetry and find similar results in both cases, consistent with the pseudogap being an effect of local pair correlations. We suggest that this state is a stripe ordered caricature of the pseudogap phase in underdoped cuprates with coexisting spin-, charge-, and pair-density wave correlations. Lastly, we also model a superconducting state which 1) evolves smoothly from the pseudogap state, 2) has a signature subgap peak in the density of states, and 3) has the coherent pair density concentrated to the nodal region. Comment: 12 pages, 12 figures, extended discussion, added references; v3, added figure of antinodal spectra for normal/pseudo/sc states
Physical review. B, Condensed matter 10/2009; 81(2). DOI:10.1103/PhysRevB.81.024501 · 3.66 Impact Factor