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تسجيل مستخدم جديدDynamic spin-response function of the high-temperature Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ superconductor form angle resolved photoemission spectra
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We introduce a formalism for calculating dynamic response functions using experimental single particle Greens functions derived from angle resolved photoemission spectroscopy (ARPES). As an illustration of this procedure we estimate the dynamic spin response of the cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$. We find good agreement with superconducting state neutron data, in particular the $(pi,pi)$ resonance with its unusual `reversed magnon dispersion. We anticipate our formalism will also be of useful in interpreting results from other spectroscopies, such as optical and Raman responses.
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Establishing the presence and the nature of a quantum critical point in their phase diagram is a central enigma of the high-temperature superconducting cuprates. It could explain their pseudogap and strange metal phases, and ultimately their high sup
erconducting temperatures. Yet, while solid evidences exist in several unconventional superconductors of ubiquitous critical fluctuations associated to a quantum critical point, in the cuprates they remain undetected until now. Here using symmetry-resolved electronic Raman scattering in the cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$, we report the observation of enhanced electronic nematic fluctuations near the endpoint of the pseudogap phase. While our data hint at the possible presence of an incipient nematic quantum critical point, the doping dependence of the nematic fluctuations deviates significantly from a canonical quantum critical scenario. The observed nematic instability rather appears to be tied to the presence of a van Hove singularity in the band structure.
We report tunneling spectra of near optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ intrinsic Josephson junctions with area of 0.09 $mu$m$^2$, which avoid some fundamental difficulties in the previous tunneling experiments and allow a stable temper
ature-dependent measurement. A d-wave Eliashberg analysis shows that the spectrum at 4.2 K can be well fitted by considering electron couplings to a bosonic magnetic resonance mode and a broad high-energy continuum. Above $T_c$, the spectra show a clear pseudogap that persists up to 230 K, and a crossover can be seen indicating two different pseudogap phases existing above $T_c$. The intrinsic electron tunneling nature is discussed in the analysis.
Angle resolved photoemission spectroscopy (ARPES) provides a detailed view of the renormalized band structure and, consequently, is a key to the self-energy and the single-particle Greens function. Here we summarize the ARPES data accumulated over th
e whole Brillouin zone for the optimally doped Bi$_2$Sr$_2$CaCu$_2$O$_{8-delta}$ into a parametric model of the Greens function, which we use for calculating the itinerant component of the dynamic spin susceptibility in absolute units with many-body effects taken into account. By comparison with inelastic neutron scattering (INS) data we show that the itinerant component of the spin response can account for the integral intensity of the experimental INS spectrum. Taking into account the bi-layer splitting, we explain the magnetic resonances in the acoustic (odd) and optic (even) INS channels.
Both electronic Raman scattering (ERS) and angle-resolved photoemission spectra (ARPES) revealed two energy scales for the gap in different momentum spaces in the cuprates. However, the interpretations were different, and the gap values were also dif
ferent in two experiments. In order to clarify the origin of these discrepancies, we directly compared ERS and ARPES by calculating ERS from the experimental data of ARPES through the Kubo formula. The calculated ERS spectra were in good agreement with the experimental results except for the B$_{1g}$ peak energies. The doping-dependent B$_{2g}$ peak energy was well reproduced from a doping-independent d-wave gap deduced from ARPES, by assuming a particular spectral weight distribution along the Fermi surface. The B$_{1g}$ peak energies could not be reproduced by the ARPES data. The difference between B$_{1g}$ ERS and antinodal ARPES became larger with underdoping, which implies that the effect of the pseudogap is different in these two techniques.
High-resolution laser-based angle-resolved photoemission measurements have been carried out on Bi$_2$Sr$_2$CaCu$_2$O$_{8+delta}$ (Bi2212) and Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+delta}$ (Bi2201) superconductors. Unexpected hybridization between the main ba
nd and the superstructure band in Bi2212 is clearly revealed. In the momentum space where one main Fermi surface intersects with one superstructure Fermi surface, four bands are observed instead of two. The hybridization exists in both superconducting state and normal state, and in Bi2212 samples with different doping levels. Such a hybridization is not observed in Bi2201. This phenomenon can be understood by considering the bilayer splitting in Bi2212, the selective hybridization of two bands with peculiar combinations, and the altered matrix element effects of the hybridized bands. These observations provide strong evidence on the origin of the superstructure band which is intrinsic to the CuO$_2$ planes. Therefore, understanding physical properties and superconductivity mechanism in Bi2212 should consider the complete Fermi surface topology which involves the main bands, the superstructure bands and their interactions.
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