Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLight Bipolarons Stabilized by Peierls Electron-Phonon Coupling
101
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
It is widely accepted that phonon-mediated high-temperature superconductivity is impossible at ambient pressure, because of the very large effective masses of polarons/bipolarons at strong electron-phonon coupling. Here we challenge this belief by showing that strongly bound yet very light bipolarons appear for strong Peierls/Su-Schrieffer-Heeger interaction. These bipolarons also exhibit many other unconventional properties, e.g. at strong coupling there are two low-energy bipolaron bands that are stable against strong on-site Hubbard repulsion. Using numerical simulations and analytical arguments, we show that these properties result from the specific form of the phonon-mediated interaction, which is of pair-hopping instead of regular density-density type. This unusual effective interaction is bound to have non-trivial consequences for the superconducting state expected to arise at finite carrier concentrations, and should favor a large critical temperature.
rate research
Read More
Electron-phonon coupling (EPC) is one of the most common and fundamental interactions in solids. It not only dominates many basic dynamic processes like resistivity, thermal conductivity etc, but also provides the pairing glue in conventional superconductors. But in high-temperature superconductors (HTSC), it is still controversial whether or not EPC is in favor of paring. Despite the controversies, many experiments have provided clear evidence for EPC in HTSC. In this paper, we briefly review EPC in cuprate and iron-based superconducting systems revealed by Raman scattering. We introduce how to extract the coupling information through phonon lineshape. Then we discuss the strength of EPC in different HTSC systems and possible factors affecting the strength. The comparative study between Raman phonon theories and experiments allows us to gain insight into some crucial electronic properties, especially superconductivity. Finally we summarize and compare EPC in the two existing HTSC systems, and discuss what role it may play in HTSC.
The superconductor at the LaAlO3-SrTiO3 interface provides a model system for the study of two-dimensional superconductivity in the dilute carrier density limit. Here we experimentally address the pairing mechanism in this superconductor. We extract the electron-phonon spectral function from tunneling spectra and conclude, without ruling out contributions of further pairing channels, that electron-phonon mediated pairing is strong enough to account for the superconducting critical temperatures. Furthermore, we discuss the electron-phonon coupling in relation to the superconducting phase diagram. The electron-phonon spectral function is independent of the carrier density, except for a small part of the phase diagram in the underdoped region. The tunneling measurements reveal that the increase of the chemical potential with increasing carrier density levels off and is zero in the overdoped region of the phase diagram. This indicates that the additionally induced carriers do not populate the band that hosts the superconducting state and that the superconducting order parameter therefore is weakened by the presence of charge carriers in another band.
Electron-phonon interaction plays an important role in metals and can lead to superconductivity and other instabilities. Previous theoretical studies on superconductivity are largely based on the Migdal-Eliashberg theory, which neglects all the vertex corrections to electron-phonon coupling and breaks down in many unconventional superconductors. Here, we go beyond the Migdal-Eliashberg approximation and develop a nonperturbative Dyson-Schwinger equation approach to deal with the superconducting transition. Remarkably, we take into account all the vertex corrections by solving two coupled Ward-Takahashi identities derived from two global U(1) symmetries and rigorously prove that the fully renormalized electron propagator satisfies a self-closed integral equation that is directly amenable to numerical computations. Our approach works equally well in the weak and strong coupling regimes and provides an efficient method to determine superconducting $T_c$ and other quantities. As an application, our approach is used to investigate the high-$T_c$ superconductivity in one-unit-cell FeSe/SrTiO$_3$.
High-temperature (high-Tc) superconductivity in the copper oxides arises from electron or hole doping of their antiferromagnetic (AF) insulating parent compounds. The evolution of the AF phase with doping and its spatial coexistence with superconductivity are governed by the nature of charge and spin correlations and provide clues to the mechanism of high-Tc superconductivity. Here we use a combined neutron scattering and scanning tunneling spectroscopy (STS) to study the Tc evolution of electron-doped superconducting Pr0.88LaCe0.12CuO4-delta obtained through the oxygen annealing process. We find that spin excitations detected by neutron scattering have two distinct modes that evolve with Tc in a remarkably similar fashion to the electron tunneling modes in STS. These results demonstrate that antiferromagnetism and superconductivity compete locally and coexist spatially on nanometer length scales, and the dominant electron-boson coupling at low energies originates from the electron-spin excitations.
The pseudogap, d-wave superconductivity and electron-boson coupling are three intertwined key ingredients in the phase diagram of the cuprates. Sr$_2$IrO$_4$ is a 5d-electron counterpart of the cuprates in which both the pseudogap and a d-wave instability have been observed. Here, we report spectroscopic evidence for the presence of the third key player in electron-doped Sr$_2$IrO$_4$: electron-boson coupling. A kink in nodal dispersion is observed with an energy scale of ~50 meV. The strength of the kink changes with doping, but the energy scale remains the same. These results provide the first noncuprate platform for exploring the relationship between the pseudogap, d-wave instability and electron-boson coupling in doped Mott insulators.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
