Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userDoping-Induced Alterations in Electronic Structure of Copper Oxide Superconductors and a New Horizon for Higher Tc materials
84
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
By paying special attention to the fact that the doped holes induce deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors, we develop a non-rigid band theory treating doping-induced alterations of energy-band structures in copper oxide superconductors. Thanks to this theory, we obtain a complete picture of the doping-induced alteration in the electronic structure of La2CuO4, from the spin-disordered insulating phase to the metallic phase. We conclude that the Fermi surface structure of this cuprate in the underdoped region consists of Fermi pockets in the antinodal region and Fermi arcs in the nodal region, and thus that the origin of a so-called pseudogap is closely related to the existence of Fermi pockets. Moreover, we show that the carriers on the Fermi pockets contribute to the phonon mechanism in d-wave superconductivity. Finally, we discuss how one will be able to find higher Tc materials, based on the conclusions mentioned above.
rate research
Read More
Mechanism of unconventional superconductivity is still unknown even if more than 25 years have been passed since the discovery of high-Tc cuprate superconductors by J.G. Bednorz and K. A. Muller. Here, we explore the cuprate phase diagram by electronic Raman spectroscopy and shed light on the superconducting state in hole doped cuprates. Namely, how superconductivity and the critical temperature Tc are impacted by the pseudogap.
An outstanding problem in the field of high-transition-temperature (high Tc) superconductivity is the identification of the normal state out of which superconductivity emerges in the mysterious underdoped regime. The normal state uncomplicated by thermal fluctuations is effectively accessed by the use of applied magnetic fields sufficiently strong to suppress long-range superconductivity at low temperatures. Proposals in which the normal ground state is characterised by small Fermi surface pockets that exist in the absence of symmetry breaking have been superseded by models based on the existence of a superlattice that breaks the translational symmetry of the underlying lattice. Recently, a charge superlattice model that positions a small electron-like Fermi pocket in the vicinity of the nodes (where the superconducting gap is minimum) has been proposed a replacement for the prevalent superlattice models that position the Fermi pocket in the vicinity of the pseudogap at the antinodes (where the superconducting gap is maximum). Although some ingredients of symmetry breaking have been recently revealed by crystallographic studies, their relevance to the electronic structure remains unresolved. Here we report angle-resolved quantum oscillation measurements in the underdoped copper oxide YBa2Cu3O6+x. These measurements reveal a normal ground state comprising electron-like Fermi surface pockets located in the vicinity of the superconducting gap minima (or nodes), and further point to an underlying superlattice structure of low frequency and long wavelength with features in common with the charge order identified recently by complementary spectroscopic techniques.
In the pseudogap state of the high-Tc copper-oxide (cuprate) superconductors, angle-resolved photoemission (ARPES) measurements have seen an Fermi arc, i.e., an open-ended gapless section in the large Fermi surface, rather than a closed loop expected of an ordinary metal. This is all the more puzzling because Fermi pockets (small closed Fermi surface features) have been suggested from recent quantum oscillation measurements. The Fermi arcs have worried the high-Tc community for many years because they cannot be understood in terms of existing theories. Theorists came up with a way out in the form of conventional Fermi surface pockets associated with competing order, with a back side that is for detailed reasons invisible by photoemission. Here we report ARPES measurements of La-Bi2201 that give direct evidence of the Fermi pocket. The charge carriers in the pocket are holes and the pockets show an unusual dependence upon doping, namely, they exist in underdoped but not overdoped samples. A big surprise is that these Fermi pockets appear to coexist with the Fermi arcs. This coexistence has not been expected theoretically and the understanding of the mysterious pseudogap state in the high-Tc cuprate superconductors will rely critically on understanding such a new finding.
It has recently been proposed that the Fermi surface of underdoped high Tc copper oxide materials within the charge-ordered regime consists of a diamond-shaped electron pocket constructed from arcs connected at vertices. We show here that on modeling the in-plane magnetotransport of such a Fermi surface using the Shockley-Chambers tube integral approach and a uniform scattering time, several key features of the normal state in-plane transport of the underdoped copper oxide systems can be understood. These include the sign reversal in the Hall coefficient, the positive magnetoresistance and magnetic quantum oscillations in the Hall coefficient.
High temperature superconducting materials have been known since the pioneering work of Bednorz and Mueller in 1986. While the microscopic mechanism responsible for high Tc superconductivity is still debated, most materials showing high Tc contain highly electronic polarizable ions, suggesting that the mechanism driving high Tc superconductivity can be related to the ion electronic polarizability in high Tc materials. Here we show that a free charge carrier polarizes the ions surrounding it and the total electrical potential generated by the charge carrier itself and the polarized ions becomes attractive in some regions of space. Our results on bulk FeSe, monolayer FeSe on SrTiO3 and La2CuO4 are in excellent agreement with the experiments. The fact that the electronic polarizability explains correctly and quantitatively the superconductivity parameters: Tc, gap and paring energies of both pnictides and cuprates with similar polarizability parameters, suggests that the same model may be applicable to other material systems within these groups as well as other high Tc groups.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
