The characteristic features of the renormalization of the electrons in the bilayer cuprate superconductors are investigated within the kinetic-energy driven superconductivity. It is shown that the quasiparticle excitation spectrum is split into its bonding and antibonding components due to the presence of the bilayer coupling, with each component that is independent. However, in the underdoped and optimally doped regimes, although the bonding and antibonding electron Fermi surface (EFS) contours deriving from the bonding and antibonding layers are truncated to form the bonding and antibonding Fermi arcs, almost all spectral weights in the bonding and antibonding Fermi arcs are reduced to the tips of the bonding and antibonding Fermi arcs, which in this case coincide with the bonding and antibonding hot spots. These hot spots connected by the scattering wave vectors ${\bf q}_{i} $ construct an octet scattering model, and then the enhancement of the quasiparticle scattering processes with the scattering wave vectors ${\bf q}_{i}$ is confirmed via the result of the autocorrelation of the ARPES spectral intensities. Moreover, the peak-dip-hump (PDH) structure developed in each component of the quasiparticle excitation spectrum along the corresponding EFS is directly related with the peak structure in the quasiparticle scattering rate except for at around the hot spots, where the PDH structure is caused mainly by the bilayer coupling. Although the kink in the quasiparticle dispersion is present all around EFS, when the momentum moves away from the node to the antinode, the kink energy smoothly decreases, while the dispersion kink becomes more pronounced, and in particular, near the cut close to the antinode, develops into a break separating of the fasting dispersing high-energy part of the quasiparticle excitation spectrum from the slower dispersing low-energy part.
The formula frequently used to describe the c-axis infrared response of the coupled electron-phonon system of bilayer cuprate superconductors and providing important insights into the physics of these materials has been originally obtained at the level of the phenomenological multilayer model. Here we derive it using diagrammatic perturbation theory.
We investigate the epitaxial growth of bilayer cuprate La2CaCu2O6+δusing pure ozone as an oxidant, and find that even the crystal with parent composition without cation substitution can show metallic behavior with the aid of epitaxial strain effect. The hole concentration is controlled simply by excess-oxygen doping, and the films grown under the optimum conditions exhibit superconductivity below 30 K. This is the first result on the superconductivity of bilayer La2CaCu2O6+δinduced purely by the excess oxygen.
The renormalization of the electrons in cuprate superconductors is characterized by the kink in the quasiparticle dispersion. Here the bilayer coupling effect on the quasiparticle dispersion kink in the electron-doped bilayer cuprate superconductors is studied based on the kinetic-energy-driven superconductivity. It is shown that the kink in the quasiparticle dispersion is present all around the electron Fermi surface, as the quasiparticle dispersion kink in the single-layer case. However, in comparison with the corresponding single-layer case, the kink effect in the quasiparticle dispersion a…
We present a theoretical model which accounts for recent angle resolved photoemission data in bilayer cuprate superconductors. Lineshapes and dispersions of the various bonding and antibonding features in the spectra are quantitatively reproduced. The observed dispersion anomalies are consistent with the interaction of electrons with a bosonic mode which is odd with respect to the layer indices, a unique property of the magnetic resonance observed by inelastic neutron scattering.
We report on an investigation of the redistribution of interlayer coherence in the trilayer cuprate Bi2Sr2Ca2Cu3O10. The experiment is performed under the same apical-oxygen phonon excitation discussed in the past for the bilayer cuprate YBa2Cu3O6.5. In Bi2Sr2Ca2Cu3O10, we observe a similar spectral weight loss at the transverse plasma mode resonance seen in YBa2Cu3O6.5. However, this feature is not accompanied by light-enhanced interlayer coherence that was seen in YBa2Cu3O6+x, for which the transverse plasma mode is observed at equilibrium even in the normal state. These new observations off…
The interplay between the superconducting gap and normal-state pseudogap in the bilayer cuprate superconductors is studied based on the kinetic energy driven superconducting mechanism. It is shown that the charge carrier interaction directly from the interlayer coherent hopping in the kinetic energy by exchanging spin excitations does not provide the contribution to the normal-state pseudogap in the particle-hole channel and superconducting gap in the particle-particle channel, while only the charge carrier interaction directly from the intralayer hopping in the kinetic energy by exchanging sp…
Changes of the 400 cm^{-1} peak in the c-axis conductivity of underdoped YBa2Cu3O6.6 upon application of a parallel magnetic field reported by Kojima et al. are shown to be consistent with the model where the peak is due to the superfluid. Results of our calculations of the c-axis response of bilayer compounds with well defined bilayer-split bands are presented and discussed. For moderate values of the bilayer splitting (Delta E comparable to 2Delta_{max}) the spectra of the superconducting state exhibit an additional mode which is due to the condensate and similar to the one of earlier phenom…
The highest superconducting transition temperatures in the cuprates are achieved in bilayer and trilayer systems, highlighting the importance of intralayer interactions for high Tc. It has been argued that interlayer hybridization vanishes along the nodal directions by way of a specific pattern of orbital overlap. Recent quantum oscillation measurements in bilayer cuprates have provided evidence for a residual bilayer-splitting at the nodes that is sufficiently small to enable magnetic breakdown tunneling at the nodes. Here we show that several key features of the experimental data can be unde…
Conductance-voltage characteristics of epitaxial interfaces between oxide ferromagnets and oxide superconductors have been measured as a function of temperature and magnetic field. Their functional form is similar to that predicted by theories of transport across nearly transparent contacts between highly spin-polarized ferromagnets and d-wave superconductors. However, their magnetic field dependencies scale in striking and unusual ways, challenging our current understanding. Existing theories fail to account for apparent nonequilibium effects that are natural for spin injection in such geomet…
Within the t-t'-J model, the electron spectrum and quasiparticle dispersion in doped bilayer cuprates in the normal state are discussed by considering the bilayer interaction. It is shown that the bilayer interaction splits the electron spectrum of doped bilayer cuprates into the bonding and antibonding components around the $(π,0)$ point. The differentiation between the bonding and antibonding components is essential, which leads to two main flat bands around the $(π,0)$ point below the Fermi energy. In analogy to the doped single layer cuprates, the lowest energy states in doped bilayer cupr…
Recent experimental studies have indicated novel superconducting proximity effects in thin-film heterostructures comprising ferromagnetic manganites and superconducting cuprates. To look for such effects microscopically, we performed scanning tunneling spectroscopy on La$_{2/3}$Ca$_{1/3}$MnO$_3$/YBa$_2$Cu$_3$O$_{7-δ}$ (LCMO/YBCO) bilayer thin films. $\emph{c}$-axis oriented films of varying thickness were grown on SrTiO$_{3}$ substrates using pulsed laser-ablated deposition. Heteroepitaxiality of the films was confirmed by cross-sectional transmission electron microscopy. Tunneling spectra wer…
We have studied tunneling-mediated local density of states (LDOS) of the surface layer of a bilayer cuprate, where a Zn impurity is located on the second Cu-O layer. When the tunneling strength between two Cu-O layers is larger than a critical value, the LDOS on the site just above the Zn impurity first exhibits a resonant peak near the Fermi surface. The larger the tunneling strength, the stronger the resonant peak. It is also shown that the height of the resonant peak oscillates decreasingly with the distance from the site just above the Zn impurity. The location of the resonant peak in the …
Within the t-J model, we study the charge transport in underdoped bilayer cuprates by considering the bilayer interaction. Although the bilayer interaction leads to the band splitting in the electronic structure, the qualitative behavior of the charge transport is the same as in the case of single layer cuprates. The conductivity spectrum shows a low-energy peak and the unusual midinfrared band. This midinfrared band is suppressed severely with increasing temperatures, while the resistivity in the heavily underdoped regime is characterized by a crossover from the high temperature metallic-like…
We report on results of our theoretical study of the c-axis infrared conductivity of bilayer high-Tc cuprate superconductors using a microscopic model involving the bilayer-split (bonding and antibonding) bands. An emphasis is on the gauge-invariance of the theory, which turns out to be essential for the physical understanding of the electrodynamics of these compounds. The description of the optical response involves local (intra-bilayer and inter-bilayer) current densities and local conductivities. The local conductivities are obtained using a microscopic theory, where the quasiparticles of t…
Twisting two monolayers of a high-$T_c$ cuprate superconductor can engender a chiral topological state with spontaneously broken time reversal symmetry $\mathcal{T}$. A crucial ingredient required for the emergence of a gapped topological phase is electron tunneling between the CuO$_2$ planes, whose explicit form (in an ideal clean sample) is dictated by the symmetry of the atomic orbitals. However, a large body of work on the interlayer transport in cuprates indicates importance of disorder-mediated incoherent tunneling which evades the symmetry constraints present in an idealized crystal. Th…
In cuprates, a precursor state of superconductivity is speculated to exist above the critical temperature $\mathrm{T_C}$. Here we show via a combination of far-infrared ellipsometry and ultrafast broadband optical spectroscopy that signatures of such a state can be obtained via three independent observables in an underdoped sample of NdBa$_2$Cu$_3$O$_{6+δ}$. The pseudogap correlations were disentangled from the response of laser-broken pairs by clocking their characteristic time-scales. The onset of a superconducting precursor state was found at a temperature $\mathrm{T_{ONS}}$ $>$ $\mathrm{T_…
Superconducting transition temperature is calculated for differently doped bilayer cuprates. Superexchange is assumed to be the dominating mechanism of high-temperature superconductivity, but the contribution from the phonon potential is not negligible, which qualitatively explains the observed weak isotopic effect. The calculated value 2$Δ_{max}/k_B T_C \simeq 4.5$ is close to the experiment in the case of optimum doping.
Physical effects of bilayer coupling on the tunneling spectroscopy of high T$_{c}$ cuprates are investigated. The bilayer coupling separates the bonding and antibonding bands and leads to a splitting of the coherence peaks in the tunneling differential conductance. However, the coherence peak of the bonding band is strongly suppressed and broadened by the particle-hole asymmetry in the density of states and finite quasiparticle life-time, and is difficult to resolve by experiments. This gives a qualitative account why the bilayer splitting of the coherence peaks was not clearly observed in tun…
We propose a novel heterostructure to achieve chiral topological superconductivity in 2D. A substrate with a large Rashba spin-orbit coupling energy is brought in proximity to a twisted bilayer of thin films exfoliated from a high-temperature cuprate superconductor. The combined system is then exposed to an out-of-plane magnetic field. The rare $d + id$ pairing symmetry expected to occur in such a system allows for nontrivial topology; specifically, in contrast to the case of the twisted bilayer in isolation, the substrate induces an odd Chern number. The resulting phase is characterized by th…
We propose and analyze a scheme for parametrically cooling bilayer cuprates based on the selective driving of a $c$-axis vibrational mode. The scheme exploits the vibration as a transducer making the Josephson plasma frequencies time-dependent. We show how modulation at the difference frequency between the intra- and interbilayer plasmon substantially suppresses interbilayer phase fluctuations, responsible for switching $c$-axis transport from a superconducting to resistive state. Our calculations indicate that this may provide a viable mechanism for stabilizing non-equilibrium superconductivi…
The recently observed bilayer splitting in high-T$_c$ cuprates is analyzed within a model where the charge carriers are coupled to a phenomenological bosonic spectrum which interpolates between the marginal Fermi liquid structure and collective mode type behavior as a function of temperature. We argue that the origin of the collective mode is probably associated with dynamic incommensurate charge density waves. Moreover it is shown that the resulting temperature dependence of the self-energy $Σ$ is in good agreement with $Σ$ as extracted from angle-resolved photoemission data.
A system of self-consistent integral equations for the superconducting gap is formulated and solved taking account of the instability of the normal phase of bilayered cuprates against charge-density waves. The critical parameters are calculated as a function of the wave vector, temperature, and doping index. It is found that the region in which superconductivity coexists with d-type charge-density waves depends strongly on the doping index. The effective energy-gap parameter, determined as the interval between the peaks of the density of states, can have a local minimum at temperatures T$<$T$_…
Quench of chiral superconductivity by quantum phase fluctuations in twisted cuprate bilayers
Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences（中国科学院物理研究所）；University of Chinese Academy of Sciences（中国科学院大学）；Department of Physics, The Hong Kong University of Science and Technology（香港科技大学物理系）；Songshan Lake Materials Laboratory（松山湖材料实验室）
In this paper we present a review of bosonic renormalization effects on electronic carriers observed from angle-resolved photoemission spectra in the cuprates. We specifically discuss the viewpoint that these renormalizations represent coupling of the electrons to the lattice, and review how the wide range of materials dependence, such as the number of CuO$_2$ layers, and the doping dependence can be straightforwardly understood as arising due to novel electron-phonon coupling.
Gap structure and phase diagram of twisted bilayer cuprates from a microscopic perspective
University of Florida（佛罗里达大学）；Niels Bohr Institute, University of Copenhagen（哥本哈根大学尼尔斯玻尔研究所）；Uppsala University（乌普萨拉大学）；Istituto dei Sistemi Complessi (ISC-CNR)（复杂系统研究所（意大利国家研究委员会））
Topological multicomponent superconductivity with sizable $s$-wave admixture in twisted bilayer cuprates
School of Physics, Nankai University（南开大学物理学院）；New Cornerstone Science Laboratory, Department of Physics, School of Science, Westlake University（西湖大学理学院物理学系新基石科学实验室）；Institute for Theoretical Sciences, Westlake University（西湖大学理论科学研究院）；Key Laboratory for Quantum Materials of Zhejiang Province, School of Science, Westlake University（西湖大学理学院浙江省量子材料重点实验室）；Institute of Natural Sciences, Westlake Institute for Advanced Study（西湖高等研究院自然科学研究院）
The energy needed to create a vortex core is the basic ingredient to address the physics of thermal vortex fluctuations in underdoped cuprates. Here we theoretically investigate its role on the occurrence of the Beresinskii-Kosterlitz-Thouless transition in a bilayer film with inhomogeneity. From the comparison with recent measurements of the penetration depth in two-unit cell thin films of Y$_{1-x}$Ca$_{x}$Ba$_{2}$Cu$_{3}$O$_{7-\d}$ (YBCO) by Hetel et al. [Nat. Phys. 3, 700 (2007)] we can extract the value of the vortex-core energy $μ$, and show that $μ$ scales linearly with $T_c$ at low dopi…
We study the twisted Hubbard model of a cuprate bilayer at a fixed twist angle $θ=53.13^{\circ}$ using the variational cluster approximation, a method that treats short-range dynamical correlations exactly. At intermediate interlayer tunneling, the phase difference $ϕ$ between the $d$-wave order parameters of two layers is $π$ in the overdoped regime, while it is zero in the underdoped regime, close to the Mott phase. At strong interlayer tunneling, we observe a clear time-reversal symmetry breaking phase near optimal doping, in which the phase difference $ϕ$ changes continuously from 0 to $π$…
We demonstrate that parametric driving of suitable collective modes in cuprate superconductors results in a reflectivity $R>1$ for frequencies in the low terahertz regime. We propose to exploit this effect for the amplification of coherent terahertz radiation in a laser-like fashion. As an example, we consider the optical driving of Josephson plasma oscillations in a monolayer cuprate at a frequency that is blue-detuned from the Higgs frequency. Analogously, terahertz radiation can be amplified in a bilayer cuprate by driving a phonon resonance at a frequency slightly higher than the upper Jos…
We review some previous studies concerning the intra-bilayer Josephson plasmons and present new ellipsometric data of the c-axis infrared response of almost optimally doped Bi_{2}Sr_{2}CaCu_{2}O_{8}. The c-axis conductivity of this compound exhibits the same kind of anomalies as that of underdoped YBa_{2}Cu_{3}O_{7-delta}. We analyze these anomalies in detail and show that they can be explained within a model involving the intra-bilayer Josephson effect and variations of the electric field inside the unit cell. The Josephson coupling energies of different bilayer compounds obtained from the op…
A generalized antiferromagnetic approach to the Mott transition is analyzed with special emphasis on electron doped cuprates, where evidence for electronic phase separation is weak or absent. Fluctuations are incorporated via a self-consistent renormalization, thereby deriving a `nearly-antiferromagnetic Fermi liquid' susceptibility. The calculation is sensitive to hot-spot effects. Near optimal doping, an approximately electron-hole symmetrical Mott gap collapse is found (quantum critical points). The calculation satisfies the Mermin-Wagner theorem (Neel transition at T=0 only -- unless inter…
Contrary to a widely accepted view the phase diagrams of La$_{2-x}$Sr$_x$CuO$_4$ and YBa$_2$Cu$_3$O$\rm_{6+y}$, in spite of similarities are remarkably different. Both the electric conduction properties and the commensurate/incommensurate spin ordering properties differ dramatically. It is argued that the role of disorder in YBCO is insignificant while the bilayer structure is crucial. On the other hand in LSCO the intrinsic disorder to a large extent drives the properties of the system. The developed approach explains the low-temperature magnetic properties of the systems. The most important …
With infrared spectroscopy we studied the out-of-plane ($c$-axis) response of the iron arsenide superconductor ACa$_2$Fe$_4$As$_4$F$_2$ (A = Rb,Cs) which has a bilayer structure similar to the high $T_c$ cuprates YBa$_2$Cu$_3$O$_7$ (YBCO) and Bi$_2$Sr$_2$CaCu$_2$O$_8$ (Bi2212). In analogy to the cuprates, we observe a superconductivity-induced transverse plasma mode (tPM) and a phonon anomaly that are both signatures of local electric field effects that arise from a large difference between the local conductivities in the intra- and inter-bilayer regions. Using a multilayer model developed for…
By constructing $d_{x^2-y^2}-d_{z^2}$ two-orbital models from first principles, we have obtained a systematic correlation between the Fermi surface warping and the evaluated $T_c$ for various bilayer as well as single-layer cuprates. This reveals that smaller mixture of the $d_{z^2}$ orbital component on the Fermi surface leads to both of larger Fermi surface warping and higher $T_c$. The theoretical correlation strikingly resembles a systematic plot for the experimentally observed $T_c$ against the Fermi surface warping due to Pavarini {\it et al.} [Phys. Rev. Lett. {\bf 87}, 047003 (2001)], …
We examine the effect of CuO intergrowths on the superconductivity in epitaxial La_{2/3}Ca_{1/3}MnO_3/YBa_2Cu_3O_{7-δ} (LCMO/YBCO) thin-film heterostructures. Scanning transmission electron microscopy on bilayer LCMO/YBCO thin films revealed double CuO-chain intergrowths which form regions with the 247 lattice structure in the YBCO layer. These nanoscale 247 regions do not appear in x-ray diffraction, but can physically account for the reduced critical temperature Tc of bilayer thin films relative to unilayer films with the same YBCO thickness, at least down to ~25 nm. We attribute the CuO int…
We compare the one-loop functional renormalization group results for the cuprates and the iron pnictides. Interestingly a coherent picture suggesting that antiferromagnetic correlation causes pairing for both materials emerges.
The Fourier transform of the observed magnetic quantum oscillations (MQO) in YBa$_{2}$Cu$_{3}$O$_{6+δ}$ high-temperature superconductors has a prominent low-frequency peak with two smaller neighbouring peaks. The separation and positions of these three peaks are almost independent of doping. This pattern has been explained previously by rather special, exquisitely detailed, Fermi-surface reconstruction. We propose that these MQO have a different origin, and their frequencies are related to the bilayer and inter-bilayer electron hopping rather than directly to the areas of tiny Fermi-surface po…
We study the momentum and frequency dependence of the dynamical spin susceptibility in the superconducting state of bilayer cuprate superconductors. We show that there exists a resonance mode in the odd as well as the even channel of the spin susceptibility, with the even mode being located at higher energies than the odd mode. We demonstrate that this energy splitting between the two modes arises not only from a difference in the interaction, but also from a difference in the free-fermion susceptibilities of the even and odd channels. Moreover, we show that the even resonance mode disperses d…
The puzzling features of recent photoemission data in cuprates have been object of several analysis in order to identity the nature of the underlying electron-boson interaction. In this paper we point out that many basilar assumptions of the conventional analysis as expected to fail in small Fermi energy systems when, as the cuprates, the Fermi energy $E_{\rm F}$ is comparable with the boson energy scale. We discuss in details the novel features appearing in the self-energy of small Fermi energy systems and the possible implications on the ARPES data in cuprates.
Experimental studies of the electronic structure remain the basic means for understanding the nature of high-temperature superconductivity (HTSC) and testing relevant theoretical models. Appreciable contributions to establish the overall picture in HTSC have recently been made by investigations on the charge dynamics in BSCCO (ref. 1) and the spin dynamics in YBCO, using Angle Resolved Photoemission Spectroscopy (ARPES) and Inelastic Neutron Scattering (INS), respectively. Concentration of each of these techniques on a "suitable" compound turns out to be a barrier on the way to a crucial quant…
In this paper, we review the low energy electronic structure of the kinetic energy driven d-wave cuprate superconductors. We give a general description of the charge-spin separation fermion-spin theory, where the constrained electron is decoupled as the gauge invariant dressed holon and spin. In particular, we show that under the decoupling scheme, the charge-spin separation fermion-spin representation is a natural representation of the constrained electron defined in a restricted Hilbert space without double electron occupancy. Based on the charge-spin separation fermion-spin theory, we have …
Twisted bilayers of high-$T_c$ cuprate superconductors have been argued to form topological phases with spontaneously broken time reversal symmetry ${\cal T}$ for certain twist angles. With the goal of helping to identify unambiguous signatures of these topological phases in transport experiments, we theoretically investigate a suite of Josephson phenomena between twisted layers. We find an unusual non-monotonic temperature dependence of the critical current at intermediate twist angles which we attribute to the unconventional sign structure of the $d$-wave order parameter. The onset of the ${…
Within the framework of the kinetic energy driven superconductivity, the electronic structure of bilayer cuprate superconductors in the superconducting state is studied. It is shown that the electron spectrum of bilayer cuprate superconductors is split into the bonding and antibonding components by the bilayer splitting, then the observed peak-dip-hump structure around the $[π,0]$ point is mainly caused by this bilayer splitting, with the superconducting peak being related to the antibonding component, and the hump being formed by the bonding component. The spectral weight increases with incre…
Recent angle-resolved photoemission data for overdoped Bi2212 are explained. Of the peak-dip-hump structure, the peak corresponds the $\vec q =0$ component of a hole condensate which appears at $T_c$. The fluctuating part of this same condensate produces the hump. The bilayer splitting is large enough to produce a bonding hole and an electron antibonding quasiparticle Fermi surface. Smaller bilayer splittings observed in some experiments reflect the interaction of the peak structure with quasiparticle states near, but not at, the Fermi surface.
Is it possible to increase Tc by constructing cuprate heterostructures, which combine the high pairing energy of underdoped layers with the large carrier density of proximate overdoped layers? We investigate this question within a model bilayer system using an effective theory of the doped Mott insulator. Interestingly, the question hinges on the fundamental nature of the superconducting state in the underdoped regime. Within a plain slave boson mean field theory, there is absolutely no enhancement of Tc. However, we do get a substantial enhancement for moderate inter-layer tunneling when we u…
High-temperature superconductivity confined to nanometer-size interfaces has been a long standing goal because of potential applications^{1,2} and the opportunity to study quantum phenomena in reduced dimensions^{3,4}. However, this is a challenging target: in conventional metals the high electron density restricts interface effects such as carrier depletion/accumulation to a region much narrower than the coherence length, the scale necessary for superconductivity to occur. In contrast, in copper oxides the carrier density is low while the critical temperature (T_c) is high and the coherence l…
We report a persistent low-energy phonon broadening around $q_{B} \sim 0.28$ r.l.u. along the Cu-O bond direction in the high-$T_c$ cuprate Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-2212). We show that such broadening exists both inside and outside the conventional charge density wave (CDW) phase, via temperature dependent measurements in both underdoped and heavily overdoped samples. Combining inelastic hard x-ray scattering, diffuse scattering, angle-resolved photoemission spectroscopy, and resonant soft x-ray scattering at the Cu $L_3$-edge, we exclude the presence of a CDW in the heavily overdoped…
We generalize the numerical renormalization group scheme to study the phonon-mediated retarded interactions in the high Tc cuprates. We find that three sets of phonon-mediated retarded quasiparticle scatterings grow under RG flow. These scatterings share the following common features: 1) the initial and final quasiparticle momenta are in the antinodal regions, and 2) the scattering amplitudes have a $x^2-y^2$ symmetry. All three sets of retarded interaction are driven to strong coupling by the magnetic fluctuations around $(π,π)$. After growing strong, these retarded interaction will trigger d…
The flux phase predicted by the $t-J$ model in the large-N limit exhibits features that make it a candidate for describing the pseudogap regime of cuprates. However certain properties, as for instance the prediction of well defined quasiparticle peaks, speak against this scenario. We have addressed these issues by computing self-energy renormalizations in the vicinity to flux phase. The calculated spectral functions show features similar to those observed in experiments. At low doping, near the flux phase, the spectral functions are anisotropic on the Fermi surface and very incoherent near the…
The optical conductivity and the spectral weight W(T) of two superconducting cuprates at optimum doping, Bi2Sr2-xLaxCuO6 and Bi2Sr2CaCu2O8, have been first measured up to 500 K. Above 300 K, W(T) deviates from the usual T2 behavior in both compounds, even though the zero-frequency extrapolation of the optical conductivity remains larger than the Ioffe-Regel limit. The deviation is surprisingly well described by the T4 term of the Sommerfeld expansion, but its coefficients are enhanced by strong correlation. This renormalization is due to strong correlation, as shown by the good agreement with …
The spin dynamics of bilayer cuprate compounds are studied in a basic model. The magnetic spectral properties are calculated in linear spin-wave theory for several stripe configurations which differ by the relative location of the stripes in the layers. We focus on the bilayer splitting of the magnon bands near the incommensurate low energy peaks as well as near the $π$ resonance, distinguishing between the odd and even channel. We find that a x-shaped dispersion near the $π$ resonance is generic for stripes. By comparison of our results to neutron scattering data for $\mathrm{YBa_2Cu_3O_{6+x}…
