Three-dimensional collective charge excitations in electron-doped copper oxide superconductors

Abstract

High temperature cuprate superconductors consist of stacked CuO2 planes, with primarily two dimensional electronic band structures and magnetic excitations [1,2], while superconducting coherence is three dimensional. This dichotomy highlights the importance of out-of-plane charge dynamics, believed to be incoherent in the normal state [3,4], yet lacking a comprehensive characterization in energy-momentum space. Here, we use resonant inelastic x-ray scattering (RIXS) with polarization analysis to uncover the pure charge character of a recently discovered collective mode in electron-doped cuprates [5-7]. This mode disperses along both the in-and, importantly, out-of-plane directions, revealing its three dimensional nature. The periodicity of the out-of-plane dispersion corresponds to the CuO2 plane distance rather than the crystallographic c-axis lattice constant, suggesting that the interplane Coulomb interaction drives the coherent out-of-plane charge dynamics. The observed properties are hallmarks of the long-sought acoustic plasmon, predicted for layered systems [8-13] and argued to play a substantial role in mediating high temperature superconductivity [13-15]. The charge dynamics of systems with periodically stacked quasi-two dimensional (2D) conducting planes are drastically affected in the presence of poorly screened interplane Coulomb interactions. In a simple layered electron gas model with conducting planes separated by dielectric spacers [8-10], the dispersion of plasmons, the collective electronic modes of the charge dynamics, evolves from optical-like to acoustic-like as a function of out-of-plane momentum qz [Fig. 1(a)], a behavior distinct from that in either pure 2D or isotropic 3D systems.For superconducting cuprates, similar charge dynamics have been postulated since they consist of conducting CuO2 planes stacked along the c-axis with poor out-of-plane screening [11][12][13]. While plasmons were observed in various spectroscopic studies at the Brillouin zone center [4,16,17] and by transmission electron energy loss spectroscopy (EELS) typically exploring in-plane

Screening of Coulomb interactions in holography

“…However, for p = 0, we obtain an 'acoustic plasmon', with a linear low-energy dispersion relation with a renormalized speed of sound. These results show that the model qualitatively reproduces recent experimental results [20]. This suggests that the Coulomb interaction between layers might play a key role in high-temperature cuprate superconductors, proving the necessity of incorporating this interaction in holographic models if we want to study properties of these layered high-T c materials.…”

“…A recent example of the interest in these multilayered systems is given in ref. [20], where the spectral function for a layered copperoxide high-temperature superconductor has been measured. These experimental results suggest that it is indeed the Coulomb interaction that governs the coupling between different layers, validating the assumptions of our toy model, and hinting at the fact that low-energy charge fluctuations might be very relevant for the description of the dynamics of high-T c superconductors.…”

Bioinspired Metamaterials: Multibands Electromagnetic Wave Adaptability and Hydrophobic Characteristics

“…It has long been known that radar and infrared stealth performance are contradictory in one material; on the one hand, radar stealth needs to absorb as much EMWs (GHz) as possible to reduce the radar cross section (RCS); on the other hand, infrared stealth needs to reflect as much EMWs (THz) as possible to reduce the infrared emissivity . For many years researchers have recognized it difficult to be achieved simply from material modification, while the bionic hierarchical MMs have solved this problem perfectly. If the micron‐scale MMs are further designed to photonic crystals and the bandgap is made within the wavelength range of 3–22 µm, that infrared emissivity can be further reduced and compatible with radar stealth of the hierarchical MMs, which is the content that need to be explored in the future.…”

Holographic fundamental matter in multilayered media

“…The most notable examples of layered systems are the copper oxides and high-T c superconductors in general. Although the attention is usually focused on the physics along the layers, relevant information is also associated with the dynamics in the orthogonal directions [1]. This motivates the quest for theoretical models which can simultaneously capture the whole in-/off-plane behavior of multilayered systems.…”

“…To describe the strongly-coupled physics of fundamental matter, we resort to AdS/CFT and consider a top-down intersecting D-brane construction. 1 The most natural intersecting D-brane configuration is the D3-D5-brane construction of [18,19]. In this setup the layer associated with directions along the (2 + 1)-dimensional D5-brane worldvolume introduces a co-dimension one defect in the ambient (3 + 1)-dimensional N = 4 super Yang-Mills theory.…”