Acoustic plasmons and conducting carriers in hole-doped cuprate superconductors

Amol Singh^1*, H. Y. Huang¹, Christopher Lane^2,3, J. H. Li⁴, J. Okamoto¹, S. Komiya⁵, Robert S. Markiewicz⁶, Arun Bansil⁶, A. Fujimori^7,1, C. T. Chen¹, D. J. Huang^1,4

¹1National Synchrotron Radiation Research Center, Hsinchu, Taiwan
²Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
³Center for Integrated Nanotechnologies, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
⁴Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan
⁵Central Research Institute of Electric Power Industry, Yokosuka, Kanagawa, 240-0196, Japan
⁶Physics Department, Northeastern University, Boston, Massachusetts 02115, USA
⁷Department of Applied Physics, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan

* Presenter:Amol Singh, email:rrcat.amol@gmail.com

The superconductivity of cuprates, which has been a mystery ever since its discovery decades ago, is created through doping electrons or holes into a Mott insulator. There, however, exists an inherent electron-hole asymmetry in cuprates. The layered crystal structures of cuprates enable collective charge excitations fundamentally different from those of three-dimensional metals, i.e., acoustic plasmons. Acoustic plasmons have been recently observed in electron-doped cuprates by resonant inelastic X-ray scattering (RIXS); in contrast, there is no evidence for acoustic plasmons in hole-doped cuprates, despite extensive measurements. This contrast led us to investigate whether the doped holes in cuprates La_2-xSr_xCuO₄ are conducting carriers or are too incoherent to induce collective charge excitation. Here we present momentum-resolved RIXS measurements and calculations of collective charge response via the loss function to reconcile the aforementioned issues. Our results provide unprecedented spectroscopic evidence for the acoustic plasmons and long-sought conducting p holes in hole-doped cuprates.

Keywords: Acoustic plasmons, Superconductivity, RIXS, Cuprates