Gapped Collective Charge Excitations and Interlayer Hopping in Cuprate Superconductors

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Cuprate superconductors exhibit complex electronic properties crucial for technological applications.
• Understanding charge dynamics, particularly plasmon behavior, is key to elucidating superconductivity mechanisms.

Purpose of the Study:

• To investigate plasmon propagation in the electron-doped cuprate superconductor Sr_{0.9}La_{0.1}CuO_{2} using resonant inelastic x-ray scattering (RIXS).
• To determine if a plasmon gap exists and characterize its properties.
• To explore the relationship between plasmon gap size and material parameters like interlayer hopping.

Main Methods:

• Resonant inelastic x-ray scattering (RIXS) was employed to probe plasmon excitations.
• Experimental data was analyzed and compared with theoretical calculations using the layered t-J-V model.

Main Results:

• A significant plasmon gap of approximately 120 meV was detected at the two-dimensional Brillouin zone center in Sr_{0.9}La_{0.1}CuO_{2}.
• The observed plasmon dispersion, including the gap, was well-reproduced by the layered t-J-V model.
• Analysis of other cuprate data suggests the plasmon gap is a generic feature, correlated with interlayer hopping (t_{z}).

Conclusions:

• Low-energy plasmons in Sr_{0.9}La_{0.1}CuO_{2} are not strictly acoustic due to the observed gap.
• The study highlights the three-dimensionality of charge dynamics in layered cuprates.
• RIXS provides a novel method for determining the interlayer hopping parameter (t_{z}) in these materials.