Local lattice distortions and dynamics in extremely overdoped superconducting YSr₂Cu_2.75Mo_0.25O_7.54

Area of Science:

• Materials Science
• Condensed Matter Physics
• Superconductivity

Background:

• Overdoped cuprates prepared with high-pressure oxygen often exhibit critical temperatures (Tc) exceeding those of optimally doped compounds.
• These materials exist at the boundary of superconducting and normal Fermi liquid states, challenging conventional understanding.
• Understanding the structural and electronic properties of these overdoped cuprates is crucial for advancing high-temperature superconductivity.

Purpose of the Study:

• To investigate the structural and electronic characteristics of high-pressure oxygen (HPO) YSr2Cu2.75Mo0.25O7.54, a superconductor with Tc = 84 K.
• To elucidate the role of molybdenum substitution and nanophase separation in the observed superconducting properties.
• To analyze the influence of structural dynamics on the critical temperature in this overdoped cuprate system.

Main Methods:

• X-ray absorption fine-structure (XAFS) measurements were performed at 52 K.
• Analysis focused on the valence state and local geometry of molybdenum (Mo).
• Copper (Cu) X-ray absorption near-edge structure (XANES) was examined to probe Cu environments.

Main Results:

• Molybdenum was found to be in the Mo(VI) valence state, occupying an undistorted octahedral site with predominantly Mo neighbors, consistent with substitution at Cu chain sites.
• Minimal perturbations were observed in the copper environments, though Cu XANES differed from other cuprates.
• The primary structural deviation identified was nanophase separation into Mo- and Cu-enriched domains, alongside altered dynamical attributes and a shift in Cu-apical oxygen distribution.

Conclusions:

• Nanophase separation into Mo- and Cu-enriched domains is a key feature of HPO YSr2Cu2.75Mo0.25O7.54.
• Altered structural dynamics, including shifts in oxygen positions, may influence the high critical temperature.
• The presence of multiple Fermi surface bands due to phase separation and a lowered Fermi level could contribute to enhanced superconductivity.