Crossover from Collective to Incoherent Spin Excitations in Superconducting Cuprates Probed by Detuned Resonant...

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• High-temperature superconductors exhibit complex electronic behaviors, particularly concerning spin excitations.
• Understanding these excitations is crucial for elucidating superconductivity mechanisms.

Purpose of the Study:

• Investigate spin excitations in overdoped cuprates Tl_{2}Ba_{2}CuO_{6+δ} and (Bi,Pb)_{2}(Sr,La)_{2}CuO_{6+δ}.
• Determine the evolution of spin excitations with doping and photon energy.
• Correlate RIXS findings with theoretical models and transport experiments.

Main Methods:

• Resonant Inelastic X-ray Scattering (RIXS) was employed to probe spin excitations.
• Experiments were conducted across varying doping levels and incident photon energies (detuning).
• Exact-diagonalization calculations of the single-band Hubbard model were used for theoretical comparison.

Main Results:

• At optimal doping, RIXS spectra showed a paramagnon feature, consistent with underdoped cuprates.
• Beyond optimal doping, a crossover to incoherent particle-hole excitations was observed.
• The RIXS spectra of both compound families were remarkably similar and theoretically reproduced.

Conclusions:

• A distinct change in spin excitation behavior occurs near optimal doping in these cuprates.
• The findings support the existence of a quantum phase transition near optimal doping, as suggested by transport studies.
• The single-band Hubbard model captures key aspects of the observed spin dynamics.