Optically induced lattice deformations, electronic structure changes, and enhanced superconductivity in YBa₂Cu₃O_6.48.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Underdoped cuprates (YBa₂Cu₃O_6+x) exhibit complex behavior under non-equilibrium conditions.
• Previous studies used X-ray diffraction to identify transient crystal structures after optical excitation.

Purpose of the Study:

• To theoretically predict electronic rearrangements accompanying structural deformations in photo-excited YBa₂Cu₃O_6+x.
• To link observed structural changes to electronic properties and spectral responses.

Main Methods:

• Density Functional Theory (DFT) calculations to model electronic structure.
• Analysis of transient crystal structures identified by prior femtosecond X-ray diffraction.
• Calculation of soft X-ray absorption spectra at the Copper (Cu) L-edge.
• Experimental probing using femtosecond X-ray pulses from a free electron laser.

Main Results:

• Predicted enhanced hole-doping of CuO₂ planes in the transient state.
• Calculated significant energy reduction of the empty chain Cu d_y²-z² orbital.
• Observed changes in soft X-ray absorption spectra consistent with theoretical predictions.

Conclusions:

• The study establishes a link between photo-induced structural changes and electronic rearrangements in underdoped YBa₂Cu₃O_6+x.
• Predicted electronic changes support enhanced c-axis transport and interlayer Josephson coupling.
• Experimental X-ray absorption data validate the theoretical predictions of electronic state modifications.