Nonlinear lattice dynamics as a basis for enhanced superconductivity in YBa2Cu3O6.5

TL;DR

This study demonstrates that nonlinear lattice excitations in YBa2Cu3O6.5 can transiently induce a state resembling superconductivity at room temperature by altering the crystal structure and electronic properties.

Contribution

The paper combines femtosecond X-ray diffraction and ab initio calculations to reveal how nonlinear lattice dynamics can enhance superconductivity in a complex oxide.

Findings

Transient superconductivity-like state observed at room temperature.

Lattice excitations cause structural changes that modify electronic properties.

Enhanced in-plane electronic dx2-y2 character favors superconductivity.

Abstract

THz-frequency optical pulses can resonantly drive selected vibrational modes in solids and deform their crystal structure. In complex oxides, this method has been used to melt electronic orders, drive insulator to metal transitions or induce superconductivity. Strikingly, coherent interlayer transport strongly reminiscent of superconductivity can be transiently induced up to room temperature in YBa2Cu3O6+x. By combining femtosecond X-ray diffraction and ab initio density functional theory calculations, we determine here the crystal structure of this exotic non-equilibrium state. We find that nonlinear lattice excitation in normal-state YBa2Cu3O6+x at 100 K causes a staggered dilation/contraction of the Cu-O2 intra/inter- bilayer distances, accompanied by anisotropic changes in the in-plane O-Cu-O bond buckling. Density functional theory calculations indicate that these motions cause dramatic changes in the electronic structure. Amongst these, the enhancement in the dx2-y2 character of the in-plane electronic structure is likely to favor superconductivity.