Coherent c-axis transport in the underdoped cuprate superconductor YBCO

TL;DR

This study reveals a transition from incoherent to coherent c-axis transport in underdoped YBCO, linking Fermi surface reconstruction, stripe order, and metallic behavior at low temperatures.

Contribution

It demonstrates the emergence of three-dimensional coherence in underdoped YBCO and connects it to Fermi surface reconstruction and stripe order phenomena.

Findings

Crossover from insulating-like to metallic c-axis resistivity at low temperature

Coherence temperature aligns with quantum oscillation splitting

Fermi surface reconstruction linked to stripe order produces 3D metallicity

Abstract

The electrical resistivity rho_c of the underdoped cuprate superconductor YBCO was measured perpendicular to the CuO_2 planes on ultra-high quality single crystals in magnetic fields large enough to suppress superconductivity. The incoherent insulating-like behavior of rho_c at high temperature, characteristic of all underdoped cuprates, is found to cross over to a coherent regime of metallic behavior at low temperature. This crossover coincides with the emergence of the small electron pocket detected in the Fermi surface of YBCO via quantum oscillations, the Hall and Seebeck coefficients and with the detection of a unidirectional modulation of the charge density as seen by high-field NMR measurements. The low coherence temperature is quantitatively consistent with the small hopping integral t_perp inferred from the splitting of the quantum oscillation frequencies. We conclude that the Fermi-surface reconstruction in YBCO at dopings from p = 0.08 to at least p = 0.15, attributed to stripe order, produces a metallic state with 3D coherence deep in the underdoped regime.