Spatially-resolved relaxation dynamics of photoinduced quasiparticles in underdoped YBa$sub 2$Cu$sub 3$O$sub {7-delta}$

TL;DR

This study uses polarized femtosecond spectroscopy to investigate the spatially-resolved relaxation dynamics of photoinduced quasiparticles in underdoped YBCO, revealing divergence of relaxation time at Tc and supporting a recombination-dominant QP dynamics scenario.

Contribution

It provides new insights into the spatially-resolved quasiparticle relaxation processes and the role of temperature-dependent and independent gaps in underdoped YBCO.

Findings

Relaxation time diverges at Tc along the b axis.

Relaxation time increases monotonically with decreasing T above Tc.

Supports a recombination-dominant scenario for quasiparticle dynamics.

Abstract

The spatially-resolved relaxation characteristics of photoinduced quasiparticles (QPs) in CuO$sub 2$ planes of underdoped YBCO are disclosed by polarized fs time-resolved spectroscopy. The relaxation time (tau) along b axis diverges at Tc, and appears to be governed by a temperature-dependent gap Delta(T) at T < Tc. Furthermore, for T > Tc, a monotonic increase of tau with decreasing T along the b axis and ab diagonal was observed and can be attributed to a temperature-independent gap Delta$sub p$. The results lend support to recombination dominant scenario of QP dynamics. However, the QP thermalization may take part along the nodal direction in the highly underdoped samples.