Ultrafast transient reflectivity measurements of optimally doped Bi2+xSr2−xCaCu2O8+

Abstract

The effect of disorder in high-T c superconductors is investigated from the viewpoint of photoinduced quasiparticle (QP) dynamics, obtained through time-resolved pump-probe spectroscopy. We perform the measurements on an optimally doped (OPD) Bi 2+x Sr 2−x CaCu 2 O 8+δ (Bi2212) with an out-of-plane disorder induced by Bi-Sr substitution (x), which is present in standard Bi2212 but is not usually controlled. Based on the systematic change of the disorder with controlled x, we identify the changes in the dynamics of QP relaxation and gap formation in superconducting (SC) and pseudogap (PG) states. The onset temperature T * of the PG response increases with an increase in x, which is more significant than the slight decrease in T c . These properties are equivalently reflected in the destruction fluences of the SC and PG states. Bi-Sr substitution also accelerates relaxation times for SC and PG QPs, which can be due to the increased phonon scattering probability caused by the disorder. In contrast, the SC gap recovery observed in the strongly excited condition shows an identical fluence dependence for various x, implying that the disorder does not significantly contribute to coherent gap formation.

Optical vortex induced spatio-temporally modulated superconductivity in a high-Tc cuprate

“…2(b) 32 . This approximation yields a saturation threshold of fluence F th = 5 µJ/cm 2 , which is consistent with previously reported results 33 . Coherent quench with fundamental Gaussian beam.…”

“…2 show the results of CQ spectroscopy with a fundamental Gaussian (vortex-free beam) D-pulse at T = 8 K. We set the D-pulse fluence as F D = 240 µJ/cm 2 , which is approximately 50 times higher than F th , and the P-pulse fluence as F P = 15 µJ/cm 2 . It is important to note that the high F D for SC destruction is accompanied by an instantaneous temperature rise in the electronic system, while the steady-state temperature rise is small (<5 K) owing to the low repetition rate of the laser pulse (270 kHz) 33 . Figure 2(c) shows the transient ∆R/R as a function of t Ppr observed at typical t DP .…”

Optical vortex induced spatio-temporally modulated superconductivity in a high-Tc cuprate

“…2 (b) 31 . This approximation yields a saturation threshold of fluence F th = 5 µJ/cm 2 , which is consistent with previously reported results 32 .…”

“…Figures 2 (c1) and (c2) show the results of CQ spectroscopy with a fundamental Gaussian (vortex-free beam) D-pulse at T = 8 K. We set the D-pulse fluence as F D = 240 µJ/cm 2 , which is approximately 50 times higher than F th , and the P-pulse fluence as F P = 15 µJ/cm 2 . It is important to note that the high F D for SC destruction is accompanied by an instantaneous temperature rise in the electronic system, while the steady-state temperature rise is small (<5 K) owing to the low repetition rate of the laser pulse (270 kHz) 32 . Figure 2 (c1) shows the transient ∆R/R as a function of t Ppr observed at typical t DP .…”