Anomalous relaxation kinetics and charge-density-wave correlations in underdoped BaPb1-xBixO3 [Physics]
Superconductivity often emerges in proximity of other symmetry-breaking ground states, such as antiferromagnetism or charge-density-wave
(CDW) order. However, the subtle interrelation of these phases remains poorly understood, and in some cases even the existence
of short-range correlations for superconducting compositions is uncertain. In such circumstances, ultrafast experiments can
provide new insights by tracking the relaxation kinetics following excitation at frequencies related to the broken-symmetry
state. Here, we investigate the transient terahertz conductivity of BaPb1−xBixO3––a material for which superconductivity is “adjacent” to a competing CDW phase––after optical excitation tuned to the CDW
absorption band. In insulating BaBiO3 we observed an increase in conductivity and a subsequent relaxation, which are consistent with quasiparticles injection across
a rigid semiconducting gap. In the doped compound BaBi0.72Pb0.28O3 (superconducting below TC = 7 K), a similar response was also found immediately above TC. This observation evidences the presence of a robust gap up to T
≃ 40 K, which is presumably associated with short-range CDW correlations. A qualitatively different behavior was observed in
the same material for
T≳ 40 K. Here, the photoconductivity was dominated by an enhancement in carrier mobility at constant density, suggestive of
melting of the CDW correlations rather than excitation across an optical gap. The relaxation displayed a temperature-dependent,
Arrhenius-like kinetics, suggestive of the crossing of a free-energy barrier between two phases. These results support the
existence of short-range CDW correlations above TC in underdoped BaPb1−xBixO3, and provide information on the dynamical interplay between superconductivity and charge order.
Publisher URL: http://feedproxy.google.com/~r/Pnas-RssFeedOfEarlyEditionArticles/~3/JdGyASXzPw0/1707079114.short
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