Fluctuating charge-density waves in a cuprate superconductor

Abstract

Cuprate materials hosting high-temperature superconductivity (HTS) also exhibit various forms of charge and spin ordering1, 2, 3, 4, 5, 6 whose significance is not fully understood7. So far, static charge-density waves8 (CDWs) have been detected by diffraction probes only at particular doping levels9, 10, 11 or in an applied external field12 . However, dynamic CDWs may also be present more broadly and their detection, characterization and relationship with HTS remain open problems. Here we present a method based on ultrafast spectroscopy to detect the presence and measure the lifetimes of CDW fluctuations in cuprates. In an underdoped La[subscript 1.9]Sr[subscript 0.1]CuO4 film (T[subscript c] = 26 K), we observe collective excitations of CDW that persist up to 100 K. This dynamic CDW fluctuates with a characteristic lifetime of 2 ps at T = 5 K that decreases to 0.5 ps at T = 100 K. In contrast, in an optimally doped La[subscript 1.84]Sr[subscript 0.16]CuO[subscript ]4 film (T[subscript c] = 38.5 K), we detect no signatures of fluctuating CDWs at any temperature, favouring the competition scenario. This work forges a path for studying fluctuating order parameters in various superconductors and other materials.