Prevailing charge order in overdoped cuprates beyond the superconducting dome

Abstract

High-temperature superconductivity in cuprates is a great surprise in quantum materials and its mechanism remains a puzzle. It has been a longstanding challenge to understand how the versatile phenomena exhibited in these materials, such as the pseudogap (PG) and strange metal states, together with a plethora of exotic electronic orders, coexist and compete with superconductivity. Among them, charge order (CO) is found to be ubiquitous in underdoped cuprates, which competes with superconductivity and is suggested for connecting to the pseudogap phase. On the other hand, the extremely overdoped cuprates are generally considered as Fermi liquid metals without exotic orders. Contrary to the conventional wisdom, here we reveal charge order in extremely overdoped La2−xSrxCuO4 (0.35 ≤ x ≤ 0.6), beyond the superconducting dome using resonant soft x-ray scattering spectroscopy. This CO has a periodicity of ∼ 6 lattice units with correlation lengths of ∼ 3 -20 lattice units and persists up to 300 K. This CO cannot be explained by either the Fermi surface instability or the doped Hubbard model, suggesting correlation effects originating from other interactions in the highly overdoped regimes. Our findings reveal that CO is prevailing in the overdoped metallic regime and distinct from the pseudogap phase ending at x = 0.19. Our results suggest that high-temperature superconductors can be obtained by doping charge-ordered metals in addition to doped Mott insulators, providing a new perspective for understanding the dome-shaped superconducting phases.

Possible enhancement of the superconducting Tc due to sharp Kohn-like soft phonon anomalies

“…Additionally, it was already argued sometime ago by Allen [41] that traditional arguments against the relevance of phonons for cuprate superconductivity were not watertight. More recently, it is becoming increasingly clear that phonons might still explain a variety of cuprate phenomenology [42], and that fluctuating CDWs cover a much larger region in the phase diagram, including the strange metallic phase [43,44] and even the Fermi liquid one [45]. This has led to various speculations about the role of CDW fluctuations for transport properties of strange metals [46,47] and about the relation of charge order with quantum criticality and high-temperature superconductivity [48,49] as well.…”