Charge order in the highly overdoped region of the cuprate superconductor La_2-xCa_xCuO₄

The interplay between charge density wave (CDW) order and superconductivity in cuprates has been a subject of wide debate. Most early studies observed the disappearance of CDW just above optimal doping and well below the doping at which superconductivity disappears [1]. This brought into question the role of CDW in shaping the superconducting dome of the cuprates. Intriguingly, several recent studies in overdoped cuprates have found the existence of CDW in the overdoped regime [1-5], thus reviving the question of CDW as an order competing against superconductivity also on the overdoped side of the phase diagram. In this talk, I will report on our resonant x-ray scattering study of CDW in highly overdoped La_2-xCa_xCuO₄ thin films, in which superconductivity remarkably persists to a doping of at least x ~ 0.50 [6]. We find that CDW persists to a doping at least as high as x = 0.50, with a domain pattern that is distinct from that observed in bulk single crystals. Furthermore, the charge ordering wavevector is observed to lock into a commensurate q ~ 0.25 at high doping, and the onset temperature is observed to increase to above room temperature for x > 0.30. I will discuss the general implications of these findings.

[1] A. Frano et al., J. Phys. Cond. Matt. 32, 374005 (2020)

[2] Y. Y. Peng et al., Nat. Mater. 17, 697 (2018)

[3] H. Miao et al., npj Quantum Materials 6, 31 (2021)

[4] Q. Li et al., Phys. Rev. Lett. 131, 116002 (2023)

[5] C. C. Tam et al., Nat. Commun. 13, 570 (2022)

[6] G. Kim et al., Proc. Natl. Acad. Sci. 118, e2106170118 (2021)