Real-space observation of charge ordering in epitaxial La2\u2212xSrxCuO4 films

Yang Wang,Zhiling Luo,Xu-Cun Ma,Menghan Liao,Yong Zhong,Ziyuan Dou,Qi-Kun Xue,Can-Li Song,Ruifeng Wang,Ding Zhang,Lin Gu,Qinghua Zhang

doi:10.1038/s41535-019-0156-1

Abstract

The cuprate superconductors exhibit ubiquitous instabilities toward charge-ordered states. These unusual electronic states break the spatial symmetries of the host crystal, and have been widely appreciated as essential ingredients for constructing a theory for high-temperature superconductivity in cuprates. Here, we report real-space imaging of the doping-dependent charge orders in the epitaxial thin films of a canonical cuprate compound La2–xSrxCuO4 using scanning tunneling microscopy. As the films are moderately doped, we observe a crossover from incommensurate to commensurate (4a0, where a0 is the Cu–O–Cu distance) stripes. Furthermore, at lower and higher doping levels, the charge orders occur in the form of distorted Wigner crystal and grid phase of crossed vertical and horizontal stripes. We discuss how the charge orders are stabilized, and their interplay with superconductivity.

Highlights

The charge ordering was more universally confirmed to extend over a wider doping range in the cuprate phase diagram by resonant X-ray scattering,[13,14] but the ultimate microscopic mechanism, its doping dependence, the exact modulated pattern and its commensurability are all as yet unclear,[2–8] due in part to the twinning and phase separation in various cuprate compounds
The opportunity to probe charge ordering locally has propelled a plethora of early scanning tunneling microscopy (STM) measurements, which provide mounting evidence for short-ranged checkboard-type structure on the cleavable Ca2–xNaxCuO2Cl2 and Bi-based cuprates.[2,3,15]
Our real-space imaging of epitaxial LSCO films provides an atomicscale basis for the description of charge orders, which constitutes the major finding in this study

Summary

INTRODUCTION

Electrons in strongly correlated materials are often susceptible to segregating into complexly ordered structures.[1–12] In particular, charge-ordered states may coexist and even compete with hightemperature (Tc) superconductivity in moderately doped cuprates,[2,6,8,9] prompting numerous investigations into their correlations with superconductivity and the mysterious “pseudogap” phenomenon.[4,7] Recently, the charge ordering was more universally confirmed to extend over a wider doping range in the cuprate phase diagram by resonant X-ray scattering,[13,14] but the ultimate microscopic mechanism, its doping dependence, the exact modulated pattern (e.g., mixture of uniaxial stripes or biaxial checkerboards) and its commensurability are all as yet unclear,[2–8] due in part to the twinning and phase separation in various cuprate compounds. The opportunity to probe charge ordering locally has propelled a plethora of early scanning tunneling microscopy (STM) measurements, which provide mounting evidence for short-ranged checkboard-type structure on the cleavable Ca2–xNaxCuO2Cl2 and Bi-based cuprates.[2,3,15]. Such pattern has been suggested to be describable equivalently by nanoscale patches of uniaxial stripes as the disorder scattering is considered.[16]. A real-space visualization of charge ordering, indispensable for identifying its microscopic nature, is lacking, since the LSCO single crystal never exhibited good cleavage as the Bi-based cuprates. Our findings shed light into the microscopic mechanism of charge orders, as well as their interplay with the superconductivity in cuprates

RESULTS

DISCUSSION

METHODS