Superconductivity-insensitive order at $q$~1/4 in electron doped cuprates

TL;DR

This study investigates charge density wave order in electron-doped cuprates, revealing that certain reflections are insensitive to superconductivity and differ from hole-doped cuprates, challenging the universality of CDW phenomena in high-$T_c$ cuprates.

Contribution

The paper provides direct experimental evidence that CDW-like reflections in electron-doped cuprates are superconductivity-insensitive and differ from hole-doped cuprates, questioning their universality.

Findings

Non-superconducting NCCO shows reflections at (~1/4, 0, l) similar to superconducting NCCO.

The observed reflections are insensitive to superconductivity.

Fermiology does not explain the wavevector of the reflections.

Abstract

One of the central questions in the cuprate research is the nature of the "normal state" which develops into high temperature superconductivity (HTSC). In the normal state of hole-doped cuprates, the existence of charge density wave (CDW) is expected to shed light on the mechanism of HTSC. With evidence emerging for CDW order in the electron-doped cuprates, the CDW would be thought to be a universal phenomenon in high-$T_c$ cuprates. However, the CDW phenomena in electron-doped cuprate are quite different than those in hole-doped cuprates. Here we study the nature of the putative CDW in an electron-doped cuprate through direct comparisons between as-grown and post-annealed Nd$_{1.86}$Ce$_{0.14}$CuO$_4$ (NCCO) single crystals using Cu $L_3$-edge resonant soft x-ray scattering (RSXS) and angle resolved photoemission spectroscopy (ARPES). The RSXS result reveals that the non-superconducting NCCO shows the same reflections at the wavevector (~1/4, 0, $l$) as like the reported superconducting NCCO. This superconductivity-insensitive signal is quite different with the characteristics of the CDW reflection in hole-doped cuprates. Moreover, the ARPES result suggests that the fermiology cannot account for such wavevector. These results call into question the universality of CDW phenomenon in the cuprates.