Real-space Observation of Incommensurate Spin Density Wave and Coexisting Charge Density Wave on Cr(001) surface

TL;DR

This study uses spin-polarized scanning tunneling microscopy to directly observe the coexistence of incommensurate spin density wave and charge density wave on Cr(001) surface, revealing their correlated structures and interactions.

Contribution

First real-space observation of incommensurate SDW and coexisting CDW on Cr(001) surface, providing new insights into their relationship and underlying mechanisms.

Findings

Observed 6.0 nm in-plane SDW period with anti-phase behavior.

Detected CDW with half the SDW period, highly correlated and in-phase.

Identified CDW gap opening below the Fermi level at -22 meV.

Abstract

In itinerant magnetic systems, a spin density wave (SDW) state can be induced by Fermi surface nesting and electron-electron interaction. It may intertwine with other orders such as charge density wave (CDW), while their relation is still yet to be understood. Here via spin-polarized scanning tunneling microscopy, we directly observed long-range spin modulation on Cr(001) surface, which corresponds to the well-known incommensurate SDW of bulk Cr. It displays 6.0 nm in-plane period and anti-phase behavior between adjacent (001) planes. Meanwhile, we simultaneously observed the coexisting CDW with half the period of SDW. Such SDW/CDW have highly correlated domain structures and are in-phase. Surprisingly, the CDW displays a contrast inversion around a density-of-states dip at -22 meV, indicating an anomalous CDW gap opened below EF. These observations support that the CDW is a secondary order driven by SDW. Our work is not only a real-space characterization of incommensurate SDW, but also provides insights on how SDW and CDW coexist.