Real-Space Observation and Ultrafast Dynamics of Spin and Charge Density Waves on Cr (001) Surface

We have conducted an in-depth investigation of spin density wave (SDW) and charge density wave (CDW) phenomena on the Cr (001) surface using spin-polarized scanning tunneling microscopy (SP-STM) and ultrafast pump-probe spectroscopy. To ensure high sensitivity to spin-dependent electronic states, we prepared the spin-polarized STM tip in situ by hard-contacting a tungsten tip with the Cr surface. Our SP-STM measurements revealed coexisting SDW and CDW features on the Cr (001) surface, exhibiting variations in their relative intensities and phase differences under different bias voltages—indicating a bias-dependent modulation of their electronic structures. Surface impurities and lattice distortions were found to alter the periodicity and orientation of both SDW and CDW. Furthermore, through near-infrared (NIR) and terahertz (THz) pump-probe experiments, we explored the dynamic behavior of these density waves in the time domain. Our findings provide valuable insights into the interplay between electronic and structural properties of the chromium surface. By understanding how SDW and CDW coexist and interact, it is possible to obtain potential pathways for the controlled manipulation of electronic orders in antiferromagnetic materials and the development of future spintronic devices.