Real-space Visualization of Charge Density Wave Induced Local Inversion-Symmetry Breaking in a Skyrmion Magnet

Abstract: Intertwining charge density wave (CDW) with spin and pairing order parameters is a major focus of contemporary condensed matter physics. Lattice distortions and local symmetry breaking resulted from CDWs are crucial for the emergence of correlated and topological states in quantum materials in general. While the presence of CDWs can be detected by diffraction or spectroscopic techniques, atomic visualization of the CDW induced lattice distortions remains limited to CDW with short wavelengths. In this letter, we realized the imaging of incommensurate long-wavelength CDWs based on cryogenic four-dimensional scanning transmission electron microscopy (cryo-4DSTEM). By visualizing the incommensurate CDW induced lattice modulations in a skyrmion magnet EuAl4, we discover two out-of-phase intra-unit cell shear modulations that specifically break the local inversion-symmetry. Our results provide direct evidence for the intertwined spin and charge orders in EuAl4 and key information about local symmetry. Furthermore, we establish cryo-4DSTEM as an indispensable approach to understand CDW induced new quantum states of matter.