Scanning tunneling microscope studies on low-dimensional transition-metal halides

Famous for their two-dimensional magnetism, the transition-metal halides with significant anisotropy and correlated d-electrons have been reduced to a low dimension and caught substantial attention in recent years. At the same time, owing to the excellent capability of discerning various degrees of freedom in solid-state systems, a scanning tunneling microscope greatly advances the understanding of low-dimensional transition-metal halides and their heterostructures by providing key results regarding structural, electronic, and magnetic properties. Here, we review the key insights about the fabrication methods, crystallography, strongly correlated electronic structures, and magnetic orders of low-dimensional revealed by scanning tunneling microscope, and introduce the latest discoveries of emergent physics under the interplay between dimensionality confinement, many-body correlation, and quantum-coupling mechanisms.