Isolating the Effect of Dimensions on Electrons
When a metal’s atomic lattice contains some disorder, the conduction electrons can become trapped in small regions—a phenomenon called Anderson localization. The effect is strongest in 1D and 2D crystals, where even weak disorder leads to localization. Given the potential importance of graphene and other 2D materials for future electronics, researchers want to verify and extend the theory for 2D localization. Now Abhay Pasupathy of Columbia University and his colleagues have directly observed the onset of localization by using scanning tunneling spectroscopy (STS)—which uses a scanning tunneling microscopy (STM) probe—to study 3D samples having progressively fewer layers until they become 2D [1].
Previous studies of 2D localization in metals involved thin films created using sputtering, evaporation, or epitaxy. These techniques tend to produce 2D samples with more severe disorder than their 3D (bulk) counterparts, making it difficult to isolate dimensionality’s role in localization. In addition, these samples would often react chemically with oxygen in air, so that it was difficult to use a surface probe such as STM to map electronic properties with high spatial resolution.
Pasupathy and his colleagues studied the recently identified layered material palladium aluminum iodide, which is stable in air and can be progressively exfoliated to produce samples as thin as a monolayer. Crucially, thin samples have the same disorder—occasional point defects—as bulk samples. The researchers’ STS data revealed several signatures of localization in their 2D samples, including maps showing nanometer-scale patches of increased electron density. The team plans to use the experiment’s high spatial resolution to explore superconducting and quantum Hall systems.
–David Ehrenstein
David Ehrenstein is a Senior Editor for Physics Magazine.
References
- M. Thinel et al., “Anderson localization in a two-dimensional metal,” Phys. Rev. Lett. 136, 096401 (2026).