Scientists at Columbia University have found that electron waves can remain trapped near atomic defects in a metal, despite the availability of pathways for them to escape. The findings confirm experimentally that quantum interference can confine electron waves in a metallic material, a possibility predicted by theory.
The phenomenon, known as a bound state in the continuum (BIC), arises when quantum interference prevents waves from spreading. Electrons behave like waves and can travel along multiple paths through a material. When these waves overlap, they can cancel one another through destructive interference, confining an electron wave even when other states in the material allow movement.
The team studied Pd₅AlI₂, a metal developed in the laboratory of Columbia chemist Xavier Roy. The material can be peeled into thin, two-dimensional layers without losing its metallic properties. Experiments showed that electrons moved more slowly than expected, prompting researchers to investigate the material’s atomic structure. They found that competing routes between atoms create a condition known as electron-hopping frustration, in which destructive quantum interference restricts electron movement.
Using atomic-scale scanning and spectroscopy, researchers working with Columbia physicist Abhay Pasupathy detected unusual patterns in the material. Further analysis showed that electron waves were confined near defects in its crystal structure. Theoretical models developed by physicist Raquel Queiroz explained how quantum interference caused the waves to remain trapped.
BICs have previously been demonstrated in light waves, with applications in lasers, optical sensing and nonlinear optics. The discovery raises the possibility of using trapped electron states in quantum sensors, information processing and quantum chemistry. However, controlling these states remains a challenge. Researchers are now exploring ways to deliberately position defects in the crystal and control the interference patterns that trap the electrons.
