This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Ever since quantum mechanics first described particles, like electrons, as rippling waves, researchers have wondered if those waves could be trapped in place. Writing today in Science a century later, a team of Columbia University researchers reports waves of electrons becoming trapped for the first time in a metal called Pd₅AlI₂.
"Quantum mechanics predicts that an electron wave can, theoretically, remain trapped even when there are infinitely many paths for it to escape. This effect is known from light waves, but it has never been seen before for electrons," said Raquel Queiroz, a theoretical physicist at Columbia. It was a surprising discovery, and one that opens new possibilities for manipulating quantum states in metals.
Metals, classically, conduct electricity because their electrons are free to spread around a material. A few years ago, researchers in Xavier Roy's chemistry lab at Columbia made a new metal, Pd₅AlI₂, that can be peeled into two-dimensional layers while retaining its metallic characteristics. Its electrons, however, moved more slowly than they expected.
Working with Queiroz and experimental physicists Cory Dean and Aravind Devarakonda (a former Columbia postdoc who is now an assistant professor of applied physics at Columbia), they determined that electrons in Pd₅AlI₂ experience frustration. The way Pd₅AlI₂'s atoms and their orbitals are arranged gives its electrons competing paths to "hop" from atom to atom. These paths cancel each other out, holding many of the electrons back.
The team published their results on frustrated electron hopping in Nature Physics last year. The team was also working with Columbia physicist Abhay Pasupathy, whose lab has specialized scanning and spectroscopy instruments that can image materials with atom-scale accuracy. During initial scans, they noticed unexpected patterns.
Upon a closer look, these turned out to be electron waves bound in place near atomic defects in the material's crystal lattice. "Bound electrons shouldn't occur in a metal, but they do in Pd₅AlI₂. What we have observed is the first clear evidence of quantum interference trapping a state in a metal," said Queiroz, who developed the models that now explain the team's physical observations.
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