# Columbia University observed localized electron states in the metallic compound Pd₅AlI₂ - Published: 2026-11-15 12:46 UTC - Section: Science › Physics - Tags: localized electrons in a metal, Pd₅AlI₂, bound states in the continuum, BIC, Raquel Queiroz, Columbia University, scanning tunneling microscopy, quantum interference, two-dimensional layers, Science - URL: https://realtech.media/news/rt-efb4a62bd4717691bca62c40_columbia_university_observed/ **Columbia physicists used scanning tunneling microscopy to see two defect-bound electron states that stay localized inside a metal, due to quantum interference.** ![Columbia University observed localized electron states in the metallic compound Pd₅AlI₂](https://realtech.media/media/2026/11/af7c4f6289dc02ba.webp) *larazon.es* Physicists at Columbia University have observed electronic states that stay localized inside a metal. The compound is Pd₅AlI₂, which can be separated into two-dimensional layers while keeping its metallic properties, larazon.es reports, citing SINC. The work was published on 22 October in Science. [1] ## Bound states in a metal A metal conducts electricity because some of its electrons can move through it, so localized states there are unusual. "Trapped electrons should not occur in a metal, but they do," said Raquel Queiroz, a theoretical physicist at Columbia. She refers specifically to this compound and to a quantum interference mechanism. [1] The result does not mean that all electrons in the metal have stopped, or that known physics has been violated. The paper describes bound states in the continuum (BIC). The novelty is observing them in a metallic environment: they stay concentrated in a region while coexisting with states that extend through the material. Similar phenomena had previously been studied with light waves. [1] ## Interference and defects In quantum mechanics, electron motion is described by waves. Contributions from different paths can reinforce or cancel each other depending on phase, and destructive interference suppresses propagation. Queiroz's group explains that the arrangement of atoms and orbitals in the crystal determines which paths can cancel. Near certain defects, an electron wave can remain localized even though the metal offers states at the same energy. [1] The researchers used scanning tunneling microscopy. The abstract identifies two defect-associated electronic states that remain localized within the metallic continuum. The measurements show the spatial and energy signals; the theoretical calculations link their existence to interference and to the geometry of the crystal lattice. [1] The team had earlier studied why electrons in this material moved more slowly than expected, with results published in Nature Physics in 2025. Localizing an electronic state can ease its study and manipulation, but it is not a processor and does not by itself demonstrate entanglement between qubits. [1] The university points to possible future uses in sensors, information processing and quantum chemistry; these remain prospects, not devices. The defects appear randomly during crystal growth, and the researchers are exploring how to place them at chosen positions to tune the interference. Controlling where the state is localized will be an important step. The finding also gives criteria for seeking similar behavior in other metals, without implying that any conductor can reproduce it. [1] ## Sources 1. [larazon.es](https://www.larazon.es/tecnologia-consumo/raquel-queiroz-fisica-columbia-electrones-atrapados-no-deberian-darse-metal-hacen-su-equipo-ha-logrado_202611156af9713803bbf30bb04d01f6.html) --- Source: RealTech, realtech.media — https://realtech.media/news/rt-efb4a62bd4717691bca62c40_columbia_university_observed/