Penn State Team Reveals Iron Telluride Is a Superconductor After Decades of Misidentification as an Ordinary Magnetic Metal
Two back-to-back Nature papers show that removing excess iron atoms from iron telluride unlocks superconductivity at 13.5 Kelvin, overturning a longstanding assumption and suggesting similar hidden quantum states may exist in other correlated materials.
Overview
Iron telluride (FeTe), a compound of iron and tellurium that researchers have studied for decades as an antiferromagnetic metal, is in fact a superconductor. A team led by Penn State physicist Cui-Zu Chang demonstrated that removing excess iron atoms from the material’s crystal lattice suppresses its magnetism and switches on zero-resistance electrical conduction at approximately 13.5 Kelvin. The findings, reported in two papers published simultaneously in Nature on April 1, 2026, resolve a puzzle that has persisted since iron-based superconductors were first discovered in 2008.
A Decades-Old Misidentification
Iron-based superconductors have attracted intense interest since their discovery, with compounds such as iron selenide (FeSe) exhibiting superconductivity under various conditions. Iron telluride, however, was consistently classified as a non-superconducting magnetic metal. As Chang explained, “the excess iron atoms had disguised its superconductivity, leading to decades-old view that FeTe was an ordinary magnetic metal.”
The problem lay in synthesis. Conventional growth methods produce FeTe crystals with surplus iron atoms that wedge themselves between the material’s atomic layers. These interstitial atoms disrupt the ideal one-to-one stoichiometric ratio of iron to tellurium and induce antiferromagnetic ordering that masks the material’s intrinsic superconducting behavior.
Methodology
To obtain pristine samples, the Penn State team used molecular beam epitaxy to grow thin films of FeTe on strontium titanate substrates, producing layers approximately 40 atoms thick. They then subjected the films to multiple cycles of tellurium vapor annealing, a process that selectively strips away the excess interstitial iron atoms without damaging the underlying crystal structure.
Once the stoichiometric one-to-one ratio was restored, the material’s antiferromagnetism vanished entirely and superconductivity emerged with a critical temperature of approximately 13.5 Kelvin, or roughly minus 260 degrees Celsius.
Moire Engineering of Superconductivity
A companion paper from the same group reported a second discovery enabled by the newly purified material. By layering FeTe films with materials possessing different crystal lattice spacings, the researchers created moire superlattices, interference patterns that arise when two periodic structures are overlaid at slightly different scales.
Using scanning tunneling microscopy, the team directly observed that superconductivity in these layered structures forms a repeating, droplet-like pattern that follows the moire geometry. This represents the first observation of Cooper-pair density modulation states engineered through moire patterning in a superconductor, and it opens a pathway toward tunable superconducting properties through interface design.
Implications for Quantum Materials
The discovery carries significance beyond iron telluride itself. Because tellurium is a heavier element than selenium, iron telluride exhibits stronger spin-orbit coupling, a quantum mechanical interaction between an electron’s spin and its orbital motion. This property makes stoichiometric FeTe a candidate for topological superconductivity, a state that could host Majorana zero modes, quasiparticles sought for their potential role in fault-tolerant quantum computing.
Pengcheng Dai of Rice University, who provided commentary on the findings, noted that the work suggests similar hidden superconducting states may exist in other correlated materials where disorder has historically obscured intrinsic quantum behavior. The results indicate that systematic efforts to remove crystallographic impurities from known magnetic compounds could yield additional superconducting materials that have been overlooked.
As Chang observed, “for superconductivity, if you follow theory and try to do something, 99 percent of the time you will fail,” underscoring the experimental persistence required to uncover the material’s true nature.