Superconductivity switched on in material once thought only magnetic

A sample of a thin film of the compound iron telluride (FeTe) — dark region on clear substrate at the center of the image — created using molecular beam epitaxy. Long thought to be an ordinary magnetic metal, researchers have now shown that exposing the thin film of FeTe to tellurium vapor removes disorder created by excess iron atoms trapped in the crystal structure of the material, revealing that FeTe is a superconductor.
Photo Credit: Chang Laboratory / Pennsylvania State University
(CC BY-NC-ND 4.0)

Scientific Frontline: Extended "At a Glance" Summary: Superconductivity in Iron Telluride (FeTe)

The Core Concept: Iron telluride (FeTe), a compound historically categorized as an ordinary magnetic metal, is intrinsically a superconductor capable of conducting electricity without energy loss. This superconducting state is achieved by eliminating hidden excess iron atoms that previously disrupted the material's structural purity.

Key Distinction/Mechanism: Unlike related iron-based superconductors such as iron selenide (FeSe), FeTe's superconductivity was masked by excess iron atoms that upset the delicate balance between magnetism and superconductivity. By exposing thin films of FeTe to tellurium vapor, researchers restored the ideal one-to-one atomic ratio, suppressing the magnetism and unlocking zero-resistance electrical flow at a critical temperature of approximately 13.5 Kelvin.

Major Frameworks/Components:

• Molecular Beam Epitaxy (MBE): A high-precision fabrication technique utilized to synthesize atomically clean and thin samples of FeTe.
• Scanning Tunneling Microscopy (STM): A specialized imaging tool used to analyze the atomic lattice, identify excess iron atoms, and directly observe repeating, droplet-like patterns of superconductivity (described as a "quantum dance").
• Moiré Superlattice Engineering: The application of a secondary material layer with a mismatched crystal structure over the FeTe to create a tunable interface that purposefully modifies the material's superconducting properties.

Branch of Science: Condensed Matter Physics, Materials Science, and Quantum Physics.

Future Application: This research directly supports the design of next-generation quantum materials and highly efficient, ultra-fast electronics. Derived applications include the advancement of magnetic resonance imaging (MRI) machines, more powerful particle accelerators, and stable hardware for quantum computing.

Why It Matters: This discovery redefines the fundamental phase diagram of iron-containing compounds and establishes a crucial new paradigm for materials science. It proves that precise disorder-control and moiré interface engineering can unearth hidden superconducting states or competing magnetic orders in other correlated materials, vastly expanding the available toolkit for discovering and stabilizing new quantum states.

Researchers identified the switch that enables superconductivity in iron telluride (FeTe) and observed a quantum dance of superconductivity. Image on the left shows a method to precisely control the purity of FeTe by exposing thin films of the material created using molecular beam epitaxy to an environment with tellurium vapor. Middle image shows the ideal one-to-one ratio of iron and tellurium atoms in FeTe that unlocked its superconductivity. Image on the right shows the quantum dance, a droplet-like pattern of superconductivity that researchers observed by creating layered structures of FeTe and a thin material with a different crystal structure.
Photo Credit: Chang Laboratory / Pennsylvania State University
(CC BY-NC-ND 4.0)

Long thought to be an ordinary magnetic metal, new research shows that removing disorder allows the compound, iron telluride, to conduct electricity with zero resistance and reveals a new quantum dance

A sample of a thin film of the compound iron telluride (FeTe) — dark region on clear substrate at the center of the image — created using molecular beam epitaxy. Long thought to be an ordinary magnetic metal, researchers have now shown that exposing the thin film of FeTe to tellurium vapor removes disorder created by excess iron atoms trapped in the crystal structure of the material, revealing that FeTe is a superconductor. Credit: Chang Laboratory / Penn State. Creative Commons

Superconductivity — the ability of a material to conduct electricity without any energy loss to heat — enables highly efficient, ultra-fast electronics essential for advanced technologies such as magnetic resonance imaging (MRI) machines, particle accelerators and, potentially, quantum computers. New research has now revealed that iron telluride (FeTe), a compound composed of the chemical elements iron and tellurium and long thought to be an ordinary magnetic metal, is in fact a superconductor. The researchers found that hidden excess iron atoms induce the material’s magnetism, and removing these atoms allows electricity to flow with zero resistance.

Two papers describing the research, both led by Penn State Professor of Physics Cui-Zu Chang, published back-to-back today (April 1) in the journal Nature. The first paper focuses on how to “switch on” superconductivity in FeTe, while the second paper reveals a new kind of “quantum dance,” where superconductivity interacts with the material’s atomic structure when a different top layer is added, allowing researchers to tune its behavior.

“Unlike the well-known iron-based superconductor iron selenide (FeSe), FeTe has long been considered a magnetic metal without superconductivity, despite having an almost identical crystal structure,” Chang said. “It has remained a mystery why FeTe doesn’t share this important property.”

To explore why these two closely related compounds behave so differently, the research team grew FeTe thin films using a technique called molecular beam epitaxy. This technique creates atomically thin, exceptionally clean samples by co-evaporating source materials onto appropriate substrates. However, when the researchers looked closely at the FeTe samples they created at the atomic scale using a specialized microscope, called scanning tunneling microscopy, they saw that the material was not perfectly ideal. Extra iron atoms were embedded within the crystal lattice of FeTe.

“These excess iron atoms disrupt the ideal one-to-one ratio of iron and tellurium atoms in FeTe and upset the balance of magnetism and superconductivity,” Chang said, explaining that the researchers theorized that removing the excess atoms to make truly pure FeTe might result in a superconductor.

The team came up with a method to precisely control the purity of FeTe by exposing the FeTe films to an environment with tellurium vapor. This compensated for the excess iron atoms and drove the material towards an ideal state.

“The resulting ideal FeTe exhibits superconductivity with a critical temperature of around 13.5 Kelvin, or about negative 435 degrees Fahrenheit,” Chang said. “The excess iron atoms had disguised its superconductivity, leading to the decades-old view that FeTe was an ordinary magnetic metal. Our findings redefine the phase diagram of this class of iron containing compounds. Similar phenomena are likely to be present in other correlated materials, where hidden superconducting states or competing magnetic orders remain concealed until disorder is removed or carefully controlled. Understanding the crucial role of disorder will help us to uncover and stabilize such hidden superconducting states in other materials.”

Researchers identified the switch that enables superconductivity in iron telluride (FeTe) and observed a quantum dance of superconductivity. Image on the left shows a method to precisely control the purity of FeTe by exposing thin films of the material created using molecular beam epitaxy to an environment with tellurium vapor. Middle image shows the ideal one-to-one ratio of iron and tellurium atoms in FeTe that unlocked its superconductivity. Image on the right shows the quantum dance, a droplet-like pattern of superconductivity that researchers observed by creating layered structures of FeTe and a thin material with a different crystal structure. Credit: Chang Laboratory / Penn State. Creative Commons

In the second paper, having established that FeTe is intrinsically a superconductor, the team further explored how its superconducting state itself can be engineered. The team created layered structures by growing a thin material with a different lattice structure on top of FeTe. Because the two materials have different atomic arrangements, a larger repeating pattern — called a moiré superlattice — forms at their interface.

“The mismatch between the crystal structures at the interface creates what we call a moiré superlattice, which modifies the superconducting properties of FeTe,” Chang said. “In recent years, moiré superlattices in two‑dimensional materials have emerged as an important platform for discovering new quantum states.”

Using scanning tunneling microscopy, which can image materials at the atomic scale, the team directly observed that superconductivity forms a repeating, droplet-like pattern — what the researchers describe as a “quantum dance” — that follows the moiré superlattice. They also found that this pattern can be adjusted by changing the material in the top layer.

“The role of crystal lattices has often been overlooked in superconductors,” Chang said. “Our findings encourage a renewed focus on the interplay between superconductivity and lattice structure and highlight how moiré interface engineering can serve as a potentially powerful tool for tuning superconductivity and designing next‑generation quantum materials.”

Funding: 

1. The research was supported by the U.S. Department of Energy (DOE), with additional support from the U.S. National Science Foundation, the Office of Naval Research (ONR), the Army Research Office, the Penn State MRSEC for Nanoscale Science, the University of Florida, and the Gordon and Betty Moore Foundation’s EPiQS Initiative.
2. The DOE, ONR, Penn State MRSEC for Nanoscale Science, Air Force Office of Scientific Research and Gordon and Betty Moore Foundation’s EPiQS Initiative funded the research.

Published in journal: Nature

Title:

1. Stoichiometric FeTe is a superconductor
2. Moiré engineering of Cooper-pair density modulation states

Authors:

1. Zi-Jie Yan, Zihao Wang, Bing Xia, Stephen Paolini, Ying-Ting Chan, Nikalabh Dihingia, Hongtao Rong, Pu Xiao, Kalana D. Halanayake, Jiatao Song, Veer Gowda, Danielle Reifsnyder Hickey, Weida Wu, Jiabin Yu, Peter J. Hirschfeld, and Cui-Zu Chang
2. Zihao Wang, Bing Xia, Stephen Paolini, Zi-Jie Yan, Pu Xiao, Jiatao Song, Veer Gowda, Hongtao Rong, Di Xiao, Xiaodong Xu, Weida Wu, Ziqiang Wang, and Cui-Zu Chang

Source/Credit: Pennsylvania State University | Sam Sholtis

Reference Number: phy040226_01

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