Scientists confirm one-dimensional electron behavior in phosphorus chains

Researchers confirm a true one-dimensional material

Scientists have experimentally confirmed, for the first time, that a material can exhibit truly one-dimensional electronic properties. The team from the Helmholtz-Zentrum Berlin (HZB) studied chains of phosphorus atoms on a silver surface.

Their work shows each individual chain acts as a genuine one-dimensional electronic system. The findings were published after experiments at the BESSY II synchrotron radiation source.

Phosphorus atoms self-assemble into chains

Under controlled conditions, phosphorus atoms organize themselves into short, straight lines on a silver substrate. Structurally, these lines appear one-dimensional.

However, neighboring chains can still interact from the side, which could disrupt true one-dimensional electronic behavior. Until now, researchers had not been able to clearly measure if the electrons were confined to a single dimension.

"Through a very thorough evaluation of measurements at BESSY II, we have now shown that such phosphorus chains really do have a one-dimensional electronic structure," says Professor Oliver Rader of HZB.

Separating signals from three directions

Dr. Andrei Varykhalov and colleagues first created the phosphorus chains and examined them with a cryogenic scanning tunnelling microscope (STM). The images showed short chains forming in three distinct directions across the silver surface, each separated by 120 degrees.

The team then mapped the electronic structure using angle-resolved photoelectron spectroscopy (ARPES) at BESSY II. "We achieved very high-quality results, enabling us to observe standing waves of electrons forming between the chains," Varykhalov says.

Isolating the one-dimensional signature

Dr. Maxim Krivenkov and Dr. Maryam Sajedi led the data interpretation. They separated the signals coming from the three differently oriented chain domains to isolate each chain's electronic signature.

"We could disentangle the ARPES signals from these domains and thus demonstrate that these 1D phosphorus chains actually possess a very distinct 1D electron structure too," Krivenkov says. This careful work confirmed the theoretical prediction of one-dimensional behavior.

A predicted semiconductor-to-metal shift

The findings also reveal a dramatic shift in behavior based on how closely the chains are spaced. When chains are farther apart, the material acts as a semiconductor.

Calculations based on density functional theory predict that if packed tightly together, the material would behave like a metal. Stronger interactions between neighboring chains would trigger this phase transition.

Key properties of the phosphorus chains include:

• Self-assembly on a silver substrate in three directions
• A confirmed one-dimensional electronic structure
• Semiconductor behavior at lower density
• Predicted metallic behavior at high density

Entering uncharted research territory

The work moves research from two-dimensional materials, like graphene, into the one-dimensional realm. Theoretical studies have suggested 1D structures could produce remarkable electro-optical effects.

"We have entered a new field of research here, uncharted territory where many exciting discoveries are likely to be made," Varykhalov says. The team's method of isolating signals from differently oriented domains provides a blueprint for studying other potential 1D systems.