"Transferring Electrons by Rotation Instead of Voltage"... UNIST Reveals Operational Principle of Helical Nanowire 'Quantum Pump' [Reading Science]

Quantized Charge Transport Achieved by Rotating the Electric Field Once
Simultaneous Generation of Orbital Angular Momentum and Spin Polarization
Collaboration with Pennsylvania State University
New Possibilities for Nanoelectronics and Spintronics Device Design

The Ulsan National Institute of Science and Technology (UNIST) and a team of U.S. researchers have theoretically demonstrated that a helical nanowire, twisted like a screw, can function as a ‘quantum pump’ that transports electrons in a fixed quantity in one direction. Notably, the process of charge transport also generates both the orbital angular momentum and spin polarization of electrons, opening up new possibilities for the development of next-generation nanoelectronic devices and spintronics technologies.

On June 4, UNIST announced that a research team led by Professor Nojung Park from the Department of Physics had collaborated with a team led by Professor Binghai Yan of Pennsylvania State University in the United States to elucidate the operational principle of phase charge pumping in one-dimensional helical materials.

A schematic diagram showing the phenomenon of 'phase charge pumping,' where charges inside a helical nanowire move in one direction when a rotating electric field is applied. During the charge transport process, orbital angular momentum is generated, some of which is converted into spin polarization through spin-orbit coupling. It also illustrates the principle where periodic changes in the electric field direction lead to changes in the electronic state, causing quantized charge transport. Courtesy of the research team

According to the research team, a nanowire with a helical structure can move charge in the quantum world in a way similar to the Archimedes pump, an ancient device used to draw water. Just as the Archimedes pump lifts water from below with only rotational motion, a helical nanowire can move electrons in a single direction simply by slowly rotating the direction of the electric field.

The key aspect of this study is that such a structure operates as a ‘phase charge pump’ (Thouless quantum pump). A phase charge pump is a quantum phenomenon in which a fixed amount of charge is transferred when external conditions are varied periodically. Unlike conventional current, which is generated by applying a voltage to drive electrons, this method periodically changes the quantum state of electrons to transfer charge.

While conventional phase charge pumps require precise control of two or more variables, the research team confirmed that by utilizing a helical structure, charge pumping can be achieved with just a single condition: rotating the direction of the electric field once.

The team theoretically demonstrated this phenomenon by analyzing time-dependent electronic states in a helical hydrocarbon model and a trigonal selenium nanowire.

Researchers photo. Professor Nojung Park (left) and Dr. Esmail Tagizadeh Sisakht. Courtesy of UNIST

The research found that during the charge pumping process, both the orbital angular momentum and spin polarization of electrons are generated. As electrons move along the helical structure, orbital angular momentum is first formed, and in the case of the selenium nanowire, a portion of this is converted into spin polarization through spin-orbit coupling. In other words, the properties of the electrons' orbital motion are transferred to their spin properties.

Professor Nojung Park stated, “We have clarified for the first time that topological charge pumping, orbital angular momentum, and spin polarization are connected as a unified mechanism in nanowires with chirality. This could serve as a foundation for the future development of new nano devices that topologically control electronic, orbital, and spin properties.”

This research was led by Dr. Esmail Tagizadeh Sisakht as the first author and was supported by the Basic Research Program of the Ministry of Science and ICT and the National Research Foundation of Korea, as well as the Human Resources Development Program of the Korea Institute for Advancement of Technology (KIAT) under the Ministry of Trade, Industry and Energy. The results were published in the international journal Nano Letters on May 13.

This content was produced with the assistance of AI translation services.