▲ On the last day of the conference, held at the Best Western Pohang Hotel, scientists gather for a group photo arranged in the shape representing a cross section of the atomic wire allowing controllable charge transport.

"17 years have passed since research on atomic wires started. Now, it's time to discuss their applicability. Worldwide leading scholars are here to discuss where to orient the application of atomic wires."

YEOM Han Woong, Director of the Center for Artificial Low Dimensional Electronic System (CALDES) within the Institute for Basic Science (IBS), opened up a new field of atomic wires in 1999. Director Yeom's face glowed with excitement as he had a meaningful conference ahead: It is the world's first conference in atomic wires that bring together renowned scholars in the field and it is especially noticeable that this meaningful conference is held in Korea.

The IBS Conference on Surface Atomic Wires was held at the Best Western Pohang Hotel from August 17 to 20. The three-day event featured presentations from 26 globally-renowned scholars and discussions on future directions of atomic wires.

Atomic wires are obtained by depositing metal atoms onto a silicon surface in ultra-high vacuum conditions. The resulting 1-2 nanometer chains of atoms are extremely thin, ranging in width from 1 to 3 atoms, and have great significance. Their properties can result in new electronic device concepts, greatly reduced power consumption and exothermic reaction, ultimately bringing smaller integrated circuits, with more sophisticated functions, closer to reality.

Yeom is the pioneering figure in research of the electronic properties of atomic wires with the world's first discovery of phase transition exhibited by indium atomic wires in 1999 when he was a lecturer at the University of Tokyo: At room-temperature, the metallic phase of indium linear chains undergoes a temperature-induced transition into a insulating phase.

Bringing together world-renowned experts in atomic wires

▲ Director Yeom Han Woong of CALDES before his interview with IBS. On the first day of the conference, Yeom readily agreed to an interview in the midst of greeting renowned foreign scholars.

Even at a glance, you can understand that it is not a piece of cake to gather more than 30 researchers of a specific field in the same place. Yeom said, "Some researchers put forward an opinion about bringing together researchers of atomic wires given 17 years of research history. He added, "The need to examine outcomes of research on atomic wires so far in an organized way and to discuss directions for the future found an echo in researchers' hearts."

The key was to bring all the major players in atomic wires to Korea, which required nearly two years of preparation. Together with generous support from IBS, the efforts resulted in the participation of most of the world's greatest scholars in this field except for few whose schedule prevented them from attending. The three-day conference, made up of a total of four sessions, held presentations and discussions on atomic wires materials such as gold, indium, and iridium. The existing achievements and limits of these materials, along with possibility for their future applications, were discussed by the participants. In addition, likely materials for new atomic wires were discussed at this event.

▲ On the first day of the conference, beginning from 2:00 p.m., August 17th, there were around 40 participants. For each presenter, 30 minutes were given. A total of seven experts gave presentations, starting with Steven C. Erwin (left) from the U.S. Researchers then actively participated in Q & A sessions.

Future directions oriented toward applicability

"Achievements in the field of atomic wires are well known. What's required now concerns mutual agreement on which has enormous potential for development and which problems are still waiting for solutions. The discrete ideas of different researchers cannot drive genuine growth in this field. In order to concentrate the efforts and achievements of the relevant players in this field, we need to articulate the most important tasks of this field."

Yeom made it clear what he wanted to achieve from this conference. Now, he said, is the time to discuss how to orient the research direction towards practical application with relevant researchers and to maintain focus on such realization. "Research on atomic wires that began 17 years ago is now approaching maturity," commented Yeom "Only in the presence of applicability, we can expect unceasing studies in this field." He added, "I would like to share the results from my research paper published in Science last year. It offers an important basis for the applicability of atomic wires." That research presented an inspirational direction of their application.

According to that research topologically protected and controllable charge transport was identified in indium atomic wires. Indium atoms deposited on a silicon surface at an elevated temperature of more than 500 ℃, self-organize into an ordered array of metallic wires consisting of double zigzag chains. The interchain coupling induces dynamical sublattice symmetry breaking and causes topological edge states called solitons to appear. Solitons are solitary traveling waves that act like particles. According to the CALDES team, in their 1D charge density wave system of indium atomic wires, charge pumping is allowed by transporting solitons which propagate in one direction only and each soliton delivers just one charge across the chain. Solitons and moving walks are similar in the way of transportation, and the research team found that such property can be utilized for simple logic operation.

Yeom regards the research outcome as most important in the past 17 years. He added that a new discipline of solitonics, combination of soliton and electronics deserves greater attention as a promising field given its bright outlook for application. He also expressed another wish of regularly holding atomic wire conferences. He said, "Fortunately, Germany and the EU have designated research on atomic wires as an important national task, so this kind of conference might be held in these regions around three years later."

Interview with Professor Shuji Hasegawa, from the University of Tokyo, and Professor Hubert Pfnur, from the Leibniz University of Hannover

▲ Shuji Hasegawa at the IBS Conference

Renowned scholars who participated in the conference included Professor Shuji Hasegawa from the University of Tokyo who succeeded in measuring electron conduction of atomic wires for the first time in the world, and Professor Herbert Pfnur from the Leibniz University of Hannover. Professor Hasegawa gave a presentation titled 'Low-Dimensionality, Symmetry Breaking, and Topology on Surfaces', and 'Plasmons in quasi one-dimensional systems' was the title of Professor Herbert Pfnur's presentation.

1. What brought you to this conference?
Prof. Hasegawa : The topic of this conference is "atomic wires" which has attracted many scientists for about the last 20 years because of their importance in fundamental physics and possible applications to technology of electronic devices. If we can make devices and sensors with artificial atomic wires in controllable ways, our computers and communication tools will be much more small and energy-saving and ubiquitous. This conference is a great opportunity to collect information on the state-of-art basic research on this topic.

Prof. Pfnur : This conference brings together the worldwide leading experts active in this field for the first time in a conference devoted exclusively to this subject. Since our research group is working on metallic atomic wires on semiconducting substrates for many years, this conference is of very high interest for us. Director Yeom took the initiative and it was a pleasure for me to assist in motivating well renowned speakers to come to this conference.

2. What are you planning to present in the conference.
Prof. Hasegawa : Prof. Hasegawa: I have studied many aspects of atomic wires and widened the scope of research to atomic-scale low-dimensional structures like atomic layers. I will present a review on my research mainly about electrical conduction at such atomic-scale structures. I have found that even a single-atomic metal layer becomes superconducting (zero resistance in electrical conduction). But nobody has found superconducting atomic wires yet. This is a very challenging subject.

Prof. Pfnur : My own contribution will be on plasmonic excitations in arrays of atomic wires. Low energy plasmons are collective excitations of the conduction electrons. In these quasi one-dimensional systems they can serve efficiently for directional transport of energy along these wires. At the moment we are still trying to understand the underlying physics in more detail before we may turn to questions how to couple external radiation into them and design optoelectronics on the scale of a few nanometers with them.

3. What do you hope to accomplish in this conference?
Prof. Hasegawa : I want to collect the most recent results on research of atomic wires. Many kinds of experimental and theoretical techniques have been applied to study the atomic wires and layers. Since the research is too much diversified by many researchers to follow, we need this kind of conference to exchange the most recent knowledge and to communicate with possible collaborators.

Prof. Pfnur : Conferences of this type allow for intense exchange of ideas between researchers. The experience from the past is that this exchange is very fruitful in stimulating new ideas for future research. I also hope that we will be able to intensify existing and to set up new collaborations world-wide.

4. Lastly, what is your opinion/impression on the IBS, organizer of this conference?
Prof. Hasegawa : The IBS program looks very successful because it enhances visibility of Korea scientists in scientific publications greatly. IBS is a very nice platform for collaboration among researchers who have different expertise, leading to fruitful synergetic results. Since IBS is supported by a big fund from the government, it should not be a collection of small research groups, rather it should have centripetal forces with big experimental facilities and forum for interaction of researchers. Therefore, it should not be a closed team, rather open to researchers outside, even internationally.

Prof. Pfnur : The IBS is a very powerful new organization to coordinate and boost basic research in South Korea. I support the general concept very much, because I think that it serves best the needs of the country for long term innovation, and for educating the most brilliant minds in close collaboration between research institutions and university groups.