From Institute for Basic Science [ 기초과학연구원](KR): “New mechanism of superconductivity discovered in graphene”

From Institute for Basic Science [ 기초과학연구원](KR)

2021-04-14 [Just now in social media.]
Park Jong Woo

Placing a 2D Bose-Einstein condensate in the vicinity of a graphene layer confers superconductivity to the material.

Superconductivity is a physical phenomenon where the electrical resistance of a material drops to zero under a certain critical temperature. Bardeen-Cooper-Schrieffer (BCS) theory is a well-established explanation that describes superconductivity in most materials. It states that Cooper pairs of electrons are formed in the lattice under sufficiently low temperature and that BCS superconductivity arises from their condensation. While graphene itself is an excellent conductor of electricity, it does not exhibit BCS superconductivity due to the suppression of electron-phonon interactions. This is also the reason that most ‘good’ conductors such as gold and copper are ‘bad’ superconductors.

Researchers at the Center for Theoretical Physics of Complex Systems (PCS), within the Institute for Basic Science (IBS, South Korea) have reported on a novel alternative mechanism to achieve superconductivity in graphene. They achieved this feat by proposing a hybrid system consisting of graphene and 2D Bose-Einstein condensate (BEC). This research is published in the journal 2D Materials.

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Figure 1. A hybrid system consisting of an electron gas in graphene (top layer) separated from a two-dimensional Bose-Einstein condensate, represented by indirect excitons (blue and red layers). The electrons in the graphene and the excitons are coupled by the Coulomb force.

Along with superconductivity, BEC is another phenomenon that arises at low temperatures. It is the fifth state of matter first predicted by Einstein in 1924. The formation of BEC occurs when low-energy atoms clump together and enter the same energy state, and it is an area that is widely studied in condensed matter physics. A hybrid Bose-Fermi system essentially represents a layer of electrons interacting with a layer of bosons, such as indirect excitons, exciton-polaritons, etc. The interaction between Bose and Fermi particles leads to various novel fascinating phenomena, which piques interests from both the fundamental and application-oriented perspectives.

In this work, the researchers report a new mechanism of superconductivity in graphene, which arises due to interactions between electrons and “bogolons”, rather than phonons as in typical BCS systems. Bogolons, or Bogoliubov quasiparticles, are excitation within BEC which has some characteristics of a particle. In certain ranges of parameters, this mechanism permits the critical temperature for superconductivity up to 70 Kelvin within graphene. The researchers also developed a new microscopic BCS theory which focuses specifically on the novel hybrid graphene-based system. Their proposed model also predicts that superconducting properties can be enhanced with temperature, resulting in the non-monotonous temperature dependence of the superconducting gap.

Furthermore, the research showed that the Dirac dispersion of graphene is preserved in this bogolon-mediated scheme. This indicates that this superconducting mechanism involves electrons with relativistic dispersion — a phenomenon that is not so well-explored in condensed matter physics.

“This work sheds light on an alternative way to achieve high-temperature superconductivity. Meanwhile, by controlling the properties of a condensate, we can tune the superconductivity of graphene. This suggests another channel to control the superconductor devices in the future.”, explains Ivan Savenko, the leader of the Light-Matter Interaction in Nanostructures (LUMIN) team at the PCS IBS.

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Figure 2. (a) Temperature dependence of the superconducting gap for bogolon-mediated process with temperature correction (dashed) and without temperature correction (solid). (b) The critical temperature of the superconductivity transition as a function of condensate density for bogolon-mediated interaction with (red dashed) and without (black solid) the temperature correction. The blue dash-dotted line shows the BKT transition temperature as a function of the condensate density.

See the full article here.

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Making Discoveries for Humanity & Society

Institute for Basic Science [ 기초과학연구원](KR) pursues excellence in basic science research. The goal of IBS is to advance the frontiers of knowledge and to train the leading scientists of tomorrow.

Accelerate Transformation through New Knowledge

Institute for Basic Science [ 기초과학연구원](KR) was established in November 2011 as Korea’s first dedicated basic science research institute. By studying the fundamental principles of nature, basic science is essential in creating new knowledge from which significant societal transformations are derived. IBS promotes the highest quality of research that will increase the national basic science capacity and generate new opportunities for this nation.

IBS specializes in long-term projects that require large groups of researchers. As research in the 21st century requires more interdisciplinary collaborations from larger groups of people, scientists at IBS work together in the same laboratory base with a long-term perspective on research. We promote autonomy in research. IBS believes scientists unleash their creative potential most effectively when they conduct research in an autonomous environment with world-class research infrastructure, including RISP, the rare isotope accelerator, to enable major scientific advances. By developing strong synergies from outstanding talents, autonomous research support systems, and world-class infrastructure, IBS is steadily growing into a major basic research institute that meets the global standards of excellence.
Ensure Excellence in Research

By pursuing excellence in research, IBS has selected global leading scientists as directors of Centers. These directors are operating 31 Centers of which research proposals are evaluated superior in the IBS peer review process. The review is carried out by a Review Panel composed of independent and expert scientists from Korea and abroad. Directors choose the themes of their research and allocate funds accordingly. Generally, Centers operate projects with no fixed term for their duration as long as the quality of research is verified in evaluations. New Centers receive an initial evaluation five years after its launch, followed by three-year interval evaluations.

IBS has been inviting top scientists from around the globe and providing them full support for their relocations. Young scientists also enjoy unique research opportunities to collaborate with world renowned scientists and to organize and operate their own research groups, broadening their professional expertise. IBS brings together outstanding talents throughout all career levels to grow and inspire each other through close collaborations.

Stimulate Collaboration Without Boundaries

IBS welcomes scientists from Korea and abroad seeking to work in a collaborative research environment. IBS’ faculty researcher program and IBS’s affiliation with the founding body of University of Science & Technology [과학 기술 연합 대학원대학교] (KR) help IBS scientists to reach out to and foster young talent outside the institution. Centers serve as a catalyst for research collaboration with universities and other government-funded research institutions through joint research and the sharing of research equipment. Other efforts are also underway to stimulate collaborations, including overseas training programs and visiting scientist programs.

To disseminate research findings, IBS holds “IBS Conferences” and develops a global network with the world’s prominent research institutions including the MPG Society for the Advancement of Science [MPG Gesellschaft zur Förderung der Wissenschaften e. V.] (DE) and the Royal Society (UK). We expect our work to make transformative changes outside as well as inside the institution. To realize this exciting vision, IBS will serve as a national R&D platform and accelerate the creation and use of new knowledge to support universities, research institutions, and businesses. As a driving force for dynamic research collaborations, IBS will continually develop and refresh its science, while always remaining receptive to outside talents and ideas.
Continue its Endeavor to Make a Brighter Future

IBS shares the same passion as other great minds to investigate the origin of the universe, nature, and life for the development of humanity, as shown in its vision Masking Discoveries for Humanity & Society. We are committed to realizing this vision through a phased endeavor as outlined in our Five-year Plan (2013 – 2017). We aim to:

Become a national hub for basic science research by 2017
Complete the construction of the rare isotope accelerator by 2021
Evolve into one of the world’s top 20 basic research institution by 2030 (measured in terms of impact on research).

Serving as a stimulus for the innovation, IBS HQ will evolve into an urban science park that will promote public outreach and community engagement. Our commitment to enhance the quality of life and make sustainable progress continues every day.