Mirror interband Andreev reflections on van der Waals contacts between graphene and niobium selenide
The February issue of the most respected scientific journal Nature Physics published an article by our leading scientist Konstantin Borisovich Efetov . Online version of the article Specular interband Andreev reflections at van der Waals
interfaces between graphene and NbSe2 This article presents the results of studying the properties of the contacts between superconductors and graphene, the experiment proved the possibility of producing high-quality contacts between the graphene and superconductors, which in turn will bring the researchers to create new electronic devices and possibly a quantum computer. Of course, this goal is in a great perspective, but researchers have already managed to observe an interesting fundamental effect - a mirror Andreev reflection.
It is noteworthy that the experiment itself was conducted by Dmitry Efetov, the son of Konstantin Borisovich.
Konstantin Borisovich already wrote for our blog an expert opinion on high-temperature superconductivity , where this effect was described in a fairly popular format, this publication caused an active discussion and approval from the community. And this time we also asked Konstantin Efetov to write a press release for us on the published article.
An international group of researchers with the participation of a scientist working under a grant at NUST MISiS published an important work on the study of the properties of contacts between superconductors and graphene. Interest in the creation and study of such nanostructures is due to the search for new possibilities for electronics arising from the use of the quantum properties of matter, as well as attempts to create a quantum computer. It is important to note that the effect, first observed in the work, has a deep fundamental nature and broadens the understanding of the most interesting effects of “nanophysics”. An article about this work is published in the latest issue of Nature Physics.
Electrons flying from a normal metal onto a superconductor are reflected exactly back in the form of holes (an absent electron is usually described as a quasiparticle-hole). This remarkable prediction was first made by the outstanding Russian physicist A.F. Andreev in 1964
The observation of this effect became possible with the development of nanotechnology and attracted great attention of both experimenters and theoreticians, since superconducting structures are used in electronic devices. Currently, the creation of arrays of superconducting islands is the main direction in the construction of a quantum computer.
New opportunities arose with the advent of graphene, a two-dimensional material consisting of carbon atoms. For its creation, A. Geim and K. Novosyolov received the Nobel Prize in 2010. Due to its extraordinary properties, graphene has gained immense popularity in recent years, and is considered as one of the most promising materials for semiconductor electronics.
In 2007, the Dutch scientist K. Beyenakker noted in his theoretical work that the Andreev reflection in this case can significantly change its properties, so that the holes will not be reflected back, but in a mirror way, as light is reflected in the mirror. This effect occurs due to the two-band electronic spectrum of graphene. These two zones are in contact at certain points, and if the electron energy is close enough to these points, it is possible that the incident electron is in the upper zone and the reflected hole is in the lower one. This is exactly what should have led to a mirror image.
Although the contacts between graphene and superconductors were fabricated already several years ago, the observation of Andreev reflection was a daunting task, since extremely pure graphene systems were required. The creation of high-quality contacts between graphene and the superconducting selenide of niobium and ultrapure graphene samples made it possible to ultimately observe the Andreev reflection.
The experiment was conducted mainly at Columbia University in New York with support from Princeton University and the National Institute of Materials Science in Japan. The experimental data were compared with the results of a theoretical calculation carried out by Konstantin Efetov (project manager in the framework of the Top 100 program) during his work at NUST “MISiS”. The good agreement between theory and experiment allowed us to conclude that it is precisely the Andreev reflection that is observed.
interfaces between graphene and NbSe2 This article presents the results of studying the properties of the contacts between superconductors and graphene, the experiment proved the possibility of producing high-quality contacts between the graphene and superconductors, which in turn will bring the researchers to create new electronic devices and possibly a quantum computer. Of course, this goal is in a great perspective, but researchers have already managed to observe an interesting fundamental effect - a mirror Andreev reflection.
The reflection of electrons from the boundary between a normal metal and a superconductor is called "Andreev" in honor of the outstanding Soviet physicist Alexander Andreev, who predicted such an behavior of an electron between an ordinary metal and a superconductor.
It is noteworthy that the experiment itself was conducted by Dmitry Efetov, the son of Konstantin Borisovich.
Konstantin Borisovich already wrote for our blog an expert opinion on high-temperature superconductivity , where this effect was described in a fairly popular format, this publication caused an active discussion and approval from the community. And this time we also asked Konstantin Efetov to write a press release for us on the published article.
Konstantin Borisovich Efetov is the Scientific Director of the project "Collective Phenomena in Quantum Matter" NUST "MISiS" as part of a grant to support research on the TOP 5-100 program. K.B. Efetov is an outstanding reviewer of the American Physical Society, Director of the Institute of Theoretical Physics of the Third Ruhr University of Bochum in Germany, an honorary member of the American Physical Society , a leading researcher of three projects funded by the German Ministry of Scientific Research, author of more than 170 publications, winner of the French Blaise Pascal Prizeestablished by the French government and the Landau-Weizman Research Award established by the Weizmann Institute in Israel. Konstantin Efetov is “an outstanding reviewer of the American Physical Society.” This Award is given for his notable contribution to reviewing articles in journals such as Physical Review Letters, Physical Review, Reviews of Modern Physics and others.
An international group of researchers with the participation of a scientist working under a grant at NUST MISiS published an important work on the study of the properties of contacts between superconductors and graphene. Interest in the creation and study of such nanostructures is due to the search for new possibilities for electronics arising from the use of the quantum properties of matter, as well as attempts to create a quantum computer. It is important to note that the effect, first observed in the work, has a deep fundamental nature and broadens the understanding of the most interesting effects of “nanophysics”. An article about this work is published in the latest issue of Nature Physics.
Electrons flying from a normal metal onto a superconductor are reflected exactly back in the form of holes (an absent electron is usually described as a quasiparticle-hole). This remarkable prediction was first made by the outstanding Russian physicist A.F. Andreev in 1964
 | Konstantin Borisovich Efetov Scientific director of the project "Collective Phenomena in Quantum Matter" NUST "MISiS" |
The observation of this effect became possible with the development of nanotechnology and attracted great attention of both experimenters and theoreticians, since superconducting structures are used in electronic devices. Currently, the creation of arrays of superconducting islands is the main direction in the construction of a quantum computer.
New opportunities arose with the advent of graphene, a two-dimensional material consisting of carbon atoms. For its creation, A. Geim and K. Novosyolov received the Nobel Prize in 2010. Due to its extraordinary properties, graphene has gained immense popularity in recent years, and is considered as one of the most promising materials for semiconductor electronics.
But what if graphene is used instead of ordinary metals in contacts with superconductors? How will electrons incident from graphene onto the surface of a superconductor be reflected?
In 2007, the Dutch scientist K. Beyenakker noted in his theoretical work that the Andreev reflection in this case can significantly change its properties, so that the holes will not be reflected back, but in a mirror way, as light is reflected in the mirror. This effect occurs due to the two-band electronic spectrum of graphene. These two zones are in contact at certain points, and if the electron energy is close enough to these points, it is possible that the incident electron is in the upper zone and the reflected hole is in the lower one. This is exactly what should have led to a mirror image.
Although the contacts between graphene and superconductors were fabricated already several years ago, the observation of Andreev reflection was a daunting task, since extremely pure graphene systems were required. The creation of high-quality contacts between graphene and the superconducting selenide of niobium and ultrapure graphene samples made it possible to ultimately observe the Andreev reflection.
The experiment was conducted mainly at Columbia University in New York with support from Princeton University and the National Institute of Materials Science in Japan. The experimental data were compared with the results of a theoretical calculation carried out by Konstantin Efetov (project manager in the framework of the Top 100 program) during his work at NUST “MISiS”. The good agreement between theory and experiment allowed us to conclude that it is precisely the Andreev reflection that is observed.
The results of the work were reported by one of the authors of the work, Dmitry Efetov (Massachusetts Institute of Technology) at the conference “Superconductivity and Magnetism”, held at NUST “MISiS” in September 2015 as part of the Top 5-100 program.The main goal of the experiment was to observe the fundamental effect. But, as often happens, the development of the technologies necessary for conducting research paves the way for the creation of new devices. At present, great hopes for constructing qubits (basic elements in a quantum computer) are assigned to “transmons” —Josephson contacts connected in parallel with capacitors. Josephson junctions are superconductors interconnected by a dielectric or a normal metal. For the construction of qubits, for example, semiconductor wires that provide good contacts with superconductors are taken as connecting material. The possibility of manufacturing high-quality contacts between graphene and a superconductor, achieved in the work,