The study reveals a large tunable drag response between a normal conductor and a superconductor

A giant drag effect was detected between the graphene layer and the surface superconductor, which can be attributed to a unique interaction between normal electrons and dynamic fluctuations of superconducting phases mediated by static Coulomb fields. Credit: Tao et al.

The Coulomb draw is a phenomenon affecting two electronic circuits, in which the charging current in one circuit causes a responsive current in an adjacent circuit only through what are called Coulomb interactions. These are electrostatic interactions between electric charges that follow Coulomb’s law, the key physics theory that describes classical electrodynamics.

Usually, this phenomenon has been investigated using adjacent circuits made of conductive materials, or . These are basically materials through which electricity can easily flow.

Researchers at the University of Science and Technology in China recently discovered what happens when one circuit is based on a conductor and another adjacent circuit is based on a superconductor (that is, materials that offer absolutely no resistance to electric current). Their findings, published in nature physicsshowed that in these cases the pull-up response is much larger than that previously observed in studies using two normal conductors.

“The drawing experiment between two electrically insulated conductors was an effective method for detecting elemental excitation and for revealing interphase coherence,” Changgan Zeng, one of the researchers who conducted the study, told “Replacing a conductor with a superconductor may open up opportunities to examine the effects of superconductivity and oscillation as well as to explore new techniques for manipulating superconductor circuits.”

The first towing experiments with conductors and superconductors were conducted in the 1990s. However, the devices used at that time were based on conventional metallic superconducting double films, such as Au/Ti-AlOX.

The withdrawal responses observed in these experiments were rather weak and uncontrolled. Furthermore, the researchers were unable to elucidate the microscopic origin of the drag effect they observed.

Thanks to the newly emerging two-dimensional (2D) materials, we have been able to revisit the problem, since There is high tunability, and the very small interlayer separation can be archived, said Lin Li, who designed and supervised this work with Zeng.

“Our experimental group at USTC led by Professor Zeng has long experience in device fabrication and investigation of transport properties of 2D materials. We engineered the unique naturally occurring graphene-LaAlO3/ SrTiO3 Heterogeneous structure to study the influence of drag in the final 2D boundary. ”

The heterostructure used by Zeng and co-workers in their experiments was fabricated using a lanthanum aluminate (LAO) layer as a natural insulating spacer between the conductive graphene and the two-dimensional electron gas formed at the interface between the LAO and the strontium titanate (STO) layer, which becomes superconductive at low temperatures. .

The researchers then adjusted for multiple parameters of their system, including temperature, magnetic field, and gate voltages. While they did so, they observed a large, tunable pull signal in the superconducting transition system of the LAO/STO interface.

“The optimal active-to-active ratio (PAR) is much higher than the typical pull-out signal between two ordinary conductors as well as between Au/Ti and SC AlOx “They were obtained in the current studies. Giant values, anomalous temperatures, and carrier dependence of PAR indicate that a new withdrawal mechanism is hidden behind our observations,” Li said.

Dr. Hong Yi Shi, prof At the Beijing Academy of Quantum Information Sciences, who recently transferred to the University of Oklahoma, he used modern quantum theory of the plethora of objects to explain the team’s observations. More specifically, he developed a theoretical description of what happens when an ordinary Coulomb-coupled conductor is paired with a superconductor.

“Ultimately, we revealed that the observed drag phenomenon can be attributed to the dynamic coupling between the quantum fluctuations of SC phases in a Josephson junction array superconductor and the charge density in a normal conductor, which we named the Josephson coulomb (JC) drag effect,” Zeng said. The unveiled JC drag effect creates a new class in cloud physics and demonstrates the unique role of quantum fluctuations in controlling interlayer processes.”

Recent work by this team of researchers shows that the drag response is normal A superconductor can be much larger than a superconductor between two normal conductors. This finding could have major implications for both physics research and technology development.

The JC clouds revealed by the researchers could be particularly promising for creating new electronics. Specifically, it could contribute to the creation of components based on superconductors that can act as current or voltage converters.

“In our next work, we would like to first perform pull experiments between two 2D superconductors,” Zeng added. Furthermore, we plan to investigate emerging interlayer coupling between larger-scale 2D systems that exhibit different quantum phases by tuning parameters, that is, a 2D semimetal/topological insulator and a 2D ferromagnet. We aim to discover new effects of several objects due to strong coupling between the interlayers of various primary excitations.

more information:
Ran Tao et al, Effect of Josephson-Coulomb drag between graphene and a LaAlO3/SrTiO3 superconductor, nature physics (2023). DOI: 10.1038/s41567-022-01902-7

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