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Study unveils a large tunable drag response between a normal conductor and a superconductor

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A huge drag effect was discovered between the graphene layer and the interfacial superconductor. Credit: Tao et al.

Colon drag is a phenomenon that affects two electronic circuits, where the charging current of one circuit induces a response current in the adjacent circuit only through the so-called colon interaction. These are electrostatic interactions between charges that obey Coulomb’s law, the key physical theory that explains classical electrodynamics.

Usually this phenomenon was investigated using adjacent circuits made of conducting materials. conductorThese are materials that inherently conduct electricity easily.

Researchers at the University of Science and Technology of China recently studied what happens when one circuit is based on a conductor and the adjacent circuit is based on a superconductor (that is, a material that offers no resistance to current flow). I investigated. Their findings were natural physicsin these examples we show that the drag response is significantly larger than previously observed in studies with two ordinary conductors.

“Drag experiments between two electrically isolated conductors were an effective approach to detect elementary excitations and reveal interlayer phase coherence,” said one of the researchers who conducted the study. , Changgan Zeng told Phys.org. “Replacing one of the conductors with a superconductor could open up opportunities to investigate the effects of superconductivity and fluctuations, and to explore new techniques for manipulating superconducting circuits. ”

The first drag experiments with conductors and superconductors were done in the 1990s. However, the devices in use at the time were based on conventional metallic superconductor bilayers such as Au/Ti-AlO.X.

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

“The emergence of two-dimensional (2D) materials has allowed us to revisit the problem. Electronic properties It is highly adjustable and even ultra-compact interlayer isolation can be archived,” said Lin Li, who designed and supervised this work together with Zeng.

“The USTC experimental group led by Professor Zeng has long experience in fabricating devices and investigating the transport properties of 2D materials. We naturally designed our own Graphene-LaAlO.3/SrTiO3 Heterostructures for studying drag effects in the ultimate 2D limit. ”

The heterostructure used by Zeng and his colleagues in their experiments consists of a lanthanum aluminate (LAO) layer between the conducting graphene and a 2D electron gas formed at the interface between the LAO and strontium titanate (STO) layers. Manufactured using as a natural insulating spacer. , becomes a superconductor at low temperatures.

The researchers then tuned multiple parameters of the system, including temperature, magnetic field, and gate voltage. When they did this, they observed a rather large and tunable drag signal in the superconducting transition region of his LAO/STO interface.

“The optimal passive/active ratio (PAR) is much higher than the typical drag signal between two ordinary conductors and the drag signal between Au/Ti and SC AlO.X “The huge values ​​and unusual temperature and carrier dependence of PAR indicate that a new drag mechanism is hidden behind our observations,” said Li.

Dr. Hong-Yi Xie theoretical physicist PhDs from the Beijing Academy of Quantum Information Science, who recently moved to the University of Oklahoma, used modern quantum many-body theory to explain the team’s observations. More specifically, we have developed a theoretical description of what happens when a Coulomb-coupled normalconductor is paired with a superconductor.

“Finally, we show that the observed drag phenomenon can be attributed to dynamic coupling between quantum fluctuations in the SC phase of Josephson junction array superconductors and the charge density of ordinary conductors. JC) drug effect,” said Zeng. “The revealed JC drag effect creates a new category in drag physics and reveals the unique role of quantum fluctuations in governing interlayer processes.”

A recent study by this team of researchers found that the normal drag response conductor Also, superconductors can be much larger than between two regular conductors. This discovery could have important implications for both physics research and technology development.

The JC drugs revealed by researchers could prove particularly promising for creating new electronics. Specifically, it may contribute to the creation of components based on superconductors that act as current transformers or voltage transformers.

“For our next work, we hope to first perform drag experiments between two 2D superconductors,” Zeng added. In addition, we plan to investigate the emergent interlayer coupling between a wide range of His 2D systems exhibiting different quantum phases, such as 2D topological semimetals/insulators and He 2D ferromagnets, by parameter tuning. Various elementary excitations. ”

For more information:
Ran Tao et al., Josephson–Coulomb drag effect between graphene and LaAlO3/SrTiO3 superconductors, natural physics (2023). DOI: 10.1038/s41567-022-01902-7

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