Conductors

Researchers from MIT and Japan's National Institute for Materials Science have directly measured superfluid stiffness for the first time in “magic-angle” graphene — two or more atomically thin sheets of graphene twisted with respect to each other at just the right angle to enable a host of exceptional properties, including unconventional superconductivity. The term “superfluid stiffness,” or the ease with which a current of electron pairs can flow, is a key measure of a material’s superconductivity.

This superconductivity makes magic-angle graphene a promising building block for future quantum-computing devices, but exactly how the material superconducts is not well-understood. Knowing the material’s superfluid stiffness will help scientists identify the mechanism of superconductivity in magic-angle graphene. The team’s measurements suggest that magic-angle graphene’s superconductivity is primarily governed by quantum geometry, which refers to the conceptual “shape” of quantum states that can exist in a given material.

Researchers at Korea's Pohang University of Science and Technology and Japan's National Institute for Materials Science have developed a way to control the properties of graphene by combining superconductors and graphene. 

Professor Lee Gil-ho of Pohang University of Science and Technology (POSTECH) and researchers from the Research Institute, in collaboration with Kenji Watanabe and Takashi Taniguchi from the National Institute for Materials Science (NIMS) in Japan, noted they have successfully improved the junction characteristics between graphene and superconducting electrodes. 

When two sheets of are stacked together and offset at a slight angle, the bilayer material can produce numerous intriguing effects, notably superconductivity. Cornell University researchers have gained new understanding on how twisted bilayer graphene achieves this state, by identifying its highest achievable superconducting temperature – 60 Kelvin. The finding is said to be mathematically exact, a rare feat in the field, and is spurring new insights into the factors that fundamentally control superconductivity. 

“Looking ahead, this paves the way for understanding what are the possible degrees of freedom that one should try to control and optimize in order to enhance the tendency towards superconductivity in these two-dimensional material platforms,” said Debanjan Chowdhury, who co-authored the recent study.

A research team consisting of private sector and academic partners and led by NETL (a U.S. Department of Energy national laboratory that drives innovation and delivers solutions for a clean and secure energy future) is working on a new ultra-conductive carbon (graphite and graphene) aluminum composite cable technology that could increase the electrical conductivity and strength of transmission cables leading to higher grid capacity and efficiency to accommodate future power generation demand.

In addition to NETL, the research team includes, Ohio University, MetalKraft Technologies, Frisk Alloy, Hydro Extensions, General Graphene Corporation and CONSOL Innovations.

Salgenx, developer of saltwater flow battery technology, has announced the expansion of its development of graphene and hard carbon-coated sand. Originally designed for use in advanced battery systems, Salgenx is now exploring a wide array of new applications for this innovative material, ranging from smart infrastructure to environmental sustainability.

The Company says that "the unique combination of graphene and hard carbon in a sand aggregate has the potential to transform the construction industry". By enhancing the electrical conductivity, mechanical strength, and durability of concrete, Salgenx’s carbon-coated sand opens up new possibilities in building and infrastructure development.

Professors Gil-Ho Lee and Gil Young Cho from Pohang University of Science and Technology (POSTECH) in South Korea have collaborated with Dr. Kenji Watanabe and Dr. Takashi Taniguchi from National Institute for Materials Science (NIMS) in Japan to successfully control the quantum mechanical properties of Andreev bound states in bilayer graphene-based Josephson junctions using gate voltage. 

Superconductors exhibit zero electrical resistance under specific conditions such as extremely low temperatures or high pressures. When a very thin normal conductor is placed between two superconductors, a supercurrent flows through it due to the proximity effect where superconductivity extends into the normal conductor. This device is known as a Josephson junction. Within the normal conductor, new quantum states called Andreev bound states are formed, which are crucial for mediating the supercurrent flow.

Researchers from Japan's Tokyo Institute of Technology and Institute for Molecular Science recently investigated the impact of high-density Ca introduction to C₆CaC₆ - a graphene-calcium compound which exhibits high critical temperature. In this compound, a layer of calcium is introduced between two graphene layers in a process called intercalation. 

While this material already has high critical temperatures, some studies have shown that critical temperatures and therefore superconductivity can be further enhanced through the introduction of high-density Ca.

An international team of researchers, led by the University of Manchester, has achieved robust superconductivity in high magnetic fields using a newly created one-dimensional system. Achieving superconductivity in the quantum Hall regime has been a longstanding challenge, which this recent work aimed to address. 

The team followed the conventional route where counterpropagating edge states were brought into close proximity to each other. However, this approach was found to be limited. “Our initial experiments were primarily motivated by the strong persistent interest in proximity superconductivity induced along quantum Hall edge states,” explained University of Mnchester's Dr. Barrier, the paper’s lead author. “This possibility has led to numerous theoretical predictions regarding the emergence of new particles known as non-abelian anyons.”

Researchers from California Institute of Technology (Caltech) and Japan's National Institute for Materials Science have shown that when tungsten diselenide is added to graphene, graphene's electrical properties can be enhanced.

When two or more graphene sheets are stacked on top of each other, the resulting material can exhibit vastly different electronic properties depending on the alignment of those sheets in relation to one another. For instance, when the second sheet of graphene is "twisted" by just 1.05 degrees (a value known as the "magic angle") in relation to the sheet it is laid on top of, the resulting stack can be either a superconductor that conducts electricity with absolutely no resistance whatsoever or an insulator that completely blocks the passage of electricity. Research conducted in 2022 shows that even untwisted graphene bilayers can exhibit superconductivity. Untwisted bilayers of graphene are easier to fabricate in bulk than their twisted counterparts, but the superconductive state in these untwisted bilayers is more delicate, harder to tune, and only occurs at temperatures that are about a hundred times lower than in twisted structures (such temperatures typically can only be achieved through the use of liquid helium). The recent research shows a way to significantly improve upon this fragile superconductivity with tungsten diselenide.

Researchers from Ohio State University, The University of Texas at Dallas and Japan's National Institute for Materials Science have reported new evidence of how graphene, when twisted to a precise angle, can become a superconductor, moving electricity with no loss of energy.

The team announced their finding of the key role that quantum geometry plays in allowing this twisted graphene to become a superconductor.