Similarities in the insulating states of twi…

Similarities in the insulating states of twisted bilayer graphene and cuprates

In recent decades, enormous research efforts have been expended on the exploration and explanation of high-temperature (high-Tc) superconductors, a class of materials exhibiting zero resistance at particularly high temperatures. Now a team of scientists from the United States, Germany and Japan explains in Nature how the electronic structure in twisted bilayer graphene influences the emergence of the insulating state in these systems, which is the precursor to superconductivity in high-Tc materials.

Finding a material which superconducts at room temperature would lead to a technological revolution, alleviate the energy crisis (as nowadays most energy is lost on the way from generation to usage) and boost computing performance to an entirely new level. However, despite the progress made in understanding these systems, a full theoretical description is still elusive, leaving our search for room temperature superconductivity mainly serendipitous.

In a major scientific breakthrough in 2018, twisted bilayer graphene (TBLG) was shown to exhibit phases of matter akin to those of a certain class of high-Tc superconducting materials—the so-called high-Tc cuprates. This represents a novel inroad via a much cleaner and more controllable experimental setup.

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From Japanese basket weaving art to nanotech…

From Japanese basket weaving art to nanotechnology with ion beams

The properties of high-temperature superconductors can be tailored by the introduction of artificial defects. An international research team around physicist Wolfgang Lang at the University of Vienna has succeeded in producing the world’s densest complex nano arrays for anchoring flux quanta, the fluxons. This was achieved by irradiating the superconductor with a helium-ion microscope at the University of Tübingen, a technology that has only recently become available. The researchers were inspired by a traditional Japanese basket weaving art. The results have been published recently in ACS Applied Nano Materials, a journal of the renowned American Chemical Society.

Superconductors can carry electricity without loss if they are cooled below a certain critical temperature. However, pure superconductors are not suitable for most technical applications, but only after controlled introduction of defects. Mostly, these are randomly distributed, but nowadays the tailored periodic arrangement of such defects becomes more and more important.

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Experiments explore the mysteries of ‘…

Experiments explore the mysteries of ‘magic’ angle superconductors

In spring 2018, the surprising discovery of superconductivity in a new material set the scientific community abuzz. Built by layering one carbon sheet atop another and twisting the top one at a “magic” angle, the material enabled electrons to flow without resistance, a trait that could dramatically boost energy efficient power transmission and usher in a host of new technologies.

Now, new experiments conducted at Princeton give hints at how this material—known as magic-angle twisted graphene—gives rise to superconductivity. In this week’s issue of the journal Nature, Princeton researchers provide firm evidence that the superconducting behavior arises from strong interactions between electrons, yielding insights into the rules that electrons follow when superconductivity emerges.

“This is one of the hottest topics in physics,” said Ali Yazdani, the Class of 1909 Professor of Physics and senior author of the study. “This is a material that is incredibly simple, just two sheets of carbon that you stick one on top of the other, and it shows superconductivity.”

Exactly how superconductivity arises is a mystery that laboratories around the world are racing to solve. The field even has a name, “twistronics.”

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A graphene superconductor that plays more than…

A graphene superconductor that plays more than one tune: Researchers at Berkeley Lab have developed a tiny toolkit for scientists to study exotic quantum physics

Researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have developed a graphene device that’s thinner than a human hair but has a depth of special traits. It easily switches from a superconducting material that conducts electricity without losing any energy, to an insulator that resists the flow of electric current, and back again to a superconductor – all with a simple flip of a switch. Their findings were reported today in the journal Nature.


“Usually, when someone wants to study how electrons interact with each other in a superconducting quantum phase versus an insulating phase, they would need to look at different materials. With our system, you can study both the superconductivity phase and the insulating phase in one place,” said Guorui Chen, the study’s lead author and a postdoctoral researcher in the lab of Feng Wang, who led the study. Wang, a faculty scientist in Berkeley Lab’s Materials Sciences Division, is also a UC Berkeley physics professor.

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Alternative material for superconducting rad…

Alternative material for superconducting radio-frequency cavity

In modern synchrotron sources and free-electron lasers, superconducting radio-frequency cavity resonators are able to supply electron bunches with extremely high energy. These resonators are currently constructed of pure niobium. Now an international collaboration has investigated the potential advantages a niobium-tin coating might offer in comparison to pure niobium.

At present, niobium is the material of choice for constructing superconducting radio-frequency cavity resonators. These will be used in projects at the HZB such as bERLinPro and BESSY-VSR, but also for free-electron lasers such as the XFEL and LCLS-II. However, a coating of niobium-tin (Nb3Sn) could lead to considerable improvements.

Superconducting radio-frequency cavity resonators made of niobium must be operated at 2 Kelvin (-271 degrees Celsius), which requires expensive and complicated cryogenic engineering. In contrast, a coating of Nb3Sn might make it possible to operate resonators at 4 Kelvin instead of 2 Kelvin and possibly withstand higher electromagnetic fields without the superconductivity collapsing. In the future, this could save millions of euros in construction and electricity costs for large accelerators, as the cost of cooling would be substantially lower.

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Pairing ‘glue’ for electrons in …

Pairing ‘glue’ for electrons in iron-based high-temp superconductors studied

Newly published research from a team of scientists led by the U.S. Department of Energy’s Ames Laboratory sheds more light on the nature of high-temperature iron-based superconductivity.

Current theories suggest that magnetic fluctuations play a very significant role in determining superconducting properties and even act as a “pairing glue” in iron-based superconductors.

“A metal becomes a superconductor when normal electrons form what physicists call Cooper pairs. The interactions responsible for this binding are often referred to as ‘pairing glue.’ Determining the nature of this glue is the key to understanding, optimizing and controlling superconducting materials,” said Ruslan Prozorov, an Ames Laboratory physicist who is an expert in superconductivity and magnetism.

The scientists, from Ames Laboratory, Nanjing University, University of Minnesota, and L’École Polytechnique, focused their attention on high quality single crystal samples of one widely studied family of iron-arsenide high-temperature superconductors. They sought an experimental approach to systematically disrupt the magnetic, electronic and superconducting ordered states; while keeping the magnetic field, temperature, and pressure unchanged.

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Physicists use light waves to accelerate sup…

Physicists use light waves to accelerate supercurrents, enable ultrafast quantum computing

Jigang Wang patiently explained his latest discovery in quantum control that could lead to superfast computing based on quantum mechanics: He mentioned light-induced superconductivity without energy gap. He brought up forbidden supercurrent quantum beats. And he mentioned terahertz-speed symmetry breaking.

Then he backed up and clarified all that. After all, the quantum world of matter and energy at terahertz and nanometer scales – trillions of cycles per second and billionths of meters – is still a mystery to most of us.

“I like to study quantum control of superconductivity exceeding the gigahertz, or billions of cycles per second, bottleneck in current state-of-the-art quantum computation applications,” said Wang, a professor of physics and astronomy at Iowa State University whose research has been supported by the Army Research Office. “We’re using terahertz light as a control knob to accelerate supercurrents.”

Superconductivity is the movement of electricity through certain materials without resistance. It typically occurs at very, very cold temperatures. Think -400 Fahrenheit for “high-temperature” superconductors.

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A peculiar ground-state phase for 2-D superc…

A peculiar ground-state phase for 2-D superconductors

The application of large enough magnetic fields results in the disruption of superconducting states in materials, even at drastically low temperature, thereby changing them directly into insulators—or so was traditionally thought. Now, scientists at Tokyo Institute of Technology (Tokyo Tech), the University of Tokyo and Tohoku University report curious multi-state transitions of these superconductors in which they change from superconductor to special metal and then to insulator.

Characterized by their zero electrical resistance, or alternatively, their ability to completely expel external magnetic fields, superconductors have fascinating prospects for both fundamental physics and applications for e.g., superconducting coils for magnets. This phenomenon is understood by considering a highly ordered relationship between the electrons of the system .Due to a coherence over the entire system, electrons form bounded pairs and flow without collisions as a collective, resulting in a perfect conducting state without energy dissipation. However, upon introducing a magnetic field, the electrons are no longer able to maintain their coherent relationship, and the superconductivity is lost. For a given temperature, the highest magnetic field under which a material remains superconducting is known as the critical field.

Often these critical points are marked by phase transitions. If the change is abrupt like in the case of melting of ice, it is a first-order transition. If the transition takes place in a gradual and continuous manner by the growth of change-driving fluctuations extending on the entire system, it is called a second-order transition. Studying the transition path of superconductors when subjected to the critical field can yield insights into the quantum processes involved and allows us to design smarter superconductors (SCs) for application to advanced technologies.

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Confirmation of old theory leads to new brea…

Confirmation of old theory leads to new breakthrough in superconductor science

Phase transitions occur when a substance changes from a solid, liquid or gaseous state to a different state—like ice melting or vapor condensing. During these phase transitions, there is a point at which the system can display properties of both states of matter simultaneously. A similar effect occurs when normal metals transition into superconductors—characteristics fluctuate and properties expected to belong to one state carry into the other.

Scientists at Harvard have developed a bismuth-based, two-dimensional superconductor that is only one nanometer thick. By studying fluctuations in this ultra-thin material as it transitions into superconductivity, the scientists gained insight into the processes that drive superconductivity more generally. Because they can carry electric currents with near-zero resistance, as they are improved, superconducting materials will have applications in virtually any technology that uses electricity.

The Harvard scientists used the new technology to experimentally confirm a 23-year-old theory of superconductors developed by scientist Valerii Vinokur from the U.S. Department of Energy’s (DOE) Argonne National Laboratory.

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A new quasi-2D superconductor that bridges a…

A new quasi-2D superconductor that bridges a ferroelectric and an insulator

Researchers at the Zavoisky Physical-Technical Institute and the Southern Scientific Center of RAS, in Russia, have recently fabricated quasi-2-D superconductors at the interface between a ferroelectric Ba0.8Sr0.2TiO3 film and an insulating parent compound of La2CuO4. Their study, presented in a paper published in Physical Review Letters, is the first to achieve superconductivity in a heterostructure consisting of a ferroelectric and an insulator.

The idea of forming a quasi-2-D superconducting layer at the interfacebetween two different compounds has been around for several years. One past study, for instance, tried to achieve this by creating a thin superconducting layer between two insulating oxides (LaAlO3 and SrTiO3) with a critical temperature of 300mK. Other researchers observed the thin superconducting layer in bilayers of an insulator (La2CuO4) and a metal (La1.55Sr0.45CuO4), neither of which is superconducting in isolation.

“Here we put forward the idea that thin charged layer on the interface between ferroelectric and insulator is formed in order to screen the electric field,” Viktor Kabanov and Rinat Mamin, two researchers who carried out the study, told via email. “This thin layer may be conducting or superconducting depending on the properties of the insulator. In order to get a superconducting layer, we chose La2CuO4 – an insulator that becomes a high Tc superconductor when it is doped by carriers.”

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