superconductivity – Lightsources.org

A New Twist for Superconductivity in Bilayer Graphene

2025/06/202025/06/24

Using the Advanced Light Source (ALS) to study twisted bilayer graphene (TBG) systems, researchers found intriguing spectroscopic features in a superconducting “magic-angle” TBG—features that are absent in non-superconducting TBG.

The results provide crucial information on superconductivity in magic-angle TBG for next-gen electronics and advanced energy technologies.

Searching for the science behind the magic

Two-dimensional materials like graphene give scientists great flexibility in engineering electronic properties because they can be stacked like sheets of paper. Besides choosing what materials to stack and in what order, researchers can manipulate the electrical and optical properties of these stacks by controlling the twist angle between layers. Because of this versatility, two-dimensional materials provide an ideal platform for investigating the complex interplay between phenomena such as band topology, strong electron correlation, magnetism, and superconductivity, all of which are relevant to next-gen electronics and advanced energy technologies.

So-called “magic-angle” twisted bilayer graphene (MATBG) attracts broad research interest primarily because of its surprising and unusual superconducting properties, which resemble those of high-temperature superconductors. The superconductivity in MATBG devices is thought to arise from flat bands that form in a material’s electronic band structure when two layers of graphene are twisted at a “magic” angle of about 1.08 degrees. Flat bands indicate a high density of states, which significantly enhances electron interactions and the resulting potential for exotic phenomena. Despite intensive experimental efforts, the origin of MATBG superconductivity remains elusive.

Advanced micro-ARPES at the ALS

Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool for probing the fine electronic structure of materials and has played a pivotal role in unraveling the mechanisms of high-temperature superconductivity and discovering novel topological quantum materials. However, due to the microscale dimensions of MATBG devices, traditional ARPES techniques, typically limited to a spatial resolution of hundreds of microns, cannot be directly applied. Persistent efforts have led to the development of advanced micro- and nano-ARPES techniques, extending ARPES research to sub-micrometer quantum materials and devices.

Here, researchers systematically characterized the electronic structure of several twisted bilayer graphene (TBG) devices using micro-ARPES at ALS Beamline 7.0.2 (MAESTRO), where a world-leading nano-ARPES system has also been developed. The high-quality moiré superlattice and superconductivity of these devices were characterized by a group at Princeton University.

Read more on ALS website

Image: Artistic depiction of a twisted bilayer graphene system. A very slight twist in the alignment of the two graphene layers creates a moiré pattern—a periodic modulation of the electronic environment that can give rise to exotic behaviors such as superconductivity. Advanced nanoscale probes provide important clues as to the connections between electronic structure and material properties.

Mapping the Quantum Landscape of Electrons in Solids

2025/03/312025/04/02

SCIENTIFIC ACHIEVEMENT

Using data from the Advanced Light Source (ALS), researchers found a way to reconstruct quantum geometric tensors (QGTs)—mathematical entities that encode how an electron’s wave function is shaped by its quantum environment.

SIGNIFICANCE AND IMPACT

The mapping of QGTs enables the discovery and control of novel quantum phenomena such as superconductivity and unconventional electronic phases.

Toward a second quantum revolution

The development of quantum mechanics—featuring concepts such as quantized energy levels, wave-particle duality, and the uncertainty principle—revolutionized physics in the early 20th century. It led to the rise of the wave function as a way to describe, mathematically, the quantum state of a system (such as electrons in a crystal).

A more recent development, the quantum geometric tensor (QGT) is also a mathematical entity, this time describing how wave functions are affected by changes in a material’s quantum “landscape” (e.g., the material’s structure, its topological properties, electron-electron interactions, and spin-orbit coupling). The QGT is therefore a fundamental physical concept that helps explain a range of quantum phenomena in materials. However, despite its importance, a generic method for measuring the QGT in solids has been lacking.

In this work, researchers outline a way to measure the momentum-resolved QGT of solids using angle-resolved photoemission spectroscopy (ARPES). In addition to being fundamentally interesting, the QGT is also important for potential applications in next-generation microelectronics and advanced energy technologies. Studies involving the QGT will contribute immensely to what’s been dubbed the “second quantum revolution,” focusing on the control and harnessing of quantum nature at the device scale.

Introducing the quasi-QGT

Previously, the tools available for determining the QGT could only measure momentum-integrated phenomena, which are summed over all electron momenta. However, the QGT is, by definition, momentum resolved. To overcome this problem, a collaboration—primarily between theorists from Seoul National University and experimentalists from Massachusetts Institute of Technology (MIT)—introduced a quasi-QGT that is proportional to the QGT in two-band systems and an excellent approximation in multiband systems.

Like the QGT, the quasi-QGT is a complex quantity with real and imaginary parts. However, unlike the QGT, the real and imaginary parts of the quasi-QGT correspond to quantities measurable using ARPES: the momentum-resolved effective mass of electrons (i.e., the band Drude weight) for the real part, and the orbital angular momentum (OAM) of photoemitted electrons for the imaginary part.

Read more on ALS website

Image: The curvature of the surface where it touches the sphere depicts one aspect of an electron’s quantum landscape: the momentum-resolved effective mass of electrons in a solid. In this work, researchers established that measurements of this quantity plus the orbital angular momentum of photoemitted electrons—both accessible using angle-resolved photoemission spectroscopy (ARPES)—enable the experimental reconstruction of the QGT. The sphere is shown as a local approximation to the curvature of the surface.

Credit: Comin lab/MIT

Researchers investigate the origins of superconductivity

2022/10/262022/11/11

The first scientific paper published with data obtained at the EMA beamline studied the relationship between skutterudite’s superconducting properties and the distance between their atoms.

In Brazil, about 7.5% of the electricity produced is lost in transmission and distribution. This happens because the materials that make up these systems are not perfect electrical conductors and dissipate part of the energy, for example, in the form of heat. Similarly, even though electric cars are much more efficient than combustion-engine vehicles, they can still lose up to 15 percent of their energy during the charging process.

Thus, the challenges of achieving sustainable development lie not only in the availability of abundant, clean, and cheap energy, but also in the development of new, efficient, and low-cost energy transport and storage systems.

In turn, these new systems require research into new materials with special properties, such as superconducting materials. Superconductivity is the property that allows certain materials to conduct electric current without resistance and therefore without energy loss. Currently, however, a major limitation for the large-scale use of superconducting materials is their need to be kept at very low temperatures, close to absolute zero (-273.15°C), which requires their association with large cooling infrastructures. In these conditions, superconductors have applications in MRI machines and other high-performance medical equipment, as well as in scientific research equipment, such as the super-magnets used in particle accelerators.

Although superconductivity has been known for more than a century, its origin is still a matter of intense debate in the scientific community. Why do certain materials exhibit superconductivity while others do not? Once this is known, it will be possible to build materials that are superconducting even under ambient temperature and pressure conditions, allowing a true technological revolution, not only in the transmission and storage of energy but also in all kinds of electrical equipment in everyday life.

The movement of electrons without resistance along a superconducting material is understood so far to be possible by the union of two electrons (called Cooper pairs) that, with the help of a deformation in the material’s lattice (called a phonon), can overcome Coulombian repulsion and start moving as a single particle.

The question to which there is still no satisfactory answer is: what makes these electrons want to come together in pairs? Among the various hypotheses, one possibility is that this phenomenon would be connected to the distance between the atoms in the superconducting material.

Thus, in research published in the journal Materials, researchers from the Brazilian Center for Research in Energy and Materials (CNPEM), and collaborators from Germany, investigated two materials (LaPt₄Ge₁₂ and PrPt₄Ge₁₂) whose crystalline structure is known as skutterudite to test the hypothesis that superconductivity would be related to the distance between the atoms of the material. This was the first scientific paper published with data obtained at the EMA beamline of CNPEM’s synchrotron light source Sirius.

Read more on the LNLS website

Advances in understanding superconducting material

2022/03/152022/03/24

Superconductivity has the potential to revolutionize technology, whether in lossless power transmission, more efficient electric motors and other applications. Recently these investigations have gained a new ally: Sirius

Imagine a future with batteries that don’t need charging, electric cars at more affordable prices, highly efficient electric motors and cheaper electricity due to ease in their transmission and storage. Gaining a deeper knowledge of the phenomenon of superconductivity is the key to this true technological revolution, which would have a potential impact on all types of electrical equipment.

This is because superconductivity is the property that allows certain materials to conduct electrical current without resistance and therefore without loss of energy. In Brazil, about 7.5% of electricity is lost in transmission and distribution, since the materials of these systems dissipate part of the energy, for example, in the form of heat. Also electric cars, even though they are much more efficient than ordinary combustion-powered cars, still lose up to 15% of the energy when charging batteries.

In view of the importance of this field, the National Center for Research in Energy and Materials (CNPEM), an organization supervised by the Ministry of Science, Technology of Innovations (MCTI), has been actively working to advance the understanding of the phenomenon of superconductivity. One of the research fronts in this area seeks to develop new tools for the experimental study of the physical phenomenon of superconductivity with the aid of superpotent X-rays generated by Sirius.

Read more on the Sirius website

Image: The Ema light line is one of the most advanced scientific tools for experiments seeking solutions for technologies involving superconductivity

Triggering room-temperature superconductivity with light

2022/02/092022/02/17

Scientists discover that triggering superconductivity with a flash of light involves the same fundamental physics that are at work in the more stable states needed for devices, opening a new path toward producing room-temperature superconductivity.

Much like people can learn more about themselves by stepping outside of their comfort zones, researchers can learn more about a system by giving it a jolt that makes it a little unstable – scientists call this “out of equilibrium” – and watching what happens as it settles back down into a more stable state.

In the case of a superconducting material known as yttrium barium copper oxide, or YBCO, experiments have shown that under certain conditions, knocking it out of equilibrium with a laser pulse allows it to superconduct – conduct electrical current with no loss – at much closer to room temperature than researchers expected. This could be a big deal, given that scientists have been pursuing room-temperature superconductors for more than three decades.

But do observations of this unstable state have any bearing on how high-temperature superconductors would work in the real world, where applications like power lines, maglev trains, particle accelerators and medical equipment require them to be stable?

A study published in Science Advances today suggests that the answer is yes.

“People thought that even though this type of study was useful, it was not very promising for future applications,” said Jun-Sik Lee, a staff scientist at the Department of Energy’s SLAC National Accelerator Laboratory and leader of the international research team that carried out the study.

Read more on the SLAC website

Image: To study superconducting materials in their “normal,” non-superconducting state, scientists usually switch off superconductivity by exposing the material to a magnetic field, left. SLAC scientists discovered that turning off superconductivity with a flash of light, right, produces a normal state with very similar fundamental physics that is also unstable and can host brief flashes of room-temperature superconductivity. These results open a new path toward producing room-temperature superconductivity that’s stable enough for practical devices.

Credit: Greg Stewart/SLAC National Accelerator Laboratory

Green information technologies: Superconductivity meets Spintronics

2021/12/022021/12/09

Superconducting coupling between two regions separated by a one micron wide ferromagnetic compound has been proved by an international team. This macroscopic quantum effect, known as Josephson effect, generates an electrical current within the ferromagnetic compound made of superconducting Cooper-pairs. Magnetic imaging of the ferromagnetic region at BESSY II has contributed to demonstrate that the spin of the electrons forming the Cooper pairs are equal. These results pave the way for low-power consumption superconducting spintronic-applications where spin-polarized currents can be protected by quantum coherence.

When two superconducting regions are separated by a strip of non-superconducting material, a special quantum effect can occur, coupling both regions: The Josephson effect. If the spacer material is a half-metal ferromagnet novel implications for spintronic applications arise. An international team has now for the first time designed a material system that exhibits an unusually long-range Josephson effect: Here, regions of superconducting YBa₂Cu₃O₇ are separated by a region of half-metallic, ferromagnetic manganite (La_2/3Sr_1/3MnO₃) one micron wide.

First light at Furka: The experiments can begin

2021/08/042021/10/07

It’s another milestone on the path to full operation of the X-ray free-electron laser SwissFEL with five experiment stations in all: “First light” at the experiment station Furka. It clears the way for experimental possibilities that are unique worldwide. Team leader Elia Razzoli explains what the Furka Group is planning to do.

Why is “first light” such an important occasion for your team?

Elia Razzoli: It means we’re in business. Or to be more specific: Now we can begin working on the first experiments.

The general public might imagine that you simply flip a switch, and then the light is there. But presumably it’s not that simple in your case . . .

No, it is a complex task. When we at SwissFEL talk about light, we do not mean visible light, but rather X-ray light with characteristics that are unique in the world. To generate that light, and for research to be able to use it, several teams at PSI have to work together. With the Furka experiment station we are, so to speak, at the end of the food chain. To generate the X-ray light of SwissFEL, electrons must be forced onto a sinuous track with the aid of magnets. In the process, they emit the X-ray light that we need to carry out the actual investigations. The magnets that redirect the electrons in this way are called undulators. And they are precisely what makes the whole thing so difficult, because they have to work exactly in sync; otherwise the X-ray light doesn’t have the quality that we need. The complexity of the system grows exponentially with the number and length of the undulators. That is why first light at Furka is already a masterful technical and organisational feat.

Read more on the PSI website

Image: Members of the team that achieved the milestone at the Furka station of SwissFEL: Eugenio Paris (left), Elia Razzoli, Cristian Svetina (right)

Credit: Paul Scherrer Institute/Mahir Dzambegovic

Understanding the physics in new metals

2021/07/192021/07/21

Researchers from the Paul Scherrer Institute PSI and the Brookhaven National Laboratory (BNL), working in an international team, have developed a new method for complex X-ray studies that will aid in better understanding so-called correlated metals. These materials could prove useful for practical applications in areas such as superconductivity, data processing, and quantum computers. Today the researchers present their work in the journal Physical Review X.

In substances such as silicon or aluminium, the mutual repulsion of electrons hardly affects the material properties. Not so with so-called correlated materials, in which the electrons interact strongly with one another. The movement of one electron in a correlated material leads to a complex and coordinated reaction of the other electrons. It is precisely such coupled processes that make these correlated materials so promising for practical applications, and at the same time so complicated to understand.

Strongly correlated materials are candidates for novel high-temperature superconductors, which can conduct electricity without loss and which are used in medicine, for example, in magnetic resonance imaging. They also could be used to build electronic components, or even quantum computers, with which data can be more efficiently processed and stored.

Read more on the BNL website

Image: Brookhaven Lab Scientist Jonathan Pelliciari now works as a beamline scientist at the National Synchrotron Light Source II (NSLS-II), where he continues to use inelastic resonant x-ray scattering to study quantum materials such as correlated metals.

Credit: Jonathan Pelliciari/BNL