high temperature – Lightsources.org

Main Attraction: Scientists Create World’s Thinnest Magnet

2021/07/202021/07/21

The development of an ultrathin magnet that operates at room temperature could lead to new applications in computing and electronics – such as high-density, compact spintronic memory devices – and new tools for the study of quantum physics.

The ultrathin magnet, which was recently reported in the journal Nature Communications, could make big advances in next-gen memory devices, computing, spintronics, and quantum physics. It was discovered by scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.

“We’re the first to make a room-temperature 2D magnet that is chemically stable under ambient conditions,” said senior author Jie Yao, a faculty scientist in Berkeley Lab’s Materials Sciences Division and associate professor of materials science and engineering at UC Berkeley.

“This discovery is exciting because it not only makes 2D magnetism possible at room temperature, but it also uncovers a new mechanism to realize 2D magnetic materials,” added Rui Chen, a UC Berkeley graduate student in the Yao Research Group and lead author on the study.

Read more on the ALS website

Image: Illustration of magnetic coupling in a cobalt-doped zinc-oxide monolayer. Red, blue, and yellow spheres represent cobalt, oxygen, and zinc atoms, respectively.

Credit: Berkeley Lab

Investigating high temperature superconductors

2020/09/222020/10/21

Researchers from the ARC Centre of Excellence in Future Low Energy Electronic Technologies (FLEET) used the Soft X-ray Spectroscopy beamline at the Australian Synchrotron to investigate the structure of a promising high-temperature superconductor, a calcium-doped graphene material.

The FLEET Centre has provided a detailed description of the research, published in The Chemistry of Materials, on their website.

In characterising the material, the investigators wanted to clarify where the calcium went after it was added to a sample consisting of a single layer of graphene on a silicon carbide substrate.

Measurements at the Australian Synchrotron were able to pinpoint that the calcium atoms were located, unexpectedly, near the silicon carbide surface.

Read more on the ANSTO website

Image: Dr Anton Tadich (far right) with SXR beamline team members and researchers from the FLEET Centre.

Superconductor exhibits “glassy” electronic phase

2019/04/232019/05/08

The study provides valuable insight into the nature of collective electron behaviors and how they relate to high-temperature superconductivity.

At extremely low temperatures, superconductors conduct electricity without resistance, a characteristic that’s already being used in cryogenically cooled power lines and quantum-computer prototypes. To apply this characteristic more widely, however, it’s necessary to raise the temperature at which materials become superconducting. Unfortunately, the exact mechanism by which this happens remains unclear.

Recently, scientists found that electrons in cuprate superconductors can self-organize into charge-density waves—periodic modulations in electron density that hinder the flow of electrons. As this effect is antagonistic to superconductivity, tremendous effort has been devoted to fully characterizing this charge-order phase and its interplay with high-temperature superconductivity.

Image: At low doping levels, the charge correlations in the copper–oxide plane possess full rotational symmetry (C_inf) in reciprocal space (left), in marked contrast to all previous reports of bond-oriented charge order in cuprates. In real space (right), this corresponds to a “glassy” state with an apparent tendency to periodic ordering, but without any preference in orientation (scale bar ~5 unit cells).

Unleashing perovskites’ potential for solar cells

2019/03/062019/03/07

Perovskites — a broad category of compounds that share a certain crystal structure — have attracted a great deal of attention as potential new solar-cell materials because of their low cost, flexibility, and relatively easy manufacturing process. But much remains unknown about the details of their structure and the effects of substituting different metals or other elements within the material. Now, researchers using the U.S. Department of Energy’s (DOE’s) Advanced Photon Source (APS) have been able to decipher a key aspect of the behavior of perovskites made with different formulations: With certain additives there is a kind of “sweet spot” where sufficient amounts will enhance performance and beyond which further amounts begin to degrade it. The findings were detailed in the journal Science.
Conventional solar cells made of silicon must be processed at temperatures above 1,400 degrees Celsius, using expensive equipment that limits their potential for production scale-up. In contrast, perovskites can be processed in a liquid solution at temperatures as low as 100 degrees, using inexpensive equipment. What’s more, perovskites can be deposited on a variety of substrates, including flexible plastics, enabling a variety of new uses that would be impossible with thicker, stiffer silicon wafers.

Image: Perovskite-based solar cells are flexible, lightweight, can be produced cheaply, and could someday bring down the cost of solar energy. Shown here is the type of perovskite solar cell measured at the CNM/XSD Hard X-ray Nanoprobe at the APS.
Credit: Rob Felt

Spin-momentum locking in cuprate high-temperature superconductors

2019/02/192019/02/26

The results open a new chapter in the mystery of high-temperature superconductors, suggesting that new, unexplored interactions and mechanisms might be at play.

In the world of superconductors, “high temperature” means that the material can conduct electricity without resistance at temperatures higher than expected, but still far below room temperature. Within this special class of high-temperature superconductors (HTSCs), cuprates—consisting of superconducting CuO₂ layers separated by spacer layers—are some of the best performers, generating interest in these materials for potential use in super-efficient electrical wires that can carry power without any loss of electron momentum.

A new spin on cuprate HTSCs

Two kinds of electron interactions have been known to give rise to novel properties in new materials, including superconductors. Scientists who study cuprate superconductors have focused on just one of those interactions: electron correlation—electrons interacting with each other. The other kind of electron interaction found in exotic materials is spin-orbit coupling—the way in which an electron’s magnetic moment interacts with atoms in the material.

Image: Chris Jozwiak, Alessandra Lanzara, Kenneth Gotlieb, and Chiu-Yun Lin.
Credit: Peter DaSilva/Berkeley Lab

New insight into high-temperature superconductors

2018/11/052018/11/13

Researchers have found evidence for an acoustic plasmon or “sound wave”, which has been predicted for layered systems and suggested to play a role in mediating high temperature superconductivity.

When electrical current propagates through a conducting material, energy dissipates due to the conductor’s electrical resistance. In a superconductor, however, the resistance can vanish completely if the material is cooled to extremely low temperatures. Such dissipationless supercurrent would be highly desirable for a plethora of electronic and technological applications, and has spawn decades of intense research dedicated to find materials with superconducting properties at elevated temperatures.

While all superconducting materials reported until the 1980’s had to be cooled below 30 K, the game changed in 1986, when the first superconductors based on copper oxide materials were discovered. These so-called high-temperature superconductors are composed of stacked layers of copper-oxygen planes and some show zero electrical resistance well above 100 K. By understanding the mechanisms mediating superconductivity in the copper oxides, the scientific community hopes to become able to devise novel materials that show zero resistance even at room temperature. However, a comprehensive understanding of these mechanisms has yet remained elusive. Nonetheless, superconductors are used already today in some technological applications, such as magnetic resonance imaging devices in the field of medicine. Future applications of room temperature superconductors could revolutionize the fields of electrical power storage and transmission, and enable rapid public transport by magnetically levitated trains.

Image: Overview of the beamline ID32 at the ESRF.
Credits: P. Jayet

Lattice Coupling conspires in the correlated cuprate high-Tc superconductivity

2018/10/152018/10/25

For the cuprate high temperature superconductivity (high-T_c) research over the past three decades, the biggest challenge is to identify the relevant low energy degrees of freedom that are critical to formulating the correct theoretical model for high-T_c superconductivity. The main difficulty lies in the closeness between various relevant energy scales. For low energy processes that are comparable to the superconducting gap energy ∆_sc, there are the spin exchange energy J, the lattice vibration (phonon) energy Ω_ph, and the van Hove singularity energy E_(π,0). However, anomalous isotope effects on T_c and superfluid density in the cuprates cannot be captured by traditional phonon-mediated superconductivity theories. Historically, a purely electronic Hamiltonian – the Hubbard model – was widely regarded to encapsulate all the core physics of the high-T_c phenomena.

In a recent paper published in Science, scientists from Stanford University and from Stanford Institute for Materials and Energy Sciences (SIMES), in collaboration with material scientists from Japan and theoreticians from Japan, the Netherlands, and Berkeley, reinstated the substantial role of the lattice vibration in the cuprate high-T_c superconductivity – however, in a subtle way that is highly intertwined with the electronic correlations. They finely straddled 18 differently hole-doped high-T_c compound Bi₂Sr₂CaCu₂O_8+δ within 8% change of hole carrier concentration, a doping range where T_c evolves from 47 K to 95 K through a putative quantum critical point, around which the electronic correlation effect experiences a sudden change. Then systematic experiments were carried out using the angle-resolved photoemission spectroscopy (ARPES) facility at SSRL Beam Line 5-4. Here, the high-resolution ARPES end station provided critical information of both the superconducting gap and the electron-lattice coupling.

Image: Intertwined growth of the superconductivity and the electron-phonon coupling tuned by the hole concentration. The red line is an illustration of the T_c in Bi-2212 (T_c^max = 95 K). The blue shade and line represent the single-layer Bi-2201 system, where the coupling to the B1g mode is weak and T max is only 38 K. The yellow ball represents the optimally doped tri-layer Bi-2223 where T_c^max is 108 K. The top-right inset shows the intertwined relation between the pseudogap and the EPC under strong electronic correlation. The Madelung potential and the lattice stacking along the c-axis are schematically depicted for the single- layer, bi-layer and tri-layer systems. The dark grey blocks represent the CuO₂^n- plane, and the light grey blocks represent the charge reservoir layers (Ca²⁺, SrO, BiO⁺). The orange dots mark the CuO₂^n- planes that experience to the first order a non-zero out-of-plane electric field.
Credit: Science, doi: 10.1126/science.aar3394