Manufacturing Bits: Aug. 14

Strange metals; mild-temp superconductors; super grids.


Strange metals
The National High Magnetic Field Laboratory (National MagLab) has unraveled the behavior in a new class of high-temperature superconductor (HTS) materials called cuprates.

Cuprates are sometimes referred as a “strange” or “bad” metal. They don’t conduct electricity well despite being a superconducting material. Superconductors are devices that have zero electrical resistance, making them attractive for a range of applications. But superconductors must be cooled down to temperatures at or near absolute zero on the Kelvin scale to work. This, in turn, limits their applications.

These so-called low-temperature semiconductor (LTS) materials operate well below 20 K (-253° C). These superconductors, such as niobium-tin and niobium-titanium, also require expensive and non-renewable liquid helium formulas to create them. Then, in the mid-1980s, the industry discovered a copper oxide superconductor compound, which operated at -238° C. One of these HTS materials, dubbed cuprates, consist of oxygen and copper layers.

The industry understands the physics of LTS, but HTS remains a mystery as it’s unclear how electrons travel through these materials.

To solve the mystery, researchers from MagLab looked at one specific cuprate, called lanthanum strontium copper oxide (LSCO). Researchers put the materials in a powerful magnet. They measured resistivity in fields up to 80 teslas. Then, they increased the strength of the magnetic field, which, in turn, caused the resistivity of LSCO to go up proportionately.

To conduct their experiments, the research team used three magnets from the MagLab’s Pulsed Field Facility, including the 60-Tesla Controlled Waveform Magnet, the 65-Tesla Multi-Shot Magnet and the world-record 100-Tesla Multi-Shot Magnet (pictured above) Source: MagLab

In metals, copper or silicon travel via conventional quasiparticles, but cuprates do not. In fact, there is evidence to suggest that LSCO may carry current using something other than quasiparticles.

In LSCO, the current doesn’t flow by way of superconductivity as well. All told, scientists aren’t yet certain how current travels through the materials. “Here we have a situation where no existing language can help,” said MagLab physicist Arkady Shekhter. “We need to find a new language to think about these materials.”

Mild-temp superconductors
Riken has mapped the patterns of electrons in iron-based superconductors.

Researchers have found evidence that electrons can pair up in two different ways in iron-based superconductors. This, in turn, could help researchers develop superconductors that operate at mild temperatures.

In the lab, Riken probed the relationship between nematicity and superconductivity in iron selenide. Iron selenide enters its nematic phase below about −183° C. “Our data clearly indicate that there is an intimate relationship between nematicity and superconductivity,” said Tetsuo Hanaguri, a researcher at Riken. “This is an important constraint for the theory of iron-based superconductivity, because the correct theory must account for this characteristic behavior.

“This may lead to the design of as-yet-unknown exotic, and hopefully high-temperature, superconductors,” said Hanaguri.

Super grids
The Karlsruhe Institute of Technology (KIT) and TenneT are exploring the use of superconductor technology as an alternative to conventional power cables for short-length grids.

Graphic representation of the superconducting cable studied by KIT for partial underground cabling. (Graphics: ITEP/KIT)

The project is part of the ENSURE Kopernikus Project in Europe. KIT is designing the superconductor cables for the project. The plan is to deploy various pilot projects. As part of those projects, KIT and grid operator TenneT plan to deploy underground cables in various locations in Germay.

The feasibility study is based on cable and cooling concepts designed for 380 kilovolts (kV). “This is a big technical challenge, because superconductor technology has never been used before on this voltage level,” said Mathias Noe, a professor at KIT’s Institute for Technical Physics. “We have now demonstrated that this is technically feasible with our new cable concepts.”

Hanno Stagge, who manages the project at TenneT, added: “A conventional cable system in the transmission grid requires twelve three-phase power cables. A superconducting cable system can transmit the same power with six cables. After the study, the cable, including the necessary coupling sleeves and terminations, will have to be produced first. Then, it will have to be tested extensively together with a cooling system.”

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