2 August 2018

"Strange metals" just got stranger

MagLab physicist Arkady Shekhter described the finding as a new way metals can conduct electricity. MagLab physicist Arkady Shekhter described the finding as a new way metals can conduct electricity. David Barfield



TALLAHASSEE, Fla. — Scientists at the National High Magnetic Field Laboratory (National MagLab) have discovered a behavior in materials called cuprates that suggests they carry current in a way entirely different from conventional metals such as copper. The research, published today in the prestigious journal Science, adds new meaning to their moniker, "strange metals."

Cuprates are high-temperature superconductors (HTS), meaning they can carry current without any loss of energy at somewhat warmer temperatures than conventional, low-temperature superconductors (LTS). Although scientists understand the physics of LTS, they haven’t yet cracked the nut of HTS materials. Exactly how the electrons travel through these materials remains the biggest mystery in the field.


Scientists have studied conventional metals for more than a century, and generally agree on how electricity travels through them. They call the units that carry charge through those metals "quasiparticles," which are essentially electrons after you've factored in their environment. These quasiparticles act nearly independently of each other as they carry electric charge through a conductor.

figureSchematic doping-field-temperature phase diagram in the vicinity of critical doping.
Reprinted with permission from Giraldo-Gallo et al., Science (2 August 2018).
But does quasiparticle flow also explain how electric current travels in the cuprates? At the National MagLab's Pulsed Field Facility at Los Alamos National Laboratory, Shekhter and his team investigated the question. They put LSCO in a very high magnetic field, applied a current to it, then measured the resistance.

The resulting data revealed that the current can not, in fact, travel via conventional quasiparticles, as it does in copper or doped silicon. The normal metallic state of the cuprate, it appeared, was anything but normal.

"This is a new way metals can conduct electricity that is not a bunch of quasiparticles flying around, which is the only well-understood and well-agreed-upon language so far," said Shekhter. "Most metals work like that."

So, if not by quasiparticles, exactly how is charge being carried in the strange metal phase of LSCO? Shekhter's group wanted to understand that, too. Their data suggests it may be some kind of team effort by the electrons.



100 tesla magnet

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).

Shekhter and his colleagues decided to test LSCO's resistivity, but using magnetic field as a parameter instead of temperature. They put the material in a very powerful magnet and measured resistivity in fields up to 80 teslas (a hospital MRI magnet, by comparison, generates a field of about 3 teslas). They discovered another case of linear resistivity: As the strength of the magnetic field increased, LSCO's resistivity went up proportionately.








Scientists from numerous institutions contributed to this study. They include (listed as they appear in the citation): Paula Giraldo-Gallo (National MagLab and the Universidad de los Andes); Jose A. Galvis (National MagLab and Universidad Central); Zachary Stegen (National MagLab and FSU); Kim Modic (Max-Planck-Institute for Chemical Physics of Solids); Fedor Balakirev and Jonathan Betts (Los Alamos National Lab); Xiujun Lian and Camille Moir (National MagLab and FSU); Scott Riggs (National MagLab); Jie Wu and Anthony Bollinger (Brookhaven National Lab); X. He (Brookhaven and Yale University); Brad Ramshaw (LANL and Cornell University); Ross McDonald (LANL); and MagLab Director Greg Boebinger.

— Story by Kristen Coyne
