
Inset: Quantum phase transition is seen as a jump in mobile electron density (∝ 1/RH) vs doping x. Horizontal lines show expected values for 0 (green) and 1 (purple) mobile f electrons per Ce. Main: on one side of the transition (CeCoIn5) the Hall resistivity grows steeply with field; on the other (1.6% Sn), the number of mobile electrons has increased sharply.
Superconductors, materials that offer no electrical resistance at low temperatures, have long been objects of study and fascination. As described recently in Science magazine, a research group including scientists from Los Alamos National Laboratory has uncovered the quantum phase transitions which may be behind the behavior of so-called “high-temperature” cuprate superconductors. For reasons previously little understood, the cuprates display their superconducting properties at temperatures as high as 100 degrees Kelvin, much higher than traditional superconductors such as lead or tin.
Researchers studied a quantum phase transition in cerium-cobalt-indium 5 (CeCoIn5), a material with similar crystal structure, transport properties, and, key to the research, superconducting properties to the cuprates. Unlike most transitions between phases of matter, quantum phase transitions are not driven by thermal parameters – heat or cold. Instead, that seen in CeCoIn5 is associated with delocalization of electrons at a transition between Fermi surfaces of different volume. Complementary experiments suggest that the change in Fermi-surface volume is not accompanied by broken symmetry in the material’s crystal structure. In cuprates, similar quantum phase transitions that appear not to be associated with a broken symmetry are thought to underlie the mechanism of superconductivity itself.
The experiment represents the first quantitative study of this class of phase transitions, greatly helping in the interpretation of recent discoveries in the cuprates. When subjected to magnetic fields of up to 73 T at the National High Magnetic Field Laboratory’s Pulsed-Field Facility (MPA-MAGLAB), the quantum phase transition in CeCoIn5 was revealed in a quantity called the Hall resistance. At (and only at) very high magnetic fields, the Hall resistance is determined by the number of mobile electrons, allowing it to be used to detect the change in electron density that occurs at the quantum phase transition.
The National High Magnetic Field Laboratory’s Pulsed Field Facility at LANL is the only pulsed field user facility in the United States. The Pulsed Field Facility develops and maintains a set of powerful, non-destructive pulsed magnets providing fields from 60 T to 101 T with different pulse widths that are tailored to support a wide variety of users.
Funding and Mission
The experiments were supported by the National Science Foundation and the Department of Energy (DOE). Design and construction of specialized equipment was funded by the DOE Basic Energy Sciences program “Science at 100 T.” This and similar work at MPA-MAGLAB focuses on quantum materials that underpin the National Quantum Initiative, as well as supporting the Global Security mission, and the Materials for the Future capability pillar.
Reference
“Evidence for a delocalization quantum phase transition without symmetry breaking in CeCoIn5,” Science, 375, 6576, 76 (2021). DOI: 10.1126/science.aaz4566. Authors: John Singleton, Johanna C. Palmstrom, Laurel Winter, Ross McDonald (National High Magnetic Field Laboratory, Los Alamos); Nikola Maksimovic, Daniel H. Eilbott, Tessa Cookmeyer, Fanghui Wan, Vikram Nagarajan, Shannon C. Haley, Eran Maniv, Amanda Gong, Stefano Faubel, Ian M. Hayes, Sooyoung Jang, Samuel Ciocys, Jacob Gobbo, Yochai Werman, Ehud Altman, Alessandra Lanzara, James G. Analytis (University of California, Berkeley, Lawrence Berkeley National Laboratory); Jan Rusz, Peter M. Oppeneer (Uppsala University); Ali Bangura (National High Magnetic Field Laboratory, Tallahassee); Ping Ai, Yi Lin (Lawrence Berkeley National Laboratory).
Technical Contact: John Singleton