Mapping multiple quantum transitions in the antiferromagnet CeRhIn5

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Zero­‐temperature pressure-­magnetic field phase diagram. Experimentally determined quantum critical pointsPc, B0* and Bc0 are compared to a multi-­parameter theoretical phase diagram illustrated by the solid curves. Pc: pressure at which the antiferromagnetic transition reaches zero­‐temperature in the absence of an applied magnetic field, B0*: critical magnetic field where there is a change at zero‐temperature from a small to large Fermi surface inside the antiferromagnetically ordered phase, Bc0: critical magnetic field needed to suppress the antiferromagnetic transition to zero‐temperature without applied pressure, SC: superconductivity, AF: antiferromagnetism with small (s) and large (L) Fermi surfaces, PML: magnetically disordered with large Fermi surface.

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Using unusually high-field magnet capabilities at the National High Magnetic Field Laboratory (NHMFL) in Tallahassee, Florida, and at the Pulsed Field Facility in Los Alamos, researchers have discovered two distinct classes of zero-temperature transitions called quantum critical points (QCPs). The study provides significant progress toward deriving a universal phase diagram for quantum critical points. Proceedings of the National Academy of Sciences of the United States of America published the research.

This work is important for understanding and developing theories about materials whose electronic and magnetic properties are controlled by quantum fluctuations that develop because of Heisenberg’s uncertainty principle. One important property that can emerge is unconventional superconductivity, which appears when a magnetic transition is tuned to zero-temperature by applying pressure to the heavy-fermion metal CeRhIn5. The CeRhIn5 and related materials display quantum-driven continuous phase transitions at absolute zero temperature, but scientists have not been able to determine whether these phase transitions exhibit universal behavior.

The researchers, which included LANL scientists and international collaborators, used short-phase 75 tesla fields at Los Alamos and the hybrid 45-tesla magnet in Tallahassee for the work reported in the publication. They took measurements of heat capacity and de Haas-van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic quantum-driven continuous phase transitions (magnetic field Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. The team detected a sharp, magnetic-field-induced change in Fermi surface at B0*≈ 30 T, well inside the antiferromagnetic phase. This sharp change is unexpected at a usual type of quantum-driven continuous phase transition. This is the first observation of a sharp Fermi surface reconstruction while applying a strong magnetic field to suppress an antiferromagnetic transition to zero temperature.

Comparisons with electronic-structure calculations and properties of the closely related material CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized to itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with earlier pressure experiments, their results demonstrate that at least two distinct classes of quantum-driven continuous phase transitions are observable in CeRhIn5: one with applying pressure and others with applying a magnetic field. This is consistent with the theoretically predicted universal phase diagram, which indicates that the two classes of quantum-driven continuous phase transitions are connected. This finding must be tested in future experiments that use simultaneously high pressures and very high magnetic fields at the National High Magnetic Field Laboratory. These experiments demonstrate that direct measurements of the Fermi surface can distinguish theoretically proposed models of quantum criticality and point to a universal description of quantum phase transitions.

Reference: “Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5,” Proceedings of the National Academy of Sciences of the United States of America 112, 638 (2015); doi: 10.1073/pnas.1413932112. Los Alamos authors are Yoshitaka Kohama, Eric Bauer, John Singleton, Marcelo Jaime, and Joe Thompson (Condensed Matter and Magnet Science, MPA-CMMS); and Jianxin Zhu (Physics of Condensed Matter and Complex Systems, T-4). The collaboration included researchers from Zhejiang University in China, Sungkyunkwan University in South Korea, Max Planck Institute for Chemical Physics of Solids in Germany, Rice University, the National High Magnetic Field Laboratory at Florida State University, and Los Alamos.

The DOE Office of Science project Complex Electronic Materials and the LANL Laboratory Directed Research and Development (LDRD) program funded different aspects of the research at Los Alamos. The National Science Foundation, State of Florida, and the DOE Basic Energy Sciences program Science at 100 T sponsored the National High Magnetic Field Laboratory. The work supports the Lab’s Energy Security mission area and the Materials for the Future science pillar by pursuing the science required to discover and understand complex and collective forms of matter that exhibit novel properties and respond in new ways to environmental conditions, enabling the creation of materials with innate functionality, such as superconductivity. Technical contact: Joe Thompson