Identifying a superconductor’s normal Fermi surface

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Los Alamos scientists conducted thermal conductivity measurements using a rotating magnetic field on the heavy-fermion superconductor Cerium-Cobalt-Indium5, thus revealing its uncondensed Landau quasiparticles. This research advances our understanding of unconventional superconductors but also opens new avenues for exploring quantum phenomena in materials. Superconductivity in CeCoIn₅ was discovered at Los Alamos. Credit: LANL

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For the first time ever, scientists at Los Alamos National Laboratory have identified a superconductor’s normal Fermi surface. Using expertise in quantum materials science, theoretical physics and nanotechnology, this work involved identifying uncondensed Landau quasiparticles inside the superconducting phase through the quantum oscillation in thermal conductivity.

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Why this matters: This work shows that thermal conductivity measurements in a rotating magnetic field can reveal the normal Fermi surface of a material even within its superconducting state, thus not only advancing our understanding of unconventional superconductors but also opening new avenues for exploring quantum phenomena in materials.

How it works: Think of a quasiparticle as a “team” in sports, one treated like a single unit even though it is made up of individual players. Landau quasiparticles are the remnants of normal particles that do not participate fully in superconductivity — they are like players sitting on the bench; they are still part of the game but do not play a main role.

To identify uncondensed Landau quasiparticles in the superconducting phase, these scientists measured thermal conductivity in a rotating magnetic field on the heavy-fermion superconductor Cerium-Cobalt-Indium5 (CeCoIn₅). The superconducting condensate does not carry heat, so only quasiparticles — essentially the “leftovers” from superconducting pairs — participate in heat conduction.

By measuring the thermal conductivity while rotating the magnetic field, they observed sharp resonances. These resonances correspond to the positions of quasiparticles interacting with the magnetic field, revealing normal parts of the Fermi surface deep inside the superconducting state. This behavior was supported by theoretical calculations of the material’s electronic structure, which showed peaks in the density of states aligning with the resonances observed.

Funding: The Laboratory Directed Research and Development program at Los Alamos and partly by the Center for Integrated Nanotechnologies, a DOE Office of Science user facility. Experimental work conducted under the auspices of the U.S. Department of Energy’s Office of Science, Basic Energy Sciences, Materials Sciences, and Engineering Division.

Technical contacts: Shi-Zeng Lin (Theoretical division) and Roman Movshovich (Materials Physics and Applications division)