PARADIM Highlight #98—External User Project (2024)
Julia Mundy (Harvard), Antia Botana (ASU), and Brad Ramshaw (Cornell)
Superconducting nickelates are a new family of materials closely resembling the high temperature cuprate superconductors. While analogy between cuprates and nickelates is natural given by the common structural motif of MO2 (M=Ni,Cu) planes, very little is known about the metallic state of the nickelates, making these comparisons difficult.
Figure 1: Electronic band structures (top row), Fermi surfaces (middle row), and Seebeck coefficient (calculated & measured, bottom row) for: n = 5 nickelate (left column), n = 3 nickelate (2nd column), cuprate Bi2201 (3rd column), and cuprate Nd-LSCO (right column).
Here users of PARADIM and their collaborators report the first Seebeck coefficient (S) measurements of superconducting nickelates. The key finding is a temperature-independent and negative ratio S/T for both, the thin-film superconducting five-layer (n = 5) and a thin-film metallic three-layer (n = 3) nickelate. The measured S/T is well described by the band dispersion calculated with density functional theory (DFT), demonstrating the presence of a semi-classical metallic state, similar to that in over-doped cuprates (Bi2201), and distinct from that in optimally doped cuprates (Nd-LSCO).
The study reflects the high elastic scattering limit of the Seebeck coefficient reflects only the underlying band structure of a weakly correlated metal (as computed from DFT), analogous to the high magnetic field limit of the Hall coefficient.
Superconducting nickelates are a new family of materials closely resembling the high temperature cuprate superconductors. While analogy between cuprates and nickelates is natural given the common structural motif of MO2 (M=Ni,Cu) planes, very little is known about the metallic state of the nickelates, making these comparisons difficult. We probe the electronic dispersion of thin-film superconducting five-layer (n=5) and metallic three-layer (n=3) nickelates by measuring the Seebeck coefficient S. We find a temperature-independent and negative ratio S/T for both nickelates, comparable to that found in overdoped Bi2201. These results are in stark contrast to the strongly temperature dependent S/T measured at similar electron filling in the optimally doped cuprate La1.36Nd0.4Sr0.24CuO4. The electronic structure calculated from density-functional theory reproduces the temperature dependence, sign, and amplitude of S/T in the nickelates using Boltzmann transport theory. This demonstrates that the electronic structure obtained from first-principles calculations provides a reliable description of the fermiology of superconducting nickelates and suggests that, despite indications of strong electronic correlations, there are well-defined, semi-classical, quasiparticles in the metallic state. We explain the differences in the Seebeck coefficient between nickelates and cuprates as originating in strong dissimilarities in impurity concentrations.
The study reflects the high elastic scattering limit of the Seebeck coefficient reflects only the underlying band structure of a metal, without strong electron correlations, analogous to the high magnetic field limit of the Hall coefficient. The study not only suggests that greater hole doping might increase Tc of the nickelates, but that the Seebeck coefficient can be used as a general probe of the existence of correlations in disordered quantum materials.
PARADIMs 62-element MBE enabled creation of the studied nickelate thin films.
The work was initialized by Julia Mundy, Antia Botana, and Brad Ramshaw.
G. Grissonnanche, G.A. Pan, H. LaBollita, D. Ferenc Segedin, Q. Song, H. Paik, C.M. Brooks, E. Beauchesne-Blanchet, J.L. Santana González, A.S. Botana, J.A. Mundy, and B.J. Ramshaw, "Electronic Band Structure of a Superconducting Nickelate Probed by the Seebeck Coefficient in the Disordered Limit," Phys. Rev. X 14, 041021 (2024).
The work of B. J. R. and G. G. was supported as part of the Institute for Quantum Matter, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Grant No. DESC0019331 (Seebeck measurements and Boltzmann transport calculations). G. A. P. and D. F. S. are primarily supported by U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, under Grant No. DE-SC0021925, and by NSF Graduate Research Fellowship Grant No. DGE1745303. G. A. P. acknowledges additional support from the Paul & Daisy Soros Fellowship for New Americans. Q. S. was supported by the Science and Technology Center for Integrated Quantum Materials, NSF Grant No. DMR1231319. J. A. M. acknowledges support from the Packard Foundation and the Gordon and Betty Moore Foundation’s EPiQS Initiative, Grant No. GBMF6760. Materials growth was supported by PARADIM under National Science Foundation (NSF) Cooperative Agreement No. DMR2039380. We acknowledge the Cornell LASSP Professional Machine Shop for their contributions to designing and fabricating equipment used in this study. H. L. and A. S. B. acknowledge the support from NSF Grant No. DMR 2045826, the ASU Research Computing Center and the Extreme Science and Engineering Discovery Environment (XSEDE) through research allocation TG-PHY220006, which is supported by NSF Grant No. ACI-1548562 for HPC resources. G. G. acknowledges support from the ANR Grants STeP2 No. ANR-22-EXES-0013, 318 QuantExt No. ANR-23-CE30-0001-01, and the France 2030 Program No. ANR-24-RRII-0004.
