Progress of ambient-pressure superconductivity in bilayer nickelate thin films

Summary

This review summarizes recent progress in achieving ambient-pressure superconductivity in bilayer nickelate La₃Ni₂O₇ thin films. Through epitaxial strain engineering, compressive strain provided by substrates such as SrLaAlO₄ successfully stabilizes the superconducting phase under ambient conditions, marking a significant breakthrough compared to the high-pressure superconductivity observed in bulk materials. In terms of experimental characterization, angle-resolved photoemission spectroscopy (ARPES) measurements reveal a controversially debated Fermi surface topology, with observations differing among research groups, likely due to variations in thin-film growth conditions. Regarding the enhancement of superconducting transition temperature (T_c), increasing compressive strain and optimizing growth techniques, such as giant oxide atomic layer epitaxy, enable T_c to reach approximately 60 K. Theoretical studies focus on electronic structures and pairing symmetries; weak-coupling approaches, including random phase approximation and functional renormalization group, predict s±-wave or d-wave pairing, while renormalized mean-field theory suggests the possibility of nodal d-wave pairing. However, key issues such as the specific role of electron pockets on the Fermi surface in superconductivity and the relationship between lattice ratio and T_c remain incompletely elucidated. These advances demonstrate that bilayer nickelate thin films serve as a highly tunable and exceptionally promising platform for studying high-temperature superconductivity.

Materials

• La₃Ni₂O₇
• La₂.85Pr₀.15Ni₂O₇
• La₂PrNi₂O₇
• La_3-xSr_xNi₂O₇

Methods

• PLD
• Gigantic-oxidative atomic-layer-by-layer epitaxy (GAE)
• ARPES
• STM
• X-ray absorption spectroscopy (XAS)
• STEM
• DFT
• DMFT
• Constrained random phase approximation (cRPA)
• Random phase approximation (RPA)
• Functional renormalization group (FRG)
• Renormalized mean-field theory (RMFT)
• Exact diagonalization

Keywords

• ambient pressure superconductivity
• epitaxial strain engineering
• fermi surface topology
• pairing symmetry
• s± wave pairing
• d wave pairing

Highlights

• The discovery of ambient-pressure superconductivity in bilayer nickelate thin films represents a major advancement following high-pressure superconductivity in bulk La₃Ni₂O₇.
• The role of the electron pocket on the Fermi surface in enabling superconductivity remains to be fully clarified.
• The relationship between lattice ratio and T_c in thin films differs from that in bulk La₃Ni₂O₇, highlighting an unresolved issue.
• Direct measurement of the superconducting gap on the Fermi surface reveals a significant gap opening on the α sheet with no signs of nodes.

Conclusions

• Epitaxial strain engineering with compressive strain from substrates like SrLaAlO₄ enables ambient-pressure superconductivity in La₃Ni₂O₇ thin films.
• ARPES measurements reveal conflicting Fermi surface topologies on bilayer nickelate thin films, likely due to differences in growth conditions.
• Increasing compressive strain and optimizing growth techniques can raise the superconducting transition temperature T_c to approximately 60 K.
• Weak-coupling methods predict s±-wave or d-wave pairing, while renormalized mean-field theory suggests nodal d-wave pairing.

Main claims

• Compressive strain from SLAO substrate stabilizes ambient-pressure superconductivity in thin films.
  • Evidence: Abstract,Summary: compressive strain from substrates like SrLaAlO₄ stabilizes superconductivity.
• ARPES measurements reveal conflicting Fermi surface topologies.
  • Evidence: Abstract,Summary: ARPES measurements show conflicting Fermi surface topologies likely due to variations in growth conditions.
• Increasing compressive strain and optimizing growth techniques can raise T_c to approximately 60 K.
  • Evidence: Abstract,Summary: increasing compressive strain and optimizing growth techniques enable T_c to reach approximately 60 K.

Workflow

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