The magic angle of Sr_2RuO_4: optimizing correlation-driven superconductivity
arxiv(2024)
摘要
A fundamental understanding of unconventional superconductivity is crucial
for engineering materials with specific order parameters or elevated
superconducting transition temperatures. However, for many of these materials,
such as Sr_2RuO_4, the pairing mechanism and the symmetry of the
superconducting order parameter remain unclear; furthermore, reliable and
efficient methods of predicting their response to tuning - e.g. via structural
distortions through strain and octahedral rotations - are lacking. Here we
investigate the response of superconductivity in Sr_2RuO_4 to distortions
via two numerical techniques, the random phase approximation (RPA) and
functional renormalization group (FRG), starting from realistic models of the
electronic structure. Comparison of the results from the two techniques
suggests that RPA misses the important interplay of competing fluctuation
channels, while FRG reproduces key experimental findings. In accordance with
earlier studies by RPA and FRG, we confirm the experimentally observed
tuneability of T_c with uniaxial strain. With octahedral rotation, we find an
even larger increase of T_c before superconductivity is completely suppressed
in FRG, a finding that confirms experiments but is not reproduced in RPA.
Throughout the parameter space investigated here, we find a dominant
d_x^2-y^2 pairing symmetry from FRG. To provide benchmark results for
determining the pairing symmetry experimentally by quasiparticle interference
using a Scanning Tunneling Microscope, we introduce the pairing interactions
into continuum local density of states calculations, enabling experimental
verification of the symmetry of the order parameter via phase-referenced
Bogoliubov Quasiparticle Interference imaging.
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