Kavli Affiliate: Bo Gu
| First 5 Authors: Xin-Wei Yi, Wei Li, Jing-Yang You, Bo Gu, Gang Su
| Summary:
Recent strain-stabilized superconductivity at ambient pressure in
La$_3$Ni$_2$O$_{7}$ films opens new avenues for nickelates research, in
parallel with its pressure-induced counterpart. Using density functional theory
calculations, we elucidate the critical factors bridging strain- and
pressure-driven superconductivity in La$_3$Ni$_2$O$_{7}$ by comprehensively
analyzing structural, electronic, magnetic, and density wave characteristics.
Consistent with recent scanning transmission electron microscopy observations,
we find an $I4/mmm$ structural transition at $-0.9%$ strain, preceding
superconductivity onset. Electronic analysis shows compressive strain lowers
Ni-$d_{z^2}$ orbital energy levels, while interfacial Sr diffusion effectively
reconstructs the $d_{z^2}$ pockets, quantitatively matching angle-resolved
photoemission spectroscopy experiments. The interlayer antiferromagnetic
coupling $J_perp$ under pressure or strain closely tracks experimental
superconducting $T_c$ variation. The dome-shaped pressure dependence and
monotonic strain dependence of $J_perp$ mainly arise from modulations in the
apical oxygen $p_z$ energy levels. Moreover, compressive strain suppresses both
charge density waves (CDW) and spin density waves (SDW) instabilities analogous
to pressure effects, with SDW vanishing concurrently with the structural
transition and CDW disappearing at $sim-3.3%$ strain. Our results indicate
that suppressed density waves and enhanced $J_perp$ are crucial for both
strain- and pressure-driven superconductivity. Accordingly, we propose several
candidate substrates capable of achieving greater compressive strain, thereby
potentially increasing $T_c$.
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