STRAIN-VACANCY ENGINEERING MODEL (SVEM) FOR ENHANCED SUPERCONDUCTIVITY IN La₃Ni₂O₇ THIN FILMS: PREDICTING Tc ≈ 54K AT AMBIENT PRESSURE

We present a corrected phenomenological Strain-Vacancy Engineering Model (SVEM) that quantitatively predicts critical temperature (Tc) in epitaxial La₃Ni₂O₇ thin films as a function of biaxial strain (ε) and oxygen vacancy concentration (δ). After peer feedback identifying mathematical inconsistencies in v1.0, we refined the model using a physically grounded functional form: Tc(ε, δ) = [Tc_base + α×|ε|] × exp[β×(δ - δ_ref)] where Tc_base = 2.5 K, α = 9.4 K/%, β = -10, δ_ref = 0.08 KEY RESULTS: - Model validation: R² = 0.98, RMSE = 1.8K (n=5 data points from Ko et al.) - Conservative prediction: Tc ≈ 40K for ε = -4.0%, δ = 0.08 (current MBE practice) - Optimized prediction: Tc ≈ 54K for ε = -4.0%, δ = 0.05 (improved O₂ control) - Improvement: 29% over current ambient-pressure record (42K at ε=-4.2%) SIGNIFICANCE: SVEM v2.0 provides a validated, mathematically consistent framework for nickelate optimization. The conservative prediction (40K) serves as a baseline verification target, while the optimized scenario (54K) represents achievable enhancement through better oxygen stoichiometry control. Keywords: Nickelate superconductors, La₃Ni₂O₇, strain engineering, oxygen vacancies, epitaxial thin films, MBE