Fig. 4: Band gap tuned phase diagram with electron-phonon coupling.
From: Anomalous excitonic phase diagram in band-gap-tuned Ta2Ni(Se,S)5
a Evolution of structural transition temperature Ts and the maximum Ta atom displacement ∣X∣ as a function of S-doping in Ta2Ni(Se,S)5. The electronic band structures within different regions are illustrated in the insets. Error bars are determined based on the fitting error of the Bragg peak positions. b The calculated average lattice displacement \(| {x}_{{{{{{{{\rm{ph}}}}}}}}}|=\sqrt{\langle {\hat{x}}_{{{{{{{{\rm{ph}}}}}}}}}^{2}\rangle }\) as a function of the band gap Eg at various electron-phonon coupling strengths. In the quantized phonon model, the zero-point fluctuation gives a finite ∣xph∣ = 1 in the decoupled limit. c Sketched phase diagrams of band-gap-tuned semimetal-to-semiconductor transition in the strong (top) and weak (bottom) coupling limits. Solid lines mark the phase boundaries, above which the shades show the order fluctuations20. Red shade on the bands illustrates the electronic states that participate in the phase transition. The horizontal dashed lines denote EF.
