(a) Heat amplification factor β_r as a function of the middle bath temperature T_m with various system–middle bath coupling strength α_m; (b) three steady state heat currents J_u/γ (u = l,m,r) as a function of T_m with the coupling strength α_m = 4, and the inset is the zoom in view of J_m/γ; (c) the 3D view of the heat amplification factor β_r by tuning T_m and α_m. The other parameters are given by ε_l = 1.0, ε_r = 0.6, Δ = 0.6, γ = 0.0002, ω_c = 10, T_l = 2, and T_r = 0.4.