Bayesian Spectroscopy with a Replica Exchange Monte Carlo Method on an Excitonic Absorption Spectrum of a Cu₂O Thin Crystal

To study a bi-axial stress effect in a Cu₂O thin crystal sandwiched by paired MgO substrates, we have applied Bayesian spectroscopy to decompose an absorption spectrum with employing a replica exchange Monte Carlo (RXMC) method. The absorption spectrum includes broad bands of an inter-band transition and an exciton continuous state simultaneously with excitonic resonance transitions. However, it had been difficult to decompose correctly because of a bottleneck in optimal solution search efficiency. To relieve the bottleneck, we introduced the RXMC method and succeeded in decomposing all spectral components. Posterior probabilities of the band-gap energy and the exciton binding energy distribute at lower energy side than those in stress-free bulk crystals, which provides statistical evidence to show that the bi-axial stress remains in the Cu₂O thin crystal sandwiched by MgO substrates.