Strong Interactions and Correlations

Band Gap Renormalization at Different Symmetry Points in Perovskites

“…These figures display the characteristic bleach at the optical BG transition at ∼2.35 eV (see Figure 1 b), mainly due to phase-space filling, 2 accompanied by a broad, weak absorption signal on the higher-energy side, due to Coulomb screening. 1 , 3 , 44 These features are consistent with previous reports on similar perovskite systems. 7 , 32 , 45 , 46 In addition, a small positive signal promptly emerges on the lower-energy side of the BG (indicated by the dashed red circle in Figure 2 a), which we attribute to BGR caused by the presence of hot carriers on time scales of tens to hundreds of femtoseconds.…”

“…We used the visible spectral region, which covers the VB1 → CB1 transition at the R point (fundamental BG transition), as previously studied. ,, Figure a shows the time-energy TA map in a 0–5 ps time window of the MAPbBr 3 perovskite excited at 3.10 eV, and Figure b shows the corresponding spectral traces at various delay times, revealing distinct negative and positive features from low to high energies along with a small positive shoulder on the lower-energy side at 0.2 and 0.4 ps. These figures display the characteristic bleach at the optical BG transition at ∼2.35 eV (see Figure b), mainly due to phase-space filling, accompanied by a broad, weak absorption signal on the higher-energy side, due to Coulomb screening. ,, These features are consistent with previous reports on similar perovskite systems. ,,, In addition, a small positive signal promptly emerges on the lower-energy side of the BG (indicated by the dashed red circle in Figure a), which we attribute to BGR caused by the presence of hot carriers on time scales of tens to hundreds of femtoseconds . As the excited hot carriers occupy fewer states at the new, lowered band edge compared to colder-carrier distributions, the TA signal at the renormalized band edge displays a photoinduced absorption (PIA), which disappears on a sub-ps time scale as the carriers rapidly cool and form neutral excitons …”

“…Semiconductors are known to exhibit large changes in their optical properties in the region of the fundamental band gap upon photoexcitation. − These changes are due to the creation of electron–hole pairs that modify the complex optical dielectric function. This is manifested by various concurrent processes, which involve single-particle states (namely, phase-space filling) and those that can be attributed to many-body interactions among the doped carriers (i.e., long-range Coulomb screening and band gap renormalization).…”