Hot carrier decay dynamics of van der Waals room temperature ferroelectric α-In ₂ Se ₃

In this study, we investigated the hot carrier decay dynamics of two-dimensional room temperature ferroelectric α-In₂Se₃<i>via</i> femtosecond transient optical spectroscopy. The photo-excited hot carriers in α-In₂Se₃ decay <i>via</i> electron-phonon coupling (<i>τ</i>₁) and inter-layer charge transfer (<i>τ</i>₂). We observe a change in the slope of the <i>τ</i>₁^-1-<i>T</i> curve near 145 K, which indicates the change in temperature-dependent phonon excitation of α-In₂Se₃. Below 145 K, the dephase rate <i>τ</i>₂^-1 shows an unusual temperature dependence, <i>τ</i>₂^-1 ∝ <i>T</i>^-1, while it exhibits a linear increase with temperature above 145 K. The temperature-dependent variation of hot-carrier decay in α-In₂Se₃ near 145 K may be related to a hidden phase transition. The dephase rate (<i>τ</i>₁^-1) exhibits a stronger temperature dependence below 145 K than above 145 K, which may arise from the more pronounced temperature dependence of optical phonon excitation at lower temperatures.