Time-resolved differential transmission in MOVPE-grown ferromagnetic InMnAs

We measured time-resolved differential transmission in InMnAs for different pump/probe schemes as a function of temperature, laser fluence, and external magnetic field. We observed tunability of the carrier relaxation time. In addition, we found that the sign of the differential transmission changed as a function of probe wavelength. The electronic structure for InMnAs was calculated for $\mathbf{B}=0$, using an eight-band k$·$p model, which includes conduction and valence band mixing as well as coupling of electrons and holes to the magnetic Mn impurities. This allows us to explain some of the carrier dynamics and the sign changes in the differential transmission.

Figure 1

(a) DT- in MOVPE-grown ferromagnetic InMnAs at 290 and 77 K with pump/probe fixed at 3.467$\mu$m. (b) A different pattern in the relaxation was observed for the pump/probe at 3.1 $\mu$m.

Figure 2

Two-color differential transmission measurements in InMnAs ferromagnetic film at 290 K and different pump fluences. The pump/probe pulses were 800 nm and 3.467 $\mu$m, respectively. The peak of the DT, $-\Delta T/T_0=(T_0-T)/T_0$, increases from $30\%$ to $\sim$$60\%$, suggesting larger photoinduced absorption at higher laser fluences.

Figure 3

Two-color differential transmission measurements in InMnAs ferromagnetic film at 290 K for different probe wavelengths in MIR. The relaxation dynamic is dominated by photoinduced absorption. The exponential fits are shifted for clarity. The inset demonstrates an example of the measurements at 77 K for pump/probe at 800 nm/3.467 $\mu$m, respectively.

Figure 4

Two-color DT measurements of InMnAs ferromagnetic film at several temperatures. The pump and probe pulses were 800 nm and 2 $\mu$m, respectively. The photoinduced bleaching is dominating the temporal evolution of the DT.

Figure 5

Two-color DT measurements of the InMnAs ferromagnetic film in two different configurations and relaxation dynamics. (a) When the film is pumped from the ferromagnetic side. (b) When the film is pumped from the GaAs side.

Figure 6

Two-color DT signals from InMnAs at different applied fields at 5 K. The exponential fits are shifted for clarity.

Figure 7

Electronic structure of ${\text{In}}_{0.96}{\text{Mn}}_{0.04}$As at $T=290$ K for $B=0$, along the [001] and [111] directions. The energy bands are spin-split due to the ferromagnetism. The allowed optical transitions for a pump wavelength of 800 nm (1.55 eV) are shown by the (red) arrows. The dotted line at 1.08 eV shows the threshold for $\Gamma$ valley electrons to scatter to the satellite $L$ valley.

Figure 8

Electronic structure of ${\text{In}}_{0.96}{\text{Mn}}_{0.04}$As at $T=290$ K for $B=0$. The energy bands are spin-split due to the ferromagnetism. The allowed optical transitions are shown for a probe wavelength of 3.5 $\mu \text{m}$ (black arrows) and 2.0 $\mu \text{m}$ (red arrows).