Abstract
Two-dimensional materials provide an interesting system to do study quasiparticle physics, because strong Coulomb interactions resulting from reduced dielectric screening and under conditions of energy level quantization due to high carrier confinement. GaSe crystals has a similar layer structure to transition metal dichalcogenides (TMDs. However, there is a vacancy in Ga atoms, it will be highly adopted, the ultra-thin GaSe will have ferromagnetism. Another unique difference is that conduction band minimum of GaSe is at the Brillouin zone center (Γ), unlike the TMDs, the conduction band minimums are at the K points. Here, we take use of optical techniques to study ultra-thin GaSe crystals. Our studies explore the unique behavior of exciton and ferromagnetism of ultra-thin GaSe.
The monolayer GaSe is ferromagnetic when the hole is highly doped. From the photoluminescence (PL) spectroscopy, absorption experiments and PL lifetime of ultra-thin GaSe, bandgap energy and some exciton information, like energy difference between free exciton and bound exciton states, can be achieved. From magneto-optic Kerr effect (MOKE) experiments, the magnetic hysteresis loop of different temperatures can be obtained, and the ferromagnetism can be understood. Remarkably, the spin properties of electrons in ultra-thin GaSe can be detected by ultrafast laser spectroscopy. The ultra-thin GaSe is under a strong magnetic field, the spin rotation can be tested by pump-probe techniques.
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