Department of Physics and Institute for Optical Sciences, University of Toronto, Toronto M5S1A7, Canada.
Phys Rev Lett. 2013 Jul 19;111(3):035701. doi: 10.1103/PhysRevLett.111.035701. Epub 2013 Jul 17.
MnAs epilayers grown on GaAs are used as a model system to study the effects of strain and epitaxial constraints on the dynamics of structural domains following 150 fs pulse pumping. Optical diffraction over 7 orders of magnitude of time is used to probe the evolution of the domains that are spatially periodic between 10 and 42 °C because of misfit strain and substrate mediated periodic elastic strain. Following excitation of 150 and 190 nm thick films, the domain fractions and the elastic strain oscillate with an ~400 ps period while the average low temperature phase fraction decreases monotonically for ~2 ns reflecting MnAs heat diffusion. Equilibrium structures are restored in 100 ns-2 μs via substrate heat diffusion. Excitation of transient periodic domains from the homogeneous low temperature phase can occur for temperatures as low as 4 °C but only after ~20 ns during film cooling.
在 GaAs 上生长的 MnAs 外延层被用作模型系统，研究应变和外延约束对 150fs 脉冲泵浦后结构畴动力学的影响。通过光学衍射，可以探测到由于失配应变和衬底介导的周期性弹性应变，在 10 到 42°C 之间具有空间周期性的畴的演变，其时间跨度为 7 个数量级。在激发 150nm 和 190nm 厚的薄膜后，畴分数和弹性应变以约 400ps 的周期振荡，而平均低温相分数在约 2ns 内单调下降，反映了 MnAs 的热扩散。通过衬底热扩散，在 100ns-2μs 内恢复平衡结构。在薄膜冷却期间，在 4°C 以下的温度下，从均匀低温相激发瞬态周期性畴可能会发生，但需要在 20ns 后。
