In this article, we present the observation of coherent elastic dynamics in a nano-scale phononic superlattice, which consists of only 4 bilayers. We demonstrate how ultra-short light pulses with a length of 40 fs can be utilized to excite a coherent elastic wave at 0.535 THz, which persist over about 20 ps. In later steps of the elastic dynamics, modes with frequency of 1.7 THz and above appear. All these modes are related to acoustic band gaps. Thus, the periodicity strongly manifests in the wave physics, although the system under investigation has only a small number of spatial periods. To further illustrate this, we show how by breaking the translational invariance of the superlattice, these features can be suppressed. Discussed in terms of phonon blocking and radiation, we elucidate in how far our structures can be considered as useful building blocks for phononic devices.
THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices
Henning Ulrichs, Dennis Meyer, Markus Müller, Steffen Wittrock, Maria Mansurova, Jakob Walowski, Markus Münzenberg; THz elastic dynamics in finite-size CoFeB-MgO phononic superlattices. J. Appl. Phys. 14 October 2016; 120 (14): 142116. https://doi.org/10.1063/1.4961978
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