Activation of nominally silent domain wall-localized phonons from GHz to THz frequencies

Unexpected Giant Microwave Conductivity in a Nominally Silent BiFeO3 Domain Wall

“…Using a simplified Ginzburg-Landau model, [18] one can show that the DW bends towards the normal direction near the surface. [30] We note that the bending of 71° DWs near the surface of BFO thin films has been experimentally observed by TEM and PFM studies. [31,32] Figure 3a shows the spatial distribution of Pz (out-of-plane component of the polarization) in the cross-section of the film, as simulated by electromechanical finite-element method.…”

“…[31,32] Figure 3a shows the spatial distribution of Pz (out-of-plane component of the polarization) in the cross-section of the film, as simulated by electromechanical finite-element method. [30] Because of the large spontaneous polarization in BFO, [21] the imbalance of Pz across the wall is comparable to polarization change across the 180° walls in h-RMnO3 [16] and h-RFeO3. [17] The asymmetric Pz profile can now couple to the out-of-plane MIM E-fields and induce DW vibration in Sample A.…”

“…We emphasize that, while the physical origin is different, the ac conductivity due to dipolar loss is equivalent to that from the electron conduction for microwave electronics. The collective vibration under an outof-plane electric field is localized perpendicular to the wall but free to propagate along the DW plane, [16,30] which may be utilized as, e.g., high-f waveguides. In that sense, this work represents an important step towards implementing DW nanoelectronics for RF applications.…”