Speaker
Description
Metal-halide perovskites (MHPs) emerged as exciting novel semiconductors with outstanding optoelectronic properties for applications in photovoltaics and light emission. More recently, these semiconductors also attract interest as promising candidates for spintronics. In the absence of inversion symmetry, spin-orbit coupling (SOC) leads to the Rashba-Dresselhaus effect, offering outlook for spin current control. Therefore, inversion symmetry breaking in MHPs with strong SOC has crucial implications. However, in structurally complex, low-dimensional hybrid organic-inorganic perovskites, the presence and exact mechanisms of inversion symmetry breaking remain elusive.
Here, employing intense, close to single-cycle, THz fields, we coherently drive and identify lattice dynamics carrying optical signatures of inversion symmetry breaking in Ruddlesden-Popper (PEA)2(MA)n-1PbnI3n+1 perovskites, despite their global centrosymmetric structure. We demonstrate coherent control by THz pulses over distinct phonons, which we tentatively assign to inorganic cage and coupled inorganic-PEA+ vibrations. By developing a general polarization analysis for THz-driven phonons, we pinpoint linear and nonlinear driving mechanisms. From this, we identify simultaneous IR- and Raman-activity of inorganic cage modes below 1.5 THz, suggesting the presence of inversion symmetry breaking. We therefore demonstrate a general experimental method to dial into the coherent dynamics of modes bearing broken inversion symmetry fingerprints, paving the way for simultaneous ultrafast control of optoelectronic and spintronic properties of 2D HOIPs.
