Spintronic devices, by harnessing the spin degree of freedom, are expected to outperform charge-based devices in terms of energy efficiency and operation speed. For technological relevance, the use of electric field to control the spin degree of freedom at room temperature has been pursued for several decades. A major hurdle that leads to slow progress is the dilemma between effective control and strong spin decoherence. For example, in a Rashba or Dresselhaus material with strong spin-orbit coupling, though the internal magnetic field could be large enough for effectively controlling the spin precession, the spin dephasing time in most cases inevitably becomes extremely short through Dyakonov-Perel scattering. To address such a dilemma, persistent spin helix – a spin density wave with its phase and amplitude immune to spin-independent scattering – has been proposed in systems with SU(2) symmetry. However, most materials systems by far hosting persistent spin helix are carefully engineered III-V quantum wells that operate at cryogenic temperature with unwanted long spin helix wavelength. In this dissertation, we show the discovery of persistent spin helix in an organic-inorganic hybrid ferroelectric halide perovskite (4,4-DFPD)2PbI4 (4,4-DFPD: 4,4-difluoropiperidinium) whose layered nature makes it intrinsically like a quantum well. We demonstrate that the spin-polarized band structure is switchable at room temperature via intrinsic ferroelectric field. We reveal the valley-spin coupling through circular photo-galvanic effect in single crystalline bulk crystals. The favored short spin helix wavelength (three orders of magnitude shorter than III-V), room temperature operation and nonvolatility make the hybrid perovskite an ideal platform in understanding symmetry-tuned spin dynamics towards designing practical spintronic materials and devices that can resolve the control-relaxation dilemma.
For controllable growth and processing for miniaturized spintronic devices, we further show the liquid-phase van der Waals epitaxy of (4,4-DFPD)2PbI4 on muscovite mica and demonstrate the feasibility on fabricating perovskite-perovskite vertical heterostructures using dissimilar Riddlesden-Popper 2D perovskite sheets. The epitaxial (4,4-DFPD)2PbI4 nanobelt array can be from multiple layers to unit-cell in thickness and are crystallographically aligned on the mica substrate. An interlayer photo emission in (4,4-DFPD)2PbI4-based heterostructure with a lifetime of about 25 ns at 120 K has been revealed. Our demonstration of epitaxial (4,4-DFPD)2PbI4 array grown on mica via liquid-phase van der Waals epitaxy provides a paradigm to prepare orderly distributed 2D hybrid perovskites for further integration into multiple heterostructures. The discovery of a new interlayer emission in (4,4-DFPD)2PbI4-based heterostructure enriches the basic understanding of interlayer charge transition in halide perovskites systems.;
August2022; School of Engineering
Dept. of Materials Science and Engineering;
Rensselaer Polytechnic Institute, Troy, NY
Rensselaer Theses and Dissertations Online Collection;
Restricted to current Rensselaer faculty, staff and students in accordance with the
Rensselaer Standard license. Access inquiries may be directed to the Rensselaer Libraries.;