Optical Spin Orientation and Transport in Layered Mono- and Di-Chalcogenide Semiconductors

Northwestern University, Evanston IL

Investigators

Abstract

Non-technical description: Electronic devices for computing logic are traditionally based on the charge of electrons, but as scaling this technology becomes increasingly difficult due to heat and size constraints, new physical systems are necessary for improving logic devices. One possibility to tackle this problem is to utilize an electron's "spin" rather than its charge, which requires less energy and produces less heat. Translating this approach to emerging nano-scale materials is likely to reveal approaches for miniaturized low-power spin-based electronics functioning at the smallest length scales possible. This research focuses on understanding how to orient and transport spin and spin-analogs in nanomaterial systems that harness the advantages of the ultimate atomic-scale limit of single layered crystals. These efforts could have broad impact by making the advantages of layered atomically-thin materials available to spin-based devices, thereby helping to smooth adoption of these exciting materials for nano-scale technologies that surpass the functionality of existing well-understood bulk systems. The supported activities facilitate mentoring of the next generation scientific workforce fluent with the intersection of optics, quantum materials, and nano-science. This research integrates into pedagogical improvements to curriculum that promote scientific interest and enthusiasm for diverse students. Technical description: The ability to use light to orient spins and induce spin currents has been a key tool in the study of spintronics in bulk materials. By studying several classes of non-centrosymmetric crystals that are already known to support spin-related phenomena, this research translates the advantages of optical methods used in three-dimensional spintronics to reveal novel effects in low dimensions. Going beyond previous work exploiting light to control spin, this project investigates several unanswered questions, including (i) how optically-excited spin transport evolves over low-dimensional interfaces, and (ii) can the non-centrosymmetric crystals common in two-dimensional materials enhance the ability to control optically-induced information. To address these questions, this research explores spin orientation and transport phenomena using two distinct, but complementary, approaches. The first theme exploits the unique atomic-scale interfacial and heterostructure capabilities of layered van der Waals materials to understand spin-valley currents. This activity aims to measure interface effects of the valley Hall effect in opto-electronic devices. The second thematic direction of this research explores predictions of favorable spin properties in few-layer mono-chalcogenides that suggest suitability of this material class for traditional optical spin orientation methods. This theme aims to measure optically-induced spin dynamics in indium selenide and control transfer of spin polarization between electron and nuclear spin ensembles. Research carried out toward these goals advances understanding of spin transport and optical orientation and expands the tools available for spin manipulation in two-dimensional materials, thereby creating opportunities for highly tailored miniaturized opto-electronics. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.