CAREER: Two-dimensional Van Der Waals systems with tunable spin-orbit coupling

College Of William And Mary, Williamsburg VA

Investigators

Abstract

NONTECHNICAL SUMMARY This CAREER award supports theoretical research and education to investigate the properties of novel materials made of stacked two-dimensional layers in which the way electrons interact with each other and with the crystal lattice, and the role of materials defects can be controlled and tuned experimentally. This research is motivated by recent experimental breakthroughs that have demonstrated that single, one-atom thick, layers of different materials can be isolated and then stacked to form novel systems, "van der Waals systems", in which the different layers are held together by a weak electrostatic interaction named after the Dutch Nobel prize winner Johannes Diderik van der Waals. The properties of van der Waals systems can be engineered and tuned to an unprecedented degree by selecting the materials forming the structure, and the stacking order. Of particular interest is the spin-orbit interaction. Electrons have an intrinsic property called spin where it appears as if the electron spins like a tiny top. The spin of the electron is also connected to its intrinsic magnetic properties; it behaves as though it was a tiny bar magnet. As an electron moves through a material it will experience a magnetic field from the atomic cores in the lattice as a consequence of the theory of relativity. The PI will investigate the effect of tunable spin-orbit interactions and crystalline imperfections on the equilibrium state of the electrons and on the way charge and spin move through van der Waals systems. Impurities are often regarded as a nuisance that spoils the properties of a clean system. However, impurities can be essential to obtain desirable physical effects and can be used as unique atomic-scale probes of the ground state of the host system. The PI plans to study impurity-induced states in van der Waals systems and to explore the possibility to use disorder to achieve novel functionalities in these materials. The educational activities supported by this award include the design and development of a portable kit to carry out demonstrations for K-12 students. This Physics in a Briefcase will be used to reach economically disadvantaged schools. The PI will also develop a new course on condensed matter physics tailored to advanced undergraduate and 1st-2nd year graduate students, and a multimedia "wikibook" created from students' contributions to present and disseminate course material to students and the public. TECHNICAL SUMMARY This CAREER award supports theoretical research and education to investigate the interplay between spin-orbit coupling, electron-electron interactions, and disorder, in newly realized van der Waals materials. The spin-orbit coupling, interactions, and disorder strength can be tuned in these materials by varying experimentally controllable quantities. The PI plans to study: (i) the effect of tunable spin-orbit coupling on correlated states; (ii) how the type and strength of disorder affects the ground state and investigate the possibility to realize disorder-tuned phase transitions between different broken-symmetry states; (iii) the effect of tunable spin-orbit coupling on the properties of impurity bound states; (iv) anomalous coupled charge-spin transport and current-driven spin torques and how they can be modified by tuning the spin-orbit coupling. To carry out this investigation the PI will use a combination of field-theoretic, diagrammatic, and computational approaches. In particular, computational methods based on a functional approach developed by the PI will be used to study the presence of disorder with a correlation length larger than the Fermi wavelength of the electrons. The theoretical description will be verified and refined via close collaboration with experimental groups. By studying van der Waals systems with tunable spin-orbit coupling, interactions, and disorder, the proposed research will provide theoretical results that will transcend the field of van der Waals systems and be directly relevant to the broad topic of the effect of spin-orbit coupling in electronic systems. The educational activities supported by this award include the design and development of a portable kit to carry out demonstrations for K-12 students. This Physics in a Briefcase will be used to reach economically disadvantaged schools. The PI will also develop a new course on condensed matter physics tailored to advanced undergraduate and 1st-2nd year graduate students, and a multimedia "wikibook" created from students' contributions to present and disseminate course material to students and the public.