Two dimensional materials are composed of layers of atoms only one or two atoms thick, arranged in a perfect lattice. Recent advances in the fabrication of these materials have led to the development of new types of electronic devices, which can help push the boundaries of scaling electronic components or introduce electronic devices based on completely new functionality. Crucially, in extremely thin layers the quantum nature of the system dominates the electronic properties in new and unusual ways. For example, spontaneous ordering, similar to ferromagnetism, can occur between layers. Electric fields can be used to modify material properties, providing new possibilities for enhancing the functionality of quantum electronic devices. This project develops a new, ultrasensitive capacitive technique to study these materials, along with new architectures for electronic devices based on two dimensional materials. The measurement toolkit will aid other scientists in the field studying devices relevant to electronics and energy harvesting, while continued advances in creating ever more perfect two dimensional devices reveal new physics of low dimensional electronic matter. Undergraduate and graduate students are trained in experimental design, device fabrication, and cryogenic measurement, advancing a new generation of condensed matter physicists ready to take on challenging problems across materials and measurement science.
This CAREER project develops a capacitive measurement technique that directly senses electronic compressibility, layer polarization, and layer polarizability in atomic bilayers, particularly within a new generation of all-van der Waals device geometries in which gate dielectric and metal materials (in addition to the channel materials) are also made of perfect two dimensional crystals. The measurement technique relies on the small difference in geometric capacitance between a bilayer and two proximal gates caused by interlayer motion of electrons, detected using a multiplexed high current gain cryogenic amplifier. The activity exhaustively catalogues integer and fractional quantum Hall effects and symmetry protected edge states in graphene heterostructures using a combination of thermodynamic and charge transport techniques which probe the bulk and edge separately. Immediate targets include ultra-clean Bernal and twisted bilayer graphene, where the technique permits the disambiguation of spin, layer, and valley symmetry breaking. Devices are fabricated using a new technique of all-van der Waals encapsulation, allowing record high mobilities rivalling or surpassing what can be achieved in all other electronic systems. Precise measurements of charge transfer in semiconductor bilayers, moreover, allows quantitative benchmarking of photo-induced processes, as are relevant for energy harvesting. In addition to providing direct, quantitative benchmarking of material parameters of use in applications of two dimensional materials, the activity has a broader impact through the seamless integration of undergraduate and graduate researcher education, and the developments of high school level classroom modules based on digital and analog electronics.
