Physics Colloquium: Qiong Ma, Massachusetts Institute of Technology
Creating and probing new phases in quantum materials
There are two fundamental ways for us to understand nature. One way is to understand our world by breaking it into smaller and smaller building blocks. Primary examples include the discoveries of chemical elements and elementary particles. The other way is: given the same building blocks, we ask what the possible ways are for them to be organized by nature. On the level of condensed matter, even with the same chemical composition and parent lattice structure, the interplay among charge, spin and lattice degrees of freedom still leads to a manifold of distinct quantum electronic phases. Such richness of emergent electronic phases brings great opportunities to realize new technologies. Meanwhile, the associated complexity also poses great challenges to engineer and control their properties.
Over the past decade, van der Waals monolayer crystals and heterostructures have been increasingly recognized as a highly-tunable material platform to create and control novel quantum phases. Remarkably, we can create moiré superlattices with the lattice constant continuously tuned over a wide range, providing artificial potential modulation that is effectively felt by electrons. This has led to a plethora of low-temperature emergent phases in lattices made out of pure carbon, including magnetism, topology, and superconductivity. In this talk, I will show an unexpected spontaneously ordered electronic phase in graphene moiré superlattices with dramatic and practical device functionalities, persisting all the way up to room temperature. Also, in order to sensitively detect the symmetry properties of such new electronic orders, I will introduce nonlinear electromagnetic responses in various forms and give an example in which the nonlinear properties are employed not only to detect but also to control an emergent electronic phase with definite chirality in a layered correlated semimetal TiSe2.
Wednesday, January 15, 2020 at 4:00pm
Higgins Hall, 310