Our research focuses on both fundamental studies, and technological applications of solid state devices at the meso- and nano-scale. General areas of study include electron transport in degenerate many body systems where strong interactions lead to new states of matter and novel electronic behaviour resulting from new device archictectures. Systems that we study include layered materials such as graphene and related heterostructures, transition metal dichalcogenides, and topological insulators as well as more conventional 2D electron systems such as III-V semiconductors. We probe these systems by combining transport studies with a variety of experimental knobs such as applied magnetic and electrostatic fields, variable tempeartures from ambient down to miliKelvin, high vacuum, spatial confinement down to the nano-scale, variable charge carrier densities, and unconventional NMR techniques.
Below please find examples of some broad research topics being studied in our lab; under the equipment tab you can learn more about our experimental capabilities.
An intriguiging feature of bilayer graphene is the ability to induce a bandgap by application of transverse electric field, where the gap grows larger with increasing displacement fied. In the transition metal dichalcogenides it is predicted that it may be possible under similar conditions to close the gap. From a device perspective, the capability to dynamically tune the electronic bandgap represents a significant technological advantage over conventional materials providing the opportunity for a new generation semiconductor devices. We explore applications to opto-electronics, tunable sensors, and novel transistors where the ability to dynamically tune electron transport characteristics in-situ offers unprecedented device functionality.
Assembling layered heterostructures consisting of graphene and its insulating isomorph, hexagonal-Boron Nitride, allows us to study emergent phenomenon in strongly interacting, reduced dimensional systems. Examples include exciton condensation and Coulomb drag in closely-spaced parallel quantum wells; fractional quantum Hall effect in a system of Dirac electrons with non-zero Berry phase; spontaneousy symmetry breaking and magnetic ordering in a multicomponent 2DEG with full control over the inherent degrees of freedom; and the evolution of non-Abelian quasiparticles in a system with tunable orbital wavefunctions.
It has long been predicted that 2D electrons subjected simultanesously to both a magnetic field and a superlattice periodic potential will exhibit a complex self-simlar fractal energy spectrum. Termed Hofstadter’s Butterfly, after the theorist who first discovered the recursive energy structure, this phenomenon has intrigued physicists for nearly 40 years, and represents a fundamental framework for understanding the generalized behaviour of electrons in electro and magnetic fields. A complete understanding of the Butterfly spectrum, however, has remained elusive owing to the stringent experimental conditions required. Recently we demonstrated that moire superlattices, arising in bilayer graphene coupled to hexagonal boron nitride provide a nearly ideal-sized periodic modulation, enabling unprecedented experimental access to the fractal spectrum. Several intriguing questions can now be explored experimentally such as the possibility of anomalous emergent behaviour within the fractal energy landscape.
Using pioneering techniques to fabricate layered heterostructures we explore both fundamental physics and novel device applications resulting from the interplay between structural form at the nano-scale and electron behaviour. Presently our efforts focus on hexagonal crystalline materials that can be exfoliated down to single atomic layers. We then build up layered heterostrucutres by successive lamination of these 2D sheets in combination with state of the art nanofabrication processes. In addition to graphene, the material list includes the transition metal dichalcogenides such as MoS2, WeSe2, NbSe2, etc. as well as the insulating isomorph of graphene, hexagonal-BN.x
When graphene is placed in contact with hexagonal boron, a moire pattern develops with long range order, which in turn looks like a crystal field to the free electrons in the graphene layer. We were able to exploit the large length-scale of the moire superlattice (~15 nm) to look for the long predicted Hofstadter butterfly energy spectrum, expected to emerge under simultaneous application of both a magnetic field and a spatially varying electrostatic field. Read more about our exciting resuls in the magazine Nature.