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Topological order and symmetry breaking in van der Waals heterostructures

Andrea Young- Assistant Professor of Physics, UCSB

Thursday, November 16, 2017
  3:40–5 p.m.

Location: Chung Hall 138
  Parking Information

Category: Colloquium


Correlated quantum states of matter can be distinguished by their symmetry, their topology, or both.  Examples of symmetry-breaking in solid state systems abound, and include most familiar phases of matter, such as ferromagnetism, superconductivity, and crystalline order.  Topological order is much rarer experimentally, having only been definitively observed at partial filling of Landau levels—flat bands of electronic states that develop when two-dimensional electrons are subjected to a large magnetic field.  Topological order manifests through global properties of the many-body wavefunction, encoded in the fractionally quantized Hall effect and fractional quantum numbers of the collective excitations supported by the interacting electron system. Theoretically, topological order can also arise within generalized ‘Chern bands,’ of which Landau levels are a limiting case.  Most famously, electrons subjected simultaneously to a periodic potential and magnetic field are confined to the fractal bands of the Hofstadter butterfly, each of which is a Chern band.

In this talk, I will describe the experimental observation of ‘fractional Chern insulators’ in van der Waals heterostructures created by combining atomically thin graphite and insulating hexagonal boron nitride.  van der Waals heterostructures provide an ideal experimental platform for investigating the correlated physics of Chern bands, allowing superlattice potentials (engineered from the interference of the mismatched graphene and boron nitride lattices) to be combined with exceptionally low disorder and strong interactions. I will describe how we distinguish the fractional Chern insulators—which feature fractionally charged excitations--from the other gapped electronic phases in these devices including those that break lattice symmetries.  Finally, I will describe prospects for using fractional Chern insulators as a substrate for engineering and detecting novel emergent quasiparticles with unconventional quantum statistics.

Additional Information:

Open to: General Public
Admission: Free
Sponsor: Physics and Astronomy

Contact Information:
Naveen Reddy