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CAMP: Complex Ordering of Ground States in Two-Dimensional Materials: Quantum Metal in NbSe2 and Valley-Orbital Polarization in Bilayer Graphene

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Benjamin Hunt, Carnegie Mellon University
When
29 March 2016 from 3:30 PM to 4:30 PM
Where
339 Davey Laboratory
Contact Name
Kin Fai Mak
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Atomically-thin transition metal dichalcogenides have recently become a very popular subject.  NbSe2, a classic layered superconductor, is the first of these that exhibits superconductivity down to one or two atomic layers.  I will discuss our recent experiments on bilayer and few-layer NbSe2 and our observation of an anomalous metallic phase in the zero-temperature limit induced by a small perpendicular magnetic field. This quantum metal phase has only been observed in highly-disordered thin film superconductors and its observation in a crystalline superconductor, along with a distinct magnetic field scaling, forces us to reexamine the diagram of possible electronic phases in two dimensions at zero temperature.

 

Bilayer graphene is another intensely studied two-dimensional system, but little is known experimentally about the interplay among the spin, valley (or layer), and orbital degrees of freedom when this eightfold degeneracy is completely lifted in intense magnetic fields.  Using a new capacitive technique we directly measure the degree of layer polarization in the bilayer system (and the accompanying orbital states) and provide new understanding of the complex ordering among these three degrees of freedom in the extreme quantum limit.

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