Thermoelectric Properties of Fe0.2Co3.8Sb12-xTex ... - Physics

Landau Level Spectroscopy of Broken Symmetry States in High Mobility
Graphene on Boron Nitride
Srijit Goswami, Paritosh Karnatak and Arindam Ghosh
The presence of spin and valley degeneracy in graphene gives rise to four-fold degenerate
Landau levels (LLs) in the presence of a magnetic field perpendicular to the plane of the
graphene. Graphene devices on silicon oxide substrates typically exhibit very low mobility,
resulting in significant broadening of LLs. As a result, any broken symmetry states are
difficult to observe at reasonable magnetic fields.
Placing graphene on atomically flat hexagonal Boron Nitride (BN) results in significantly
higher carrier mobility. We have fabricated such high mobility graphene-BN
heterostructures and show that the four-fold degeneracy of the LLs is completely lifted at
moderate magnetic fields. Such broken symmetry states have been observed in a few
studies previously, however their exact nature is still a matter of debate.
We also show that charge transfer between graphene and a nearby defect site gives rise to
discrete jumps in the resistance. In the presence of a magnetic field the size and nature of
these resistance jumps is particularly sensitive to the position of the Fermi level. We discuss
some preliminary results which indicate that such a graphene-defect system may allow for a
more sensitive spectroscopy of the LLs, as compared to time averaged transport.