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Solidification of electrons in the flatland - Manohar Kumar

Laboratoire Pierre Aigrain, ENS, Paris

LPS – amphi Blandin

Competition between liquid and solid states in two-dimensional electron gas system is an intriguing problem in condensed matter physics, where competition between Coulomb energy and kinetic energy leads to formation of different quantum phases. This problem has been studied for long time on surface of liquid Helium and in deeply buried two-dimensional electron gas in GaAs/AlGaAs. Like, in Helium, 2-dimensional electron gas is found on the surface of graphene, an inherent property of atomically thin structure, making them amenable to external probes. Here we have investigated competing electronic solid phase i.e. Wigner crystal and fractional quantum Hall ( FQH ) liquid phases in suspended graphene devices in Corbino geometry. The high quality of our suspended sample and the idiosyncrasy of geometrically induced topological states in Corbino geometry has led to the detection of such competing ordered states.

We probed these states at 20 mK with magnetoconductance and transconductance measurements. Our magneto/trans-conductance measurments indicate strong charge density dependent modulation of electron transport and resolved a distinctive sets of incompressible FQH states i.e. \nu = -1/3, 1/5, 2/7, 4/13, 1/3, 2/5, 3/7, 4/9, 4/7, 3/5, 4/5, 4/3. Of these \nu = 4/13, 4/11, they do not fit the standard Jain’s series for conventional FQH states, instead they appear to originate from residual interactions of composite fermions in partially filled higher Landau levels. And at very low charge density with filling factors \nu < 1/5, electrons crystallize into an ordered Wigner solid which eventually transforms into an incompressible Hall liquid at filling factors around \nu 1/7. We probe these states by I-V and microwave resonance spectroscopy.

In conclusion, our measurments on Corbino sample geometry pave the way for enhanced understanding of the ordered phases of interacting electrons.


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