Colloquium Ehrenfestii - Philip Kim (Harvard University): 'Correlated electrons in graphene'



19:30 hrs; dinner at 18:00 hrs


Sitterzaal, Oort building, Leiden


The symmetry protected Dirac spectrum near the charge neutrality has been a source of exotic physical behaviors observed in graphene. In a disorder-free clean sample, attained by encapsulating graphene in between hexa-boron nitride, we can tune the Fermi energy to be much smaller than any relevant energy scales. In this presentation, we will discuss several examples where extremely small Fermi energy plays a critical role. In the first example, we present the Andreev reflection realized in graphene in contact with van der Waals superconductor NbSe2 with a clean interface. By reducing the Fermi energy of graphene smaller than the superconducting gap, we observe the evidence of a long-sought specular Andreev reflection, where the superconducting Cooper pairs split into a pair of electron and hole across the charge neutrality point. In the second example, we will discuss a drastic enhancement of the electronic thermal conductivity at the charge neutrality as the Fermi energy becomes smaller than thermal energy. We report a strong violation of the Wiedemann-Franz law at the charge neutrality, suggesting the realization of the relativistic hydrodynamic transport. Finally, we will also discuss our recent experimental results on quantized Hall-drag resistance in double bilayer graphene system where evidence for the exciton condensation phases across Landau levels with different filling factors can be inferred. 

Please Note: The Colloquium Ehrenfestii takes place on Wednesday evenings starting at 19:30 hours in the main auditorium of the Oort building. Before the Colloquium, there is a common dinner in the canteen located on the ground floor of the Oort building. This dinner starts at 18:00 hours sharp and is FREE of charge, under the condition that one attends the colloquium and that one has made a reservation before noon on the Tuesday preceding the colloquium.
The registration form is only accessible from within the University (to block spammers); if you would like to register for the dinner from outside the University, please send an email to fran [at] The revolving doors to the Oort building are accessible until 9 pm. After that, they are locked and one should instead use the sliding doors directly adjacent to the Huygens building: these can be opened with an electronic key.