Transport phenomena in double-layer exciton condensates

Date: 9 July 2018

Venue: University of Antwerp - Campus Groenenborger, Building U, Room 244 - Groenenborgerlaan 171 - 2020 Antwerpen

Time: 4:00 PM - 5:00 PM

Organization / co-organization: Condensed Matter Theory

Short description: Physics Department Colloquium presented by Dr. Timo Hyart from the international research center MagTop, Poland

Transport phenomena in double-layer exciton condensates


Exciton condensate states can be realized in systems consisting of two closely spaced layers, where one of the layers has excess electrons and the other equal number of excess holes. A particularly well-studied system for this purpose is the double-layer quantum Hall state occurring when the Landau level filling is fractional in each separate layer but the total filling is an integer [1]. This state is theoretically expected to realize a Bose-Einstein condensate of excitons, which is characterized by remarkable electronic properties such as counterflow superconductivity and a tunneling supercurrent similar to the Josephson current between two superconductors. Experimentally, a spectacular enhancement of the tunneling conductance at small interlayer bias voltage and almost dissipationless counterflow currents have been observed. In this talk, I will review the experimental observations in quantum Hall exciton condensates and I will show that they can be well-described using a theory which takes into account disorder-induced fractionally charged topological defects (merons) [2]. I will also discuss the analogies and differences between the Josephson effects in superconductors and double-layer exciton condensates.

Finally, I will talk about some interesting recent predictions and observations related to transport phenomena in double-layer exciton condensates. In particular, I will discuss our theoretical prediction of a confinement-deconfinement transition in helical quantum Hall exciton condensates [3] and the experimental observation of Josephson-like tunneling in double bilayer graphene in the absence of magnetic field [4]. 


[1] J. P. Eisenstein and A. H. MacDonald, “Bose–Einstein Condensation of Excitons in Bilayer Electron Systems,” Nature 432, 691 (2004).
[2] T. Hyart and B. Rosenow, “Quantitative Description of Josephson-Like Tunneling in 𝜈T=1  Quantum Hall Bilayers,” Phys. Rev. B 83, 155315 (2011).
[3] D. I. Pikulin, P. G. Silvestrov, and T. Hyart, “Confinement-Deconfinement Transition Due to Spontaneous Symmetry Breaking in Quantum Hall Bilayers,” Nat. Commun. 7, 10462 (2016).
[4] G. W. Burg, N. Prasad, K. Kim, T. Taniguchi, K. Watanabe, A. H. MacDonald, L. F. Register, and E. Tutuc, “Strongly Enhanced Tunneling at Total Charge Neutrality in Double-Bilayer Graphene-WSe2  Heterostructures,” Phys. Rev. Lett. 120, 177702 (2018).

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