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Inducing superconducting correlation in quantum Hall edge states
Lee, Gil-Ho,Huang, Ko-Fan,Efetov, Dmitri K.,Wei, Di S.,Hart, Sean,Taniguchi, Takashi,Watanabe, Kenji,Yacoby, Amir,Kim, Philip NATURE PUBLISHING GROUP 2017 NATURE PHYSICS Vol.13 No.7
The quantum Hall (QH) effect supports a set of chiral edge states at the boundary of a two-dimensional system. A superconductor (SC) contacting these states can provide correlations of the quasiparticles in the dissipationless edge states. Here we fabricated highly transparent and nanometre-scale SC junctions to graphene. We demonstrate that the QH edge states can couple via superconducting correlations through the SC electrode narrower than the superconducting coherence length. We observe that the chemical potential of the edge state exhibits a sign reversal across the SC electrode. This provides direct evidence of conversion of the incoming electron to the outgoing hole along the chiral edge state, termed crossed Andreev conversion (CAC). We show that CAC can successfully describe the temperature, bias and SC electrode width dependences. This hybrid SC/QH system could provide a novel route to create isolated non-Abelian anyonic zero modes, in resonance with the chiral edge states.
Controlled Electrochemical Intercalation of Graphene/<i>h-</i>BN van der Waals Heterostructures
Zhao, S. Y. Frank,Elbaz, Giselle A.,Bediako, D. Kwabena,Yu, Cyndia,Efetov, Dmitri K.,Guo, Yinsheng,Ravichandran, Jayakanth,Min, Kyung-Ah,Hong, Suklyun,Taniguchi, Takashi,Watanabe, Kenji,Brus, Louis E. American Chemical Society 2018 Nano letters Vol.18 No.1
<P>Electrochemical intercalation is a powerful method for tuning the electronic properties of layered solids. In this work, we report an electrochemical strategy to controllably intercalate lithium ions into a series of van der Waals (vdW) heterostructures built by sandwiching graphene between hexagonal boron nitride (<I>h</I>-BN). We demonstrate that encapsulating graphene with <I>h</I>-BN eliminates parasitic surface side reactions while simultaneously creating a new heterointerface that permits intercalation between the atomically thin layers. To monitor the electrochemical process, we employ the Hall effect to precisely monitor the intercalation reaction. We also simultaneously probe the spectroscopic and electrical transport properties of the resulting intercalation compounds at different stages of intercalation. We achieve the highest carrier density >5 × 10<SUP>13</SUP> cm<SUP>2</SUP> with mobility >10<SUP>3</SUP> cm<SUP>2</SUP>/(V s) in the most heavily intercalated samples, where Shubnikov-de Haas quantum oscillations are observed at low temperatures. These results set the stage for further studies that employ intercalation in modifying properties of vdW heterostructures.</P> [FIG OMISSION]</BR>
Ultrafast Graphene Light Emitters
Kim, Young Duck,Gao, Yuanda,Shiue, Ren-Jye,Wang, Lei,Aslan, Ozgur Burak,Bae, Myung-Ho,Kim, Hyungsik,Seo, Dongjea,Choi, Heon-Jin,Kim, Suk Hyun,Nemilentsau, Andrei,Low, Tony,Tan, Cheng,Efetov, Dmitri K. American Chemical Society 2018 Nano letters Vol.18 No.2
<P>Ultrafast electrically driven nanoscale light sources are critical components in nanophotonics. Compound semiconductor-based light sources for the nanophotonic platforms have been extensively investigated over the past decades. However, monolithic ultrafast light sources with a small footprint remain a challenge. Here, we demonstrate electrically driven ultrafast graphene light emitters that achieve light pulse generation with up to 10 GHz bandwidth across a broad spectral range from the visible to the near-infrared. The fast response results from ultrafast charge-carrier dynamics in graphene and weak electron-acoustic phonon-mediated coupling between the electronic and, lattice degrees of freedom. We also find that encapsulating graphene with hexagonal boron nitride (hBN) layers strongly modifies the emission spectrum by changing the local optical density of states, thus providing up to 460% enhancement compared to the gray-body thermal radiation for a broad peak centered at 720 run. Furthermore, the hBN encapsulation layers permit stable and bright visible thermal radiation with electronic temperatures up to 2000 K under ambient conditions as well as efficient ultrafast electronic cooling via near-field coupling to hybrid polaritonic modes under electrical excitation. These high-speed graphene light emitters provide a promising path for on-chip light sources for optical communications and other optoelectronic applications.</P>