NCTS (South)



PLACER49223, Second Physics Building , NCKU

FIELDQuantum Information Science

SPEAKER Dr. Kuei-Lin Chiu - Cavendish Laboratory, United Kingdom

TITLETransport properties of graphene nanodevices-nanoribbons, quantum dots and double quantum dots

ABSTRACTIn this talk I will presents my work on graphene transport research, including graphene nanoribbons (GNRs), single quantum dots (SQDs) anddouble quantum dots (DQDs).
We first study the transport properties of a lithographic defined GNR at a temperature of 1.4 K. The sharp resonances appeared in the transport gap and its corresponding Coulomb diamond provide evidences that many QDs are formed along the GNR. We have demonstrated how the conductance can be enhanced upon applying magnetic field. We also show how UCF amplitude could be reduced by heating device and find a characteristic temperature which separates two different electron hopping mechanisms.
We next demonstrate how a graphene SQD can be used to detect the formation of LLs of the inline GNR in magnetic fields. We see the conductance ridge of GNR is superimposed in the graphene specific Fock-Darwing spectrum and help us to understand the origin of the postive magnetoconductance observed in many GNRs.
We then research into an all graphene defined double quautum dot device. This device at low temperature displays a honeycomb-like charge stability diagram and triangle-like triple points upon applying bias. We then study the evolution of those features under the influence of increasing magnetic field. Our result shows, owing to the different magnetic chirality of electron/hole puddles, the charging energy hence the size of the dot varies with magnetic fireld. A field induced excited state is also studied to support this charge rearrangement picture.
Finally, we perform the charge pumping experiemnt on two different DQD devices through applying RF signal. For the device on the doped wafer we measure a rectified current which is dependent on the RF amplitude and phase difference. We successfully measured the pumping current from the device on an undoped wafer.