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Giant energy dissipation on twistedbilayer graphene at magic angle twistA. Ollier¹,2, M. Kisiel1, U. Gysin1 and E. Meyer¹¹Department of Physics, University of Basel, Klingelbergstrasse 82, CH-4056 Basel, Switzerland2Swiss Nanoscience Institut, Klingelberstrasse 82, CH-4056 Basel, SwitzerlandCAPRI SPRING SCHOOL12/05/2022A. Ollier – alexina.ollier@unibas.ch
INTRODUCTION TBGCapacitance measurement on twisted bilayergraphene, showing a capacitance drop at halffilling (insulating state).Transport measurements on TBG showpeaks in resistivity at correlated insulatingstates. The angle dependence is strong:48𝜃 2𝑛𝑠 𝐴3𝐴2Y. Cao, et al., Correlated insulator behaviour at half-filling in magic-angle graphene superlattices, Nature 556, 80 (2018).12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 2
INTRODUCTION Pendulum AFM – p-AFMTuning fork𝐹𝑚𝑖𝑛 Low stiffness: k 0.18 N/mHigh quality factor: Q 50000012/05/2022 – Capri Spring School2𝑘𝐵 𝑇𝒌𝜋𝑓𝑸Spatial resolution (m)A. Ollier – alexina.ollier@unibas.chUniversity of Basel 3
EXPERIMENT SampleScale bar 2umAFM image of TBG device (red rectangle) iscontacted by 8 gold wires. Only two of them areconnected and we kept them grounded.Cantilever tip as an oscillating andsensing top-gate, coupled capacitivelyto the underlying TBG.12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 4
RESULTS Energy dissipation vs Gate voltageelectronsholesVCPD 8Vd 150 nm12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 5
RESULTS Back gate and dopingBack gate capacitance (Cox) is equal to:𝜀0 𝜀 3.9 8.854 10 12𝐶𝑜𝑥 1.15 10 4 𝐹. 𝑚 2𝑡𝑜𝑥300𝑛𝑚The doping concentration: 𝑛 𝑛 𝑛𝑠 8𝜃 23𝑎2𝐶𝑜𝑥 𝑉𝐵𝐺𝑞 2.83 1012 𝑐𝑚 2Our graphene is not exactly 1.08o twisted. The twist angle is 1.1o.12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 6
RESULTS Back gate and doping-ns/4ns/4Due to disorder, thespatially averaged DOSat Dirac point is notzero. A disorder densitynd 5.109cm-2 can becalculated from CPDshift.(nd 1 . 1010 cm 2 inCao et. al. case)12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 7
RESULTS Twist angle distributionTopography50nmWe measured dissipation spectra at every point along the line (30 points). Next, wematch the position of the dissipation peaks to the superlattice density ns. Thus, we canlocally determine the twist angle : 𝜃 12/05/2022 – Capri Spring School3 1464 𝑛𝑠 𝑎A. Ollier – alexina.ollier@unibas.chUniversity of Basel 8
RESULTS Twist angle distributionThe twist angle is equalto 1.06 0.04 Twist angle distributionis only 3-4% off fromthe magic twist.12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 9
RESULTS Constant height dissipation mapsThe angle distribution is also visible inconstant height dissipation imageswhere we observe domains withdifferent relaxation of the graphene(dashed lines).Graphene quantum dot (CB CoulombBlockade)Scale bar 50nmQiao, Jia-Bin and Jiang et.al., Boundstatesinnanoscalegraphenequantum dots in a continuousgraphene sheet, PRB95, 081409(2017).12/05/2022 – Capri Spring SchoolTopographyEnergy dissipation imagesCBns/4B 0TV 17,1Vns/2B 0TV 23V10
CONCLUSIONSP-AFM spectroscopy: local probe tool, can study band filling of TBG: Energy dissipation is sensitive tocharge filling of flat bands, Dissipation peaks: ¼ filling, halffilling , filling and full filling, Rise of frictional lose at CNP,(electron-hole scattering).Angle distribution investigation: Quantitative: average angle of 1.06 andangle distribution about 3-4% Qualitative: the constant height tip imagingallows to map the twist angle distribution ofTBG and observe CB rings.12/05/2022 – Capri Spring SchoolA. Ollier – alexina.ollier@unibas.chUniversity of Basel 11
ACKNOWLEDGEMENT Group members:Prof. Ernst MeyerProf. Alexis BaratoffDr. Thilo GlatzelDr. Urs GysinDr. Laurent MarotDr. Marcin KisielDr. Rémy PawlakDr. Antoine HinautDr. Yimin SongDr. Chao LiRoland SteinerYves Pellmont12/05/2022 – Capri Spring School-Kunal SoniSebastian ScherbMarco ZutterFabien SanchezJung-Ching LiuPaul HiretOuthmane ChahibShuyu HuangGema NavarroAkash Gupta Funding:European Research Council (ERC)Swiss Nanoscience Institute (SNI)A. Ollier – alexina.ollier@unibas.chUniversity of Basel 12
Thank you for your attention !26/04/2022 – QCQT Lunch SeminarUniversity of Basel 13
CAPRI SPRING SCHOOL 12/05/2022 Giant energy dissipation on twisted bilayer graphene at magic angle twist. INTRODUCTION TBG A. Ollier -alexina.ollier@unibas.ch University of Basel 2 Y. Cao, et al., Correlated insulator behaviour at half-filling in magic-angle graphene superlattices, Nature 556, 80 (2018). Capacitance measurement on twisted bilayer graphene, showing a capacitance drop at .
