Electron Transport in/across the van der Waals Interfaces Philip Kim Physics Department, Harvard University Acknowledgement Amelia Barreiro, Dmitri Efetov, Cheol Ho Lee, Austin Fong, Patrick Maher, Wei Tsen, Xiaomeng Xue Collaborators Collaborators: Current Members Collaborating Students/postodcs Horst Stormer, Aron Pinczuk, Tony Heinz, Abhay Yue Zhao Cory Dean, Inanc Meric, Lei Wang, Jim Hone, Ken Shepard, Tony Heinz, Cory Dean (Columbia), Jing Guo (UF) Pasupathy, Latha Venkataraman Mitsuhide Takekoshi Sebastian Sorgenfrei, Kevin Knox, Nayung Louis Brus, George Flynn, Colin Nuckolls, Andrea Jung, Seok Ju Kang, Jun Yan, YanwenWatanabe Tan, G. C.Young Yi (SNU), Takashi Taniguchi, Kenji (NIMS) Jim Hone, Ken Shepard, Louis Campos, Rick Osgood Dmitri Efetov Kevin Knox Fereshte Ghahari Patrick Maher Young-Jun Yu (jointly with GRL, POSTECH) Vikram Deshpande (jointly with Hone group) Paul Cadden-Zimansky (Columbia Frontier of Science Fellow) Chenguang Lu (jointly with Hone and Herman T. Taniguchi, K, Watanabe Andre Geim, Kostya Novoselov, Sanka Das Sarma Past Members Melinda Han (Ph.D. 2010, Frontier of Science Fellow, Columbia University) Meninder S. Purewal (Ph.D. 2008) Josh Small (Ph.D. 2006) Yuanbo Zhang (Ph.D. 2006, Professor, Fundan University) Yuri Zuev (Ph.D. 2011, IBM Fishkill) Kirill Bolotin (Assistant Professor, Department of Physics, Vanderbilt University) Byung Hee Hong (Associate Professor, Department of Chemistry, Seoul National University) Pablo Jarillo-Herrero (Assistant Professor, Department of Physics, MIT) Kim Keunsoo Kim (Assistant Professor, Department of Physics, Sejong University) Namdong Kim (Research Scientist, POSTECH) Barbaros Oezyilmaz (Assistant Professor, Department of Physics, National University of Singapore) Funding: group and friends (2011) Pick-up Technique and Edge Contacts for Multilayer vdW Stacking (Columbia Team) •  Creation of multilayer systems with colamination techniques •  Encapsulated graphene in hBN •  Completely ballistic at low temperature Edge contacting method Contac Resistance: 100 Ω µm Mobility ~ 106 cm2/Vsec Mean free path > 10 µm L. Wang et al, Science (2013) Magnetic Focusing in Graphene (collaboration with Cory Dean) L = 7.5 µm L = 15 µm Similar result in Taychatanapat et al. (2013) Fractional Quantum Hall Effect in Moire Superlattice Single layer graphene on hBN @ 20 mK up to 35 T Hall Conductivity Fractional Quantum Hall Effect -1 σxy (mS) 0 1 Rxx Rxy 2/3 B (T) 4/3 5/3 7/3 Vg (V) •  Fractal quantum Hall effect due to the periodic electric potential form graphene/hBN moire. 4/3 5/3 7/3 8/3 10/3 13/3 (ν) σxx (e2/h) •  Competition between fractional and fractal quantum Hall effect in the extreme quantum condition. In collaboration with C. Dean (Columbia) Noise Thermometry and Hydrodynamic Transport Johnson noise thermometry 5 µm hBN encapsulated graphene with low inhomogeneity Crossno et al. (2015) Breakdown of Wiedeman Franz law Enhancement of electric contribution of thermal transport at charge neutrality due to hydrodynamic transport Effect of CDW Dimensionality: Thin TaS2 Electrical transport in encapsulated TaS2 Encapsulated TaS2 on SiN membrane for TEM study Electron diffraction from TEM •  Nearly commensurate to commensurate CDW phase transition is suppressed due to increasing disorder contribution in thin samples. •  CDW phase transition can be modulated by current Tsen et al (2015) (Collaboration with Pasupathy group) Andreev Reflections – between NbSe2 & Graphene Efetov et al. (2015) graphene 5 µm NbSe2 Tc = 7 K Hc2 = 4.5 T Graphen Hall-bar With NbSe2 as a current injection electrode Andreev reflection between graphene and NbSe2 across vdW interface Gate Depedent Andreev Reflections – Sign of Specular Andreev Reflection Efetov et al. (2015) Normal AR (EF > Δ) Specular AR (EF < Δ) Inter valley AR (eV > EF) Intra valley AR (eV < EF) Atomically Thin PN junction: MoS2/WSe2 Vertical & Lateral Channels W2 WSe2 M1 W1 MoS2 J. A. =8.8 µm2 - Al contact to MoS2 for electron injection - Pd contact to WSe2 for hole injection 10 -5 10 -6 10 -7 10 -8 10 -9 10 -10 10 -11 10 -12 -60 0.1 Illumination Dark Vds = 0.5 V WSe2 p-type MoS2 n-type I (nA) Ids (A) -4 M2 M3 PN diode characteristics Field Effect Transistor Characteristics 10 5 µm Active zone 0 Off Off -0.1 -0.5 -40 VgVg (V)(V) 2020 1010 00 -10 -10 -20 -20 -20 0 Vg (V) 20 40 60 0.0 0.5 1.0 Vds (V) ds Atomically thin tunable photovoltaic cell! C. Lee et al. Nature Nano (2014) Electric Field Effect Tunable PL: MoS2/WSe2 Van der Waal Heterostructures Graphene (semimetal) Graphene hBN MoS2 WSe2 NbSe2 TaS2 Cr2Ge2Te6 Bi2Se3 Twisted stacking Hofstadter BuAerﬂy; tunneling SchoAky diode SchoAky diode Andreev reﬂecFon Super laGce potenFal MagneFc insulaFng ContacFng surface states Twisted stacking EncapsulaFon EncapsulaFon EncapsulaFon, tunneling EncapsulaFng, tunneling Control exchange interacFon EncapsulaFng, tunneling Twisted stacking Atomic pn juncFon Supercond / Semicond junFon Super laGce modulaFon MagneFc semiconductor Valley tronics Twisted stacking Supercond / Semicond junFon Super laGce modulaFon MagneFc semiconductor Valley tronics Josephson coupling CompeFng order parameters Triplet superconductor Majorana C-‐axis CDW orders CompeFng order parameters Super laGce modulaFon C-‐axis magneFc orders CreaFng gap in TI surface hBN (insulator) MoS2 (n-‐semicond) WSe2 (p-‐semicond) NbSe2 (supercond.) TaS2 (CDW) Cr2Ge2Te6 (magneFc) AnnihilaFon of TI surface states Bi2Se3 (T. I.) performed in-‐progress Planned Acknowledgement Amelia Barreiro, Dmitri Efetov, Cheol Ho Lee, Austin Fong, Patrick Maher, Wei Tsen, Xiaomeng Xue Collaborators Collaborators: Current Members Collaborating Students/postodcs Horst Stormer, Aron Pinczuk, Tony Heinz, Abhay Yue Zhao Cory Dean, Inanc Meric, Lei Wang, Jim Hone, Ken Shepard, Tony Heinz, Cory Dean (Columbia), Jing Guo (UF) Pasupathy, Latha Venkataraman Mitsuhide Takekoshi Sebastian Sorgenfrei, Kevin Knox, Nayung Louis Brus, George Flynn, Colin Nuckolls, Andrea Jung, Seok Ju Kang, Jun Yan, YanwenWatanabe Tan, G. C.Young Yi (SNU), Takashi Taniguchi, Kenji (NIMS) Jim Hone, Ken Shepard, Louis Campos, Rick Osgood Dmitri Efetov Kevin Knox Fereshte Ghahari Patrick Maher Young-Jun Yu (jointly with GRL, POSTECH) Vikram Deshpande (jointly with Hone group) Paul Cadden-Zimansky (Columbia Frontier of Science Fellow) Chenguang Lu (jointly with Hone and Herman T. Taniguchi, K, Watanabe Andre Geim, Kostya Novoselov, Sanka Das Sarma Past Members Melinda Han (Ph.D. 2010, Frontier of Science Fellow, Columbia University) Meninder S. Purewal (Ph.D. 2008) Josh Small (Ph.D. 2006) Yuanbo Zhang (Ph.D. 2006, Professor, Fundan University) Yuri Zuev (Ph.D. 2011, IBM Fishkill) Kirill Bolotin (Assistant Professor, Department of Physics, Vanderbilt University) Byung Hee Hong (Associate Professor, Department of Chemistry, Seoul National University) Pablo Jarillo-Herrero (Assistant Professor, Department of Physics, MIT) Kim Keunsoo Kim (Assistant Professor, Department of Physics, Sejong University) Namdong Kim (Research Scientist, POSTECH) Barbaros Oezyilmaz (Assistant Professor, Department of Physics, National University of Singapore) Funding: group and friends (2011)