Browsing by Author "Taniguchi, T."
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Item A Fermi-Level-Pinning-Free 1D Electrical Contact at the Intrinsic 2D MoS₂–Metal Junction(Wiley-VCH Verlag, 2019-05-08) Yang, Z.; Kim, C.; Lee, K. Y.; Lee, M.; Appalakondaiah, S.; Ra, C. -H; Watanabe, K.; Taniguchi, T.; Cho, Kyeongiae; Hwang, E.; Hone, J.; Yoo, W. J.; 0000-0003-2698-7774 (Cho, K); Cho, KyeongiaeCurrently 2D crystals are being studied intensively for use in future nanoelectronics, as conventional semiconductor devices face challenges in high power consumption and short channel effects when scaled to the quantum limit. Toward this end, achieving barrier-free contact to 2D semiconductors has emerged as a major roadblock. In conventional contacts to bulk metals, the 2D semiconductor Fermi levels become pinned inside the bandgap, deviating from the ideal Schottky–Mott rule and resulting in significant suppression of carrier transport in the device. Here, MoS₂ polarity control is realized without extrinsic doping by employing a 1D elemental metal contact scheme. The use of high-work-function palladium (Pd) or gold (Au) enables a high-quality p-type dominant contact to intrinsic MoS₂, realizing Fermi level depinning. Field-effect transistors (FETs) with Pd edge contact and Au edge contact show high performance with the highest hole mobility reaching 330 and 432 cm² V⁻¹ s⁻¹ at 300 K, respectively. The ideal Fermi level alignment allows creation of p- and n-type FETs on the same intrinsic MoS₂ flake using Pd and low-work-function molybdenum (Mo) contacts, respectively. This device acts as an efficient inverter, a basic building block for semiconductor integrated circuits, with gain reaching 15 at V_{D} = 5 V. ©2019 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Quantum Parity Hall Effect in Bernal-Stacked Trilayer Graphene(National Academy of Sciences, 2019-05-03) Stepanov, P.; Barlas, Y.; Che, S.; Myhro, K.; Voigt, G.; Pi, Z.; Watanabe, K.; Taniguchi, T.; Smirnov, D.; Zhang, Fan; Lake, R. K.; MacDonald, A. H.; Lau, C. N.; 0000-0003-4623-4200 (Zhang, F); Zhang, FanThe quantum Hall effect has recently been generalized from transport of conserved charges to include transport of other approximately conserved-state variables, including spin and valley, via spin- or valley-polarized boundary states with different chiralities. Here, we report a class of quantum Hall effect in Bernal- or ABA-stacked trilayer graphene (TLG), the quantum parity Hall (QPH) effect, in which boundary channels are distinguished by even or odd parity under the system's mirror reflection symmetry. At the charge neutrality point, the longitudinal conductance σₓₓ is first quantized to 4e²=h at a small perpendicular magnetic field B⊥, establishing the presence of four edge channels. As B⊥ increases, σₓₓ first decreases to 2e²=h, indicating spin-polarized counterpropagating edge states, and then, to approximately zero. These behaviors arise from level crossings between even- and odd-parity bulk Landau levels driven by exchange interactions with the underlying Fermi sea, which favor an ordinary insulator ground state in the strong B⊥ limit and a spin-polarized state at intermediate fields. The transitions between spin-polarized and -unpolarized states can be tuned by varying Zeeman energy. Our findings demonstrate a topological phase that is protected by a gate-controllable symmetry and sensitive to Coulomb interactions. ©2019 The Authors. All rights reserved.