Field-induced superconductivity in MoS 2
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Field-induced superconductivity in MoS2 Y. J. Zhang1, J. T. Ye1, and Y. Iwasa1,2 1
Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan 2 CERG, RIKEN, Hirosawa 2-1, Wako 351-0198, Japan ABSTRACT We fabricated MoS2 transistor adopting electric double layer (EDL) as gate dielectric. So far, EDL has realized p-type conducting MoS2 in addition to well-known n-type conduction showing ambipolar operation. In our study, field-effect superconducting transition of MoS2 was realized with maximum TC around 10 K. This TC is the highest not only within MoS2 compounds but also among whole TMDs. The highest TC discovered in this study lies in the carrier density region much smaller than chemically investigated region. Such compounds with small doping level have never been successfully synthesized by chemical method. Furthermore, by combining HfO2 (typical high-k material for FETs) gating with EDL gating, continuous control of carrier density, and thus quantum phase, was demonstrated. As a result, we successfully obtained the phase diagram of MoS2. Interestingly, the TC exhibits strong carrier density dependence, showing dome-shaped superconducting phase. Superconducting dome in other materials than cuprates has been reported only a few times in doped 2D semiconductors. Since FET charge accumulation is basically two dimensional, our result implies the existence of common mechanism for superconducting dome in 2D band insulators. INTRODUCTION Recent years saw a great success in making two-dimensional electronic systems starting from the discovery of new ways to prepare ultra-thin single crystals pioneered by the research of graphene, a monolayer of graphite, using a simple method of cleaving bulk graphite with Scotch tapes [1–3]. The success of graphene immediately raised the possibility of applying similar technique to other layered materials. The early examples include atomic layers of boron nitride, transition-metal dichalcogenides, and complex oxides like layered high Tc cuprate. The prepared nano-sheets appeared to be stable 2D crystals under ambient conditions exhibiting high crystal quality on a macroscopic scale [2]. Since many layered material were well-studied with varieties of properties of charge, orbital, and spin in their bulk form, isolating them into atomically thin nano-sheets provide new opportunities to study them in a different paradigm [4]. Apart from the development of making nano-sheets, independently, people have been dreamed for a long-time to modulate quantum phase transition using electric field effect. One of the most well-known ideas is to manipulate the superconducting transition using field effect generated by a transistor. Early theory [5–7] and experimental effect [8] started even in the dawn of superconductivity. Later, the introduction of strong gate dielectrics (ferroelectric) significantly improved the control on transition temperature Tc from 10-4 K [8] to a level of ~10 K [9,10]. Complete switching ON/OFF of a
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