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Gate-tunable phase transitions in thin flakes of 1T-TaS2

Abstract

The ability to tune material properties using gating by electric fields is at the heart of modern electronic technology. It is also a driving force behind recent advances in two-dimensional systems, such as the observation of gate electric-field-induced superconductivity and metal–insulator transitions. Here, we describe an ionic field-effect transistor (termed an iFET), in which gate-controlled Li ion intercalation modulates the material properties of layered crystals of 1T-TaS2. The strong charge doping induced by the tunable ion intercalation alters the energetics of various charge-ordered states in 1T-TaS2 and produces a series of phase transitions in thin-flake samples with reduced dimensionality. We find that the charge-density wave states in 1T-TaS2 collapse in the two-dimensional limit at critical thicknesses. Meanwhile, at low temperatures, the ionic gating induces multiple phase transitions from Mott-insulator to metal in 1T-TaS2 thin flakes, with five orders of magnitude modulation in resistance, and superconductivity emerges in a textured charge-density wave state induced by ionic gating. Our method of gate-controlled intercalation opens up possibilities in searching for novel states of matter in the extreme charge-carrier-concentration limit.

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Figure 1: Gate-controlled intercalation in a 1T-TaS2-based iFET.
Figure 2: CDW phases in pristine 1T-TaS2 thin flakes with varying thicknesses.
Figure 3: Gate-modulation depth and repeatability of 1T-TaS2 iFET.
Figure 4: Electronic transport in 1T-TaS2 thin flakes under gate-controlled intercalation.
Figure 5: Doping–temperature phase diagrams of 1T-TaS2 flakes in three thickness regimes.

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Acknowledgements

The authors thank D-H. Lee for critical reading of the manuscript, Z-X. Shen, P. Kim, F. Wang, L. Zhou, J. Zhao, Y. Wang, W. Wu, P. Darancet and J. Liu for helpful discussions, and X. Hong, L. He, K. Yu and L. Sun for assistance with measurements. Part of the sample fabrication was conducted at Fudan Nano-fabrication Laboratory. Y.Y., F.Y., L.M. and Y.Z. acknowledge financial support from the National Basic Research Program of China (973 Program) under grants nos. 2011CB921802 and 2013CB921902, and from the NSF of China under grant no. 11034001. X.F.L., Y.J.Y. and X.H.C. are supported by the ‘Strategic Priority Research Program (B)’ of the Chinese Academy of Sciences (grant no. XDB04040100) and the NSF of China (grant no. 11190021). Y-W.S. is supported by the NRF of Korea grant funded by MEST (QMMRC, no. R11-2008-053-01002-0). The work at Rutgers is funded by the Gordon and Betty Moore Foundation’s EPiQS Initiative through Grant GBMF4413 to the Rutgers Center for Emergent Materials, and the work at Postech is supported by the Max Planck POSTECH/KOREA Research Initiative Program (grant no. 2011-0031558) through the NRF of Korea funded by MEST.

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Contributions

Y.Z. conceived the project. X.F.L., Y.J.Y., Y.H.C., S.W.C. and X.H.C. grew bulk 1T-TaS2 crystal. Y.Y. fabricated 1T-TaS2 thin-film devices, performed electric measurements and analysed the data. F.Y. made the solid electrolyte. L.M. carried out scanning tunnelling microscopy measurement on 1T-TaS2 thin films. Y.Y. and Y.Z. analysed the data. X.N. and D.F. performed angle-resolved photoemission spectroscopy measurement on bulk 1T-TaS2 crystal. S.K. and Y.W.S. carried out ab initio calculations. S.L. helped with low-temperature measurements. Y.Y. and Y.Z. wrote the paper and all authors commented on it.

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Correspondence to Yuanbo Zhang.

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Yu, Y., Yang, F., Lu, X. et al. Gate-tunable phase transitions in thin flakes of 1T-TaS2. Nature Nanotech 10, 270–276 (2015). https://doi.org/10.1038/nnano.2014.323

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