Differences in Chemical Doping Matter: Superconductivity in Ti1‿i>xTaxSe2 but Not in Ti1‿i>xNbxSe2

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• 作者：Huixia Luo ; Weiwei Xie ; Jing Tao ; Ivo Pletikosic ; Tonica Valla ; Girija S. Sahasrabudhe ; Gavin Osterhoudt ; Erin Sutton ; Kenneth S. Burch ; Elizabeth M. Seibel ; Jason W. Krizan ; Yimei Zhu ; Robert J. Cava
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：March 22, 2016
• 年：2016
• 卷：28
• 期：6
• 页码：1927-1935
• 全文大小：598K
• ISSN：1520-5002

文摘

We report that 1T-TiSe₂, an archetypical layered transition metal dichalcogenide, becomes superconducting when Ta is substituted for Ti but not when Nb is substituted for Ti. This is unexpected because Nb and Ta should be chemically equivalent electron donors. Superconductivity emerges near x = 0.02 for Ti_1–xTa_xSe₂, while, for Ti_1–xNb_xSe₂, no superconducting transitions are observed above 0.4 K. The equivalent chemical nature of the dopants is confirmed by X-ray photoelectron spectroscopy. ARPES and Raman scattering studies show similarities and differences between the two systems, but the fundamental reasons why the Nb and Ta dopants yield such different behavior are unknown. We present a comparison of the electronic phase diagrams of many electron-doped 1T-TiSe₂ systems, showing that they behave quite differently, which may have broad implications in the search for new superconductors. We propose that superconducting Ti_0.8Ta_0.2Se₂ will be suitable for devices and other studies based on exfoliated crystal flakes.