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The T_d phase of WTe₂ has been shown to be a quantum spin Hall (QSH) insulator in the monolayer limit. Outside this limit, T_d-WTe₂ acts as a topological semimetal due to the closing of its band gap. This makes it challenging to obtain an intrinsic QSH effect and restricts the coherence length of the QSH edge channels. Recently, it was shown that strain can induce an appreciably large band gap in WTe₂ beyond single layer thickness [1]. In this talk, we present our studies of strained T_d-WTe₂ grown by molecular beam epitaxy (MBE). The strain is achieved by choosing a proper seed layer for T_d-WTe₂ on sapphire. We have previously shown that layered 2D materials grown by MBE can be strained [2]. We characterize the strain along two characteristic orthogonal axes using in-situ reflection high energy electron diffraction. Transport measurements confirm that our few layer strained T_d-WTe₂ is gapped, and magneto-transport studies demonstrate an unconventional linear magnetoresistance (MR). The origins of the linear MR, such as diffusive transport of QSH edge channels, will be discussed.

[1] C. Zhao, et. al., PRL 125, 046801 (2020)
[2] C. Chen, et. al., ACS Appl. Mater. Interfaces 12, 34, 38744 (2020)