Fluctuations in Planar Magnetotransport Due to Tilted Dirac Cones in Topological Materials.

Fluctuations in planar magnetotransport are ubiquitous in topological HgTe structures, in both tensile (topological insulator) and compressively strained layers (Weyl semimetal phase). We show that the common reason for the fluctuations is the presence of tilted Dirac cones combined with the formation of charge puddles. The origin of the tilted Dirac cones is the mix of the Zeeman term due to the in-plane magnetic field and quadratic contributions to the dispersion relation. We develop a network model that mimics the transport of tilted Dirac fermions in the landscape of charge puddles. The model captures the essential features of the experimental data. It should be relevant for the interpretation of planar magnetotransport in a variety of topological and small band gap materials.

Strain-engineering the Schottky barrier and electrical transport on MoS2.

Strain provides an effective means to tune the electrical properties while retaining the native chemical composition of the material. Unlike three-dimensional solids, two-dimensional materials withstand higher levels of elastic strain making it easier to tune various electrical properties to suit the technology needs. In this work we explore the effect of uniaxial tensile-strain on the electrical transport properties of bi-and few-layered MoS2, a promising 2D semiconductor. Raman shifts corresponding to the in-plane vibrational modes show a redshift with strain indicating a softening of the in-plane phonon modes. Photoluminescence measurements reveal a redshift in the direct and the indirect emission peaks signaling a reduction in the material bandgap. Transport measurements show a substantial enhancement in the electrical conductivity with a high piezoresistive gauge factor of ∼321 superior to that for Silicon for our bi-layered device. The simulations conducted over the experimental findings reveal a substantial reduction of the Schottky barrier height at the electrical contacts in addition to the resistance of MoS2. Our studies reveal that strain is an important and versatile ingredient to tune the electrical properties of 2D materials and also can be used to engineer high-efficiency electrical contacts for future device engineering.