  Elastoresistance describes the relative change of a material's resistance
when strained. It has two major contributions: strain induced geometric and
electronic changes. If the geometric factor dominates, like in ordinary metals
such as copper, the elastoresistance is positive and rather small, i.e.
typically of order 1. In a few materials, however, changes in electronic
structure dominate, which gives rise to larger and even negative values, such
as (-11) for Bi. Here, we report that the transition metal dichalcogenide
(TMDC) WTe$_{2}$ is a member of the second group, exhibiting a large and
non-monotonic elastoresistance that is about (-20) near 100 K and changes sign
at low temperatures. We discover that an applied magnetic field has a dramatic
effect on the elastoresistance in WTe$_{2}$: in the quantum regime at low
temperatures, it leads to quantum oscillations of the elastoresistance, that
ranges between (-80) to 120 within a field range of only half a Tesla. In the
semiclassical regime at intermediate temperatures, we find that the
elastoresistance rapidly increases and changes sign in a magnetic field. We
provide a semi-quantitative understanding of our experimental results using a
combination of first-principle and analytical low-energy model calculations.
Understanding bulk properties of TMDCs under uniaxial strain is an important
stepping stone toward strain engineering of 2D TMDCs.
