  We use ultra-high resolution, tunable, VUV laser-based, angle-resolved
photoemission spectroscopy (ARPES) and temperature and field dependent
resistivity and thermoelectric power (TEP) measurements to study the electronic
properties of WTe2, a compound that manifests exceptionally large, temperature
dependent magnetoresistance. The temperature dependence of the TEP shows a
change of slope at T=175 K and the Kohler rule breaks down above 70-140 K
range. The Fermi surface consists of two electron pockets and two pairs of hole
pockets along the X-Gamma-X direction. Upon increase of temperature from 40K,
the hole pockets gradually sink below the chemical potential. Like BaFe2As2,
WTe2 has clear and substantial changes in its Fermi surface driven by modest
changes in temperature. In WTe2, this leads to a rare example of temperature
induced Lifshitz transition, associated with the complete disappearance of the
hole pockets. These dramatic changes of the electronic structure naturally
explain unusual features of the transport data.
