  Magnetoresistance is the change of a material's electrical resistance in
response to an applied magnetic field. In addition to its intrinsic scientific
interest, it is a technologically important property, placing it in "Pasteur's
quadrant" of research value: materials with large magnetorsistance have found
use as magnetic sensors 1, in magnetic memory 2, hard drives 3, transistors 4,
and are the subject of frequent study in the field of spintronics 5, 6. Here we
report the observation of an extremely large one-dimensional positive
magnetoresistance (XMR) in the layered transition metal dichalcogenide (TMD)
WTe2; 452,700 percent at 4.5 Kelvin in a magnetic field of 14.7 Tesla, and 2.5
million percent at 0.4 Kelvin in 45 Tesla, with no saturation. The XMR is
highly anisotropic, maximized in the crystallographic direction where small
pockets of holes and electrons are found in the electronic structure. The
determination of the origin of this effect and the fabrication of
nanostructures and devices based on the XMR of WTe2 will represent a
significant new direction in the study and uses of magnetoresistivity.
  *The published version of the paper includes co-authors Tian Liang and Max
Hirschberger.
  **This paper has been published with new MR data to 60T where the MR of WTe2
reaches 13 million percent (at 0.5K) and still shows no signs of saturation. We
also have new electron diffraction patterns to lower temperature (10K). We
discuss the possible origin of the MR as coming from an electron-hole
'resonance' condition established by a perfect n/p ratio of 1 (more details in
a new "extended data" section). This makes WTe2, possibly, the first
realization of a perfectly balanced semimetal.
  ***The paper is published as "Large non-saturating magnetoresistance in WTe2"
in Nature (2014), DOI:10.1038/nature13763
