  The Kitaev model on a honeycomb lattice predicts a paradigmatic quantum spin
liquid (QSL) exhibiting Majorana Fermion excitations. The insight that Kitaev
physics might be realized in practice has stimulated investigations of
candidate materials, recently including alpha-RuCl3. In all the systems studied
to date, non-Kitaev interactions induce magnetic order at low temperature.
However, in-plane magnetic fields of roughly 8 Tesla suppress the long-range
magnetic order in alpha-RuCl3 raising the intriguing possibility of a
field-induced QSL exhibiting non-Abelian quasiparticle excitations. Here we
present inelastic neutron scattering in alpha-RuCl3 in an applied magnetic
field. At a field of 8 Tesla, the spin waves characteristic of the ordered
state vanish throughout the Brillouin zone. The remaining single dominant
feature of the response is a broad continuum centered at the Gamma point,
previously identified as a signature of fractionalized excitations. This
provides compelling evidence that a field-induced QSL state has been achieved.
