  Modern theories of quantum magnetism predict exotic multipolar states in
weakly interacting strongly frustrated spin-1/2 Heisenberg chains with
ferromagnetic nearest neighbor (NN) inchain exchange in high magnetic fields.
Experimentally these states remained elusive so far. Here we report the
evidence for a long-sought magnetic field-induced nematic state arising above a
field of $\sim 13$ T in the edge-sharing chain cuprate LiSbCuO$_4$ $\equiv$
LiCuSbO$_4$. This interpretation is based on the observation of a field induced
spin-gap in the measurements of the $^7$Li NMR spin relaxation rate $T_1^{-1}$
as well as a contrasting field-dependent power-law behavior of $T_1^{-1}$ vs.
$T$ and is further supported by static magnetization and ESR data. An
underlying theoretical microscopic approach favoring a nematic scenario is
based essentially on the NN XYZ exchange anisotropy within a model for
frustrated spin-1/2 chains. It is investigated by the DMRG technique. The
employed exchange parameters are justified qualitatively by electronic
structure calculations for LiCuSbO$_4$.
