  In most unconventional superconductors, like the high-Tc cuprates, iron
pnictides, or heavy fermion systems, superconductivity emerges in the proximity
of an electronic instability. Identifying unambiguously the pairing mechanism
remains nevertheless an enormous challenge. Among these systems, the
orthorhombic uranium ferromagnetic superconductors have a unique position,
notably because magnetic fields couple directly to ferromagnetic order, leading
to the fascinating discovery of the re-emergence of superconductivity in URhGe
at high field. Here we show that uniaxial stress is a remarkable tool allowing
fine-tuning of the pairing strength. With a relatively small stress, the
superconducting phase diagram is spectacularly modified, with a merging of the
low and high field superconducting states and a significant enhancement of
superconductivity. The superconducting critical temperature increases both at
zero field and under field, reaching 1K, more than twice higher than at ambient
pressure. The enhancement of superconductivity is directly related to a change
of the magnetic dimensionality with an increase of the transverse magnetic
susceptibility, demonstrating that in addition to the Ising-type longitudinal
ferromagnetic fluctuations, transverse magnetic fluctuations also play an
important role in the superconducting pairing.
