Low-lying neutron<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>f</mml:mi><mml:mi>p</mml:mi></mml:mrow></mml:math>-shell intruder states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mrow/><mml:mn>27</mml:mn></mml:msup></mml:math>Ne

The quenching of the $N=20$ shell gap in neutron-rich nuclei is investigated by studying the single-particle structure of ${}^{27}$Ne via neutron transfer using a ${}^{26}$Ne beam. Two low-lying negative-parity intruder states have been observed, the lowest of which is identified as ${J}^{\ensuremath{\pi}}=3/{2}^{\ensuremath{-}}$, confirming earlier speculations. A level identified as 7/2${}^{\ensuremath{-}}$ is observed higher in energy than the 3/2${}^{\ensuremath{-}}$, contrary to the ordering at $\ensuremath{\beta}$-stability and at an energy significantly different from the predictions of previous shell-model calculations. The measured energies and deduced spectroscopic factors are well reproduced in full (0,1)-$\ensuremath{\hbar}\ensuremath{\omega}$ $0s$-$0p$-$0d$-$1s$-$0f$-$1p$ calculations in which there is a significant ad hoc reduction ($\ensuremath{\sim}0.7$ MeV) in the $N=20$ shell gap.