Excitations in a perfect magnetized quantum spin ladder

The strong-leg $S=1/2$ Heisenberg spin ladder system C$_7$(D$_{10}$N)$_2$CuBr$_4$ is investigated in applied magnetic fields using inelastic neutron scattering anf DMRG calculations. The spectrum in the high-field Tomonaga-Luttinger spin liquid phase is found to be qualitatively different from that in the low-field spin gap phase. In the former, numerous spectral featrures, including incommensurate excitations and multi-spinon continua are identified. In contrast, the latter is dominated by long-lived magnon excitations and two-magnon bound states [1]. An unprecedented quantitive agreement between experiment and numerical claculations is achieved.\\[4pt] [1] D. Schmidiger, P. Bouillot, S. Muhlbauer, S. Gvasaliya, C. Kollath, T. Giamarchi, A. Zheludev, Phys. Rev. Lett. {\bf 108}, 167201 (2012).