Abstract:
Observing separate spin and charge Fermi seas in a strongly correlated one-dimensional conductor: An electron is usually considered to have only one form of kinetic energy, but could it have more, for its spin and charge, by exciting other electrons? In one dimension (1D), the physics of interacting electrons is captured well at low energies by the Tomonaga-Luttinger model, yet little has been observed experimentally beyond this linear regime. Here, we report on measurements of many-body modes in 1D gated wires using tunnelling spectroscopy. We observe two parabolic dispersions, indicative of separate Fermi seas at high energies, associated with spin and charge excitations. By comparing a series of devices consisting of 1D wires between 1 and 10 μm long, made using large numbers of air bridges, we observe the emergence of two additional 1D “replica” modes that strengthen with decreasing wire length, as predicted by the most recent theory. The interaction strength is varied by changing the amount of 1D intersubband screening by more than 45%. Our findings not only demonstrate the existence of spin-charge separation in the whole energy band outside the low-energy limit of the Tomonaga-Luttinger model but also set a constraint on the validity of the newer nonlinear Tomonaga-Luttinger theory. We have also measured the power-law suppression of tunnelling at electron temperatures down to 10mK and explain why it changes when the second and third 1D subbands become occupied.