Observing separate spin and charge Fermi seas in a strongly correlated one-dimensional conductor

An electron is usually considered to have only one type of kinetic energy, but could it have more, for its spin and charge, or by exciting other electrons? In one-dimension (1D), the physics of interacting electrons is captured well at low energies by the linear Tomonaga-Luttinger Liquid (TLL) model, with hallmark predictions, such as spin-charge separation, having already been observed [1]. Recent theoretical work has focused on extending the theory to deal with more realistic curved dispersions [2, 3], however, little has been observed experimentally to date [4].

Here, we report on measurements of many-body modes in gated 1D wires connected via air-bridges [5] and using a momentum-resolved tunnelling spectroscopy technique (Fig. 1A). We map the 1D dispersion in a variety of devices, both in and out of equilibrium, and observe the formation of two separate Fermi seas at high energies, associated with spin and charge excitations, which cannot be accounted for by the non-interacting model (Fig. 1B) [6]. We are able to control the electron density in the wires by tuning the level of confinement down to a density of about 18 electrons per micron. Similarly, by progressively occupying more 1D subbands we are able to change the amount of inter-subband screening by over 50%, consequently varying the effective interaction strength, in situ, all the way from the non-interacting limit g=1 down to g=0.5 (Fig. 1C). Our spectroscopy technique offers an important tool for probing strongly correlated systems of varying interaction strength.

[1] Y. Jompol et al., Science 325, 597-601 (2009)
[2] A. Imambekov and L. Glazman, Science 323, 228-231 (2009)
[3] O. Tsyplyatyev et al., Phys. Rev. Lett. 114, 196401 (2015)
[4] Y. Jin et al., Nat. Commun. 10, 2821 (2019)
[5] Y. Jin, P. Vianez, et al., Appl. Phys. Lett. 118, 162108 (2021)
[6] P. Vianez et al., arXiv : 2102.05584 (2021)