Abstract
Two- or three-dimensional metals are usually well described by weakly interacting, fermionic quasiparticles. This concept breaks down in one dimension due to strong Coulomb interactions. There, low-energy electronic excitations are expected to be bosonic collective modes, which fractionalize into independent spin- and charge-density waves. Experimental research on one-dimensional metals is still hampered by their difficult realization, their limited accessibility to measurements, and by competing or obscuring effects such as Peierls distortions or zero bias anomalies. Here we overcome these difficulties by constructing a well-isolated, one-dimensional metal of finite length present in mirror-twin boundaries. Using scanning tunneling spectroscopy we measure the single-particle density of the interacting electron system as a function of energy and position in the 1D box. Comparison to theoretical modeling provides unambiguous evidence that we are observing spin-charge separation in real space.
1 More- Received 1 November 2018
DOI:https://doi.org/10.1103/PhysRevX.9.011055
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Popular Summary
Every physicist has encountered the particle in a 1D box in lectures on quantum mechanics. This problem assumes independent, noninteracting particles. However, in real systems that approximate a 1D box, such as carbon nanotubes or metallic wires on semiconductors, electrons do interact strongly. The impact of these interactions—as described by the Tomonaga-Luttinger liquid theory—is dramatic: it results in spin-charge separation, an unusual behavior in which the spin and charge of an electron appear to split. Here, we report on the first direct observation of this behavior in a 1D box.
Our 1D box is created between two monolayer islands of molybdenum disulfide, one of which is the mirror image of the other. The finite, straight line at their interface hosts the confined 1D states. Using a scanning tunneling microscope, we measure the single-particle density of the interacting electron system in the 1D box as a function of energy and position. The data can be explained only by assuming the presence of a Tomonaga-Luttinger liquid. Because of the liquid’s confinement, the spin and charge excitations become visible individually, each with their own specific energy, probability density distribution, and spin or charge character, respectively.
This new approach provides a direct and quantitative comparison of experimental data with Tomonaga-Luttinger liquid theory and may enable exploration of its limitations. This will become increasingly relevant in the future as miniaturization of devices reaches atomic limits.