2. Low dimensionality

The substance NbSe3 has been extensively cited as a quasi-low dimensional material since its discovery, because it is highly anisotropic in its structure, mechanical or electrical properties. In past few decades it is found that low-dimensionality of the material leads to interesting physical behaviors, thanks to efforts of many researchers including those from our laboratory.

Especially, NbSe3 is now regarded as a model material of charge density wave (CDW) electronic state, which is a macroscopic quantum state peculiar to low dimensional systems. CDW state occur at low temperature as a result of, in a similar manner to superconductivity, condensed electron-hole pairs coupling through interaction mediated by phonons. After a CDW transition, electron density will be periodically modulated as seen in below picture.

Although versatile properties of CDW have been understood until now, effect of systems with closed-loop topologies on CDW is barely getting considered as a real issue. For instance, CDW in a closed-loop geometry possibly interfere with itself quantum-physically, as a single electron traveling in a thin metal loop would do. However, it is contradict to simple doubt that such a macroscopic object like collective electrons would never show a quantum nature. This kind of problem is called as an issue of macroscopic quantum coherence (MQC). Our discovery may pave the way to an empirical demonstration of the problem.