Atomic-like behaviors and orbital-related Luttinger liquid in carbon nano-peapod quantum dots

We report influence of encapsulated C60 molecules on electron transport in carbon-nanotube peapod quantum dots. We find atomic-like behaviors with doubly degenerate electronic levels, which exist only around ground states, by single electron spectroscopy measured at low back-gate voltages (Vbg). Correlation with presence of nearly free electrons (NFEs) unique to the peapods is discussed. Moreover, we find anomalously high values of power a observed in power laws in conductance versus energy relationships, which are strongly associated with the doubly degenerate levels. It is revealed that the powers originate from Tomonaga-Luttinger liquid via the occupied doubly degenerate levels. Our observations clarify that the encapsulated C60 molecules form doubly degenerate levels only at ground state in peapod quantum dots and do not eliminate a ballistic charge transport.