Fig. 2: Low-temperature evolution of R and VTh of MATBLG, contrasted with the expected thermopower of band fermions.
From: Thermopower probes of emergent local moments in magic-angle twisted bilayer graphene
a, R as a function of ν plotted for several T. For visual clarity, each dataset is offset by 10 KΩ along the y axis with increasing T. In general, R(T) shows metallic behaviour except at the DP (ν = 0), and at ν = ±4 when the bands are fully filled, where R(T) shows insulating behaviour. Additional peaks in R(ν) emerge at positive integer filling (ν = 1, 2 or 3), that is, for the conduction band, but are weaker for the valence band. b, VTh(ν) for several T with an offset of 10 μV. VTh is symmetric for the conduction and valence bands with opposite signs (except at 6 K), which is in stark contrast to the asymmetry of resistance data. The sign of VTh changes at DP and ν = ±4 with additional points at νcross ≈ ±1. It is important to note that the location of νcross barely changes with increasing T. c, Non-interacting single-particle DOS of flat bands using a continuum model10 with the inclusion of parabolic dispersive bands5. d, Thermopower in shifted plot calculated semi-classically (SSC) using the DOS in c. Note that, at low T, SSC shows crossing between 0 < ∣ν∣ < 4, which is strongly dependent on T and vanishes beyond 18 K. SSC at higher T becomes positive (negative) for the conduction (valence) band caused by the thermal broadening (−df/dε).
