Magnetic-Field Dependence of Tunnel Couplings in Carbon Nanotube Quantum   Dots
  By means of sequential and cotunneling spectroscopy, we study the tunnel couplings between metallic leads and individual levels in a carbon nanotube quantum dot. The levels are ordered in shells consisting of two doublets with strong- and weak-tunnel couplings, leading to gate-dependent level renormalization. By comparison to a one- and two-shell model, this is shown to be a consequence of disorder-induced valley mixing in the nanotube. Moreover, a parallel magnetic field is shown to reduce this mixing and thus suppress the effects of tunnel renormalization. 
K. Grove-Rasmussen, S. Grap, J. Paaske, K. Flensberg, S. Andergassen,   V. Meden, H. I. J{\o}rgensen, K. Muraki, and T. Fujisawa
cond-mat.str-el cond-mat.mes-hall