Resonant Tunneling with Dissipation in a Spin-full Quantum Dot.

We study resonant tunneling through a nanotube quantum dot subject to a dissipative environment. It has been previously shown that in the spin-less case, a quantum critical point is realized when the system is tuned on-resonance with symmetric coupling to the leads. At that point, conductance at low temperatures reaches e²/h and several scaling laws are observed. Here, we demonstrate a qualitatively different behavior in the case of a spin-full resonance. In particular, the positions of resonant peaks change in a non-trivial fashion as a function of temperature, which is attributed to the lack of the particle-hole symmetry; and the peak height is not quantized and varies with dissipation strength. We argue that these signatures indicate the presence of the intermediate fixed point.