Transmission through a quantum dot with two orbitals

Transmission coefficient through a quantum dot, which contains two Orbitals, is calculated in the weak-tunneling regime, taking into account the Coulomb interaction within the dot. Transmitted waves through these orbitals acquire phase shifts which differ by π from each other in the present model. The transmission coefficient as a function of gate voltage exhibits symmetric and asymmetric line shapes, depending on temperature T. A nearly symmetric line shape appears in the temperature region of 0.05 ≲ k_BT/δ ≲ 0.25, where δ is the single-particle energy level separation in the dot. This behavior is understood by a combined action of the above-mentioned phase difference and the Coulomb interaction. A possibility that this mechanism explains the recent experiment is suggested.