Electron Number Dependence of Spin Triplet-Singlet Relaxation Time

In a GaAs single quantum dot, the relaxation time T_{1} between spin triplet and singlet states has been measured for the last few even number of electrons. The singlet-triplet energy separation E_{ST} is tuned as a control parameter for the comparison of T_{1} between different electron numbers. T_{1} shows a steady decrease from 2-electrons, 4-electrons, to 6-electrons, and we found this implies an enhancement of the spin-orbital coupling strength in a multi-electron quantum dot.