  We investigate the influence of thermal energy on the current flow and
electron spin states in double quantum dots in series. The quadruplet Pauli
spin blockade, which is caused by the quadruplet and doublet states, occurs at
low temperatures affecting the transport properties. As the temperature
increases, the quadruplet Pauli spin blockade occurs as a result of the thermal
energy, even in regions where it does not occur at low temperatures. This is
because the triplet state is formed in one dot as a result of the gradual
change of the Fermi distribution function of the electrodes with increasing
temperature. Moreover, the thermally assisted Pauli spin blockade results in
coexistence of the Coulomb and Pauli spin blockades. Conversely, for the
standard triplet Pauli spin blockade, which occurs as a result of the triplet
and singlet states, the current through the double dots monotonously smears out
as the temperature increases. Therefore, the thermally assisted Pauli spin
blockade is not clearly observed. However, the coexistence of the Coulomb and
triplet Pauli spin blockades as a result of the thermal energy is clearly
obtained in the calculation of the probability of the spin state in the double
dots.
