Spin and valley splittings in multilayered massless Dirac fermion system

The interlayer magnetoresistance in a multilayered massless Dirac fermion system, alpha-(BEDT-TTF)(2)I(3), under hydrostatic pressure was investigated. We succeeded in detecting the zero-mode (n=0) Landau level and its spin splitting in the magnetic field normal to the two-dimensional plane. We demonstrated that the effective Coulomb interaction in the magnetic field intensifies the spin splitting of zero-mode Landau carriers. At temperatures below 2 K, magnetic fields above several Tesla break the twofold valley degeneracy.