Antiferromagnetic characteristics in Sr- and Ba-doped phenanthrene superconductors

It’s very important to clarify the competition between magnetism and superconductivity in alkaline earth metals doped phenanthrene. To achieve this, we have recently studied the crystal structures of Mg-, Ca-, Sr- and Ba- doped phenanthrene and found the most stable ones, which have the lowest energy by first-principles calculations. The result shows that only the most stable Sr_1.5phenanthrene and Ba_1.5phenanthrene show the weak AFM behavior and the others are non-magnetic. The Sr and Ba atoms intercalate the intralayer region and stay close to benzene-ring. By calculating the different charge density we found that the most stable Sr_1.5phenanthrene and Ba_1.5phenanthrene structures have charge redistribution and C atoms have gained electrons obviously. From the spin-charge density, we see inequitable phenanthrene molecules have opposite spin polarizations. The density of states (DOS) of the two structures shows that spin-up and spin-down electrons have the unsymmetrical distribution. Combining these results we conclude that the spin polarization of electrons transferring from metal atoms to C-2p orbitals atoms causes the local AFM behavior. This indicates that superconducting Sr_1.5phenanthrene and Ba_1.5phenanthrene are near the AFM ground state.