Electronic Structure in the Antiferromagnetic State of Possible Topological Ni-doped TlCo₂Se₂

In this work, we present angle-resolved photoemission spectroscopy study for 122* type TlCo_2-xNi_xSe₂ (x=0, 0.6, 1.2, 1.6, 1.9, 2.0) samples. The parent TlCo₂Se₂ (x=0) sample has an incommensurate spiral spin structre. With the increase of Ni doping content, the Néel temperature increase firstly and then decrease above x_c, in conjunction with the variation of lattice parameters. The AFM ordering disappears at x~1.7 eventually after which superconductivity occurs with maximum T_C~4 K for x=2. The superconducting temperature becomes higher with the doping concentration increases. ARPES results show a Dirac cone band along Z-M momentum path. It shifts down rigidly with doping which should be owing to the change of chemical potential. The photoemission circular dichroism suggests the chirality of the orbital angular momentum. Our results thus strongly suggest their possible topological origin. We also shown that the change of effective bandwidth, which is closely related to the iternerant and electron correlation. The study of Fermi surfaces evolution can clarify the carrier-doping-induced phase transition in this system. Our results faciliate to figure out the electronic structure for deep understanding on the complex phase diagram in the system.