Camelback-shaped band reconciles heavy electron behavior with weak   electronic Coulomb correlations in superconducting TlNi2Se2
  Using high-resolution photoemission spectroscopy and first-principles calculations, we characterize superconducting TlNi$_2$Se$_2$ as a material with weak electronic Coulomb correlations leading to a bandwidth renormalization of 1.4. We identify a camelback-shaped band, whose energetic position strongly depends on the selenium height. While this feature is universal in transition metal pnictides, in TlNi$_2$Se$_2$ it lies in the immediate vicinity of the Fermi level, giving rise to a pronounced van Hove singularity. The resulting heavy band mass resolves the apparent puzzle of a large normal-state specific heat coefficient (Phys. Rev. Lett. 112, 207001) in this weakly correlated compound. 
N. Xu, C. E. Matt, P. Richard, A. van Roekeghem, S. Biermann, X. Shi,   S.-F. Wu, H. W. Liu, D. Chen, T. Qian, N. C. Plumb, ...
cond-mat.supr-con cond-mat.mtrl-sci