Electronic Structure of Unconventional Superconductor YFe₂Ge₂ studied by ARPES

YFe₂Ge₂ is a new unconventional superconductor with a critical temperature equal to 1.8 K [1]. Enhanced value of the Sommerfeld coefficient (γ = 100 mJ/mole K²) suggests significance of electron correlations in this material. Departure from the Fermi liquid behavior is visible in temperature dependency of electrical resistivity which follows a power law: ρ∼T^3/2. These facts, together with a presence of large fluctuating moments in paramagnetic phase (μ_Fe ≈ 1 μ_B), suggest that YFe₂Ge₂ is as quantum critical metal governed by Hund’s coupling.



In this talk we will present systematic studies of a band structure of YFe₂Ge₂ performed by means of angle-resolved photoelectron spectroscopy (ARPES) at low temperature (T=14 K). Our measurements have been performed on ultra-high quality samples. We observe that steep bands coexist with flat bands in the electronic structure of YFe₂Ge₂, similarly to heavy fermion systems, and we discuss the origin of these states and their relevance for the physical properties of this system. Presence of heavy electron bands is consistent with recent results of quantum oscillation measurements [2].