Strong correlations and spin-density-wave phase induced by a massive spectral weight redistribution inα-Fe1.06Te

Abstract

The electronic structure of α-Fe1.06Te is studied with angle-resolved photoemission spectroscopy. We show that there is substantial spectral weight around Γ and X, and lineshapes are intrinsically incoherent in the paramagnetic state. The magnetic transition is characterized by a massive spectral-weight transfer over an energy range as large as the band width, which even exhibits a hysteresis loop that marks the strong first order transition. Coherent quasiparticles emerge in the magnetically ordered state due to decreased spin fluctuations, which account for the change of transport properties from insulating behavior to metallic behavior. Our observation demonstrates that Fe1.06Te distinguishes itself from other iron-based systems with more local characters and much stronger interactions among different degrees of freedom, and how a spin density wave is formed in the presence of strong correlation.The discovery of iron-based high-temperature superconductors (Fe-HTSCs) has generated great interests [1]. So far, two classes of Fe-HTSC have been discovered. They are iron pnictides, e.g., SmO 1−x F x FeAs or Ba 1−x K x Fe 2 As 2 [2, 3], and iron chalcogenides, e.g., Fe 1+y Te 1−x Se x [4]. Although, both classes of materials share many common aspects, such as similarly high maximal superconducting transition temperature (T c ) (Fe 1+y Se possesses a T c of 37 K under hydrostatic pressure of 7 GPa [5]) and similar band structures from density-functional theory (DFT) calculations [6,7]. However, their parent compounds exhibit quite different spin density wave (SDW) states. A collinear commensurate antiferromagnetic order has been identified for the pnictides [8,9], while a bicollinear and 45-degree rotated antiferromagnetic order was identified for Fe 1+y Te [10,11]. Furthermore, the transport properties of Fe 1+y Te respond abruptly to the first order magnetic/structural transition. In the paramagnetic state, it shows insulatorlike resistivity [ Fig. 1(e)], and optical conductivity without a Drude peak, while the resistivity becomes metalliclike, and a Drude peak emerges in the SDW state [12,13].Like the cuprates, the nature of magnetic order and spin fluctuations in Fe-HTSC are most likely crucial for its superconductivity. Yet the origin of the magnetic ordering in iron pnictides/chacogenides is still under heated debate. For the iron pnictides, previous studies have shown that the large reconstruction of the band structure dominates the savings of electronic energy, and would be * Electronic address: dlfeng@fudan.edu.cn responsible for the SDW [14][15][16], while there are also suggestions that the SDW might be dominated by Fermi surface nesting [17]. For the iron chalcogenides, a connection between the electronic structure and the bicollinear magnetic structure has not been established, except that Fermi surface nesting has been ruled out [12,18]. Many fundamental questions are yet to be addressed for iron chalcogenides: is there any connection between the electronic structure and magnetic ordering; and why is i...

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