Interplay of electronic and lattice degrees of freedom inA1−xFe2−ySe

Abstract

The local structure and electronic properties of Rb1−xFe2−ySe2 are investigated by means of site selective polarized x-ray absorption spectroscopy at the iron and selenium K-edges as a function of pressure. A combination of dispersive geometry and novel nanodiamond anvil pressure-cell has permitted to reveal a step-like decrease in the Fe-Se bond distance at p 11 GPa. The position of the Fe K-edge pre-peak, which is directly related to the position of the chemical potential, remains nearly constant until ∼ 6 GPa, followed by an increase until p 11 GPa. Here, as in the local structure, a step-like decrease of the chemical potential is seen. Thus, the present results provide compelling evidence that the origin of the reemerging superconductivity in A1−xFe2−ySe2 in vicinity of a quantum critical transition is caused mainly by the changes in the electronic structure.

Unraveling the Peculiarities in the Temperature-Dependent Structural Evolution of Black Phosphorus

“…Recently, in this class of materials, it was found that oxygen ordering plays a critical role in determining the macroscopic properties of the system [1][2][3]. In fact, our own research works in diverse materials such as hydrogen storage materials [4], lithium battery materials [5], several nano-material systems [6][7][8], newly discovered Fe-based superconductors [9][10][11][12], novel magnetic materials [13,14] and solar cell materials [15], etc., were indeed aimed at understanding the structure-function relations. Black phosphorus (BP) is an emerging two-dimensional system offering several perspectives for applications.…”

Comparison of the local structures of Ca 0.82 La 0.18 FeAs 2 and Ba 0.64 K 0.36 Fe 2 As 2 pnictide superconductors using atomic pair distribution function analysis

“…For example, in the alkali metal intercalated iron-chalcogenide superconductors, the Fe vacancy ordering (involving a regular structural modulation) produces superlattice peaks in the diffraction pattern [38], however, system has an inherently large local disorder [40]. This system with a peculiar electronic structure involving interconnected conducting filamentary phase that is embedded in an insulating texture [26] shows an interesting evolution of the local structure under hydrostatic pressure which induces a uniform lattice compression [25]. In their atomic PDF study on BaFe 2 As 2 , Niedziela et al [28] also noted that depending on the local scale considered, the lattice parameter which describes the structure varies without any symmetry change.…”

“…The present results on the atomic pair distribution function studies of Ca 0.82 La 0.18 FeAs 2 and Ba 0.64 K 0.36 Fe 2 As 2 together with the inputs from the local structural studies on the Fe-based systems (see for example Refs. [23][24][25][27][28][29]) indicate that indeed a nanoscopic manipulation of the electronically active layer rather than its isotropic structural tuning is the key to modulate the electronic and superconducting properties of the iron-based compounds.…”

“…[23,24]) or under hydrostatic pressure (see for example Ref. [25]), local scale changes, particularly that of the active layer, are more complex than an isotropic structural compression or expansion. Another prominent member in the Fe-based compounds is the alkali-metal intercalated iron-chalcogendies.…”

“…This system, with a peculiar electronic structure involving interconnected conducting filamentary phase that is embedded in an insulating texture [26], shows interesting evolution of the regular structural modulation involving the Fe vacancy order and the local structure under hydrostatic pressure conditions [25]. In this class of materials, an important input from the space resolved electronic structure investigation [26] and the local structure under hydrostatic pressure [25] is that a key parameter to control the superconducting properties is the nanoscopic manipulation of the electronically active layer. The present results on the atomic pair distribution function studies of Ca 0.82 La 0.18 FeAs 2 and Ba 0.64 K 0.36 Fe 2 As 2 together with the inputs from the local structural studies on the Fe-based systems (see for example Refs.…”