[Paper Review] Emergence of superconductivity in strongly correlated hole-dominated Fe1-xSe

S. L. Ni, Jianping Sun+18 more|arXiv (Cornell University)|Dec 29, 2019

Iron-based superconductors research1 references4 citations

TL;DR

This study establishes a comprehensive phase diagram for Fe1-xSe by investigating nonstoichiometric and nearly stoichiometric single crystals, revealing that strong electronic correlations in hole-dominated Fe1-xSe lead to the emergence of superconductivity upon electron doping. The superconducting dome appears in the strongly correlated hole-rich regime, while the tetragonal-to-orthorhombic transition persists only at higher electron-doping levels in the electron-dominated regime.

ABSTRACT

Here we establish a more complete phase diagram for FeSe system, based on experimental results of nonstoichiometric Fe1-xSe single crystals that we have developed recently, as well as nearly stoichiometric FeSe single crystals. The electronic correlation is found to be strongly enhanced in hole-dominated Fe1-xSe, as compared with electron-dominated FeSe, from the magnetic susceptibility and electrical transport measurements in the normal state. A superconducting dome is found to emerge starting from the strongly correlated hole-dominated regime with electron doping, while the tetragonal-orthorhombic phase transition at ~90 K is observed only at higher electron-doping levels in the electron-dominated regime.

Motivation & Objective

• To map the complete phase diagram of Fe1-xSe across varying hole and electron doping levels.
• To investigate the role of electronic correlations in hole-dominated Fe1-xSe compared to electron-dominated phases.
• To determine the conditions under which superconductivity emerges in strongly correlated regimes.
• To clarify the relationship between structural phase transitions and superconducting order in FeSe.
• To resolve discrepancies in prior studies by using high-quality nonstoichiometric and nearly stoichiometric single crystals.

Proposed method

• Synthesis of high-quality nonstoichiometric Fe1-xSe single crystals with controlled deviations from stoichiometry.
• Measurement of magnetic susceptibility to probe electronic correlations in the normal state.
• Electrical transport measurements to identify superconducting transitions and phase boundaries.
• Systematic variation of doping levels to track the evolution of superconducting dome and structural transitions.
• Comparison of results between hole-dominated and electron-dominated regimes to assess correlation strength.
• Use of high-resolution data to construct a refined phase diagram for FeSe.

Experimental results

Research questions

• RQ1 How do electronic correlations evolve in hole-dominated Fe1-xSe compared to electron-dominated FeSe?
• RQ2 At what doping level does superconductivity emerge in the strongly correlated hole-rich regime of Fe1-xSe?
• RQ3 What is the relationship between the tetragonal-to-orthorhombic structural transition and superconducting order in Fe1-xSe?
• RQ4 Does the superconducting dome extend into the hole-dominated region of the phase diagram?
• RQ5 How do nonstoichiometric and nearly stoichiometric Fe1-xSe crystals differ in their electronic and superconducting properties?

Key findings

• Strong electronic correlations are significantly enhanced in hole-dominated Fe1-xSe compared to electron-dominated FeSe, as evidenced by magnetic susceptibility and transport data.
• A superconducting dome emerges in the hole-dominated regime upon electron doping, indicating that superconductivity is stabilized in a strongly correlated environment.
• The tetragonal-to-orthorhombic phase transition at ~90 K is only observed at higher electron-doping levels, indicating its suppression in the hole-rich regime.
• The phase diagram reveals a clear distinction between the electronic behavior in hole-dominated and electron-dominated Fe1-xSe, with superconductivity appearing in the former only after electron doping.
• High-quality single crystals enable precise mapping of the phase boundaries, resolving inconsistencies in prior studies.
• The results support a scenario where strong correlations in the hole-doped regime play a crucial role in mediating superconductivity in FeSe.