# Crystal structures and the sign reversal Hall resistivity in iron-based superconductors Lix(C3H10N2)0.32FeSe (0.15<x<0.4)

## TL;DR

This study investigates the crystal structures, superconducting properties, and electronic behavior of iron-based superconductors Lix(C3H10N2)0.32FeSe, revealing how Li concentration influences structure, Fermi surface topology, and induces a Lifshitz transition.

## Contribution

It provides new insights into the relationship between Li doping, structural orientation, and electronic transitions in FeSe-based superconductors.

## Key findings

- Li doping affects molecule orientation within FeSe layers.
- Superconductors exhibit quasi-two-dimensional behavior.
- Li doping induces a Lifshitz transition in the Fermi surface.

## Abstract

We report the crystal structure, superconductivity and normal state properties of two iron-based materials, Li0.15(C3H10N2)0.32FeSe(P-4) and Lix(C3H10N2)0.32FeSe(P4/nmm, 0.25<x<0.4) with superconducting transition temperature from 40~46K. The determined crystal structures revealed a coupling between Li concentration and the oritation of 1,2-Diaminopropane molecules within the hyper expanded FeSe layers. Further fitting on resistivity in terms of the Lawence-Doniach model suggests the two superconductors belong to the quasi-two dimonsional system. With increasing temperature, a differences in crystal structures and doping levels. First principle calculations revealed the increase in FeSe layer diatance will restruct the Fermi surface and generate a new hole pocket around Gamma point in the Brillouin Zone. Our findings support that the increase in two dimensionalities will leads to a temperature induced Lifshitz transition in electron doped FeSe superconductors.

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Source: https://tomesphere.com/paper/1901.02580