Signature of coexistence of superconductivity and ferromagnetism in two-dimensional NbSe2 triggered by surface molecular adsorption.

Xiaojiao Zhu,Jiyin Zhao,Hao Cheng,Yi Xie,Yuqiao Guo,Jun Dai,Changzheng Wu,Xingda An,Kangzhen Tian,Xiao Cheng Zeng,Shiqiang Wei

doi:10.1038/ncomms11210

Abstract

Ferromagnetism is usually deemed incompatible with superconductivity. Consequently, the coexistence of superconductivity and ferromagnetism is usually observed only in elegantly designed multi-ingredient structures in which the two competing electronic states originate from separate structural components. Here we report the use of surface molecular adsorption to induce ferromagnetism in two-dimensional superconducting NbSe2, representing the freestanding case of the coexistence of superconductivity and ferromagnetism in one two-dimensional nanomaterial. Surface-structural modulation of the ultrathin superconducting NbSe2 by polar reductive hydrazine molecules triggers a slight elongation of the covalent Nb–Se bond, which weakens the covalent interaction and enhances the ionicity of the tetravalent Nb with unpaired electrons, yielding ferromagnetic ordering. The induced ferromagnetic momentum couples with conduction electrons generating unique correlated effects of intrinsic negative magnetoresistance and the Kondo effect. We anticipate that the surface molecular adsorption will be a powerful tool to regulate spin ordering in the two-dimensional paradigm.

Highlights

Ferromagnetism is usually deemed incompatible with superconductivity
The surface molecular adsorption of strong reductive hydrazine successfully realized the surface-structural modulation of 2D NbSe2 nanosheets as well as the preservation of the NbSe2 framework, as schematically illustrated in Fig. 1, where the adsorption site and the resultant structural distortion were highlighted in the green background
The strong polarity of 1.83 Debye of the reductive hydrazine molecules facilitated the surface molecular adsorption due to the electrostatic interactions between the surfaces of the negatively charged NbSe2 nanosheets and the adsorbed polar hydrazine molecules, which enabled the attraction of the polar hydrazine molecules to the surfaces of the NbSe2 nanosheets, as revealed by the attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra

Summary

Introduction

Ferromagnetism is usually deemed incompatible with superconductivity. the coexistence of superconductivity and ferromagnetism is usually observed only in elegantly designed multi-ingredient structures in which the two competing electronic states originate from separate structural components. The well-established correlated systems that exhibit these two competing electronic states are usually prepared by fabricating two separate structures, taking advantage of the inherent properties of each individual parent ingredient Such systems include the hybrid [Ni0.66Al0.33 (OH)2][TaS2] system, which is composed of ferromagnetic cation layers and superconducting anion layers[12]; Fe/Nb/Fe trilayers consisting of one single SC layer (Nb layer) between two FM layers (Fe layer)[13]; and the layered [(Li1 À xFex)OH](Fe1 À yLiy)Se system, which consists of ferromagnetic (Li1 À xFex)OH and superconducting (Fe1 À yLiy)Se layers[14]. This work provides a route for achieving the integration of ordered magnetism and SC in 2D systems

Methods

Results

Conclusion