Brookhaven National Laboratory

Abstract: 

The discovery of superconductivity in square planar low valence nickelates has attracted significant interest, declaring a “nickel age” of superconductivity. However, regarding their essential electronic properties, it remains under debate whether they have appreciable oxygen charge-transfer character akin to the cuprates or are in a distinct Mott-Hubbard regime where oxygen plays a minimal role. It is also unclear if there are any electronic instabilities such as charge order near the superconductivity dome.In this talk, I will show how we resolve these questions using the modern resonant inelastic x-ray scattering (RIXS)technique based on synchrotron light source and interpret the results with exact diagonalization calculations [1,2]. We find that the nickelates are in the mixed charge-transfer / Mott-Hubbard regime of the Zaanen-Sawatzky-Allen (ZSA) schemewith the Coulomb repulsion U of similar size to the charge transfer energy Δ. Consequently, the superexchange interaction remains significant, with an appreciable hole occupation of the ligand O orbitals, and a Ni site centered charge order is realized.Our results clarify the essential characteristics of low valence nickelates and put strong constraints on theoretical interpretations of superconductivity in these materials.

Reference:

[1] J. Q. Lin et al., Phys. Rev. Lett. 126, 087001 (2021).

[2] Y. Shen et al., Phys. Rev. X 12, 011055 (2022).

Brief CV of Dr. Yao Shen:

Dr. Yao Shen is currently a postdoc in the Condensed Matter Physics and Materials Science Department at Brookhaven National Laboratory. He obtained his PhD in Condensed Matter Physics from Fudan University in 2019. His research has been focusing on using advanced x-ray and neutron techniques to study strongly correlated materials such as quantum spin liquids and unconventional superconductors.

Please download and install the App in advance (the overseas version of Tencent Meeting is called VooV Meeting, https://voovmeeting.com/download-center.html?from=1002 ). You can enter the online meeting room by logging on the live link, or by entering the meeting ID and the password. Please use your real name for user name.

Host: Prof. Tianping Ying, Key Lab for Advanced Materials & Electron Microscopy

Contact: Shujuan Cui（崔书娟）

Email: sjcui@iphy.ac.cn

Tel: 010-82649894

系列报告采用腾讯会议室+网络直播的形式，相关信息将及时在网站http://iysf.iphy.ac.cn/更新，敬请关注！

Online Meeting Room ID (Tencent Meeting): 994-468-278

Password: 0706

Live link: https://meeting.tencent.com/l/hvsjL0vHr6YM