PhD Defenses

PHYSICS PHD DISSERTAITON DEFENSE: Haiyu Lu

Date
Mon March 8th 2021, 5:30pm

Ph.D. Candidate:  Haiyu Lu
Research Advisor:  Zhi-Xun Shen

Date: Monday, March 8th, 2021
Time: 17:30 PST
Public Session Zoom Link: https://stanford.zoom.us/j/94904970606

Zoom Password: Email mariaf67 [at] stanford.edu (mariaf67[at]stanford[dot]edu) for password


Title: Investigation of Magnetic Excitations in Infinite-layer Nickelates with Resonant Inelastic X-ray Scattering 


Abstract: Resonant inelastic x-ray scattering (RIXS) has emerged as a powerful element-specific and momentum-resolved technique for investigating various elementary excitations in condensed matter physics [1]. In this talk, I will focus on a RIXS study of the recently discovered superconducting infinite-layer nickelate Nd1-xSrxNiO2 thin films [2]. Besides a similar crystal structure, the infinite-layer nickelate is nominally isoelectronic to the high-Tc cuprates superconductor, since the unusual monovalent Ni+ is characterized by the same 3d9 electronic configuration as the Cu2+ in cuprates [3]. At this early stage, it is important to experimentally investigate the similarities and differences between cuprates and nickelates, particularly the respective electronic and magnetic structures. Here, by utilizing the high-resolution RIXS at the Ni L3-edge, we found that the parent compound of the infinite-layer nickelate NdNiO2 is not a charge-transfer material, like cuprates. Instead, it is probably closer to a Mott-insulator with an additional coupling with Nd 5d metallic states. Furthermore, we also found a branch of dispersive magnetic excitations with a bandwidth of approximately 200 meV in the parent compound NdNiO2. Although these modes are significantly damped, they are reminiscent of the spin-wave of strongly coupled, anti-ferromagnetically aligned spins on a square lattice. Upon doping, the spectral weight and energy decrease slightly, while the modes become overdamped. The dispersion, doping dependence, damping effect of the magnetic excitation, and the added complexity due to the presence of the Nd 5d metallic pockets, together with its comparison with the magnetic excitation in cuprates, will be discussed [4].

 

References:

[1]: Ament, L. J. et al. Resonant inelastic x-ray scattering studies of elementary excitations. Rev. Mod. Phys. 83, 705-767 (2011)

 

[2]: Li, D. et al. Superconductivity in an infinite-layer nickelate. Nature 572, 624-627 (2019)

 

[3]: Hepting, M. et al. Electronic structure of the parent compound of superconducting infinite-layer nickelates. Nat. Mater. 19, 381-385 (2020).

 

[4]: Lu, H. et al. Magnetic excitations in infinite-layer nickelates (submitted)