[Paper Review] Magnetic Order Driven Ultrafast Phase Transition in NdNiO$_3$

V. Stoica, D. Puggioni+13 more|arXiv (Cornell University)|Apr 7, 2020

High-pressure geophysics and materials4 citations

TL;DR

This study demonstrates that magnetic order is the primary driver of the ultrafast insulator-to-metal transition (IMT) in NdNiO₃, with femtosecond X-ray and THz probes revealing that magnetic order collapses in less than 180 fs after photoexcitation, preceding the structural collapse and IMT. The results establish that coherent magneto-structural coupling—driven by photoexcited inter-site charge transfer—controls the transition, offering a pathway for ultrafast, light-induced manipulation of electronic phases in quantum materials.

ABSTRACT

Ultrashort x-ray pulses can be used to disentangle magnetic and structural dynamics and are accordingly utilized here to study the photoexcitation of NdNiO$_3$ (NNO), a model nickelate exhibiting structural and magnetic dynamics that conspire to induce an IMT. During the course of the photoinduced insulator to metal transition (IMT) with above gap excitation, we observe an ultrafast ($

Motivation & Objective

• To disentangle the roles of magnetic, structural, and electronic degrees of freedom in the photoinduced insulator-to-metal transition (IMT) in NdNiO₃.
• To determine the sequence and timescales of magnetic order suppression, lattice distortion, and charge redistribution during ultrafast excitation.
• To establish whether magnetism acts as a primary order parameter or a secondary response in driving the IMT.
• To investigate the coupling between magnetic order and coherent phonons in a strongly correlated oxide.
• To provide a framework for ultrafast control of electronic phase transitions via tailored light excitation in quantum materials.

Proposed method

• Employed ultrashort x-ray pulses (from LCLS) to probe electronic and magnetic dynamics in NdNiO₃ with sub-100 fs temporal resolution.
• Combined time-resolved X-ray absorption spectroscopy (XAS) to track Ni 3d occupancy and oxidation state changes.
• Used THz transmission spectroscopy to monitor the evolution of the insulating gap and collective lattice modes.
• Applied density functional theory (DFT) calculations to model inter-site charge transfer and its impact on magnetic and charge order.
• Performed multimodal ultrafast measurements to correlate magnetic, structural, and electronic responses in real time.
• Analyzed coherent phonon coupling to magnetic order to identify dynamic magneto-structural interactions.

Experimental results

Research questions

• RQ1 What is the role of magnetic order in initiating the photoinduced insulator-to-metal transition in NdNiO₃?
• RQ2 What are the relative timescales of magnetic order quenching, structural distortion, and electronic phase transition?
• RQ3 How is the coherent lattice mode (specifically the E′ phonon) coupled to magnetic and charge degrees of freedom?
• RQ4 Does inter-site charge transfer induced by photoexcitation directly destabilize antiferromagnetic order?
• RQ5 Can ultrafast light pulses be used to selectively manipulate magnetic order to trigger electronic phase transitions?

Key findings

• Magnetic order in NdNiO₃ collapses in less than 180 fs after photoexcitation, preceding the structural collapse and IMT.
• The quenching of antiferromagnetic order is driven by photoexcited inter-site charge transfer, as confirmed by DFT calculations.
• The collapse of the insulating phase, probed by THz transmission, occurs at 450 fs, lagging behind magnetic order suppression.
• A coherent E′ phonon mode is directly coupled to the magnetic order, demonstrating magneto-structural coupling on ultrafast timescales.
• The system exhibits a simultaneous order-disorder response at Ni sites and a displacive response at Nd sites, indicating coexisting magnetic and lattice dynamics.
• The results establish that magnetism is the fundamental order parameter stabilizing the insulating phase, with structural and charge orders responding secondarily.