Ultrafast coupled charge and spin dynamics in strongly correlated NiO

• Published in: arXiv.org
• Main Authors: Gillmeister, Konrad, Golež, Denis, Cheng-Tien, Chiang, Bittner, Nikolaj, Pavlyukh, Yaroslav, Berakdar, Jamal, Werner, Philipp, Wolf Widdra
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 02.09.2019
• Subjects: Antiferromagnetism; Computer simulation; Excitation; Mathematical models; Nickel oxides; Oscillations; Photoelectric emission; Photonic band gaps; Physics - Strongly Correlated Electrons; Spin dynamics
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1909.00828

Charge excitations across an electronic band gap play an important role in opto-electronics and light harvesting. In contrast to conventional semiconductors, studies of above-band-gap photoexcitations in strongly correlated materials are still in their infancy. Here we reveal the ultrafast dynamics controlled by Hund's physics in strongly correlated photo-excited NiO. By combining time-resolved two-photon photoemission experiments with state-of-the-art numerical calculations, an ultrafast (\(\lesssim\) 10\,fs) relaxation due to Hund excitations and related photo-induced in-gap states are identified. Remarkably, the weight of these in-gap states displays long-lived coherent THz oscillations up to 2\,ps at low temperature. The frequency of these oscillations corresponds to the strength of the antiferromagnetic superexchange interaction in NiO and their lifetime vanishes as the Néel temperature is approached. Numerical simulations of a two-band \(t\)-\(J\) model reveal that the THz oscillations originate from the interplay between local many-body excitations and long-range antiferromagnetic order.