Theoretical X-ray Spectroscopies

Resonant Inelastic X-ray Scattering (RIXS)

Resonant inelastic x-ray scattering or RIXS is powerful and unique technique in obtaining elementary excitations in strongly correlated materials. Many experimental conditions, including different absorption edge, incoming and outgoing light polarization, and momentum resolution etc, can be tuned to selectively highlight the specific elementary excitation through enabling different intermediate state pathways. My studies using state-of-the-art numerical calculations have completed the understanding of RIXS cross-section for cuprates in several key aspects[1-5]. In these studies, RIXS cross-section as a complicated four-particle process has been calculated for absorption edges (both Cu L-edge and K-edge), polarizations (cross-polarized, parallel-polarized etc) and incoming phonon energies. Similarities and differences between RIXS cross-section and charge/spin dynamical structure factor in these circumstances have been addressed.

References:

[1] M Hepting, D Li, CJ Jia*, H Lu, E Paris, Y Tseng, X Feng, M Osada, E Been, Y Hikita, Y-D

Chuang, Z Hussain, KJ Zhou, A Nag, M Garcia-Fernandez, M Rossi, HY Huang, DJ Huang, ZX

Shen, T Schmitt, HY Hwang, B Moritz, J Zaanen, TP Devereaux, WS Lee* (*co-corresponding author),

"Electronic structure of the parent compound of superconducting infinite-layer nickelates",

Nature Materials 19, 381-385 (2020)

[2] Chunjing Jia*, Krzysztof Wohlfeld* (*equal contribution), Yao Wang, Brian Moritz, Thomas

P. Devereaux, "Using RIXS to uncover elementary charge and spin excitations", Physical Review X

6, 021020 (2016)

[3] H. Y. Huang, C. J. Jia, Z. Y. Chen, K. Wohlfeld, B. Moritz, T. P. Devereaux, W. B. Wu, J.

Okamoto, Wei-Sheng Lee, Makoto Hashimoto, Yu He, Z. X. Shen, Yoshiyuki Yoshida, Hiroshi

Eisaki, C. Y. Mou, C. T. Chen, and D. J. Huang, "Raman and fluorescence behavior of magnetic

excitations in superconducting cuprate", Scientific Reports 6, 19657 (2016)

[4] C. J. Jia, E. A. Nowadnick, K.Wohlfeld, Y. F. Kung, C.-C. Chen, S. Johnston, T. Tohyama,

B. Moritz, T. P. Devereaux, "Persistent Spin Excitations in Doped Antiferromagnets Revealed by

Resonant Inelastic Light Scattering", Nature Communications 5, 3314 (2014)

[5] C. J. Jia, C.-C. Chen, A. P. Sorini, B. Moritz, and T. P. Devereaux, "Uncovering Selective Excitations

Using the Resonant Profile of Indirect Inelastic X-ray Scattering in Correlated Materials:

Observing Two-magnon Scattering and Relation to the Dynamical Structure Factor", New Journal

of Physics 14, 113038 (2012)

Pump-probe Spectroscopies

Time adds a new dimension to the study of quantum materials. By using this extra dimension, it is possible to directly access excited states and non-equilibrium dynamics as a means to decipher underlying equilibrium properties — that is, unoccupied states, certain elementary excitations and excited-state and quasiparticle lifetimes.

By pushing a quantum material out of equilibrium, novel states of matter can be stabilized, such as those that have no equilibrium analogue or may not be easily accessible by standard approaches of chemical substitution. These exotic states may emerge from the light–matter interactions through precise engineering of new terms or modification of existing terms in the many-body Hamiltonian. By modulating or manipulating the eigenstate manifold, exotic states can be stabilized through strong pump fields or pump fields that persist over a sufficient period of time to enable the formation and resolution of distinguishing characteristics and features of these states

Selected Publications:

[1] Yao Wang, Martin Claassen, Chaitanya Das Pemmaraju, Chunjing Jia, Brian Moritz, Thomas

P Devereaux, "Theoretical understanding of photon spectroscopies in correlated materials in and

out of equilibrium", Nature Reviews Materials 3, 312 (2018)

[2] Y Wang, Y Chen, C Jia, B Moritz, TP Devereaux, "Time-Resolved Resonant Inelastic X-Ray

Scattering in a Pumped Mott Insulator", Physical Review B 101, 165126 (2020)