Würzburg ToCoTronics Colloquium

Obtaining an accurate theoretical description of the emergent electronic and magnetic phenomena of strongly correlated materials is a major challenge in condensed matter physics. One of the techniques which have gained a lot of popularity over the last decades is dynamical mean-field theory (DMFT), often combined with first principles techniques such as density functional theory (DFT). Whereas most DMFT studies still focus on understanding properties qualitatively on a model level, the combination with DFT allows for material-realistic simulations that can -in principle- be directly compared to experiment. However, comprehensive studies of specific materials that aim at a quantitative understanding of several different experimentally accessible quantities from the same theoretical simulation remain an exception.

In this seminar, we will discuss both the predictive power and the limitations of a cluster extension of DMFT (C-DMFT) on two different test case materials belonging to the cuprate family. 

The first, a thin film of tetragonal CuO, is structurally one of the simplest cuprates and was studied by powerful experimental tools such as angle-resolved photoemission (ARPES) and resonant inelastic x-ray scattering (RIXS). Using C-DMFT, we will give a formal justification for the weak coupling assumption that has previously been proposed for the interconnected sublattices within a single layer of t-CuO and compute momentum-resolved spectral functions. The agreement with photoemission spectroscopy indicates that a single-band Hubbard model is sufficient to capture the material's low energy physics. As an outlook, we will make predictions for an eventual superconducting state in the hole-doped regime and discuss the influence of oxygen vacancies at the interface between t-CuO thin film and substrate [1,2].

The second example, Na-doped Ca2CuO2Cl2 (Na-CCOC), will be studied by applying C-DMFT on a minimal model derived from DFT simulations. The interest here is twofold: On one side certain well known spectral features of cuprates will be discussed for Na-CCOC in direct comparison to ARPES measurements. On the other side, the line-shape of para-magnons as measured within RIXS will be discussed through the lens of quantities accessible by C-DMFT [3]. In particular the comparison between RIXS and ARPES spectra will allow us to identify spin fluctuations as the common mechanism dominating the low-energy properties of this material.

References

[1] M. Bramberger, B. Bacq-Labreuil, M. Grundner, S. Biermann, U. Schollwöck, S. Paeckel, and B. Lenz, SciPost Phys. 14, 010 (2023)
[2] B. Bacq-Labreuil, B. Lenz, and S. Biermann, Phys. Rev. B 106, 235155 (2022)
[3] B. Lebert, B. Bacq-Labreuil, M.P.M. Dean, K. Ruotsalainen, A. Nicolaou, S. Huotari, I. Yamada, H. Yamamoto, M. Azuma, N.B. Brookes, F. Yakhou, H. Miao, D. Santos-Cottin, B. Lenz, S. Biermann, and M. d’Astuto, Phys. Rev. B 108, 024506 (2023)