In this contribution, I will focus on four families of materials, BaNi₂(As_1-xP_x)₂ [1], FeSe_1-xS_x [2-3] Ta₂(Ni_1-xCo_x)Se₅ [4,5] and CsV₃Sb₅ [6], that show rich phase diagrams containing nearly degenerate electronic states. In these materials the electronic properties (e.g. nematicity, charge- and magnetic ordering) can be altered by tuning the interplay between the structural and electronic degrees of freedom, for instance by chemical doping or by applying hydrostatic pressure. The prerequisite for detailed experimental exploration, is the design and crystal growth of high-quality single crystals. We have been implementing chemical vapor transport and crystallization by flux for the growth of the selected materials as high-quality single crystals (see Fig. 1) and characterized these by chemical analysis, x-ray diffraction and magnetic measurements. I will explain the current experimental results and discuss promising future directions.

References

[1] T. Lacmann, A.-A. Haghighirad, S-M. Souliou, M. Merz, G. Garbarino, K. Glazyrin, R. Heid, and M. Le Tacon, Phys. Rev. B 108, 2241115 (2023).

[2] M. Watson, A.-A Haghighirad, L. C. Rhodes, M. Hoesch and T. K. Kim, New Journal of Physics 19, 103021 (2017).

[3] P. Reiss, D. Graf, A.-A. Haghighirad, M. Knafo, L. Drigo, M. Bristow, A.J. Schofield, A. Coldea, Nat. Phys. 16, 89-94 (2020).

[4] M.D. Watson, I. Marković, E.A. Morales, P. Le Févre, M. Merz, A.-A. Haghighirad, P.D.C. King, Phys. Rev. Res. 2, 013236 (1-6) (2020).

[5] N. Maraytta, P. Nagel, F. Ghorbani, A. Ghiami, S. Pakhira, M. Ye, B. Wehinger, F. Abbruciati, G. Garbarino, M. Le Tacon, S. Schuppler, A.-A. Haghighirad & M. Merz, Sci. Reports 15, 35019 (2025).

[6] F. Stier, A.-A. Haghighirad, G. Garbarino, S. Mishra, N. Stilkerich, D. Chen, C. Shekhar, T. Lacmann, C. Felser, T. Ritschel, J. Geck and M. Le Tacon, Phys. Rev. Lett. 133, 236503 (2024).

Acknowledgments: DFG, project ID 422213477-TRR288 (Project no. B03).