Pressure Tuning of Electronic Correlations and Flat Bands in CsCr$_3$Sb$_5$

Abstract

CsCr$_3$Sb$_5$ is a newly identified strongly correlated kagome superconductor, characterized by non-Fermi-liquid behavior at elevated temperatures and intertwined charge- and spin-density-wave order below $T_{DW}\approx 54$K. Under external pressure, this order is suppressed and a superconducting phase emerges. This phase diagram, which closely resembles that of high-$T_c$ superconductors, together with a kagome flat band near the Fermi level and possible altermagnetic order, has motivated extensive theoretical and experimental investigations. To better understand how pressure influences the ordered states, we present a systematic study of the evolution of the electronic properties under applied pressure. Performing DFT+DMFT (density functional theory combined with dynamical mean field theory) calculations, we uncover a complex interplay between the redistribution of spectral weight in the flat bands and the strength of electronic correlations under pressure. Our results further strengthen the interpretation that pressure effectively weakens electronic correlations through enhanced orbital hybridization. This, in turn, strongly suggests that superconductivity emerges as a direct consequence of the suppression of the system's ordered phase.

Figures (4)

• Figure 1: The bandstructure of CsCr$_3$Sb$_5$ along the high-symmetry-path for 0 Gpa pressure in panel (a) and for 8 Gpa pressure in panel (b) from DFT. The orbital weights for a the indicated selectoion of orbitals are color-coded by their linewidth. The width of the dots corresponds to the weight of the respective orbital. We observe that pressure induces a reduction in size of the electron pocket near the $\Gamma$ point with largest weight on the Antimony $p_z$ orbital
• Figure 2: Imaginary part of the orbital-resolved self-energy as a function of Matsubara frequencies for pressure $P=0$ GPa in panel (a) and $P=8$ GPa in panel (b). The self-energies are overall smaller for a finite pressure, revealing that the system is less correlated. At $P=0$ GPa we find strong orbital selectivity, with the $d_{xz}$, $d_{yz}$ and $d_{x^2-y^2}$ orbitals being strongly correlated.
• Figure 3: DFT+DMFT spectral function (in color) as a function of momentum and energy (panel (a) $P=0$ GPa, panel (b) $P=8$ GPa), accompanied by the local density of states (DOS) (panel (c)). The spectral function plots reveal that the flat bands are located very close to the Fermi energy ($E_F=0$). At $P=8$ GPa, weight is redistributed within the flat band, which remains highly weighted only at parts of the momentum path. The DOS at $P=0$ GPa is more stronly renormalized compared to $P=8$ GPa, as a direct consequence of the larger degree of correlations, observed from the self-energy.
• Figure 4: DFT+DMFT orbitally-resolved density of states (DOS) at $P=0$ GPa in panel (a) and $P=8$ GPa in panel (b). The three orbitals that mainly contribute to the flat bands are $d_{xz}$, $d_{yz}$ and $d_{x^2-y^2}$, which are the most strongly correlated orbitals, as illustrated by the self-energy data.