Intertwining of Magnetism and Charge Ordering in Kagome FeGe

Abstract

Recent experiments report a charge density wave (CDW) in the antiferromagnet FeGe, but the nature of the charge ordering and the associated structural distortion remains elusive. We discuss the structural and electronic properties of FeGe. Our proposed ground state phase accurately captures atomic topographies acquired by scanning tunneling microscopy. We show that the 2 × 2 × 1 CDW likely results from the Fermi surface nesting of hexagonal-prism-shaped kagome states. FeGe is found to exhibit distortions in the positions of the Ge atoms instead of the Fe atoms in the kagome layers. Using in-depth first-principles calculations and analytical modeling, we demonstrate that this unconventional distortion is driven by the intertwining of magnetic exchange coupling and CDW interactions in this kagome material. The movement of Ge atoms from their pristine positions also enhances the magnetic moment of the Fe kagome layers. Our study indicates that magnetic kagome lattices provide a material candidate for exploring the effects of strong electronic correlations on the ground state and their implications for transport, magnetic, and optical responses in materials.

Electron-Correlation-Induced Charge Density Wave in FeGe

“…For 𝑘𝑧 = 0.5 plane, the Fermi surface evolved to contain h-hexagonal-shaped pockets, which has similar features with 𝑘𝑧 = 0 plane to some extent, as suggested in Ref. [70]. As can be seen from Fig.…”

“…The correlation-induced renormalization and the topological features in FeGe have also been explored. [72] FeGe exhibits a sequence of phase transitions: (1) An A-type antiferromagnetism (AFM) phase appears below the high magnetic transition temperature up to 𝑇c ∼ 410 K. [74] (2) A CDW phase [67][68][69][70] takes place at 𝑇CDW ∼ 100 K and the system becomes stable in 2 ×2×2 superstructure and induces an emergent anomalous Hall effect (AHE) possibly associated with a chiral flux phase as previously reported in metal 𝐴V3Sb5. [21][22][23][24][25][26]35,36,55] (3) The magnetic moment weakly cants along the 𝑐 direction, giving a 𝑐-axis double cone AFM structure below a lower transition temperature 𝑇canting around 60 K. [75][76][77][78][79][80] Subsequent reports reveal that the vHSs in FeGe, which are originally far from Fermi surface in a nonmagnetic system, are brought to the vicinity of Fermi level due to spin exchange splitting of about 1.8 eV caused by magnetic order.…”

“…[15][16][17] However, it may be due to the large energy separation between flat bands and vHSs that CDW order and magnetic order have not been generally observed simultaneously in one material. [65,66] Very recently, the discovery of CDW order coexists with magnetic order in the Kagome material FeGe, [65,[67][68][69][70][71][72][73] reported from a joint experimental study of angle-resolved photoemission spectroscopy (ARPES), [65,67] neutron and x-ray scattering, [67][68][69] scanning tunneling microscopy [67,68,70,71] and photoemission, [68] which offers a fascinating platform to investigate interplay between the CDW and magnetism. The correlation-induced renormalization and the topological features in FeGe have also been explored.…”

“…[65][66][67] Though FeGe exhibits the existence of vHSs at the 𝑀 point near the Fermi level similar to 𝐴V3Sb5, it is noteworthy that the imaginary phonon around the 𝑀 point present in 𝐴V3Sb5 [29,32] is not observed in the theoretically calculated phonon spectrum of FeGe. [65,69,70] Therefore, a comprehensive study of the band structures, Fermi surfaces, nesting function, and the mechanism of CDW transition in kagome FeGe is an emergency issue. We address it in this work based on first principles study.…”

“…[94] The 2 ×2×2 supercell structure of CDW phase corresponding to the hightemperature non-magnetic pristine phase is suggested by experimental results. [67][68][69][70] As mentioned above, the CDW transition in FeGe takes place at 𝑇CDW around 100 K, below the magnetic transition temperature 410 K. Since the A-type AFM structure has already enlarged unit cells dou-bled along the 𝑧-direction, we focus the in-plane 𝑞 vector in the following, and obtain the nesting function 𝜉(𝑞𝑥, 𝑞𝑦, 0), as illustrated in Fig. 2.…”