Strongly Entangled Kondo and Kagome Lattices and the Emergent Magnetic Ground State in Heavy-Fermion Kagome Metal YbV$_6$Sn$_6$

Abstract

Applying angle-resolved photoemission spectroscopy and density functional theory calculations, we present compelling spectroscopic evidence demonstrating the intertwining and mutual interaction between the Kondo and kagome sublattices in heavy-fermion intermetallic compound YbV$_6$Sn$_6$. We reveal the Yb 4$f$-derived states near the Fermi level, along with the presence of bulk kagome bands and topological surface states. We unveil strong interactions between the 4$f$ and itinerant electrons, where the kagome bands hosting the Dirac fermions and van Hove singularities predominate. Such findings are well described using a $c$-$f$ hybridization model. On the other hand, our systematic characterization of magnetic properties demonstrates an unusually enhanced antiferromagnetic ordering, where the kagome-derived van Hove singularities near $E_F$ play a vital role in determining the unconventional nature of the Ruderman-Kittel-Kasuya-Yosida interaction and Kondo coupling. These unique kagome-state-mediated exchange interactions have never been reported before and could lead to a novel phase diagram and various quantum critical behaviors in YbV$_6$Sn$_6$ and its siblings. Our results not only expand the family of exotic quantum phases entangled with kagome structure to the strongly correlated regime, but also establish YbV$_6$Sn$_6$ as an unprecedented platform to explore unconventional many-body physics beyond the standard Kondo picture.

Figures (4)

• Figure 1: (a),(b) Side and top views of the YbV$_6$Sn$_6$ crystal structure, respectively. (c) Bulk and (001)-projected surface BZs. (d) Temperature-dependent angle-integrated photoemission intensity ($h\nu$ = 182 eV). The Yb$^{2+}$ and Yb$^{3+}$ components are marked out by the red and blue bars, respectively. (e) Temperature-dependent relative peak areas of Yb$^{2+}$ and Yb$^{3+}$ features. Before the normalization, a Shirley-type background has been subtracted from both components. (f) Temperature dependence of the estimated Yb valence.
• Figure 2: (a) X-ray photoelectron spectroscopy spectrum ($h\nu$ = 100 eV) (left) and corresponding integrated energy distribution curve (right) measured on the V$_3$Sn termination. (b)-(d) Constant-energy ARPES images [$h\nu$ = 80 eV, linear horizontal (LH) polarization] from the V$_3$Sn termination at the energies of 0, -0.05, and -0.20 eV, respectively. (e),(f) Corresponding ARPES intensity plots ($T$$\approx$ 2 K) around $\bar{M}$ and $\bar{K}$, respectively. The momentum locations are illustrated in the insets. The 50-eV photons were used to better reveal the TSSs and DP.
• Figure 3: (a) Experimental band structures of YbV$_6$Sn$_6$ along the $\bar{\Gamma}$-$\bar{M}$-$\bar{K}$-$\bar{\Gamma}$ lines at 2 K. The typical kagome bands are guided by the red dashed curves (without including the effect of $c$-$f$ hybridization). (b) DFT calculated bulk bands with the integration over entire $k_z$. The contribution of the Yb 4$f$ shell is not included. (c),(d) ARPES intensity plots along the $\bar{\Gamma}$-$\bar{K}$-$\bar{M}$ directions at 2 K recorded by 53-eV photons with LH and LV polarizations, respectively.(e) Same as (c) along the $\bar{\Gamma}$-$\bar{M}$ direction. (f),(g) Schematic band diagrams along the $\bar{K}$-$\bar{M}$-$\bar{K}$ directions without and with considering the $c$-$f$ hybridization, respectively. A simple band hybridization model is constructed. (h) Sketches of the hybridization between $\delta$ band and 4$f_{7/2}^{13}$ state at $\bar{\Gamma}$. Inset: Calculated bulk bands along the $M$-$\Gamma$-$M$ direction.
• Figure 4: (a) Zero-field specific heat of YbV$_6$Sn$_6$ and YbMn$_6$Sn$_6$ plotted as $C_p$/$T$ vs $T^2$. The green curve is adopted from Ref. [JiaS2023Yb]. (b) Low-temperature specific heat of YbV$_6$Sn$_6$ in zero field. (c) Temperature-dependent specific heat of YbV$_6$Sn$_6$ in different magnetic fields ($H$$\parallel$$c$). (d) Temperature dependence of zero-field-cooling and field-cooling magnetization of YbV$_6$Sn$_6$ ($H$$\parallel$$ab$). Inset: Field-dependent magnetization at 1.8 K ($H$$\parallel$$ab$).(e) Temperature-dependent zero-field resistivity of YbV$_6$Sn$_6$ ($I$$\parallel$$ab$). Inset shows temperature range close to $T_{\rm N}$. (f) $T_{\rm N}$ of YbV$_6$Sn$_6$ as a function of unit cell volume. The green dot is adopted from Ref. [JiaS2023Yb].