Disentangle Intertwined Interactions in Correlated Charge Density Wave with Magnetic Impurities

Abstract

Magnetic impurities in strongly correlated electronic systems serve as sensitive probes to a wide range of many-body quantum phenomena. Broken symmetries in such a system can lead to inequivalent lattice sites, and magnetic impurities may interact selectively with particular orbitals or sublattices. However, the microscopic mechanisms behind such site-specific interactions have been poorly understood. Here, we explore the behavior of individual Fe adatoms on a cluster-Mott charge-density-wave (CDW) system of 1T-TaS2 utilizing scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). Our measurements uncover pronounced site-dependent electronic states of CDW clusters with Fe adatoms, indicating distinct local coupling to cluster-Mott states. DFT calculations identify three distinct types of interactions; hybridization with localized correlated electrons, distorting the CDW cluster, and charge transfer. In particular, the hybridization of Fe 3d and half-filled Ta 5dz2 orbitals suppresses the Mott insulating state for an adatom at the center of a CDW cluster. While the results underscore a crucial role of the direct orbital hybridization and the limitation of the prevailing single-site Kondo impurity model, they suggest the possibility of controlling entangled interactions separately in a cluster Mott insulator.

Figures (5)

• Figure 1: STM images and STS line profiles for three distinct Fe adsorption configurations on 1T-TaS$_2$. (a) Representative STM topography of the commensurate CDW phase in 1T-TaS$_2$ with Fe adsorbates ($V_b$ = -0.5 V, $I$ = 50 pA, scale bar = 5 nm). The periodic protrusions correspond to David-star (DS) clusters, while brighter features indicate adsorbed Fe atoms. (b-d) Zoomed-in STM images showing Fe atoms at three characteristic adsorption configurations: (b) on-center, (c) on-edge, and (d) off-cluster sites. (e-g) Corresponding STS line profiles acquired along the arrows in (b-d), across the Fe sites (see Supplementary Fig. 2). (h) Schematic illustration of a single DS cluster forming the $\sqrt{13} \times \sqrt{13}$ CDW superstructure. (i) Theoretical LDOS of pristine single-layer 1T-TaS$_2$. Gray-filled curve shows the total DOS from all thirteen Ta atoms within a DS cluster (scaled by 1/3 for clarity). Dashed line represents the states localized at the central Ta atom, while red and blue filled curves represent spin-resolved contributions from the central Ta $5d_{z^2}$ orbital. Right: Spatial isosurfaces of $d_{z^2}$-like charge density corresponding to the lower and upper Hubbard bands, highlighting the Mott-localized states. The spin density is provided by color density. (j) Bilayer 1T-TaS$_2$. Right: Charge density maps at the central Ta site, integrated over energy windows of $-0.2$ to $0.0$ eV (top) and $-1.0$ to $0.0$ eV (bottom, top view), illustrating $d_{z^2}$ orbital character and CDW-induced modulation in the bilayer system, respectively.
• Figure 2: On-center Fe adsorption coupled to surface-correlated electrons. (a) Point STS spectra measured at the Fe adsorption site (red), a nearby pristine region (green), and a neighboring CDW center (gray filled),corresponding to the respectively colored markers in Fig. 1(b). (b) Theoretical LDOS. Red lines represent states localized at the Fe atom (scaled by 1/10), while green lines correspond to states on neighboring Ta atoms. Gray-filled curve represents the total Ta states of the pristine surface for comparison. The inset shows the atomic structure of the on-center adsorbed DS cluster with the brown sphere representing the Fe atom. (c) Spin-resolved LDOS at the top layer. Gray-filled curve represents the total Ta states of the Fe adsorbed DS cluster. Red and blue filled curves represent spin-resolved contributions from the central Ta $5d_{z^2}$ orbital. Fe-related states (red and blue lines) are scaled by 1/6 for clarity. (d) Charge density plots corresponding to the energy windows used in Fig. 1(j), highlighting the $d_{z^2}$-like character (top) and CDW modulations (bottom). In the bottom panel, the charge density is shown as the difference from the pristine surface. (e) Experimental $dI/dV$ maps (top) and theoretical charge density plots (bottom) at energies corresponding to the Fe-related state and LHB, respectively.
• Figure 3: On-edge Fe adsorption with weakly coupled charge-transfer. (a) Point STS spectra taken at the Fe site (red), the CDW center beneath the Fe adatom (green), and a neighboring CDW center (filled with gray), corresponding to the respectively colored markers in Fig. 1(c). (b) Theoretical LDOS showing Fe-localized states (red) and the adjacent central Ta atom (green), with the pristine Ta LDOS shown for comparison (gray filled). The inset illustrates the on-edge DS adsorption geometry. (c) Spin-resolved LDOS at the top layer, showing the total Ta states (gray filled), spin-resolved contributions from the central Ta $5d_{z^2}$ orbital (red and blue filled curves), and Fe-derived states (red and blue lines, scaled by 1/3 for clarity). (d) Charge-density plots corresponding to the energy windows in Fig. 1(j), highlighting the $d_{z^2}$-like character (top) and CDW modulations (shown as charge difference, bottom).
• Figure 4: Off-cluster Fe adsorption coupled to the CDW order. (a) Point STS spectra taken at the Fe site (red), the CDW center beneath the Fe adatom (green), and a neighboring CDW center (gray filled), corresponding to the respectively colored markers in Fig. 1(d). (b) Theoretical LDOS showing Fe-localized states (red) and the adjacent central Ta atom (green), with the pristine Ta LDOS shown for comparison (gray filled). The inset illustrates the off-cluster DS adsorption geometry. (c) Spin-resolved LDOS at the top layer, showing the total Ta states (gray filled), spin-resolved contributions from the central Ta $5d_{z^2}$ orbital (red and blue filled curves), and Fe-derived states (red and blue, scaled by 1/3 for clarity). (d) Charge-density plots corresponding to the energy windows in Fig. 1(j), highlighting the $d_{z^2}$-like character (top) and CDW modulations (shown as charge difference, bottom).
• Figure 5: DFT band structures for a on-center Fe or a on-center Co adatom on a single-layer 1T-TaS$_2$, using a $\sqrt{13}$$\times$$\sqrt{13}$ cell. (a) Pristine 1T-TaS$_2$ CDW structure for comparison. (b) Fe/1T-TaS$_2$. (c) Co/1T-TaS$_2$. (d) Co/1T-TaSe$_2$. Red (blue) filled circles indicate the majority (minority) spin states localized on Ta $d_{z^2}$ orbitals (LHB/UHB), while red (blue) open circles represent majority (minority) spin states localized on Fe and Co $d$ orbitals. The purple-colored bands in (c) and (d) represent spin-degenerate states, where the majority and minority spin states overlap.