Surface band-selective moiré effect induces flat band in mixed-dimensional heterostructures

Abstract

In this work, we reveal a curious type of moiré effect that selectively modifies the surface states of bulk crystal. We synthesize mixed-dimensional heterostructures consisting of a noble gas monolayer grow on the surface of bulk Bi(111), and determine the electronic structure of the heterostructures using angle-resolved photoemission spectroscopy. We directly observe moiré replicas of the Bi(111) surface states, while the bulk states remain barely changed. Meanwhile, we achieve control over the moiré period in the range of 25 Å to 80 Å by selecting monolayers of different noble gases and adjusting the annealing temperature. At large moiré periods, we observe hybridization between the surface band replicas, which leads to the formation of a correlated flat band. Our results serve as a bridge for understanding the moiré modulation effect from 2D to 3D systems, and provide a feasible approach for the realization of correlated phenomena through the engineering of surface states via moiré effects.

Figures (4)

• Figure 1: (a) Crystal structure of bismuth, the inside rhombohedron is the primitive unit cell and the outside hexagonal is the conventional cell. (b) Bulk Brillouin zone(black) and surface Brillouin zone(pink) of bismuth.(c) Long-range moiré pattern of mAr/Bi in real space, right picture is the center zoomed-in area. (d) Moiré effect of Bi/mAr, the pink/green/black line is Bi/Ar/moiré Brillouin zone
• Figure 2: (a) Fermi surface mapping of Bi(111) along $\bar{\Gamma}$ - $\bar{M}$ - $\bar{\Gamma}$ direction. (b) Band structure measured along $k_{x}=1.3Å^{-1}$ in (a), red curve is MDC at fermi level. (c, d) Same as (a, b) but measure from monolayer Ar and Bi(111) heterostructure, the red arrows point to the moiré replicas. (e) Schematic moiré effect in noble gas monolayer on Bi(111) surface. (f-i) Same as (a, b) but measured from monolayer Kr/Xe and Bi(111) heterostructure. (j, k, l) Temperature dependence of $\Delta\Gamma$, $a_{m}$, $a_{gas}$.
• Figure 3: (a) Pristine Bi band structure measured along $\Gamma$-K direction in second Brillouin zone. (b) Bi(111)/mAr band structure measured along $\bar{\Gamma}-\bar{K}$ direction in second Brillouin zone, the moiré effect flat band $\delta’$ is point by black arrow. (c, d) Curvature of (a, b). (e, f) EDC from band structure in $\Gamma$-K direction with and without monolayer Ar, the black dash line indicates flat band $\delta’$. (g) Fermi surface mapping of Bi(111)/mAr in second Brillouin zone. (h) Typical band structure in (g) at $k_{y}$=-0.24$Å^{-1}$ (cut1), -0.12$Å^{-1}$ (cut2), 0$Å^{-1}$ (cut3), 0.12$Å^{-1}$ (cut4), 0.24$Å^{-1}$ (cut5). (i, j) Evolution of band $\delta$, black dots are EDC peak fitting, green line is dots fitting of band $\delta$ and $\delta’$, red line is theoretical moiré band $\delta_{m}$ curve at $\Gamma - K$ direction. (k)Schematic of pristine and moiré replicas of band $\delta$, green part is pristine band $\delta$ and red part is theoretical moiré band $\delta_{m}$.
• Figure 4: (a, b) Pristine Bi and Bi(111)/mKr band structure measured along $\bar{\Gamma}-\bar{M}$ direction, pristine band $\delta$ and moiré band $\delta$' are point by the black arrows. (c, d) Curvature of a, b. (e, f) the EDC curvature of a and b, hybridization band $\delta$’ are traced by black dots.(g) Evolution of band $\delta$, black dots are EDC peak fitting, green line and blue line are dots fitting of band $\delta$ and $\delta’$, red line is theoretical moiré band $\delta_{m}$ curve alone $\bar{\Gamma}-\bar{M}$. (h)Comprehension between theoretical moiré replicas and the real hybridization band, the red and green dash lines are same as (g) and black dots are EDC peak fitting of $\delta$' in (b). (i)Schematic of pristine and moiré replicas of band $\delta$, green part is pristine band $\delta$ and red part is theoretical moiré band $\delta_{m}$. (j)Schematic of the Bi(111)/Kr hybridization $\delta$' band.