Figure 1

STM images of ${\mathrm{La}}_{5/8}{\mathrm{Ca}}_{3/8}{\mathrm{MnO}}_3(001)$ surfaces with a post annealing time of (a) 0 min, (b) 10 min, and (c) 30 min. The (d) and (f) are the high resolution zoom-in images of (a) and (c), which show clearly the ($1\times 1$) and the $(\sqrt{2}\times \sqrt{2})R45°$ lattices, respectively. (e) is the line profile of the white mark in (b), showing the height difference of 1.3 Å of the two domains. The image areas are $60\mathrm{nm}\times 60\mathrm{nm}$ for (a), (b), and (c), and $16\mathrm{nm}\times 12\mathrm{nm}$ for (d) and (f).Reuse & Permissions

Figure 2

Flowchart of the structure evolution between ($1\times 1$) and $(\sqrt{2}\times \sqrt{2})R45°$. Arrows indicate the conversion from annealing in oxygen (green, print in black) or UHV (blue, print in gray), respectively. Annealing the sample with the ($1\times 1$) structure (a) in oxygen at $820°\mathrm{C}$ for 10 min (b) and 30 min (c), coexist with the ($1\times 1$) structure, more and more $(\sqrt{2}\times \sqrt{2})R45°$ patches show up, and finally a full $(\sqrt{2}\times \sqrt{2})R45°$ structure (d) forms. Annealing the sample with the $(\sqrt{2}\times \sqrt{2})R45°$ structure (d) in UHV at $400°\mathrm{C}$ for 10 min (e) and 30 min (f), $(\sqrt{2}\times 2\sqrt{2})R45°$ [insert in (e)] and $(\sqrt{2}\times 3\sqrt{2})R45°$ [inset in (f)] patches show up, and finally a full ($1\times 1$) structure (a) forms. (b), (c), (e), and (f) are $150\mathrm{nm}\times 150\mathrm{nm}$, (a), (d) and all the high resolution insets are $16\mathrm{nm}\times 12\mathrm{nm}$. The fast Fourier Transform (FFT) of the STM images with $(\sqrt{2}\times 2\sqrt{2})R45°$ and $(\sqrt{2}\times 3\sqrt{2})R45°$structures are also shown as additional insets in (e) and (f).Reuse & Permissions

Figure 3

STM images of the LCMO surface before (a), and after (b), a STM tip scratching as described in the text ($18\mathrm{nm}\times 18\mathrm{nm}$). (c) is the zoom in ($13\mathrm{nm}\times 8\mathrm{nm}$) of (b). The blue dots show the$(\sqrt{2}\times \sqrt{2})R45°$ lattice, while the red dots indicate the ($1\times 1$) lattice; both unit cells are marked with black squares.Reuse & Permissions

Figure 4

Side view (upper panel) and top view (lower panel) of the stick and ball models for ($1\times 1$) and$(\sqrt{2}\times \sqrt{2})R45°$ structures, with red (print in small black), large blue (print in large black), and small blue (print in small gray) balls representing Mn, O atoms located atop the ${\mathrm{MnO}}_6$ octahedra, and O at the ${\mathrm{MnO}}_6$ layer, respectively. The unit cells of ($1\times 1$), $(\sqrt{2}\times \sqrt{2})R45°$, $(\sqrt{2}\times 2\sqrt{2})R45°$, and $(\sqrt{2}\times 3\sqrt{2})R45°$ are outlined in the lower panel.Reuse & Permissions

Figure 5

Scanning tunneling spectroscopy $I/V$ curves (shown in logarithmic scale) obtained at set points of $1.8\mathrm{V}/30\mathrm{pA}$ and $0.6\mathrm{V}/200\mathrm{pA}$ from the $(\sqrt{2}\times \sqrt{2})R45°$and the ($1\times 1$) surfaces, respectively. The ($1\times 1$) surface shows no band gap while the $(\sqrt{2}\times \sqrt{2})R45°$ surface shows a 1.35 eV band gap. Note that the band gap for the $(\sqrt{2}\times \sqrt{2})R45°$ is intrinsic because it remains unchanged when the tip is placed further from the surface at different set points.Reuse & Permissions