Atomistic origin of metal versus charge-density-wave phase separation in indium atomic wires on Si(111)

Sun Kyu Song and Han Woong Yeom

Phys. Rev. B 104, 035420 – Published 14 July 2021

Abstract

We investigate in atomic scale the electronic phase separation occurring in the well known quasi-one-dimensional (quasi-1D) charge-density wave (CDW) phase of an In atomic wire array on a Si(111) surface. The characteristic atomic scale defects, originating from excess In atoms, are found to be actively involved in the formation of the phase boundary between the metallic and the CDW phases by extensive analysis of scanning tunneling microscopy images at various temperatures. These particular defects flip the phase of the quasi-1D CDW to impose strong local constraints in the CDW correlation. We show that such local constraints and the substantial interwire CDW interaction induce local condensates of CDW and the phase separation between the metallic and the CDW phases. This work unveils the atomistic origin of the electronic phase separation, highlighting the importance of atomic scale structures of defects and their collective interaction in electronically inhomogeneous materials.

Received 7 December 2020
Revised 19 May 2021
Accepted 7 June 2021

DOI:https://doi.org/10.1103/PhysRevB.104.035420

Physics Subject Headings (PhySH)

Charge density waves Phase separation Surface states

1-dimensional systems Peierls transition Surfaces

Scanning tunneling microscopy

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Sun Kyu Song¹ and Han Woong Yeom ^1,2,*

¹Center for Artificial Low Dimensional Electronic Systems, Institute for Basic Science (IBS), Pohang 37673, Republic of Korea
²Department of Physics, Pohang University of Science and Technology (POSTECH), Pohang 37673, Republic of Korea

^*yeom@postech.ac.kr

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Issue

Vol. 104, Iss. 3 — 15 July 2021

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Images

Figure 1
(a) STM topographic images ( $V_{s} = - 0.5$ V) of the electronic phase separation in the In/Si(111) surface taken at 78 K with its pristine CDW transition at 130 K. Blue lines indicate domain boundaries between the metallic (bright) and the insulating CDW (dark) phases. The yellow box indicates two chiral solitons clustered. Blue dots and red triangles indicate characteristic the atomic-scale defects zoomed in (b) and (d), respectively [their empty state images with $V_{s} = 0.5$ V are shown in (c) and (e), respectively]. Dots indicate local structures of both defects for filled states. (f) Atomic structure model of the “M”-shaped defect shown in (b) and (c), which contains one excess In atom [27]. Blue (gray) balls indicates the indium (silicon) atoms. Red lines indicates the In hexagon structure characteristic of the CDW state.
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Figure 2
(a) STM topographic images ( $V_{s} = - 0.5$ V) of a single $4 \times 1$ metallic domain and its domain boundaries with the $8 \times 2$ CDW phase (outlined by black lines) at 78 K. Dots indicate local protrusions of the atomic scale defects (PFDs) as defined in Figs. 1 and 1. Red and blue bars denote the opposite CDW orientations imposed by the PFDs. (b) Schematics of the frustrated CDW orientations due to the PFDs (indicated by the dots). Red and blue stripes indicate the presumed phase coherent segments of within a single wire with its CDW orientations fixed by the PFDs, following the orientation of red and blue bars in (a). (c) Schematics of frustrated CDW orderings to induce the electronic phase separation. Red and blue ovals indicate the CDW orientations and yellow region indicates the interwire or intrawire disorder.
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Figure 3
(a),(b) STM topographic images ( $V_{s} = - 0.5$ V) of two small domains in the $8 \times 2$ CDW state surrounded by typical PFDs (dots) and metallic domains at 95 K. Red and blue bars denote the CDW orientation imposed by defects. (c),(d),(e) Close-up STM images of two metallic structures of $4 \times 1$ and $4 \times 2$ and the $8 \times 2$ CDW structures at 95 K, respectively.
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Figure 4
(a) STM topographic images ( $V_{s} = - 0.5$ V) of the electronic phase separation at 120 K slightly below the pristine CDW transition temperature of 130 K. White boxes indicate some local $8 \times 2$ patches formed near defect clusters. Blue dots and red triangles indicate typical PFDs in Figs. 1 and 1. (b),(c) Close-up STM images showing very short $8 \times 2$ or $4 \times 2$ structures decaying rapidly from defect clusters. (d),(e) Two consecutive STM images of a short $8 \times 2$ structure formed in between two neighboring PFDs.
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