April 22 - 26, 2024
Seattle, Washington
May 7 - 9, 2024 (Virtual)

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2024 MRS Spring Meeting
CH04.07.03

Imaging Mobility of Charge Order Topology via Charge Density Wave Interferometery

When and Where

Apr 25, 2024
9:00am - 9:15am
Room 443, Level 4, Summit

Presenter(s)

Co-Author(s)

Suk Hyun Sung1,2,Noah Schnitzer3,Ismail El Baggari1,Lena Kourkoutis3,Robert Hovden2

Harvard University1,University of Michigan2,Cornell University3

Abstract

Suk Hyun Sung1,2,Noah Schnitzer3,Ismail El Baggari1,Lena Kourkoutis3,Robert Hovden2

Harvard University1,University of Michigan2,Cornell University3
Charge density waves (CDWs) are emergent correlated electron behavior that span crystals with strong electron-lattice coupling and are associated with exciting phenomena such as metal–insulator transitions and superconductivity. Often described as a superlattice crystal of electrons, CDWs can also accommodate defects such as dislocations and elastic deformations. CDW defects are of a particular interest as they are believed to dominate conductance [1] and mediate phase transitions of the charge lattice itself [2–4]. Topological defects in a CDW are even expected to locally host superconductivity [5]. Therefore, understanding the formation, destruction, and mechanics of CDW defects is paramount to harnessing the full potential of charge ordered materials.<br/><br/>TaS<sub>2</sub> is prototypical layered CDW system that hosts multiple CDW phases tuned by temperature, thickness and polytype [6–8]. Octahedrally coordinated 1T-TaS<sub>2</sub> at room temperature hosts a nearly-commensurate (NC-) CDW lacking long-range order, and a long-range ordered commensurate (C-) CDW below 200 K. While the nature of order in NC-CDW phase remains unclear, it is generally accepted that NC-CDW incorporates discommensurations (i.e., slips in the CDW phase) [3, 4]. Real space measurement of the nanoscale structure of the NC-CDW is complicated by out-of-plane incoherence of the CDW; features are washed out in atomic resolution measurements. Here we use CDW moiré engineering to magnify and image the structure of CDW dislocations in the NC-CDW phase of TaS<sub>2</sub>.<br/><br/>We generate a CDW moiré by synthesizing an endotaxial polytype heterostructure [9] that stabilizes both NC- and C-CDW phase layers embedded in a metallic prismatic matrix. Here the long-range ordered C-CDW serves as a grating with which the NC-CDW interferes. The resulting moiré interference pattern resolves a topological defect present in the NC-CDW. This pattern effectively encodes and magnifies the phase information in the NC- and C-CDW phases, taking advantage of the fact that NC- and C-CDWs diffract electrons with only slightly different momentum. By collecting scanned nanobeam diffraction patterns (i.e., 4D scanning transmission electron microscopy (STEM)) with the convergence angle and camera length tuned such that both C and NC reflections are incident on a single pixel of an electron microscope pixel array detector (EMPAD), moiré interference patterns are speedily acquired in parallel at every point in reciprocal space that the superlattice peaks nearly coincide.<br/><br/>In summary, we image CDW defects by employing 4D-STEM on polytype heterostructures of TaS<sub>2</sub>. The interference from C and NC-CDW forms a moiré pattern that encodes the phase disorder of the NC phase, allowing defects to be imaged despite the out of plane incoherence inherent to the system. This work suggests a new experimental framework that can shed light on difficult-to-study CDW mechanics.<br/> <br/>[1] AW Tsen et al., <i>Proc. Natl. Acad. Sci.</i> <b>112</b> (2015) p.15054.<br/>[2] WL McMillan, <i>Phys. Rev. B</i> <b>12</b> (1975) p. 1187.<br/>[3] WL McMillan, <i>Phys. Rev. B </i><b>14</b> (1976) p. 1496.<br/>[4] K Nakanish and H. Shiba, <i>J. Phys. Soc. Jpn.</i> <b>43</b> (1977) p.1839.<br/>[5] B Leridon et al., <i>New J. Phys.</i> <b>22</b> (2020) 073075.<br/>[6] JA Wilson, FJ Di Salvo, S Mahajan <i>Adv. Phys.</i> <b>24</b> (1975) p.117.<br/>[7] Y Yu et al., <i>Nat. Nanotech. </i><b>10</b> (2015) 270.<br/>[8] E Martino et al., <i>npj 2D Mater. App.</i> <b>4</b> (2020) 7.<br/>[9] SH. Sung et al., <i>Nat. Commun.</i> <b>13</b> (2022) p.413.

Keywords

2D materials

Symposium Organizers

Yuzi Liu, Argonne National Laboratory
Michelle Mejía, Dow Chemical Co
Yang Yang, Brookhaven National Laboratory
Xingchen Ye, Indiana University

Session Chairs

Qian Chen
Yuzi Liu
Judith Yang

In this Session