More Like this

1. Two-dimensional charge order stabilized in clean polytype heterostructures

   https://doi.org/10.1038/s41467-021-27947-5  

   Sung, Suk Hyun; Schnitzer, Noah; Novakov, Steve; El Baggari, Ismail; Luo, Xiangpeng; Gim, Jiseok; Vu, Nguyen M.; Li, Zidong; Brintlinger, Todd H.; Liu, Yu; et al (December 2022, Nature Communications)

   Abstract Compelling evidence suggests distinct correlated electron behavior may exist only in clean 2D materials such as 1T-TaS 2 . Unfortunately, experiment and theory suggest that extrinsic disorder in free standing 2D layers disrupts correlation-driven quantum behavior. Here we demonstrate a route to realizing fragile 2D quantum states through endotaxial polytype engineering of van der Waals materials. The true isolation of 2D charge density waves (CDWs) between metallic layers stabilizes commensurate long-range order and lifts the coupling between neighboring CDW layers to restore mirror symmetries via interlayer CDW twinning. The twinned-commensurate charge density wave (tC-CDW) reported herein has a single metal–insulator phase transition at ~350 K as measured structurally and electronically. Fast in-situ transmission electron microscopy and scanned nanobeam diffraction map the formation of tC-CDWs. This work introduces endotaxial polytype engineering of van der Waals materials to access latent 2D ground states distinct from conventional 2D fabrication. 

   more » « less
2. Control of Charge‐Spin Interconversion in van der Waals Heterostructures with Chiral Charge Density Waves

   https://doi.org/10.1002/adma.202310768  

   Chi, Zhendong; Lee, Seungjun; Yang, Haozhe; Dolan, Eoin; Safeer, C. K.; Ingla‐Aynés, Josep; Herling, Franz; Ontoso, Nerea; Martín‐García, Beatriz; Gobbi, Marco; et al (May 2024, Advanced Materials)

   Abstract A charge density wave (CDW) represents an exotic state in which electrons are arranged in a long‐range ordered pattern in low‐dimensional materials. Although the understanding of the fundamental character of CDW is enriched after extensive studies, its practical application remains limited. Here, an unprecedented demonstration of a tunable charge‐spin interconversion (CSI) in graphene/1T‐TaS₂van der Waals heterostructures is shown by manipulating the distinct CDW phases in 1T‐TaS₂. Whereas CSI from spins polarized in all three directions is observed in the heterostructure when the CDW phase does not show commensurability, the output of one of the components disappears, and the other two are enhanced when the CDW phase becomes commensurate. The experimental observation is supported by first‐principles calculations, which evidence that chiral CDW multidomains in the heterostructure are at the origin of the switching of CSI. The results uncover a new approach for on‐demand CSI in low‐dimensional systems, paving the way for advanced spin‐orbitronic devices. 

   more » « less
3. Frustrated charge density wave and quasi-long-range bond-orientational order in the magnetic kagome FeGe

   https://doi.org/10.1038/s41467-025-58725-2  

   Subires, D; Kar, A; Korshunov, A; Fuller, C A; Jiang, Yi; Hu, H; Călugăru, D; McMonagle, C; Yi, C; Roychowdhury, S; et al (December 2025, Nature Communications)

   Abstract The intrinsic frustrated nature of a kagome lattice is amenable to the realization of exotic phases of matter, such as quantum spin liquids or spin ices, and the multiple-qcharge density waves (CDW) in the kagome metals. Despite intense efforts to understand the mechanism driving the electronic modulations, its origin is still unknown and obscured by competing interactions and intertwined orders. Here, we identify a dimerization-driven 2D hexagonal charge-diffuse precursor in the antiferromagnetic kagome metal FeGe and demonstrate that the fraction of dimerized/undimerized states is the relevant order parameter of the multiple-qCDW of a continuous phase transition. The pretransitional charge fluctuations with propagation vectorq = q_Mat T_CDW < T < T^*(125 K) are anisotropic, hence holding a quasi-long-range bond-orientational order. The broken translational symmetry emerges from the anisotropic diffuse precursor, akin to the Ising scenario of antiferromagnetic triangular lattices. The temperature and momentum dependence of the critical scattering show parallels to the stacked hexatic B-phases reported in liquid crystals and transient states of CDWs and highlight the key role of the topological defect-mediated melting of the CDW in FeGe. 

   more » « less
4. Real-space visualization of a defect-mediated charge density wave transition

   https://doi.org/10.1073/pnas.2402129121  

   Hart, James L; Pan, Haining; Siddique, Saif; Schnitzer, Noah; Mallayya, Krishnanand; Xu, Shiyu; Kourkoutis, Lena F; Kim, Eun-ah; Cha, Judy J (August 2024, Proceedings of the National Academy of Sciences)

   We study the coupled charge density wave (CDW) and insulator-to-metal transitions in the 2D quantum material 1T-TaS₂. By applying in situ cryogenic 4D scanning transmission electron microscopy with in situ electrical resistance measurements, we directly visualize the CDW transition and establish that the transition is mediated by basal dislocations (stacking solitons). We find that dislocations can both nucleate and pin the transition and locally alter the transition temperatureT_cby nearly ~75 K. This finding was enabled by the application of unsupervised machine learning to cluster five-dimensional, terabyte scale datasets, which demonstrate a one-to-one correlation between resistance—a global property—and local CDW domain-dislocation dynamics, thereby linking the material microstructure to device properties. This work represents a major step toward defect-engineering of quantum materials, which will become increasingly important as we aim to utilize such materials in real devices. 

   more » « less
5. Encoding multistate charge order and chirality in endotaxial heterostructures

   https://doi.org/10.1038/s41467-023-41780-y  

   Husremović, Samra; Goodge, Berit H.; Erodici, Matthew P.; Inzani, Katherine; Mier, Alberto; Ribet, Stephanie M.; Bustillo, Karen C.; Taniguchi, Takashi; Watanabe, Kenji; Ophus, Colin; et al (December 2023, Nature Communications)

   Abstract High-density phase change memory (PCM) storage is proposed for materials with multiple intermediate resistance states, which have been observed in 1T-TaS₂due to charge density wave (CDW) phase transitions. However, the metastability responsible for this behavior makes the presence of multistate switching unpredictable in TaS₂devices. Here, we demonstrate the fabrication of nanothick verti-lateralH-TaS₂/1T-TaS₂heterostructures in which the number of endotaxial metallicH-TaS₂monolayers dictates the number of resistance transitions in 1T-TaS₂lamellae near room temperature. Further, we also observe optically active heterochirality in the CDW superlattice structure, which is modulated in concert with the resistivity steps, and we show how strain engineering can be used to nucleate these polytype conversions. This work positions the principle of endotaxial heterostructures as a promising conceptual framework for reliable, non-volatile, and multi-level switching of structure, chirality, and resistance. 

   more » « less