More Like this

1. Pressure-induced suppression of charge density phases across the entire rare-earth tritellurides by optical spectroscopy

   https://doi.org/10.1039/d2tc02137d  

   Kopaczek, Jan; Li, Han; Yumigeta, Kentaro; Sailus, Renee; Sayyad, Mohammed Y.; Moosavy, Seyed Tohid; Kudrawiec, Robert; Tongay, Sefaattin (August 2022, Journal of Materials Chemistry C)

   The rare-earth tritellurides (RTe 3 ) are a distinct class of 2D layered materials that recently gained significant attention due to hosting such quantum collective phenomena as superconductivity or charge density waves (CDWs). Many members of this van der Waals (vdW) family crystals exhibit CDW behavior at room temperature, i.e. , RTe 3 compound where R = La, Ce, Pr, Nd, Sm, Gd, and Tb. Here, our systematic studies establish the CDW properties of RTe 3 when the vdW spacing/interaction strength between adjacent RTe 3 layers is engineered under extreme hydrostatic pressures. Using a non-destructive spectroscopy technique, pressure-dependent Raman studies first establish the pressure coefficients of phonon and CDW amplitude modes for a variety of RTe 3 materials, including LaTe 3 , CeTe 3 , PrTe 3 , NdTe 3 , SmTe 3 , GdTe 3 , and TbTe 3 . Results further show that the CDW phase is eventually suppressed at high pressures when the interlayer spacing is reduced and interaction strength is increased. Comparison between different RTe 3 materials shows that LaTe 3 with the largest thermodynamic equilibrium interlayer spacing (smallest chemical pressure) exhibits the most stable CDW phases at high pressures. In contrast, CDW phases in late RTe 3 systems with the largest internal chemical pressures are suppressed easily with applied pressure. Overall results provide comprehensive insights into the CDW response of the entire RTe 3 series under extreme pressures, offering an understanding of CDW formation/engineering in a unique class of vdW RTe 3 material systems. 

   more » « less
2. Endotaxial stabilization of 2D charge density waves with long-range order

   https://doi.org/10.1038/s41467-024-45711-3  

   Sung, Suk Hyun; Agarwal, Nishkarsh; El_Baggari, Ismail; Kezer, Patrick; Goh, Yin Min; Schnitzer, Noah; Shen, Jeremy M; Chiang, Tony; Liu, Yu; Lu, Wenjian; et al (December 2024, Nature Communications)

   Abstract Charge density waves are emergent quantum states that spontaneously reduce crystal symmetry, drive metal-insulator transitions, and precede superconductivity. In low-dimensions, distinct quantum states arise, however, thermal fluctuations and external disorder destroy long-range order. Here we stabilize ordered two-dimensional (2D) charge density waves through endotaxial synthesis of confined monolayers of 1T-TaS₂. Specifically, an ordered incommensurate charge density wave (oIC-CDW) is realized in 2D with dramatically enhanced amplitude and resistivity. By enhancing CDW order, the hexatic nature of charge density waves becomes observable. Upon heating via in-situ TEM, the CDW continuously melts in a reversible hexatic process wherein topological defects form in the charge density wave. From these results, new regimes of the CDW phase diagram for 1T-TaS₂are derived and consistent with the predicted emergence of vestigial quantum order. 

   more » « less
3. Field‐Effect Transistors from Artificial Charged Domain Walls in Stacked Van der Waals Ferroelectric α‐In ₂ Se ₃

   https://doi.org/10.1002/adma.202523096  

   Nahid, Shahriar Muhammad; Dong, Haiyue; Nolan, Gillian M; Nam, SungWoo; Mason, Nadya; Huang, Pinshane Y; van_der_Zande, Arend M (April 2026, Advanced Materials)

   ABSTRACT Ferroelectric charged domain walls (CDWs) offer emergent electronic states that can serve as functional elements in high‐density nonvolatile memory and neuromorphic computing. Yet, poor conductivity, structural instability, and lack of deterministic control limit their practical use. Moreover, the CDWs are typically out‐of‐plane and buried interfaces, which prohibits electrical access and prevents gate control of their carrier density. This work demonstrates the fabrication of artificial in‐plane CDWs by stacking oppositely polarized flakes of van der Waals (vdW) ferroelectric ‐In₂Se₃. Edge contact is utilized to electrically access the CDWs and integrate them into CDW‐based field‐effect transistors (CDW‐FETs). CDW‐FETs exhibit room‐temperature conductance up to four orders of magnitude higher than single domains, exceeding previously reported CDWs by 2–9 orders of magnitude. Electron microscopy imaging reveals atomic reconstruction and interfacial heterogeneity in CDWs. Temperature and gate‐dependent electrical and magneto‐transport measurements confirm that interfacial band bending governs transport. Two transport mechanisms are identified in these CDW‐FETs: variable‐range hopping and thermally activated traps, showing a transition temperature of 80 K. These results establish artificial CDWs as on‐demand, designable conductive channels in vdW ferroelectrics, advancing the understanding of CDW conduction mechanisms and bridging the gap toward device integration. 

   more » « less
4. 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
5. Displacive In‐Plane Ferroelectricity with Domain‐Specific Curie Temperature in Van der Waals Semiconductors

   https://doi.org/10.1002/advs.202518341  

   Sutter, Peter; Sutter, Eli (January 2026, Advanced Science)

   Van der Waals bilayers assembled by mechanical stacking of 2D layers have been shown to realize symmetry‐breaking mechanisms, such as sliding‐ or moiré ferroelectricity, which are without equivalent in 3D ferroelectrics. Here, we discuss emergent, highly unconventional behavior in thicker semiconducting few‐layer SnS(e) van der Waals ferroelectrics crystallizing in a distorted polar structure, obtained by bottom‐up synthesis. Electron diffraction at variable temperature demonstrates a gradual displacive transformation between the polar low‐temperature and symmetric high‐temperature phase, with significant variability in both the lattice constants and the Curie temperature (TC) where the transition is completed. Strikingly, such variations are even found among stripe domains in individual crystals, where lattice constants and distortion angles change periodically between adjacent domains. The resulting spontaneously formed homo‐materials superlattices imply that such ferroelectrics adopt domain‐specific Curie temperatures, in sharp contrast with the long‐held notion of TC as a global materials parameter for a given ferroelectric. 

   more » « less