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1. Charge‐Density‐Wave Resistive Switching and Voltage Oscillations in Ternary Chalcogenide BaTiS ₃

   https://doi.org/10.1002/aelm.202300461  

   Chen, Huandong; Wang, Nan; Liu, Hefei; Wang, Han; Ravichandran, Jayakanth (November 2023, Advanced Electronic Materials)

   Abstract Phase change materials, which show different electrical characteristics across the phase transitions, have attracted considerable research attention for their potential electronic device applications. Materials with metal‐to‐insulator or charge density wave (CDW) transitions such as VO₂and 1T‐TaS₂have demonstrated voltage oscillations due to their robust bi‐state resistive switching behavior with some basic neuronal characteristics. BaTiS₃is a small bandgap ternary chalcogenide that has recently reported the emergence of CDW order below 245 K. Here, the discovery of DC voltage / current‐induced reversible threshold switching in BaTiS₃devices between a CDW phase and a room temperature semiconducting phase is reported. The resistive switching behavior is consistent with a Joule heating scheme and sustained voltage oscillations with a frequency of up to 1 kHz are demonstrated by leveraging the CDW phase transition and the associated negative differential resistance. Strategies of reducing channel sizes and improving thermal management may further improve the device's performance. The findings establish BaTiS₃as a promising CDW material for future electronic device applications, especially for energy‐efficient neuromorphic computing. 

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2. Absence of phonon softening across a charge density wave transition due to quantum fluctuations

   https://doi.org/10.1073/pnas.2507135122  

   Chen, Yubi; Kongruengkit, Terawit; Salinas, Andrea Capa; Yang, Runqing; Quan, Yujie; Zhang, Fanghao; Pokharel, Ganesh; Kautzsch, Linus; Wilson, Stephen D; Mu, Sai; et al (August 2025, Proceedings of the National Academy of Sciences)

   Kagome metals have emerged as a frontier in condensed matter physics due to their potential to host exotic quantum states. Among these, CsV₃Sb₅has attracted significant attention for the unusual coexistence of charge density wave (CDW) order and unconventional superconductivity, presenting an ideal system for exploring the emergent phenomena from the interplay of phonons, electronic fluctuations, and topological effects. The nature of CDW formation in CsV₃Sb₅is unconventional and has sparked considerable debate. In this study, we examine the origin of the CDW state via ab initio finite-temperature simulations of the lattice dynamics. Through a comparative study of CsV₃Sb₅and 2H-NbSe₂, we demonstrate that the experimental absence of phonon softening—a hallmark of conventional CDW transition—in CsV₃Sb₅along with the presence of a weakly first-order transition, can be attributed to quantum zero-point atomic motion. This zero-point motion smears the free energy landscape of CDW, effectively stabilizing the pristine structure even below the CDW transition temperature. We argue that this surprising behavior could cause coexistence of pristine and CDW structures across the transition and lead to a weak first-order transition. Our predicted lattice dynamical behavior is supported by coherent phonon spectroscopy in single-crystalline CsV₃Sb₅. Our results provide crucial insights into the formation mechanism of CDW materials that exhibit little to no phonon softening, including cuprates, and highlight the surprising role of quantum effects in emergent properties of relatively heavy-element materials like CsV₃Sb₅. 

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3. 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. 

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4. Robust superconductivity and the suppression of charge-density wave in the quasi-skutterudites ${\text{Ca}}_3({\text{Ir}}_{1-x}{\text{Rh}}_x{)}_4{\text{Sn}}_{13}$ single crystals at ambient pressure

   https://doi.org/10.1088/1361-648X/ad5485  

   Krenkel, Elizabeth H; Tanatar, Makariy A; Ghimire, Sunil; Joshi, Kamal R; Chen, Shuzhang; Petrovic, Cedomir; Prozorov, Ruslan (June 2024, Journal of Physics: Condensed Matter)

   Abstract Single crystals of the quasi-skutterudite compounds Ca₃(Ir_1-xRh_x)₄Sn₁₃(3–4–13) were synthesized by flux growth and characterized by x-ray diffraction, energy dispersive x-ray spectroscopy, magnetization, resistivity, and radio frequency magnetic susceptibility techniques. The coexistence and competition between the charge density wave (CDW) and superconductivity was studied by varying the Rh/Ir ratio. The superconducting transition temperature, $T_{\mathrm{c}}$, varies from 7 K in pure Ir (x = 0) to 8.3 K in pure Rh (x = 1). Temperature-dependent electrical resistivity reveals monotonic suppression of the CDW transition temperature,T_CDW(x). The CDW starts in pure Ir,x = 0, atT_CDW≈ 40 K and extrapolates roughly linearly to zero at $x_c\approx$0.53–0.58 under the superconducting dome. Magnetization and transport measurements show a significant influence of CDW on superconducting and normal states. Meissner expulsion is substantially reduced in the CDW region, indicating competition between the CDW and superconductivity. The low-temperature resistivity is higher in the CDW part of the phase diagram, consistent with the reduced density of states due to CDW gapping. Its temperature dependence just above $T_{\mathrm{c}}$shows signs of non-Fermi liquid behavior in a cone-like composition pattern. We conclude that the Ca₃(Ir_1-xRh_x)₄Sn₁₃alloy is a good candidate for a composition-driven quantum critical point at ambient pressure. 

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5. Competing itinerant and local spin interactions in kagome metal FeGe

   https://doi.org/10.1038/s41467-023-44190-2  

   Chen, Lebing; Teng, Xiaokun; Tan, Hengxin; Winn, Barry L; Granroth, Garrett E; Ye, Feng; Yu, D H; Mole, R A; Gao, Bin; Yan, Binghai; et al (December 2024, Nature Communications)

   Abstract The combination of a geometrically frustrated lattice, and similar energy scales between degrees of freedom endows two-dimensional Kagome metals with a rich array of quantum phases and renders them ideal for studying strong electron correlations and band topology. The Kagome metal, FeGe is a noted example of this, exhibiting A-type collinear antiferromagnetic (AFM) order atT_N ≈ 400 K, then establishes a charge density wave (CDW) phase coupled with AFM ordered moment belowT_CDW ≈ 110 K, and finally forms ac-axis double cone AFM structure aroundT_Canting ≈ 60 K. Here we use neutron scattering to demonstrate the presence of gapless incommensurate spin excitations associated with the double cone AFM structure of FeGe at temperatures well aboveT_CantingandT_CDWthat merge into gapped commensurate spin waves from the A-type AFM order. Commensurate spin waves follow the Bose factor and fit the Heisenberg Hamiltonian, while the incommensurate spin excitations, emerging belowT_Nwhere AFM order is commensurate, start to deviate from the Bose factor aroundT_CDW, and peaks atT_Canting. This is consistent with a critical scattering of a second order magnetic phase transition with decreasing temperature. By comparing these results with density functional theory calculations, we conclude that the incommensurate magnetic structure arises from the nested Fermi surfaces of itinerant electrons and the formation of a spin density wave order. 

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