17 Search Results

In this study, we perform ultrafast time-resolved reflectivity measurements to track the evolution of charge density wave (CDW) correlations in Sn-doped Kagome superconductor CsV_3⁢Sb_5−𝑥⁢Sn_𝑥. By extracting the coherent phonon spectrum, we evidence robust signatures of CDW correlations at temperature and doping ranges far beyond the phase boundary of long-range CDW order. Remarkably, we show that short-range CDW correlations survive up to room temperature in 𝑥 = 0.32 Sn-doped CsV₃⁢Sb₅, supported by synchrotron x-ray diffraction measurements. We point out that the introduction of quenched disorder by Sn doping can pin the CDW and form static short-range CDW, which can explain themore » observed persistent CDW signatures. Our results thus corroborate the ubiquity and robustness of CDW correlations in Sn-doped CsV_3⁢Sb₅ and provide new insights on the role of disorders on the CDW correlations in AV₃⁢Sb₅ family.« less

Here, we report on the structural characterization and physical properties of Eu₂⁢InTe₅, a distorted square-net motif antiferromagnetic semiconductor. Single crystal x-ray diffraction measurements reveal a distortion of the Te square-net layers such that an orthorhombic supercell is necessary to accurately describe the structure. Magnetization, resistivity, and specific heat measurements confirm antiferromagnetic ordering at 𝑇_𝑁 = 7.3K. Anisotropy in magnetization data suggests the magnetic moments are oriented parallel to the 𝑐 axis. We observe an unconventional transverse magnetoresistance and Hall resistivity in the paramagnetic state (𝑇 ≤ 80K), indicating strong coupling between localized Eu²⁺ magnetic moments and conduction electrons. Resistivity andmore » Hall measurements indicate the material is a heavily doped semiconductor, with impurity states related to disorder. Our findings highlight a relatively unexplored Eu-based antiferromagnetic semiconductor with unconventional magnetotransport behavior.« less

The intricate competition between coexisting charge density waves (CDWs) can lead to rich phenomena, offering unique opportunities for phase manipulation through electromagnetic stimuli. Here, leveraging time-resolved x-ray diffraction, we demonstrate ultrafast control of a CDW in EuTe₄ upon optical excitation. At low excitation intensities, the amplitude of one of the coexisting CDW orders increases at the expense of the competing CDW, whereas at high intensities, it exhibits a nonmonotonic temporal evolution characterized by both enhancement and reduction. This transient bidirectional controllability, tunable by adjusting photoexcitation intensity, arises from the interplay between optical quenching and phase-competition-induced enhancement. Our findings, supported bymore » phenomenological time-dependent Ginzburg-Landau theory simulations, not only clarify the relationship between the two CDWs in EuTe₄, but also highlight the versatility of optical control over order parameters enabled by phase competition.« less

Frustration of long-range order via lattice geometry amplifies fluctuations and generates ground states that are highly sensitive to perturbations. Traditionally, geometric frustration is used to engineer unconventional magnetic states; however, the charge degree of freedom and bond order can be similarly frustrated. Finding materials that host both frustrated magnetic and bond networks holds promise for engineering structural and magnetic states with the potential of coupling to one another via either magnetic or strain fields. Here we identify an unusual instance of this coexistence in the triangular lattice antiferromagnets LnCd₃P₃ (Ln = lanthanides). These compounds feature two-dimensional planes of unique trigonalmore » planar CdP₃ units with an underlying bond instability that is frustrated via emergent kagome ice correlations. This bond instability is interleaved in between layers of frustrated magnetic moments. Furthermore, our results establish LnCd₃P₃ as a rare materials class in which frustrated magnetism is embedded within a dopable semiconductor with a frustrated bond order instability.« less

The search for thin film electro-optic materials that can retain superior performance under cryogenic conditions has become critical for quantum computing. Barium titanate thin films show large linear electro-optic coefficients in the tetragonal phase at room temperature, which is severely degraded down to ≈200 pm V⁻¹ in the rhombohedral phase at cryogenic temperatures. There is immense interest in manipulating these phase transformations and retaining superior electro-optic properties down to liquid helium temperature. Utilizing the thermodynamic theory of optical properties, a large low-temperature electro-optic response is designed by engineering the energetic competition between different ferroelectric phases, leading to a low-symmetry monoclinicmore » phase with a massive electro-optic response. The existence of this phase is demonstrated in a strain-tuned BaTiO₃ thin film that exhibits a linear electro-optic coefficient of 2516 ± 100 pm V⁻¹ at 5 K, which is an order of magnitude higher than the best reported performance thus far. Importantly, the electro-optic coefficient increases by 100 × during cooling, unlike the conventional films, where it degrades. Further, at the lowest temperature, significant higher order electro-optic responses also emerge. These results represent a new framework for designing materials with property enhancements by stabilizing highly tunable metastable phases with strain.« less

This article reports how two different charge density waves with slightly different wavevectors can exist in the same crystal and create moiré superstructure. Advances in heterostructure fabrication have opened new frontiers in moiré physics. Here we extend moiré engineering from artificially assembled thin flakes with mismatched lattice parameters to materials that host incommensurate orders, presenting a long-period moiré superlattice in a layered charge-density-wave compound, EuTe₄. Using high-momentum-resolution X-ray diffraction, we found two coexisting incommensurate charge density waves with slightly mismatched in-plane wavevectors. The interaction between these two charge density waves leads to joint commensuration with the lattice and a moirémore » superstructure with a period of ~13.6 nm, offering key insights into the unique properties of EuTe4, such as the temperature-invariant incommensurate wavevectors and unconventional in-gap states. Owing to interlayer phase shifts, the moiré superstructure exhibits a clear thermal hysteresis, accounting for the large hysteresis in electrical resistivity and numerous metastable states. Our findings open new directions for moiré engineering based on incommensurate lattices and highlight the important role of interlayer ordering in stacked structures.« less

The interplay between superconductivity and charge correlations in the kagome metal CsV_3⁢Sb₅ can be tuned by external perturbations such as doping or pressure. Here we present a study of charge correlations and superconductivity upon hole doping via Ti substitution on the V kagome sites in CsV_3−𝑥⁢Ti_𝑥⁢Sb₅ via synchrotron x-ray diffraction and scanning superconducting quantum interference device measurements. While the superconducting phase, as viewed via the vortex structure, remains conventional and unchanged across the phase diagram, the nature of charge correlations evolves as a function of hole doping from the first superconducting dome into the second superconducting dome. For Ti dopingmore » in the first superconducting dome, competing 2×2×2 and 2×2×4 supercells form within the charge density wave state and are suppressed rapidly with carrier substitution. In the second superconducting dome, no charge correlations are detected. Here, comparing these results to those observed for CsV₃⁢Sb_5−𝑥⁢Sn_𝑥 suggests important differences between hole doping via chemical substitution on the V and Sb sites, particularly in the disorder potential associated with each dopant.« less

Here we present the discovery and characterization of a series of antimonides 𝐿⁢𝑛₂⁢Ti_9⁢Sb₁₁ (Ln: La–Nd) that exhibit well-isolated, 𝑛 = 2 rare-earth spin ladders. We discuss the structure of these compounds, with a particular focus on the magnetic Ln spin ladders. Nd₂⁢Ti₉⁢Sb₁₁ and Ce₂⁢Ti₉⁢Sb₁₁ exhibit antiferromagnetic interactions and a well-defined doublet ground state, whereas Pr₂⁡Ti_9⁢Sb₁₁ exhibits a weakly magnetic singlet ground state. Nd₂⁢Ti₉⁢Sb₁₁ is a poor metal with an electrical resistivity of 0.1m⁢Ω cm at 300 K and weak temperature dependence. The thermal conductivity along the ladder exhibits significant field dependence even at 40 K, considerably higher than the magnetic orderingmore » temperature of 1.1 K. Compared to compounds with transition metal spin ladders, the rare-earth elements impart much lower energy scales, making these compounds highly tunable with external stimuli like magnetic fields. In conclusion, the diverse magnetism of the rare-earth ions and Ruderman-Kittel-Kasuya-Yosida interactions further contribute to the potential for a wide array of rich magnetic ground states, positioning these materials as a rare example of an inorganic square spin-ladder platform.« less

Here we resolve the real-space nature of the high-temperature, short-range charge correlations in the kagome metal ScV₆Sn₆. Diffuse scattering appears along a frustrated wave vector q_H = ($$\frac{1}{3}, \frac{1}{3}, \frac{1}{2}$$) at temperatures far exceeding the charge order T_CO = 92 K, preempting long-range charge order with wave vectors along q$$_{\bar{K}}$$ = ($$\frac{1}{3}, \frac{1}{3}, \frac{1}{3}$$). Using a combination of real space and reciprocal space analysis, we resolve the nature of the interactions between the primary out-of-plane Sc-Sn chain instability and the secondary strain-mediated distortion of the in-plane V kagome network. Finally, a minimal model of the diffuse scattering data reveals amore » high-temperature, short-ranged "zig-zag" phase of in-plane correlations that maps to a frustrated triangular lattice Ising model with antiferromagnetic interactions and provides a real-space understanding of the origin frustrated charge order in this material.« less