The performance of carbon nanotube (CNT) cables, a contender for copper-wire replacement, is tied to its metallic and semi-conducting-like conductivity responses with temperature; the origin of the semi-conducting-like response however is an underappreciated incongruity in literature. With controlled aspect-ratio and doping-degree, over 61 unique cryogenic experiments including anisotropy and Hall measurements, CNT cable performance is explored at extreme temperatures (65 mK) and magnetic-fields (60 T). A semi-conducting-like conductivity response with temperature becomes temperature-independent approaching absolute-zero, uniquely demonstrating for the first time the necessity of heterogeneous fluctuation induced tunneling; complete de-doping leads to localized hopping, contrasting graphite’s pure metallic-like response. High-field magneto-resistance (including novel +22% longitudinal magneto-resistance near room-temperature) is analyzed with hopping and classical two-band models, both yielding a similar parameter useful for conductor development. Varying field-orientation angle uncovers significant two- and four-fold symmetries that are shown to be from Aharonov-Bohm-like corrections to the curvature-induced bandgap, a first for macroscale CNT fibers. Tight-binding calculations using Green's Function formalism model the largest, coherent transport to-date in commensurate CNT bundles in magnetic-field, revealing non-uniform transmission across bundle cross-sections with doping restoring uniformity; independent of doping, transport in bundle-junction-bundle systems are predominantly from CNTs adjacent to the other bundle—demonstrating that smaller bundles are more efficient for electronic transport. The final impact is predicting the ultimate conductivity of heterogeneous CNT cables using temperature and field-dependent transport, surpassing conductivity of traditional metals.

CdGeP 2 is a non-centrosymmetric uniaxial crystal whose birefringence is too low for phase-matching in its transparency range; however, it has been successfully applied in THz generation using near-IR laser pump sources. We present measurements of the linear thermal expansion of CdGeP 2 in the 12-820 K temperature range by X-ray diffraction using powdered samples. The results indicate strong anisotropy with negligible compression along the optical axis.

Two-dimensional materials that combine ferroelectric and ferromagnetic orders could exhibit a range of exotic physical properties and find use in applications such as energy-efficient spintronics. However, long-range ferroic orders in two dimensions are prone to destruction. For example, depolarization fields can destabilize ferroelectric order and thermal fluctuations can suppress magnetic order. Here we report multiferroic van der Waals heterostructures made from atomic layers of ferroelectric CuCrP2S6 and ferromagnetic Fe3GeTe2. We demonstrate reversible, non-volatile ferroelectric control of the magnetic anisotropy of two-dimensional Fe3GeTe2, and with this, probe the interferroic magnetoelectric coupling. Polarization switching of CuCrP2S6 changes the magnetic coercivity of a 3.8-nm-thick Fe3GeTe2 layer by approximately 14 mT at a testing temperature of 153 K, with a control efficiency around 65

The kagome RMn_6Sn_6 material family has attracted significant attention as high-temperature metallic magnets with a host of different magnetic orderings and anisotropy. Theoretical studies point to the rare-earth (R) as the determining factor for both the direction of magnetic anisotropy and the type of magnetic ordering in a given compound. This motivates studying high-entropy forms of RMn_6Sn_6 to examine how the interplay of several rare-earth elements leads to different magnetic states in a single crystal. Here, we present a rare-earth mix of Tb, Dy, Ho, Er, Tm, and Lu that produces phase transitions from a paramagnet to an easy-plane ferrimagnet (FiM) below T_C = 380 K, then to a FiM easy-axis state at T_SR1 = 207 K, to a canted FiM ground state below T_SR2 = 79 K. This behavior is consistent with previously reported high-entropy RMn_6Sn_6 compounds; however, uniquely, the rare-earth mix studied here exhibits a broad transition from easy-plane to easy-axis anisotropy from 270 K to 170 K, and reveals a nonmonotonic magnetoresistance. Using neutron scattering data, we found that both observations correlate with an incommensurate modulated contribution to the spin state due to competing rare-earth interactions. This magnetoresistive behavior and the correlated spin structures underscore the potential for rare-earth engineering of magnetism.

Air-sensitive 2D materials present a fundamental challenge for device integration. Encapsulation is often required to preserve intrinsic properties, yet conventional protection strategies often fail for thicker layers and complicate fabrication. Here, we demonstrate that electron-beam (e-beam) evaporated aluminum oxide (AlO_x) serves as both an effective encapsulation layer and a platform for direct device fabrication. Unlike transfer-based approaches, this scalable method is compatible with thicker flakes and full device or wafer coverage. It requires no stacking procedures and enables contacts without post-encapsulation etching. Using rare-earth tritellurides (RTe_3, R = La, Er), semimetallic WTe_2, and superconducting FeTe_xSe_1-x, we show that AlO_x suppresses oxidation and preserves intrinsic optical and electronic properties. We establish substrate-dependent optimization of encapsulation across a range of flake thicknesses, demonstrate that ultrathin AlO_x preserves WTe_2's plasmonic response and maintains superconducting performance in FeTe_xSe_1-x. Thus we overcome the longstanding tradeoff between encapsulation and straightforward device fabrication in fragile quantum materials.

Abstract Layered chalcogenides like CuInP2S6 are attracting attention as room-temperature ferroelectrics with enhanced polarization under compression and the ability to undergo pressure-assisted aging. Less has been done to reveal the impact of combined physical and chemical pressure. In this work, we integrate diamond anvil cell techniques with synchrotron-based infrared absorbance and Raman scattering spectroscopies, lattice dynamics calculations, and an analysis of the energy landscape to explore symmetry and space group progressions in the ABP2S6 family of materials (A = Cu, Ag; B = Cr, Sc, V, In). All four of the B-site substituted systems host a common set of pressure-driven structural phase transitions near 4 and 12 GPa that follow trends in metal ion size. Within the Cc space group, smaller cations stabilize new states at significantly lower pressures. For instance, while CuInP2S6 displays a monoclinic Cc → trigonal P31c symmetry restoration across PC,1 = 4.6 GPa, the Sc analog hosts the same progression at 2.6 GPa. We extend these structure–property relations to quaternary systems (many involving magnetic and/or ferroelectric functionality), further supporting the development of pressure-tunable electronic devices for environmental sensing, robotics, health monitoring, and biomachine interfaces.

Layered chalcogenides like CuInP2S6 are room temperature ferroelectrics. Modest compression even increases the electric polarization, raising questions about the origin of this unusual trend and other properties under pressure. In this work, we combine synchrotron-based infrared and Raman scattering spectroscopies, x-ray diffraction, and resistivity measurements with first-principles calculations of the lattice dynamics and energy landscape to unravel the influence of pressure on symmetry, polarization, and metallicity. We uncover a remarkable series of phase transitions across a series of polar space groups: monoclinic Cc → trigonal P31c (prismatic sulfur) → P31c (octahedral sulfur). True metallicity develops above 63 GPa, significantly higher than in related MPS3 materials (M = Mn, Co, Fe, Ni), offering a picture of competing states of matter that is different than previously supposed. Detailed examination of pressure trends within the Cc phase also reveals phonon lifetime changes and streaking of satellite x-ray peaks that correlate with the maximum polarization. We discuss these tendencies in terms of Cu+ ion migration, phase formation, and the overall energy landscape. Our findings place the high pressure behavior of CuInP2S6 on a firm foundation and pave the way for the development of structure-property relations in this family of complex chalcogenides.

CuInP2S6 (CIPS) is an emerging 2D room-temperature ferroelectric material that has recently attracted much attention. Its ferroelectricity is mainly affected by the motion of copper (Cu) ions in the lattice, so understanding the properties of Cu ions therein is imperative for potential applications. Here, we report the direct observation of electron beam induced Cu ion migration and aggregation dynamics in CIPS by using a combination of in situ transmission electron microscopy and simulations. Both electron beam irradiation experiments and density functional theory (DFT) calculations confirm the instability of Cu ions, with electron beam irradiation experiments capturing high mobility structural degradation dynamics at the atomic scale. The results further suggest that the lateral electric field resulting from the positive sample charging induced by the electron-matter interactions can influence the collective migration dynamics of Cu ions. Furthermore, it is found that these migrated Cu ions tend to aggregate at physical boundaries either set by the substrate or the sample itself and eventually form Cu nanoparticles. This work thus provides a comprehensive understanding of the behavior of Cu ions in CIPS ranging from the atomic scale to the mesoscopic scale, and will help guide the design of novel CIPS-based electronic devices.

Selectorless resistive random-access memory is essential for scaling high-density crossbar arrays, yet suppressing sneak path currents (SPCs) without external selector components remains a major challenge. In this work, we investigated a two-dimensional (2D) van der Waals (vdW) mixed cation crystal Cu0.5Ag0.5InP2S6 (CAIPS) as a switching layer and systematically compared its resistive switching with CuInP2S6 (CIPS) and AgInP2S6 (AIPS). The coexistence of Cu+ and Ag+ ions produces asymmetric out-of-plane diffusion barriers, as confirmed by first-principles density functional theory (DFT) calculations, leading to self-rectifying transport and the intrinsic suppression of leakage in arrays. CAIPS-based devices exhibit stable bipolar resistive switching, a high intrinsic nonlinearity factor (>10 under a V/3 read scheme), a large memory window (>9× at Vread = 0.1 V), and low variability (coefficient of variation down to 5.1%), surpassing the performance of both CuInP2S6 (CIPS) and AgInP2S6 (AIPS). These features, combined with low operational switching voltages, robust endurance, and built-in nonlinearity highlight CAIPS as a promising material for scalable selectorless memory arrays, with direct relevance to energy-efficient neuromorphic and edge-computing architectures.

We report a magnetic and neutron diffraction study on the ground state magnetism and field evolution of single crystal van der Waals multiferroic CuCrP2S6. The ordered moments align along the b axis in the A-type antiferromagnetic configuration with a spin-flop transition along the same direction. Field application along a introduces a smooth transition to a fully-polarized ferromagnetic state via in-plane spin rotation. These findings resolve the ambiguity of the ground state magnetization direction in CuCrP2S6 and uncover its field responses, providing a firm basis for future magnetoelectric study. A magnetoelastic coupling effect connecting the interlayer spacing and the magnetic order was further revealed, highlighting the out-of-plane strain as an effective control knob for tuning magnetism both in this system and in related van der Waals magnets.

Abstract We report a facile strategy to exfoliate and disperse transition metal dichalcogenides (WS2, MoS2, VS2) and MXene (Ti3C2Tx) directly within liquid crystals (LCs), yielding stable multifunctional nanocomposites. The multifunctional composite films exhibited unique properties, highlighted by the nanomaterial-mediated cholesteric-to-isotropic transition in the LC/Ti3C2Tx composite films at lower applied fields than the LC film alone. In addition, we demonstrated the preparation of free-standing LC/Ti3C2Tx composite films having both distinct LC and nanomaterial optical characteristics. Our solvent-free approach also enabled alignment-layer-free blade coating of birefringent composite films without postsynthesis processing. Significant polarization-dependent absorption was observed for LC/MoS2 films due to the anisotropy of the composite. The facile film processing and composite film properties are appealing for the fabrication of next-generation optoelectronics.

Single-crystal X-ray diffraction and nonlinear optical measurements, especially second- and third-harmonic generation (SHG/THG) are comprehensively investigated for the van der Waals layered material AgScP2S6 with a non-centrosymmetric P31c (159) space group. Linear optical constants are extracted using spectroscopic ellipsometry and applied in fitting the harmonic generation behavior. Polarization-resolved SHG and THG measurements exhibit pronounced anisotropy, with emission patterns well-described by theoretical models derived from the khi(2) and khi(3) tensor elements. The material demonstrates exceptionally high nonlinear susceptibilities, with khi(2) 10^(-8) m/V and khi(3) 10^(-17) m^2/V^2 which is a few orders of magnitude greater than comparable 2D materials reported in the literature. Temperature-dependent SHG and THG measurements from 300 K to 25 K reveal exponential decay in harmonic signal intensities, attributed to reduced carrier mobility, with no evidence of structural phase transitions, consistent with results from single crystal diffraction and heat capacity measurements. Polarization-resolved SHG and THG measurements also reveal distinct orientation and ellipticity trends, highlighting the anisotropic nonlinear tensor contributions and contrasting polarization selection rules in the material. These results establish AgScP2S6 as a high-performance, thermally stable, and highly anisotropic nonlinear candidate material suitable for compact photonic applications such as ultrafast optical modulators, polarization-sensitive detectors, and wavelength-tunable light sources.

Multiferroic tunnel junctions (MFTJs) represent a class of multistate, non-volatile spintronic devices, in which electron tunnelling can be manipulated by switching long-range lattice and spin orders. In contrast to conventional oxide-based MFTJs, MFTJs constructed from two-dimensional van der Waals (vdW) crystals promise minimal defect concentration in the constituents and at interfaces, which may allow for probing intrinsic tunnelling physics and the development of high-performance devices. Here we construct Fe3GeTe2/CuInP2S6/Fe3GeTe2 all-vdW MFTJs by assembling multilayer flakes of ferromagnetic Fe3GeTe2 electrodes and a ferroelectric CuInP2S6 spacer. These MFTJs exhibit four non-volatile resistance states featuring sizable tunnelling magnetoresistance of ∼102% and tunnelling electroresistance of ∼104%. To tune the properties of the vdW MFTJ, we make use of the flexibility in material choice offered by vdW heterostructure devices; we use Fe3GeTe2/Fe5GeTe2 asymmetric electrodes to boost the tunnelling electroresistance by 103%, we integrate In2Se3 as a ferroelectric with a smaller bandgap to enhance the ON-state current density by 104% to 104 A cm-2 and we use Fe3GaTe2 electrodes to demonstrate room temperature operation. Furthermore, when we combine the asymmetric ferromagnetic electrodes with the small-bandgap ferroelectric spacer to construct Fe3GeTe2/In2Se3/Fe5GeTe2 MFTJs, we simultaneously realized tunnelling electroresistance of 106% and an ON-state current density of 104 A cm-2, both two orders of magnitude higher than the highest values achieved with conventional oxide-based MFTJs. In the future, our all-vdW MFTJs with the tailorability of all functional layers may make it possible to investigate fundamental aspects of interlayer tunnelling and enable the design of functional magnetoelectric nanodevices.

CuCrP2S6 is a van der Waals multiferroic where the tunable Cu+ sublattice underpins its exceptional ferroelectric and electronic switching properties. Yet, the microscopic mechanism governing Cu+ ordering has remained elusive. Here, we combine single-crystal X-ray and neutron diffraction with pair distribution function analysis to uncover a temperature-driven evolution of Cu+ ordering, giving rise to an incommensurate quasi-antipolar phase between the paraelectric and antiferroelectric states. The modulation originates from correlated Cu+ occupancy redistribution coupled to breathing distortion of surrounding S3 triangles, establishing a symmetry-adapted lattice distortion mode. Diffuse scattering persisting over 35 K above the transition confirms that the structural instability follows an order-disorder mechanism. The spontaneous off-centering of Cu+ positions CuCrP2S6 as a model platform for correlated order-disorder phenomena in 2D layered ferroics, and provides design principles for next-generation memory and logic devices.

Linear thermal expansion in the 76-310 K range, and nanohardness and Young’s modulus at room temperature are measured for the newly developed quaternary nonlinear optical crystal Ba 2 Ga 8 GeS 16 with hexagonal symmetry, applicable in the mid-IR part of the spectrum. The results reveal quasi-isotropic behavior of all these properties.

Layered chalcogenides like CuInP2S6 are attracting attention as room-temperature ferroelectrics with enhanced polarization under compression and the ability to undergo pressure-assisted aging. Less has been done to reveal the impact of combined physical and chemical pressure. In this work, we integrate diamond anvil cell techniques with synchrotron-based infrared absorbance and Raman scattering spectroscopies, lattice dynamics calculations, and an analysis of the energy landscape to explore symmetry and space group progressions in the ABP2S6 family of materials (A = Cu, Ag; B = Cr, Sc, V, In). All four of the B-site substituted systems host a common set of pressure-driven structural phase transitions near 4 and 12 GPa that follow trends in metal ion size. Within the Cc space group, smaller cations stabilize new states at significantly lower pressures. For instance, while CuInP2S6 displays a monoclinic Cc -> trigonal P31c symmetry restoration across P C,1 = 4.6 GPa, the Sc analog hosts the same progression at 2.6 GPa. We extend these structure-property relations to quaternary systems (many involving magnetic and/or ferroelectric functionality), further supporting the development of pressure-tunable electronic devices for environmental sensing, robotics, health monitoring, and biomachine interfaces.

Chiral phonons are mirror-symmetric vibrations with nonzero angular momenta that correspond to twisting and rotational motions of multiple atoms. In chiral crystals, these include low-energy terahertz (THz)-range vibrations of the molecular segments involving dozens of atoms with energies sensitive to molecular chirality. Here, we present spectral signatures of chiral phonons in circularly polarized Raman optical activity (ROA) spectra from enantiomers of amino acid crystals. Along with complementary THz circular dichroism (TCD) measurements, our ROA data reveal several vibrational bands in enantiomers of valine, alanine, tyrosine, and proline between 30 and 150 cm-1 (∼1-4.5 THz) that exhibit opposite intensities. Density functional theory calculations confirm their assignment to twisting and shearing molecular motions. The simultaneous registration of chiral phonon modes by ROA and TCD demonstrates the necessity of these complementary techniques to identify complex mirror-asymmetric vibrational modes and offers new insights into their interactions with circularly polarized light.

CdGeP2 is a non-centrosymmetric uniaxial crystal whose birefringence is too low for phase-matching in its transparency range; however, it has been successfully applied in THz generation using near-IR laser pump sources. We present measurements of the linear thermal expansion of CdGeP2 in the 12-820 K temperature range by X-ray diffraction using powdered samples. The results indicate strong anisotropy with negligible compression along the optical axis.

Linear thermal expansion in the 76-310 K range, and nanohardness and Young's modulus at room temperature are measured for the newly developed quaternary nonlinear optical crystal Ba2Ga8GeS16 with hexagonal symmetry, applicable in the mid-IR part of the spectrum. The results reveal quasi-isotropic behavior of all these properties. Published by Optica Publishing Group under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.