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Rare-earth titanate pyrochlores have attracted significant attention for their unique magnetic frustration; however, research on the origin of low-temperature dielectric dispersion and the relationship between dielectric properties and structure lags far behind. Here, by systematically investigating the dielectric properties of representative rare-earth titanates R2Ti2O7 (R = La, Nd, Sm, Er, Yb, and Lu), we demonstrate that R2Ti2O7 with a cubic pyrochlore structure exhibits low-temperature dielectric dispersion behavior, while the other compounds with a monoclinic perovskite-like layered structure possess no dispersion behavior but excellent temperature-stable dielectric property. The dielectric dispersion in cubic pyrochlores arises from the structural distortion. Furthermore, the existence of structural distortion is affirmed by the anomalous phonon softening of A1g Raman mode around the dielectric dispersion temperature, and the origin of the structural distortion is attributed to anharmonic phonon–phonon interactions induced by intrinsic vacant oxygen at Wyckoff 8a sites. In addition, with increasing ionic radius from R = Lu to Sm, the increased lattice parameter leads to varied bond length and bond angle of Ti-O(1)-Ti, which strengthens the local lattice distortion of TiO(1)6 octahedra and thus enhances diffusion degree of dielectric dispersion. On the other hand, the absence of intrinsic vacant oxygen site hardly gives rise to the local structural distortion and thus no dielectric dispersion in monoclinic R2Ti2O7. Our work not only clarifies the mechanism of dielectric dispersion but also gives a comprehensive perspective on the structure–property relationship of rare-earth titanates R2Ti2O7, and thus lays a solid foundation for further work on related materials. [ABSTRACT FROM AUTHOR]

The layered van der Waals material Fe5GeTe2 (F5GT) has emerged as a captivating candidate for room-temperature spintronics, boasting inherent ferromagnetic behavior. Nevertheless, the intricate magnetic characteristics of F5GT beckon a deeper exploration. Here, we present the synthesis of (Fe1−xCox)5GeTe2 (x = 0–0.47) single crystals and a comprehensive investigation of cobalt (Co) doping effects on the magnetic and transport properties. The Curie temperature (TC) enhancement of F5GT is revealed in magnetic measurements, surpassing room temperature and reaching 325 K at x = 0.24. Furthermore, Co doping induces an adjustment of the easy magnetization direction of F5GT toward the in-plane orientation, affording a significant amplification of magnetic anisotropy. Notably, for x = 0.47, an antiferromagnetic ground state emerges with a transition temperature (TN) of 340 K, accompanied by field-induced spin-flop transitions. In addition, our electrical transport measurements yield complementary insights into the influence of Co doping on F5GT, unraveling the understanding of the strong spin-charge coupling within the materials. First-principles calculations demonstrate that Co doping plays an important role in the influence of interlayer stacking and magnetic ground state. This investigation unlocks the enormous potential of Co-doped F5GT for high-performance room-temperature spintronics applications. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals ferroelectrics with in-plane polarization are less vulnerable to the depolarization field effect, making them practically more favorable in device applications. Herein, symmetric planar memristor based on two-dimensional van der Waals WO2Cl2 was fabricated and electrically characterized, showing significant memory effect with a current ON/OFF ratio up to 104 and stable switching cycles. Both short-term plasticity and long-term potentiation were observed in synaptic simulations by applying consecutive positive and negative pulses, respectively, which demonstrates the potential capability of this WO2Cl2 memristor in neuro-morphic computing as an artificial synapse. [ABSTRACT FROM AUTHOR]

Two-dimensional van der Waals ferroelectrics with in-plane polarization are less vulnerable to the depolarization field effect, making them practically more favorable in device applications. Herein, symmetric planar memristor based on two-dimensional van der Waals WO2Cl2 was fabricated and electrically characterized, showing significant memory effect with a current ON/OFF ratio up to 104 and stable switching cycles. Both short-term plasticity and long-term potentiation were observed in synaptic simulations by applying consecutive positive and negative pulses, respectively, which demonstrates the potential capability of this WO2Cl2 memristor in neuro-morphic computing as an artificial synapse. [ABSTRACT FROM AUTHOR]

While the unique geometrical frustration of pyrochlore Yb2Ti2O7 has attracted attention, the dielectric and other properties of this pyrochlore beyond frustrated magnetism are not well understood. Here, we report on the fascinating low-temperature dielectric relaxation of Yb2-xBaxTi2O7-δ (x = 0–0.20) and demonstrate that this phenomenon is related to structural distortion. A-site Ba substitution, which increases the density of point defects and introduces a different atomic radius, enhances the chemical disorder and structural distortion. As a result, the increases in oxygen vacancies and nonmagnetic Ba2+ and Yb2+ ions dilute the ferromagnetic Yb3+–Yb3+ interactions, as indicated by the decrease in effective magnetic moment. On the other hand, the distorted octahedra facilitate the hopping of Yb ions, and the random distribution of Ba2+ ions at the Yb3+ sites gives rise to additional random fields, leading to significantly increased dielectric relaxation. The room-temperature dielectric constant is improved to ∼170, twice that of pristine Yb2Ti2O7. This work provides a comprehensive view of the structural, magnetic, and dielectric properties of Yb2Ti2O7 and lays the foundation for additional research into pyrochlore compounds. [ABSTRACT FROM AUTHOR]

The layered van der Waals material Fe5GeTe2 (F5GT) has emerged as a captivating candidate for room-temperature spintronics, boasting inherent ferromagnetic behavior. Nevertheless, the intricate magnetic characteristics of F5GT beckon a deeper exploration. Here, we present the synthesis of (Fe1−xCox)5GeTe2 (x = 0–0.47) single crystals and a comprehensive investigation of cobalt (Co) doping effects on the magnetic and transport properties. The Curie temperature (TC) enhancement of F5GT is revealed in magnetic measurements, surpassing room temperature and reaching 325 K at x = 0.24. Furthermore, Co doping induces an adjustment of the easy magnetization direction of F5GT toward the in-plane orientation, affording a significant amplification of magnetic anisotropy. Notably, for x = 0.47, an antiferromagnetic ground state emerges with a transition temperature (TN) of 340 K, accompanied by field-induced spin-flop transitions. In addition, our electrical transport measurements yield complementary insights into the influence of Co doping on F5GT, unraveling the understanding of the strong spin-charge coupling within the materials. First-principles calculations demonstrate that Co doping plays an important role in the influence of interlayer stacking and magnetic ground state. This investigation unlocks the enormous potential of Co-doped F5GT for high-performance room-temperature spintronics applications. [ABSTRACT FROM AUTHOR]

A convenient approach to modulate the fingerprint textures of methyl red (MR) doped cholesteric liquid crystals by asymmetric photoalignment in the green-light waveband is presented, resulting in the generation of voltage-controllable helical superstructures. The interaction between the MR molecules and the incident light polarization determines the initial twisted planar geometry, providing a multivariant control over the stripe directions of fingerprint textures by applying a proper electric field. The key factors for precise manipulation of fingerprint stripes in a predictable and rewritable manner are analyzed theoretically and investigated experimentally, which involves the alignment asymmetry, the ratio of cell gap to natural pitch length, and the chirality of chiral dopant. Dynamic periodic fingerprint textures in shapes of dashed curve and dashed line are further demonstrated by utilizing a facile one-step polarization holography process using two beams with orthogonal circular and orthogonal linear polarizations, respectively. It is believed that the practical approach described in this study would enrich the research contents of self-assembled hierarchical superstructures using soft liquid crystal building blocks. [ABSTRACT FROM AUTHOR]

We propose a scheme for subwavelength electromagnetic diode by employing cascading nonlinear meta-atoms. One-way response is conceptually demonstrated on a microwave transmission line comprising of three metallic ring resonators acting as meta-atoms and a varactor as the nonlinear medium inclusion. Experiments show that our implementation can operate simultaneously as forward diode and backward diode at different frequencies. A transmission contrast of up to 14.7 dB was achieved between forward and backward transmission. Subwavelength size of our diode should be useful for miniaturization of integrated optical nanocircuits. [ABSTRACT FROM AUTHOR]

This study theoretically and experimentally investigates the transmission properties of a metamaterial slab comprised of two layers of metallic fish-scale structure arrays and a sandwiched dielectric layer. Calculations show that the asymmetric transmission can be tuned by varying the slab thickness, due to near-field interlayer coupling. The spatial evolution of the electric field indicates that the twist structure functions as a perfect polarization transformer at certain frequencies. Measured transmission spectra are in good agreement with calculated results when material dissipation is considered. [ABSTRACT FROM AUTHOR]

Synchrotron-based in situ photoelectron spectroscopy investigations demonstrate effective surface transfer p-type doping of epitaxial graphene (EG) thermally grown on 4H–SiC(0001) via the deposition of MoO3 thin film on top. The large work function difference between EG and MoO3 facilitates electron transfer from EG to the MoO3 thin film. This leads to hole accumulation in the EG layer with an areal hole density of about 1.0×1013 cm-2, and places the Fermi level 0.38 eV below the graphene Dirac point. [ABSTRACT FROM AUTHOR]

The molecular orientation of copper(II) phthalocyanine (CuPc) thin films on monolayer C60 on Ag(111) was studied by in situ near-edge x-ray absorption fine structure measurements and low-temperature scanning tunneling microscopy. It is found that in densely packed thin films, CuPc molecules adopt a standing-up configuration with the molecular π-plane tilting slightly from the surface normal on monolayer C60. [ABSTRACT FROM AUTHOR]

In situ synchrotron-based near-edge x-ray absorption fine structure measurements and photoemission spectroscopy have been used to investigate the effect of molecular orientation on the interfacial dipole and the energy level alignment at the interfaces of organic heterojunctions comprising copper-hexadecafluoro-phthalocyanine (F16CuPc) on both standing-up and lying-down copper(II) phthalocyanine (CuPc) thin films. It is found that F16CuPc thin films adopt the same molecular orientation of the underlying CuPc thin films. An interfacial dipole of 0.45 eV forms at the interface of lying-down F16CuPc/CuPc on highly ordered pyrolytic graphite. In contrast, a much larger interfacial dipole of 1.35 eV appears at the interface of standing-up F16CuPc/CuPc on octane-1-thiol terminated Au(111). [ABSTRACT FROM AUTHOR]