Journal of Physics: Condensed Matter最新文献

Non-Hermitian systems reveal a wide range of fascinating physical phenomena beyond those found in Hermitian systems, drawing significant interest. Among these phenomena, the non-Hermitian skin effect (NHSE) is particularly notable. This effect enables the bulk states to collapse toward the boundaries and manifest as localized states. In this study, we report an experimental realization of a tunable higher-order NHSE in the Su-Schrieffer-Heeger (SSH) topolectrical circuits. Our experiments were conducted on specially designed one-dimensional and two-dimensional SSH tight-binding circuit networks. Two types of NHSEs with distinct angular localized modes (the diagonal distributed topological-skin mode and the isolated skin-skin angular mode) have been confirmed theoretically and experimentally. By controlling operational amplifiers and other electronic components, we could predict and tunable the skin effect modes in varying dimensions. The tunable NHSEs can be applied to guide waves into target regions, which can offer a number of valuable potential applications.

We report the topological phase transition (TPT) in compounds of relatively less explored Zintl family RbZn₄X₃(X = P, As) viafirst-principlescalculation. These intermetallic compounds have already been experimentally synthesized in aKCu₄S₃-typetetragonal structure (P4/mmm) and reported to have a topologically trivial semimetallic nature with a direct band gap. We thoroughly studied the electronic structure, stability of RbZn₄X₃(X = P, As) and demonstrated the TPTs in these materials with external applied pressure and epitaxial strain. The dynamical and mechanical stabilities of these compounds are verified through phonon dispersion and Born stability criteria at ambient and TPT pressure/strain. A topologically non-trivial phase in RbZn₄P₃(RbZn₄As₃) is observed at 45 GPa (38 GPa) of hydrostatic pressure and 10% (8%) of epitaxial strain. This non-trivial phase is identified by band inversion betweenZn-sandP/As-p_zorbitalsin the bulk band structure of these materials which is further confirmed using the surface density of states and Fermi arc contour in(001)-plane. The ℤ₂topological invariants (ν₀; ν₁ν₂ν₃) for these materials are calculated using the product of parities of all filled bands (Kane and Mele model) and the evolution of Wannier charge centers (Wilson loop method). The change in values of (ν₀; ν₁ν₂ν₃) from (0; 000) to (1; 000), at the particular values of pressure and strain, is another signature of the TPT in these materials.

Lead-free perovskite halide CsSnI₃has emerged as a promising material for optoelectronic applications due to its direct bandgap (1.3-1.4 eV), high charge carrier mobility, and strong visible-spectrum absorption. Among its polymorphs, the green phase, with a favorable bandgap of ∼1.24 eV, demonstrates enhanced structural stability and resistance to phase degradation under ambient conditions. In this study, we investigate the green polymorph of CsSnI₃and observe pyroelectric behavior, indicative of ferroelectric-like properties despite its globally centrosymmetric (Pa3-) cubic structure. Utilizing Piezo-force microscopy, dielectric measurements, impedance spectroscopy, and Raman spectroscopy, we identified local non-centrosymmetry influencing hysteresis and conduction properties. Impedance spectroscopy further reveals the interaction of grains and grain boundaries under a low AC electric field, both before and after light exposure and poling. A reduction in relaxation time with increasing temperature in poled samples is observed, while the combined effects of light exposure and poling result in an increased relaxation time. Our results indicate that local non-centrosymmetry plays a critical role in influencing hysteresis and conduction behavior. These findings highlight the importance of phase transitions and vibrational mode dynamics in optimizing the performance of CsSnI₃-based devices, paving the way for their broader application in advanced optoelectronic technologies.

Azulene molecule, consisting of a pair of five and seven-membered rings, represents a promising precursor for the on-surface synthesis of nonbenzenoid, nonalternant carbon nanostructures with exotic properties. However, controlling the selective C-C coupling between azulene molecules remains elusive, undermining the structural uniformity of the attained carbon nanostructures. Here, we report that the on-surface C-C coupling reactivity of different carbon atom sites in azulene relies on the spatial distribution of its frontier orbitals. By performing surface reactions of a tribrominated azulene molecule on Au(111), the probability of C-C coupling between carbon atoms at different sites of azulene has been revealed by scanning tunneling microscopy and non-contact atomic force microscopy. These findings are in accordance with the density functional theory-calculated energy barriers for the corresponding C-C coupling reaction steps.

Defects, that are irregularities in crystal lattices, create special sites or regions of particular geometry, electronic structure and activity that influence the physical and chemical behavior of the materials in a significant way. Here we examine published work on defects in two-dimensional (2D) oxide systems. The latter have attracted interest and significance in many areas of modern science and technology in recent years. The defects are classified according to their dimensionality: point defects, line defects and 2D specific topological defects are considered. Key features of the different defect types are illustrated and discussed with selected prototypical examples.

Low-dimensional frustrated magnetic square networks feature a variety of unconventional phases with novel emergent excitations. Often these excitations are intertwined and manifest into intriguing phenomena, an area that has remained largely unexplored in square-lattice systems, especially, double perovskites (A₂BB'O₆). In this study, we explore these interactions between the fundamental excitations such as phonons and magnons in square-lattice Sr₂CuTeO₆, Sr₂CuWO₆, and Ba₂CuWO₆isostructural double perovskites that exhibit both short-ranged (T_max) as well as long-ranged Néel antiferromagnetic (T_N) transitions. Our Raman measurements at variable temperatures reveal an intriguing broad peak (identified as 2-magnon (2M)) surviving beyondT_maxfor W-based compositions contrary to the Te-based system, suggesting a key role of diamagnetic B'-site cation on their magnetism. The thermal response of 2M intriguingly shows signatures of correlation with phonons and control over their anharmonicity, depicting magnon-phonon interaction. Further, a few phonons exhibit anomalies across the magnetic transitions implying the presence of spin-phonon coupling. In particular, the phonon modes at ∼194 cm^-1of Sr₂CuTeO₆and ∼168 cm^-1of Sr₂CuWO₆, that show a strong correlation with the 2M, exhibit the strongest spin-phonon coupling suggesting their roles in mediating magnon-phonon interactions in these systems.

The depletion of fossil fuels and the environmental impact of chemical batteries, coupled with the rapid proliferation of portable electronic devices and the Internet of Things, have created an urgent demand for high-performance, lightweight, and sustainable energy systems. Flexible triboelectric nanogenerators (TENGs) have emerged as a promising technology for powering self-sufficient devices, offering advantages such as simple structure, flexibility, low cost, and environmental adaptability. In particular, electrospun nanofiber-based TENGs stand out due to their enhanced surface area, superior charge collection capabilities, and improved mechanical durability. This review presents a comprehensive overview of recent advancements in electrospun nanofiber-based TENGs, focusing on material selection, structural design, fabrication techniques, and their integration into applications ranging from self-powered sensors to wearable electronics. Furthermore, the review discusses the challenges and future directions in optimizing the performance and scalability of TENGs to meet the growing demands of next-generation, energy-efficient technologies. It is hoped that this review will help researchers to gain a deeper understanding of this field and promote its development to a new stage.

In recent years, the rapid development of two-dimensional (2D) magnetic materials has revolutionized the field of spintronics, driven by their unique ability to combine magnetism and electronic functionality at the atomic scale. Here, we investigate the monolayer CuCr₂Se₂X₂(X = Cl, Br, I), which exhibit robust ferromagnetic (FM) behavior and half-metallicity with 100% spin polarization. The strong FM coupling, mediated by superexchange interactions, is rooted in the unique electronic structure of the Crd-orbitals. Our findings reveal high Curie temperatures (TC) exceeding room temperature, with the Br variant achieving a remarkable 586 K. These exceptional properties, including the ability to modulate exchange interactions through strain engineering, highlight CuCr₂Se₂X₂as a versatile platform for flexible, high-performance spintronic devices, paving the way for advancements in next-generation electronic applications.

1T-VSe₂is a narrow band transition metal chalcogenide that shows charge density wave (CDW) state below T_CDW= 110 K. Here, we have explored the relevance of Kohler's rule and the thermal transport properties of VSe₂across the CDW state in the presence of magnetic field. The magnetoresistance (MR) follows Kohler's rule above T_CDW, while an extended Kohler's rule is employed below T_CDW. Interestingly, we observed an anomaly in MR around T ∼ 20 K, below which MR value decreases on lowering temperature. This anomaly is also reflected in the slope (κ) of Kohler's plots and the relative change in the thermal excitation induced carrier density (n_T). Despite a strong magnetic field of 14 Tesla, the T_CDWremains largely unaffected in both electrical resistivity (ρ(T)) and Seebeck coefficient (S), although the application of magnetic field does enhance the peak intensity of S around T ∼ 60 K. The crossover of S curves measured at different magnetic fields at T ∼ 20 K suggests the existence of a novel feature within the CDW state of VSe₂i.e., the presence of a locally exact isosbestic point.

Positron annihilation spectroscopy provides a sensitive toolset for defect characterization. In beam based studies of single-layer targets, the form of implantation profiles is well established, depending on the kinetic energy and angle of incident positrons relative to the target surface and the density and average atomic number of the target. For multilayer systems, the difference in density and across the layers makes derivation of an analytical form difficult. To date, the determination of positron stopping profiles in multilayer targets has primarily involved Monte Carlo simulations. We present here an alternative approach that estimates the energy distributiondN/dEof those positrons transmitted past each layer boundary, by fitting the remaining tail of the stopping profile after each layer with a basis set comprised of calculated stopping profiles in the same material they are transmitted through. The stopping profile in the next layer is then found by summing a series of stopping profiles in the new medium in proportion to the determined distributiondN/dE. The results of our model are compared with simulation results in a system of alternating layers of Al and Au and find reasonable agreement in the predicted profile and excellent agreement in the predicted mean implantation depth. Lastly, we derived a simple formula-based approach for the calculation of the mean implantation depth in two-layer systems that provides results in excellent agreement with the full model.