Journal of Physics: Condensed Matter最新文献

Temperature dependent magnetic, electrical transport and thermal properties of polycrystalline orthorhombic CeFe₂Al₈intermetallic compound have been studied along with its isostructural La counterpart, LaFe₂Al₈. For the cerium compound, low fielddcmagnetization exhibits an antiferromagnetic like ordering (T_N) ∼ 4 K. The main feature of the magnetic susceptibility plot is a broad hump spanning a large temperature range, indicating mixed valence of Ce in the compound, in good agreement with reported literature. However, contrary to the reported observations we find that the mixed valence state is very robust and was evident even up to very high magnetic fields (> 2 T). Further, in this work we report 3d core level photoemission spectra of cerium in CeFe₂Al₈, to understand the valence state of cerium ions in this system. Additionally, from resistivity measurements it is found that, CeFe₂Al₈is metallic with no indication of any anomaly, till the lowest temperature of measurement. Specific heat measurements show very low value of heat capacity and electronic contribution. The isostructural La analogue, LaFe₂Al₈compound shows broadness in susceptibility with maxima around 44 K which may be attributed to ordering of Fe moments. The comparison of Ce and La compounds brings out the role of Fe magnetic moments which may be responsible for competing with cerium moments and resulting in the dilution of long-range magnetic order, also contributing to magnetic frustration in CeFe₂Al₈.

Herein, we report a systematic investigation of the effect of Titanium doping on the structural, elastic, mechanical, thermodynamic, and thermoelectric (TE) dynamics of Mg₂Si Compounds using first-principle investigation. The present study has been carried out using the full potential linearized augmented plane wave method as implemented inWien2kcode undermBJexchange potentials. The investigations revealed that Mg_2-xTi_xSi compounds have structural stability with cubic phase (Fm-3msymmetry) and possess degenerate semiconducting nature. The analysis of elastic constants revealed mechanical stability of the investigated compounds following Born criteria. Thermodynamic investigations have been carried out in the temperature range of 100-1500 K at zero pressure and the quantities like heat capacity, Debye temperature, Grüneisen constant, and thermal expansion coefficient have been critically analyzed. Lastly, the TE performance of Mg_2-xTi_xSi compounds has been predicted by estimating the thermopower (S²σ) and TE figure of merit (zT) in the temperature range of 300-1500 K. The predicted value ofzT_maxfor Mg_2-xTi_xSi compound is 0.67 at 800 K forx= 0.25 titanium content, suggesting materials promising application for TE energy harvesting and mechanical devices.

One of the most important phenomena in magnetism is the exchange interaction between magnetic centres. In this topical review, we focus on the exchange mechanism in transition-metal compounds and establish kinetic-energy-driven two-sublattice double-exchange as a general mechanism of exchange, in addition to well-known mechanisms like superexchange and double exchange. This mechanism, which was first proposed (Sarmaet al2000Phys. Rev. Lett.852549), in the context of Sr₂FeMoO₆, a double-perovskite compound, later found to describe a large number of 3d and 4d or 5d transition metal-based double perovskites. The magnetism in multi-sublattice magnetic systems like double-double and quadrupolar perovskites involving 3d and 4d or 5d transition-metal ions have also been found to be governed by this as a primary mechanism of exchange. For example, the numerical solution of a two-sublatice double exchange with additional superexchange couplings for the FeRe-based double double and quadrupolar perovskites are found to reproduce the experimentally observed magnetic ground state as well as the high transition temperature of above 500 K. The applicability of this general mechanism extends beyond the perovskite crystal structures, and oxides, as demonstrated for the pyrochlore oxide, Tl₂Mn₂O₇and the square-net chalcogenides KMnX₂(X = S, Se, Te). The counter-intuitive doping dependence and pressure effect of magnetic transition temperature in Tl₂Mn₂O₇is explained, while KMnX₂(X = S, Se, Te) compounds are established as half-metallic Chern metals guided by two sublattice double exchange. While the kinetic energy-driven two-site double-exchange mechanism was originally proposed to explain ferromagnetism, a filling-dependent transition can lead to a rare situation of the antiferromagnetic metallic ground state, as found in La-doped Sr₂FeMoO₆, and proposed for computer predicted double perovskites Sr(Ca)₂FeRhO₆. This opens up a vast canvas to explore.

We study a hybrid system of a plasmonic cavity coupled to a pair of different molecular vibration modes with the strong optomechanical-like interactions. Here, this plasmonic cavity is considered as a quantum data bus and then assist several applications. For instance, it can first establish a bimolecular interface to ensure the reciprocal or non-reciprocal information transmission, and then engineer both molecules into the steady-state quantum entanglement of the continuous variable through the dissipative method. In contrast to the traditional optomechanical system, this hybrid system can provide the stronger optomechanical-like interactions and more convenient controls to the molecular quantum units. This investigation is believed to be able to further expand the practical application range of quantum technology.

During the line width reduction, electron scattering caused by various defects in metal interconnects increases dramatically, which causes leakage or short circuit problems in the device, reducing device performance and reliability. Point defects are one of the important factors. Here, using density functional theory and non-equilibrium Green's function methods, we systematically study the effects of point defects on the transport properties of metals Al, Cu, Ag, Ir, Rh, and Ru, namely vacancy defects and interstitial doping of C atom. The results show that the conductivity of all systems decreases compared to perfect systems, because defects cause unnecessary electron scattering. Since the orbital hybridization of the C atom with the Al, Cu and Ag atoms is stronger than that metals Ir, Rh and Ru, the doping of C atom significantly reduces the conductivity of metals Al, Cu and Ag compared to vacancy defects. In contrast, vacancy defects have a greater impact than doping on the transport properties of metals Ir, Rh and Ru, which is mainly attributed to the larger charge transfer of the host atoms around the vacancies caused by lattice distortion. In addition, metal Rh exhibits excellent conductivity in all systems. Therefore, in order to optimize the transport properties of interconnect metals, our work points out that the doping of impurity atoms should be avoided for metals Al, Cu and Ag, while the presence of vacancy defects should be avoided for metals Ir, Rh and Ru, and Rh may be an excellent candidate material for future metal interconnects.

We consider a classical Heisenberg model on the kagomé and the square kagomé lattice, where at zero magnetic field non-coplanar cuboctahedral ground states with twelve sublattices exist if suitable exchange couplings are introduced between the other neighbors. Such 'cuboc ground states' are remarkable because they allow for chiral ordering. For these models, we discuss the magnetization process in an applied magnetic fieldHby both numerical and analytical methods. We find some universal properties that are present in all models. The magnetization curveM(H) usually contains only non-linear components and there is at least one magnetic field driven phase transition. Details of theM(H) curve such as the number and characteristics (continuous or discontinuous) of the phase transitions depend on the lattice and the details of the exchange between the further neighbors. Typical features of these magnetization processes can already be derived for a paradigmatic 12-spin model that we define in this work.

Using ground state density functional theory (DFT) and implementing an occupation-constrained DFT (occ-DFT) for self-consistent excited state calculations, we decipher the electronic structure of the Mn dopant and other 3ddefects in GaN across the band gap. Our analysis, validated with broad agreement with defect levels (ground-state calculations) and photoluminescence data (excited-state calculations), mandates reinterpretation and reassignment of 3ddefect data in GaN. The Mn_Gadefect is determined to span stable charge states from (1-) inn-type GaN through (2+) inp-type GaN. The Mn(2+) is predicted to be ad²ground state spin triplet defect with a singlet excited state, isoelectronic with the defect associated with the 1.19 eV photoluminescence inn-type GaN. The combined analysis of defect levels and excited states invites reassessment of alld²-capable dopants in GaN. We demonstrate that the 1.19 eV defect, a candidate defect for optically controlled quantum applications, cannot be the Cr(1+) assumed in literature and instead must be the V(0). The combined ground-state/excited-state DFT analysis is shown to be able to chemically fingerprint defects.

Vertical stacks of two-dimensional (2D) materials with interlayer van der Waals (vdW) force have provided a versatile approach for creating hybrid materials and modulating various properties. In this work, the structural and electronic properties of trilayerγ-graphyne, involving different stacking patterns, have been investigated through first-principles approaches. The result indicates that a metal-to-semiconducting transition can be triggered simply by switching the stacking order of trilayerγ-graphyne. More interestingly, in addition to typical vdW homostructures, new 2D carbon allotropes with novel carbon networks can be achieved on the basis of trilayerγ-graphyne, arising from the absence of intralayer acetylene linkages during the structural relaxation. One of the new 2D carbon allotropes possesses an intrinsic semiconducting nature with a wide bandgap of 1.827 eV, coupled with superior structural stability beyond single-layerγ-graphyne. Moreover, the biaxial strain effect on the new 2D carbon allotrope, as well as the trilayer vdW stacks, has also been revealed in this work. Correspondingly, the in-plane tensile strain is demonstrated to further enlarge the electronic bandgaps in these carbon sheets. Therefore, the results of this work imply the great potential of few-layer graphyne in future carbon-based nanoelectronic devices, and simultaneously provide a new approach for developing and synthesizing novel 2D carbon allotropes via the vertical stacking of graphyne with inherent acetylene linkages.

The non-trivial magnetic and electronic phases occurring in topological magnets are often entangled, thus leading to a variety of exotic physical properties. Recently, the BaAl₄-type compounds have been extensively investigated to elucidate the topological features appearing in their real- and momentum spaces. In particular, the topological Hall effect and the spin textures, typical of the centrosymmetric Eu(Al,Ga)₄family, have stimulated extensive experimental and theoretical research. In this topical review, we discuss the latest findings on the Eu(Al,Ga)₄topological antiferromagnets and related materials, arising from a wide range of experimental techniques. We show that Eu(Al,Ga)₄represents a suitable platform to explore the interplay between lattice-, charge-, and spin degrees of freedom, and associated emergent phenomena. Finally, we address some key questions open to future investigation.

We report the structure and properties of a new Ce-based compound Ce₃TiAs₅synthesized under high-pressure and high-temperature conditions. It crystallizes in a hexagonal Hf₅Sn₃Cu-anti type structure with zig-zag like Ce chains along thecaxis. This compound is metallic and undergoes a magnetic phase transition atT_N= 13 K. A metamagnetic transition occurs at ∼0.7 T. The Sommerfeld coefficient for the compound is determined to be about 215 mJ/(Ce-mol*K²), demonstrating a heavy Fermion behavior. The resistivity is featured with two humps, which arises from the synergistic effect of crystal electric field and magnetic scattering. The magnetic ordering temperatureT_Ngradually increases in the sequence of Ce₃TiPn₅with Pn = Bi, Sb, and As, which implies that the Ruderman-Kittel-Kasuya-Yosida interaction should be still predominant in Ce₃TiAs₅.