Journal of Physics: Condensed Matter最新文献

A₂Ir₂O₇iridates were proven to crystallise in the geometrically frustrated pyrochlore structure, which remains stable upon rare-earth cation substitution, temperature variation, and external pressure application. However, the change of interatomic distances and local distortions in the lattice frequently leads to complex electronic properties. The low-temperature behaviour in light-A iridates has been thoroughly investigated, including its evolution with pressure. The present pressure study reports the electrical transport and magnetotransport properties in heavy rare-earth Lu₂Ir₂O₇and Er₂Ir₂O₇. Both compounds reveal a semiconductor-insulator transition induced by the antiferromagnetic ordering of the all-in-all-out (AIAO) type in the Ir sublattice. The transition monotonously shifts to a higher temperature under applied pressure by approximately 20 K at 3 GPa. As the transition in resistivity originates in the antiferromagnetic order, the latter is expected to be enhanced with the applied pressure as well. Upon cooling the compound in a magnetic field, the AIAO/AOAI domain structure with non-zero net magnetic moment is formed, mirroring itself in an asymmetric term in the magnetoresistivity of Lu₂Ir₂O₇. The application of pressure then enhances the asymmetric term. The same behaviour is proposed for the whole heavy rare-earth A₂Ir₂O₇series (A= Gd-Lu), although with magnetoresistivity features masked significantly by a stronger response of magneticAcations.

Quasiparticle interference has been used frequently for the purpose of unraveling the electronic states in the vicinity of the Fermi level as well as the nature of the superconducting gap in the unconventional superconductors. Using the metallic spin-density wave state of iron pnictides as an example, we demonstrate that the quasiparticle interference (QPI) can also be used as a probe to provide crucial insight into the interplay of the electronic bandstructure and correlation effects in addition to bringing forth the essential features of electronic states in the vicinity of the Fermi level. Our study reveals that the features of QPI pattern can help us narrow down the interaction parameter window and choose a more realistic tight-binding model. For the three widely used five-orbital models, we find a model-dependent behavior of the QPI together with a different degree of sensitivity to the largest Coulomb interaction parameterU. The patterns in the model of Ikedaet alare relatively robust against change inU,and the real-space modulation vector along the direction with antiferromagnetic arrangement of magnetic moments is consistent with the experiments. The rest of the models show a higher degree of sensitivity toU,and the modulation vector deviates from the experiment. On the other hand, for a realistic range ofU, none of the models exhibit nearly one-dimensional modulation as observed in the experiments, clearly indicating a suppressed role played by the Dirac points, which, otherwise, could have led to a one-dimensional pattern in the absence of additional pockets.

In this Review, we synthesize and critically evaluate past and recent findings on the rheology of microgels based on poly(N-isopropylacrylamide) (PNIPAM), versatile soft materials with tunable properties, providing a comprehensive analysis of their flow behaviour. Differences and similarities are pointed out depending on their structure: homopolymeric, core-shell, copolymeric and interpenetrate polymer networks microgels. We discuss rotational and oscillatory shear rheology measurements and examine the influence of crosslinker density, temperature, pH, and polymer concentration. Additionally, we highlight the practical implications in the knowledge of the rheological properties for applications. Through this review, therefore, we aim to create a solid starting point for all scientists involved in this research area with a powerful source identifying current challenges and potential future research directions.

The use of iron phosphate glass as a wasteform is contingent both on its response to the addition of waste products and on its evolution in response to radiation emitted by these waste products. We perform molecular dynamics simulations of high-energy radiation damage in caesium iron phosphate glasses to study the mobility of caesium, a nuclear decay product, in vitreous wasteforms and their effect on the glass network. We simulate overlapping 70 keV cascades and examine the structural and topological effects that caesium has on the iron phosphate glasses before and after these cascades. We find that the glass network is substantially altered by the presence of caesium as a potent network modifier and that radiation cascades produce qualitatively different effects from those in pure iron phosphate glasses. Overlapping cascades produce minimal effects on the mobility of caesium at low loading. At higher loading, the glass network accommodates caesium atoms less well, particularly after irradiation. We explain this in terms of caesium's role as an excluded network modifier in comparison to iron, which is tightly incorporated into the glass network.

Ionic liquid gating (ILG) is an emergent technique for controlling multiple types of ionic doping and leads to numerous attractive physical properties in quantum materials. This study widens its intriguing applications in metal-free graphitic carbon nitride (g-C₃N₄) semiconductor which is distinct by various extrinsic defects (vacancies, interlayer defects, etc) and intrinsic defects (irregular melon chains, dangling bonds, etc.). Here, the efficient passivation of defects is realized in g-C₃N₄through combined electrostatic and electrochemical mechanisms. By optimizing the ionic liquid concentration and applying a negative electric field, the gated g-C₃N₄exhibit a changed local bonding environment, an increased bandgap, as well as a suppression of photoluminescence (PL) intensity over 80%. Our results demonstrate that the charged ions from the mixed electrolyte passivate the charged defect centers, redistribute the charges within the g-C₃N₄framework, leading to the improved photogenerated carries separation, which is verified by the enhanced photocatalytic efficiency of treated g-C₃N₄. In particular, the changes of the density of states near the Fermi level reflect ionic interaction induced defect passivation in g-C₃N₄, which plays a key role in regulating its PL properties. These findings provide novel insights in ILG mechanisms in layered porous materials and shed light on its potential prospects in other semiconductors with controlled defect engineering.

We consider a junction consisting of an extended one-dimensional Kitaev chain which incorporates both time-reversal symmetry (TRS) breaking and long-range interaction, sandwiched between two metallic leads from two sides. In this hybrid device, we study electrical transport under voltage bias for varying strengths of the TRS breaking phase. We compare the transport characteristics of the long-range type Kitaev chain with those of the short-range Kitaev chain as the strength of the TRS breaking phase varies. We find that the TRS breaking modifies the density of states and localisation/delocalisation property of the eigenstates, which in turn affect the transport characteristics. Moreover, we find that the impact of the TRS breaking is not identical for the long-range Kitaev chain and its short-range counterpart. Therefore, noticeable differences in the transport properties can be observed due to the interplay between the TRS breaking and the range of interaction.

Quantum spin liquids (QSLs), first proposed by Anderson back in 1973 through the resonating-valence-bond state, are expected to be central to understanding high-temperature superconductivity and advancing topological quantum computation. However, conclusive experimental evidence for QSLs remains elusive, largely due to two factors: first, most two-dimensional strongly frustrated spin models are not exactly solvable, leading to inconsistent results across numerical methods; second, real materials often include spin-spin interaction perturbations that disrupt the fragile QSL ground state. This review focuses on the kagome Heisenberg antiferromagnet (KHA), which is considered a promising experimental realization of QSLs. Among the existing KHA candidates, YCu₃(OH)_6.5Br_2.5(YCOB) stands out as the most promising, showing no conventional magnetic ordering down to 50 mK despite a strong antiferromagnetic coupling of ∼60 K. This paper reviews key experimental and theoretical studies on YCOB, addressing ongoing challenges and future directions.

Efficient manipulation of energy at the nanoscale is crucial for advancements in modern computing, energy harvesting, and thermal management. Specifically, controlling quasiparticle currents is critical to these ongoing technological revolutions. This work introduces a novel and physically consistent approach for computing polarization-resolved transmission functions, a crucial element in understanding and controlling energy transport across interfaces. We show that this new method, unlike several previously derived formulations, consistently yields physically meaningful results by addressing the origin of unphysical behavior in other methods. We demonstrate that while multiple decompositions of the transmission function are possible, only there is a unique and unambiguous route to obtaining physically meaningful results. We highlight and critique the arbitrary nature of these alternative decompositions and their associated failures. While developed within the framework of phonon transport, the individual Caroli formula is general and applicable to other fermionic and bosonic quasiparticles, including electrons, and to internal degrees of freedom such as spin and orbital polarization. Through a comparative analysis using a simple model system, we validate the accuracy and reliability of the individual Caroli formula in capturing polarization-specific transmission properties. This new method provides a more accurate understanding of both phonon and electron transport, offering novel ways for optimization of thermoelectric devices and energy-efficient computing technologies.

This study presents a theoretical exploration of light-matter interaction in crystal (CuCl₂4-aminoacetophenone) and cocrystal (CuCl₂4-aminoacetophenone 1,4-diiodotetraflourobenzene) systems using the density functional theory approach. The findings not only identify realistic charge transfer (CT) channels within these systems but also reveal their implications for the field of materials science. The natural bond orbital analysis on the molecules shows that the copper atoms produce lone pair interactions and constructπ-conjugated pathways with ligands. Density of states analysis reveals that compared to the parent crystal, the cocrystal accumulates more electronic states. The exciton descriptors likeD_index,H_index, Sr,t_index, hole delocalization index, and electron delocalization index were used to study the exciton dynamics. Both compounds have CT and local excitation (LE) character, and CT is dominant over LE. The descriptor values revealed how strong or weak the exciton pair is regarding binding energy. The binding energy strength is illustrated with exciton descriptor indexes and a graphical overlap integral. It is evident that as the excitation states increase, the binding energy of the exciton gradually decreases. After the excitation process, the e-h delocalization spreads within the molecular unit, validating the theoretical coexistence of Frenkel-CT excitons with a radius of a few angstroms (Å) and an immense binding energy.

Neutron three-axis spectrometry has been used to determine the interplanar magnetic exchange parameter in the magnetic van der Waals compound CoPS₃. The exchange is found to be small and antiferromagnetic, estimated to be0.020±0.001meV, which is surprising considering that the magnetic structure is correlated ferromagnetically between theabplanes. A possible explanation, involving a small anisotropy in the exchanges, is proposed. The results are discussed with reference to the other members of the transition metal-PS₃compounds.