Search Results (17)

This work aims to explore the algebraic and spectral properties of a novel parametric Hermitian non-Pauli spin basis. The primary motivation for this work is to introduce an alternative to the Pauli spin basis for investigating systems where conventional quantum statistics no longer apply. This study explores the symmetries, commutation relations, Lie algebra structures, and ladder operators of the proposed spin matrices. Additionally, it provides discussions on key findings, potential applications, and concludes with some final remarks. An example for modeling the spectrum of a quantum system is provided. Full article

Three new coordination polymers, {[M(nbpdc)(DMF)(H₂O)₂]·H₂O}_∞ (M = Co and Ni) and [Zn(nbpdc)(DMF)(H₂O)]_∞, were synthesized from 2-nitrobiphenyl-4,4′-dicarboxylate (nbpdc²⁻). The isomorphous Co(II) and Ni(II) compounds exhibited a two-dimensional coordination network in which the chains with single-water bridges and the chains with single-nbpdc²⁻ bridges intersected each other by sharing the metal ions. The coordination networks were connected with uncoordinated water molecules through hydrogen bonds. The rarely identified single-water-bridged coordination chain was reinforced by water-based intrachain hydrogen bonds. The single-water bridges mediated modest antiferromagnetic superexchange in both Co(II) and Ni(II) compounds and afforded a spin-canting structure for the Co(II) compound at low temperatures. Water molecules played a distinct structural role in the Zn(II) compound, which was a one-dimensional coordination polymer with single-nbpdc²⁻ bridges. Instead of bridging metal ions, each water molecule was coordinated to one metal ion and hydrogen-bonded to the coordination spheres of other two metal ions, resulting to an infinite ladderlike hydrogen-bonding motif. The ladders interlinked the nbpdc-bridged chains into a three-dimensional supramolecular architecture featuring the 5-conneted {4⁴.6⁴} net. Full article

The current developments in the theory of quantum static triplet correlations and their associated structures (real r-space and Fourier k-space) in monatomic fluids are reviewed. The main framework utilized is Feynman’s path integral formalism (PI), and the issues addressed cover quantum diffraction effects and zero-spin bosonic exchange. The structures are associated with the external weak fields that reveal their nature, and due attention is paid to the underlying pair-level structures. Without the pair, level one cannot fully grasp the triplet extensions in the hierarchical ladder of structures, as both the pair and the triplet structures are essential ingredients in the triplet response functions. Three general classes of PI structures do arise: centroid, total continuous linear response, and instantaneous. Use of functional differentiation techniques is widely made, and, as a bonus, this leads to the identification of an exact extension of the “classical isomorphism” when the centroid structures are considered. In this connection, the direct correlation functions, as borrowed from classical statistical mechanics, play a key role (either exact or approximate) in the corresponding quantum applications. Additionally, as an auxiliary framework, the traditional closure schemes for triplets are also discussed, owing to their potential usefulness for rationalizing PI triplet results. To illustrate some basic concepts, new numerical calculations (path integral Monte Carlo PIMC and closures) are reported. They are focused on the purely diffraction regime and deal with supercritical helium-3 and the quantum hard-sphere fluid. Full article

In the current literature, there exists a lack of analysis regarding the coordination of the spinning reserve and time-shift characteristics of hydrogen storage systems (HSS) and flexible carbon capture systems (FCCS) in terms of low-carbon economic operation. They are presently used solely as a tool to capture carbon dioxide, without fully utilizing the advantages of their flexible operation. The coordination and complementarity of the FCCS and HSS can ensure stable power supply and improve renewable energy (RE) consumption. Combined with demand side response (DSR), these factors can maximize the RE consumption capacity, reduce carbon emissions, and improve revenue. In this paper, a source-storage-load flexible scheduling strategy is proposed by considering the complementary nature of FCCS and HSS in terms of rotating standby and time-shift characteristics. First, the operational mechanisms of FCCS, HSS, and demand side response (DSR) are analyzed, and their mathematical models are constructed to improve flexibility in grid operation and regulation. Next, deficiencies in FCCS and HSS operation under rotating reserve requirements are analyzed to design a coordinated operation framework for the FCCS and HSS. This operational framework aims to enable the complementarity of the rotating reserve and time-shift characteristics of FCCS and HSS. Finally, based on the carbon emission trading mechanism, a three-stage ladder carbon emission trading cost model is constructed, and a source-storage-load flexible scheduling strategy is established to achieve an effective balance between low carbon emissions and economic performance. The simulation results demonstrate that the strategy reduces the overall cost by 8.57%, reduces the carbon emissions by 35.33%, and improves the renewable energy consumption by 3.5% compared with the unoptimized scheme. Full article

The spin-1/2 quantum transverse Ising model, defined on a ladder structure, with nearest-neighbor and four-spin interaction on a plaquette, was studied by using exact diagonalization on finite ladders together with finite-size-scaling procedures. The quantum phase transition between the ferromagnetic and paramagnetic phases has then been obtained by extrapolating the data to the thermodynamic limit. The critical transverse field decreases as the antiferromagnetic four-spin interaction increases and reaches a multicritical point. However, the exact diagonalization approach was not able to capture the essence of the dimer phase beyond the multicritical transition. Full article

We review the magneto-structural properties of electron–electron correlated quasi-one- dimensional (1D) molecular organics. These weakly localized quarter-filled metallic-like systems with pronounced spin 1/2 antiferromagnetic (AF) interactions in stack direction exhibit a spin charge decoupling where magnetoelastic coupling picks up spin 1/2 to pair into S = 0 singlet dimers. This is well illustrated by the observation of a spin-Peierls (SP) instability in the (TMTTF)2X Fabre salts and related salts with the o-DMTTF donor. These instabilities are revealed by the formation of a pseudo-gap in the spin degrees of freedom triggered by the development of SP structural correlations. The divergence of these 1D fluctuations, together with the interchain coupling, drive a 3D-SP ground state. More surprisingly, we show that the Per2-M(mnt)2 system, undergoing a Kondo coupling between the metallic Per stack and the dithiolate stack of localized AF coupled spin ½ (for M = Pd, Ni, Pt), enhances the SP instability. Then, we consider the zig-zag spin ladder DTTTF2-M(mnt)2 system, where unusual singlet ground state properties are due to a combination of a 4k_F charge localization effect in stack direction and a 2k_F SP instability along the zig-zag ladder. Finally, we consider some specific features of correlated 1D systems concerning the coexistence of symmetrically different 4k_F BOW and 4k_F CDW orders in quarter-filled organics, and the nucleation of solitons in perturbed SP systems. Full article

Haldane conjectures the fundamental difference in the energy spectrum of the Heisenberg antiferromagnetic (HAF) of the spin S chain is that the half-integer and the integer S chain have gapless and gapped energy spectrums, respectively. The ground state (gs) of the HAF spin-1/2 and spin-1 chains have a quasi-long-range and short-range correlation, respectively. We study the effect of the exchange interaction between an HAF spin-1/2 and an HAF spin-1 chain forming a normal ladder system and its gs properties. The inter-chain exchange interaction $J_{\perp }$ can be either ferromagnetic (FM) or antiferromagnetic (AFM). Using the density matrix renormalization group method, we show that in the weak AFM/FM coupling limit of $J_{\perp }$, the system behaves like two decoupled chains. However, in the large AFM $J_{\perp }$ limit, the whole system can be visualized as weakly coupled spin-1/2 and spin-1 pairs which behave like an effective spin-1/2 HAF chain. In the large FM $J_{\perp }$ limit, coupled spin-1/2 and spin-1 pairs can form pseudo spin-3/2 and the whole system behaves like an effective spin-3/2 HAF chain. We also derive the effective model Hamiltonian in both strong FM and AFM rung exchange coupling limits. Full article

The new heterometallic compounds, [{Cu(pn)₂}₂Ni(NCS)₆]_n·2nH₂O (1), [{Cu^II(trien)}₂Ni(NCS)₆Cu^I(NCS)]_n (2) and [Cu(tren)(NCS)]₄[Ni(NCS)₆] (3) (pn = 1,2-diaminopropane, trien = triethylenetetramine and tren = tris(2-aminoethylo)amine), were obtained and characterized by X-ray analysis, IR spectra, XAS and magnetic measurements. Compounds 1, 2 and 3 show the structural diversity of 2D, 1D and 0D compounds, respectively. Depending on the polyamine used, different coordination polyhedron for Cu(II) was found, i.e., distorted octahedral (1), square pyramidal (2) and trigonal bipyramidal (3), whereas coordination polyhedron for nickel(II) was always octahedral. It provides an approach for tailoring magnetic properties by proper selection of auxiliary ligands determining the topology. In 1, thiocyanate ligands form bridges between the copper and nickel ions, creating 2D layers of sql topology with weak ferromagnetic interactions. Compound 2 is a mixed-valence copper coordination polymer and shows the rare ladder topology of 1D chains decorated with [Cu^II(tren)]²⁺ antennas as the side chains attached to nickel(II). The ladder rails are formed by alternately arranged Ni(II) and Cu(I) ions connected by N2 thiocyanate anions and rungs made by N3 thiocyanate. For the Cu(I) ions, the tetrahedral thiocyanate environment mixed N/S donor atoms was found, confirming significant coordination spheres rearrangement occurring at the copper precursor together with the reduction in some Cu(II) to Cu(I). Such topology enables significant simplification of the magnetic properties modeling by assuming magnetic coupling inside {Ni^IICu^II₂} trinuclear units separated by diamagnetic [Cu(NCS)(SCN)₃]³⁻ linkers. Compound 3 shows three discrete mononuclear units connected by N-H…N and N-H…S hydrogen bonds. Analysis of XAS proves that the average ligand character and the covalency of the unoccupied metal d-based orbitals for copper(II) and nickel(II) increase in the following order: 1 → 2 → 3. In 1 and 2, a weak ferromagnetic coupling between copper(II) and nickel(II) was found, but in 2, additional and stronger antiferromagnetic interaction between copper(II) ions prevailed. Compound 3, as an ionic pair, shows, as expected, a spin-only magnetic moment. Full article

¹H spin-diffusion solid-state NMR was utilized to elucidate the domain size in multiblock-copolymers (BCPs) poly-(block poly(dimethylsiloxane)-block ladder-like poly(phenylsiloxane)) and poly-(block poly((3,3′,3″-trifluoropropyl-methyl)siloxane)-block ladder-like poly(phenylsiloxane). It was found that these BCPs form worm-like morphology with rigid cylinders dispersed in amorphous matrix. By using the combination of solid-state NMR techniques such as ¹³C CP/MAS, ¹³C direct-polarization MAS and 2D ¹H EXSY, it was shown that the main factor which governs the diameter value of these rigid domains is the presence of interpenetrating segments of soft blocks. The presence of such interpenetrating chains leads to an increase of rigid domain diameter. Full article

We determined the spin exchanges between the Cu²⁺ ions in the kagomé layers of volborthite, Cu₃V₂O₇(OH)₂·2H₂O, by performing the energy-mapping analysis based on DFT+U calculations, to find that the kagomé layers of Cu²⁺ ions are hardly spin-frustrated, and the magnetic properties of volborthite below ~75 K should be described by very weakly interacting antiferromagnetic uniform chains made up of effective S = 1/2 pseudospin units. This conclusion was verified by synthesizing single crystals of not only Cu₃V₂O₇(OH)₂·2H₂O but also its deuterated analogue Cu₃V₂O₇(OD)₂·2D₂O and then by investigating their magnetic susceptibilities and specific heats. Each kagomé layer consists of intertwined two-leg spin ladders with rungs of linear spin trimers. With the latter acting as S = 1/2 pseudospin units, each two-leg spin ladder behaves as a chain of S = 1/2 pseudospins. Adjacent two-leg spin ladders in each kagomé layer interact very weakly, so it is required that all nearest-neighbor spin exchange paths of every two-leg spin ladder remain antiferromagnetically coupled in all spin ladder arrangements of a kagomé layer. This constraint imposes three sets of entropy spectra with which each kagomé layer can exchange energy with the surrounding on lowering the temperature below ~1.5 K and on raising the external magnetic field B. We discovered that the specific heat anomalies of volborthite observed below ~1.5 K at B = 0 are suppressed by raising the magnetic field B to ~4.2 T, that a new specific heat anomaly occurs when B is increased above ~5.5 T, and that the imposed three sets of entropy spectra are responsible for the field-dependence of the specific heat anomalies. Full article

The iron-based superconductors had a significant impact on condensed matter physics. They have a common structural motif of a two-dimensional square iron lattice and exhibit fruitful physical properties as a strongly correlated electron system. During the extensive investigations, quasi-one-dimensional iron-based spin-ladder compounds attracted much attention as a platform for studying the interplay between magnetic and orbital ordering. In these compounds, BaFe₂S₃ and BaFe₂Se₃ were found to exhibit superconductivity under high pressure, having a different crystal and magnetic structure at low temperature. We report a brief review of the iron-based spin-ladder compound and recent studies for BaFe_2+δ(S_1−xSe_x)₃. BaFe₂(S_0.75 Se_0.25)₃ is in the vicinity of the boundary of two different magnetic phases and it is intriguing to perform high pressure experiments for studying superconductivity, since effects of large magnetic fluctuations on superconductivity are expected. The effect of iron stoichiometry on the interplay between magnetism and superconductivity is also studied by changing the iron concentration in BaFe_2+δSe₃. Full article

Hole doping into a correlated antiferromagnet leads to topological stripe correlations, involving charge stripes that separate antiferromagnetic spin stripes of opposite phases. The topological spin stripe order causes the spin degrees of freedom within the charge stripes to feel a geometric frustration with their environment. In the case of cuprates, where the charge stripes have the character of a hole-doped two-leg spin ladder, with corresponding pairing correlations, anti-phase Josephson coupling across the spin stripes can lead to a pair-density-wave order in which the broken translation symmetry of the superconducting wave function is accommodated by pairs with finite momentum. This scenario is now experimentally verified by recently reported measurements on La${}_{2-x}$Ba${}_x$CuO${}_4$ with $x=1/8$. While pair-density-wave order is not common as a cuprate ground state, it provides a basis for understanding the uniform d-wave order that is more typical in superconducting cuprates. Full article

The effect of temperature and storage time at a constant temperature on the stability of poly-(o-aminophenylene)naphthoylenimide solutions in N-methylpyrrolidone has been analyzed using rotational rheometry. A temperature–time window beyond which an irreversible change in the viscoelastic properties of solutions due to cumulative reactions of continuous polymerization and possible intramolecular cyclization has been detected. The influence of polymer concentration and its molecular weight on the rheological properties of solutions determining the choice of methods for their processing into fibers and films has been investigated. The effect of non-solvents (water and ethanol) additives on the rheological properties of solutions and the kinetics of their coagulation has been studied. Dosed addition of non-solvent into the solution promotes a significant increase in the viscoelasticity up to gelation and phase separation. Non-solvent presence in the polymer solutions reduces the activity of the solvent, accelerates the movement of the diffusion front at coagulation, and minimizes the number of macro defects. The combination of parameters under investigation renders it possible for the first time to develop new principles modifying dopes for wet spinning into aqueous or ethanol coagulation bath and finally to obtain a heat- and fire-resistant polynaphthoylenebenzimidazole fibers. Full article

We report reversible structural transformation that occurs in two ladder compounds: Cu₂CO₃(ClO₄)₂(NH₃)₆ (1) and Cu₂CO₃(ClO₄)₂(NH₃)₅(H₂O) (2), when they are exposed to gaseous vapors. The ladder structures of both 1 and 2 consist of two Cu²⁺ ions and one CO₃²⁻ ion. In 1, the Cu²⁺ ions are coordinated by three NH₃ molecules on each side, while those in 2 are coordinated by three NH₃ molecules on one side, and two NH₃ molecules and one H₂O molecule on the other side. We demonstrated reversible transformation of 1 and 2 via the exposure of 1 to H₂O vapor and the exposure of 2 to NH₃ vapor using a simple bench-scale method. The minor structural change observed led to a significant difference in physical properties, which we observed using several methods. Full article

While the observation of magnetic monopoles has defied all experimental attempts in high-energy physics and astrophysics, sound theoretical approaches predict that they should exist, and they have indeed been observed as quasiparticle excitations in certain condensed-matter systems. This indicates that, even though they are not ubiquitous contrary to electrons, it is possible to get them as excitations above a background. In this report, we show that phonons or lattice shear strain generate topological monopoles in some low-dimensional quantum antiferromagnets. For the Heisenberg ladder, phonons are found to generate topological monopoles with nonzero density due to quantum spin fluctuations. For the four-leg Heisenberg tube, longitudinal shear stress generates topological monopoles with density proportional to the strain deformation. The present theory is based on mapping the spin degrees of freedom onto spinless fermions using the generalized Jordan–Wigner transformation in dimensions higher than one. The effective magnetic field generated by the motion of the spinless fermions has nonzero divergence when phonons or shear stress are present. A possible material where the present kind of monopoles could be observed is BiCu ${}_2$ PO ${}_6$ . Full article