Journal of Physics: Condensed Matter

Single crystals of disordered Mn 4– x Cr x Al 11 have been synthesized via the flux method. EDS on several crystals of various sizes and shapes revealed an average molar ratio of 17:9:74 for Mn:Cr:Al, while X-ray diffraction on three different crystals yield compositions Mn 2.26 Cr 1.74 Al 11 (Mn 4– x Cr x Al 11 , x = 1.74), Mn 0.83 Cr 3.17 Al 11 , and Mn 1.07 Cr 2.93 Al 11 . This compound crystallizes in space group P –1, isostructural with both Mn 4 Al 11 and Cr 4 Al 11 . Magnetic measurements on several crystals show that this disordered compound is ferrimagnetic with a low effective moment of μ eff ≈1.012±0.004 μ B /f.u. and a non-reachable transition temperature. DFT calculations display opening of a bandgap in the spin-up channel near the Fermi level with increasing Cr content, an indication of half-metallicity.

Neutron three-axis spectrometry has been used to determine the interplanar magnetic exchange parameter in the magnetic van der Waals compound CoPS 3 . The exchange is found to be small and antiferromagnetic, estimated to be 0.020 ±0.001 meV, which is surprising considering that the magnetic structure is correlated ferromagnetically between the ab planes. 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-PS 3 compounds.

Quantum chemical modeling of iridium oxide nanoparticles—(IrO 2)n , n=1,2,3—adsorbed on (5, 5) carbon nanotubes (CNTs) is presented. Energetic, geometric, and electronic aspects have been analyzed in depth to understand the main features of the nanoparticles in the gas phase and the adsorption process involved. Covalent Ir–C bonding resulted from the interaction of the (IrO 2)1 and (IrO 2)3 particles with the CNT. To evaluate the performance of the material, the dissociation of water into H (ads) and OH (ads) has been investigated. Our results revealed that the intrinsic charge polarization of the iridium oxide clusters favors the water dissociation process, with low activation energies. Moreover, the nanoparticles remain stable and maintain covalent interactions with the CNT surface during the water dissociation process.

The dynamics of quantum phase transitions of topological systems has attracted interest. Here we consider the effect of long-range hopping terms on the dynamic behavior. The long-range hoppings preserve chiral symmetry and decay as a function of distance, with an exponent β. We also consider a situation where the hoppings are modulated by oscillations. We compare the results with those obtained for short-range models such as the Su–Schrieffer–Heeger model or its extension to second neighboring cells. While often the lowest critical times coincide with the first peak of the Loschmidt rate, several anomalous cases are identified. Also, the number of critical times often exceeds the absolute value of the change of the winding number in a quench. Various correlation functions are considered, and their time-dependence may often be used to identify the early-time dynamical phase transitions.

In this paper we showcase the strengths of polarized neutron imaging as a magnetic imaging technique through a case study on field-cooled multifilamentary YBCO tape carrying a transport current while containing a trapped magnetic field. The measurements were done at J-PARC’s RADEN beamline, and the analysis is based on a radiograph of a single polarization component, to showcase the analysis potential for fast measurements with short acquisition time. Regions of internal damage are easily and accurately identified as the technique probes the internal magnetic field of the sample directly. Quantitative measurements of the integrated field strength in various regions are acquired using time-of-flight information. Finally, the strength of the screening currents in each filament of the superconductor are estimated by simulating an experiment with a model sample and comparing it to data. With this, we show that polarized neutron imaging is not only a useful tool for investigating magnetic structures but also for investigating currents.

We propose an algorithm for determining the zeros of the electric conductivity in large molecular nanonstructures such as graphene sheets. To this end, we employ the inverse graph method, whereby non-zeros of the Green's functions are represented graphically by a segment connecting two atomic sites, to visually signal the existence of a conductance zero as a line that is missing. In rectangular graphene structures the topological properties of the inverse graph determine the existence of two types of Green function zeros that correspond to absolute conductance cancellations with distinct behavior in the presence of external disorder. We discuss these findings and their potential applications in some particular cases.

We calculate the non-linear charge currents in a two-dimensional electron system with Rashba (α) and Dresselhaus (β) linear spin–orbit interactions (SOIs) in the presence of in-plane electric E and magnetic B fields. Working in a rotated system of coordinates that introduces α±β as effective couplings on perpendicular directions, we show that the currents, quadratic in the electric field, exist for all values of the chemical potential µ, above or below the band crossing energy E0. Our formalism uses a second order correction to the particle distribution function δf(2) derived in a semi-classical approximation that takes into account the local change in the single-particle energy under the action of the electric field. In a quantum well, where μ>E0, for a spin–orbit energy larger than the Zeeman splitting, the non-linear currents that flow perpendicular on the direction of the magnetic field are found to be proportional with α±β when E⊥B and with (α±β)2/(α∓β) when E∥B, a result independent of the presence of any additional SOIs, such as the cubic Dresselhaus or warping.

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 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 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 quasiparticle interference pattern can help us narrowing down the interaction parameter window and choose a more realistic tight-binding model. \textcolor{blue}{For the three widely used five-orbital models, we find a model-dependent behavior of the quasiparticle interference together with a different degree of sensitivity to the largest coulomb interaction parameter U. The patterns in the model of Ikeda \textit{et. al.} are relatively robust against change in U and the real-space modulation vector along the direction with antiferromagnetic arrangment of magnetic moments is consistent with the experiments. Rest of the models show higher degree of sensitivity to U and the modulation vector deviates from the experiment. On the other hand, for a realistic range of U, none of the models exhibit nearly one dimensional modulation as observed in the experiments, clearly indicating a suppressed roles played by the Dirac points, which, otherwise, could have led to one-dimensional pattern in the absence of additional pockets.

We investigate the superconducting pairing symmetry in pressurized La3Ni2O7 based on a bilayer two-orbital model. There are two symmetric bands α and γ, as well as two antisymmetric ones β and δ. It is found that the γ band induces considerable ferromagnetic spin fluctuation and prefers an odd-frequency, s-wave spin triplet pairing state. The addition of the other bands gradually enhances some antiferromagnetic spin fluctuations which eventually surpass the ferromagnetic one. The superconducting pairing then evolves from a spin triplet into a d-wave spin singlet, and finally into an s -wave one. The competition between the d-wave and s -wave pairings relies on the relative strength of the ferromagnetic spin fluctuation to the antiferromagnetic ones.

The temperature-dependent electronic transport and the metal-insulator transition in ABO3 perovskite-type NdNiO3 are highly sensitive to chemical substitutions and lattice-mismatch induced strain in thin films. We synthesized two series of NdNi1-xAlxO3 (x = 0–0.50) thin films on LAO (001) single crystal substrates using the pulsed laser deposition technique: one with varied Al doping level (x = 0–0.50) and the other with fixed doping (x = 0.5) but different thickness (10–200 nm). Substituting Al at Ni-site modifies the Ni oxidation state, as observed by x-ray photoelectron spectroscopy. A Raman mode around 693 cm⁻¹ emerges with just 2% Al-doping at the Ni-site, which is otherwise absent in undoped NdNiO3 film. This mode is associated with an anti-stretching of BO6 octahedra in perovskites. With increasing doping, this mode strongly emerges in a dominating manner in the spectra, clearly indicating a further enhancement of octahedral anti-stretching. This mode exhibits a blue shift with increasing Al doping and a red shift with increasing thickness at x = 0.50. Temperature-dependent Raman spectra, analyzed using Balkanski and Grüneisen models, reveal anharmonicity and Red-shifting behaviors. The undoped film shows a metal-to-insulator transition temperature (TMI) of ∼77 K, which systematically increases with greater anti-stretching of octahedra and Al doping. At higher doping levels (x = 0.20 and 0.50), the films show insulating behavior below room temperature. As the thickness of NdNi0.50Al0.50O3 films varies from 10 nm to 200 nm, the anti-stretching mode got affected, resulting in systematic decrease in resistivity. Our findings confirm that the anti-stretching mode arises by Al doping, and it is associated with the insulating behavior of Al-doped NdNiO3 thin films.

A novel phenanthrenyl-pyrenyl chalcone (PPC) dye was successfully designed and synthesized via the Claisen-Schmidt condensation method. In this molecular structure, the enone moiety serves as an efficient π-bridge, connecting the phenanthrene donor to the pyrene substituents. The structural identity of PPC was confirmed through single-crystal X-ray diffraction analysis, which revealed the presence of intermolecular C–H···O hydrogen bonds and π–π interactions, forming a head-to-tail arrangement. These interactions play a crucial role in stabilizing the molecular framework and influencing its electronic properties. Hirshfeld surface analysis and 2D fingerprint plots were employed to quantitatively assess the intermolecular interactions within PPC. The structural configuration of PPC enables effective tuning of charge transfer characteristics and optical absorption properties, yielding a narrow energy gap of 2.77 eV. Preliminary findings indicate that PPC holds significant potential as a dye sensitizer for DSSC applications, warranting further evaluation of its photovoltaic performance.

We investigated the thermally induced covalent coupling of cobalt porphyrin (CoP) molecules on an Au(111) surface using scanning tunnelling microscopy and first-principle calculations. While CoP molecules deposited at room temperature remain isolated due to electrostatic repulsion, annealing the substrate leads to their aggregation into chain-like structures with covalent bonding. Three distinct bonding motifs are identified, with calculations revealing weak magnetic coupling between the S = 1/2 Co ions. This work evidences a straightforward method for synthesising multinuclear complexes with magnetically coupled spins on surfaces, offering potential applications in molecular spintronics.

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-C3N4 through combined electrostatic and electrochemical mechanisms. By optimizing the ionic liquid concentration and applying a negative electric field, the gated g-C3N4 exhibit 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-C3N4 framework, 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 address the possible protonation of g-C3N4 in passivating the defects and regulating the PL properties. These findings provide novel insights in ILG mechanisms in layered porous organic materials and shed light on its potential prospects in other organic semiconductors with controlled defect engineering.

Understanding the temperature-dependent properties of intrinsic two-dimensional magnets is crucial for both fundamental research and technological applications. In this work, we employ nonlinear spin-wave theory, which incorporates magnon-magnon interactions, to evaluate the Curie temperature and spin-wave dispersions of several Cr- and Cu-based two-dimensional magnets. We find that the resulting Curie temperatures are generally lower than those predicted by mean-field and linear-response approaches, yet they more closely match results obtained from accurate quantum Monte Carlo and random phase approximation methods, as well as experimental data. Our approach provides a robust and efficient computational framework for evaluating the corrected Curie temperature of two-dimensional magnets.

In the field of valleytronics, significant advancements have been made in valley manipulation in linear optical processes. However, the exploration of relevant nonlinearity is crucial for developing coherent optical sources and signal processing in on-chip photonic devices, yet it remains relatively underexplored. Here we demonstrate all-optical valley regulation by leveraging nonlinear parametric scattering processes within monolayer transition metal dichalcogenides embedded in a semiconductor microcavity. Specifically, by utilizing three excitation laser beams (signal, pump, and idler lasers), we observe that the signals from both valleys can be synchronously amplified or suppressed by adjusting the phase of the pump laser. Remarkably, we can independently and effectively control the signals from each valley, with the amplification or suppression of either valley being regulated by the degree of circular polarization or phase difference between circularly polarized components of the pump laser. These advancements in all-optical valley manipulation deepen the understanding of nonlinear optical processes and thus facilitate their potential applications in opto-valleytronic devices.

The recent discovery of orientation-dependent superconductivity in KTaO3-based interfaces has attracted considerable interest, while the underlying origin remains an open question. Here we report a different approach to tune the interfacial electron gas and superconductivity by forming interfaces between rare-earth (RE) metals (RE being La, Ce, Eu) and KTaO3 substrates with different orientations. We found that the interfacial superconductivity is strongest for the Eu/KTaO3 interfaces, becomes weaker in La/KTaO3 and is absent in Ce/KTaO3. Using in-situ photoemission, we observed distinct valence bands associated with RE metals, as well as a pronounced orientation dependence in the interfacial electronic structure, which can be linked to the orientation-dependent superconductivity. The photoemission spectra show similar double-peak structures for the (111) and (110) oriented interfaces, with an energy separation close to the LO4 phonon of KTaO3. Detailed analyses suggest that this double-peak structure could be attributed to electron–phonon coupling, which might be relevant for the interfacial superconductivity.

Synchrotron x-ray spectroscopy was employed to determine the effects of nanostructuring on electronic band structure in V2O5, a promising cathode material and widely used catalyst. V2O5 nanoparticle powders were characterized via P-XRD, TEM, and diffuse reflectance UV-Vis-NIR spectroscopy to confirm the optical bandgap. XES revealed the nanoparticle valence band O 2p states to be upshifted relative to the bulk, while XAS and RIXS showed the lowest V 3d conduction band states to be static. Together, these changes (in conjunction with an increased density of unoccupied lower conduction band states) produce a shrunken bandgap in the V2O5 nanoparticles that defies the Burstein Moss effect. Changes in nanoparticle band structure are generally attributed to oxygen vacancy defects. While nanostructure bandgap reduction is in line with much previous computational work, it is unexpected from most previous experimental results. To our knowledge, this is the first synchrotron x-ray spectroscopy study of a shrunken bandgap achieved in pure V2O5 nanoparticles.

The ballistic electronic transport and tunneling magnetoresistance (TMR) in a ferromagnetic/normal/ferromagnetic (F/N/F) gapless phosphorene junction have been investigated. This study focuses on the effects of structural disorder-specifically, variations in the width and height of the electrostatic potential barrier and magnetic field-on transport and TMR properties. A low-energy two-band Hamiltonian, derived from the tight-binding model along the armchair direction of phosphorene, is used. Transmission, conductance, and magnetoresistance are calculated using the transfer matrix technique, the Landauer-Büttiker formalism, and the TMR relation, respectively. The findings reveal that structural disorder related to barrier width reduces transmission oscillations and moderately suppresses conductance. A key result is that even slight combined structural disorder significantly degrades TMR properties in a gapless phosphorene F/N/F junction. Furthermore, maintaining transport properties, particularly TMR, in this device requires precise control over fluctuations in externally applied fields, especially the magnetic field.

The nature of magnetism in the cubic spinel Cr 0.1 Mn 0.9 Fe 0.2 Co 1.8 O 4 is reported based on systematic investigations by means of magnetization (M), ac susceptibilities (χ) and heat capacity (C P ) measurements, as well as by neutron diffraction. Structural characterization of the sample was done using x-ray absorption spectroscopy, neutron and synchrotron x-ray diffraction. The M vs. T variation in different magnetic fields indicates ferrimagnetic ordering below T C = 230 K, followed by a magnetic field and anisotropy induced spin reorientation at T SR ~ 150 K. With increasing T starting from 2 K, the coercivity H C and anisotropy field H K decrease and become negligible for T > T SR . A model to explain the H C vs. T data shows that T SR is due to reorientation of M along applied H when H > H K . The C P vs. T data shows a weak λ-type anomaly at T C with changes in magnetic entropy smaller than those observed below T SR suggesting that long-range magnetic ordering is completed only below T SR . For T SR < T < T C , the presence of weakly interacting magnetic clusters having weak short-range interactions is evident based on analysis of magnetization and ac susceptibilities. Exchange constants (J AA /k B = 7.9 K, J AB /k B = 22.6 K and J BB /k B = -5.3 K) are determined from the temperature dependence of paramagnetic susceptibility for T > T C . This analysis also shows the low-spin S = 0 state of Co ³⁺ ions on the B sites along with negligible H K for T SR < T < T C produces weakly interacting magnetic clusters in this magnetic semiconductor with bandgap ~0.57 eV.

We introduce and illustrate use of two closely related range-separated hybrid (RSH) van der Waals density functionals (vdW-DFs), denoted AHBR-mRSH and AHBR-mRSH*, for total-energy and quasiparticle characterizations of molecules using generalized Kohn–Sham (gKS) density functional theory (DFT). For comparison, we also introduce and document a traditional design for a long-range corrected (LRC) vdW-DF, denoted ‘B86R-LRC’. All three new vdW-DFs set the exchange potential as free of asymptotic screening in the coupling between the electron and its associated exchange hole. Our two AHBR-mRSHs are key members of a broader class ‘AHBR-mRSH(γ)’ defined by an inverse length scale γ for a crossover in weighting short- and long-ranged exchange contributions; we obtain a highly accurate predictor of general molecular-energy differences by keeping γ = 0.106 (inverse Bohr) deliberately fixed in AHBR-mRSH. We obtain an optimally tuned (OT) form AHBR-mRSH* = AHBR-mRSH( γ∗) by computing a plausible value of γ∗ for specific types of systems. This AHBR-mRSH* permits characterizations of molecular quasiparticles and generalizes (1) the existing ‘OT-RSH’ (Stein et al 2010 Phys. Rev. Lett. 105 266802; Rafaely–Abramson et al 2012 Phys. Rev. Lett. 109 226405) approach by a systematic inclusion of truly nonlocal correlations, and (2) more traditional LRC forms (e.g. B86R-LRC) by setting the short-range exchange description as in vdW-DF2-ahbr (Shukla et al 2022 Phys. Rev. X 12 041003). Importantly, we may view AHBR-mRSH and AHBR-mRSH* as internally consistent functionals for gKS-DFT, being simultaneously accurate on molecular energies and quasiparticles. This is possible because the ‘AHBR-mRSH(γ)’ class has enough transferability to almost always limit adverse impacts of tuning γ, as tested here on the GMTKN55 benchmark suite (Goerigk et al 2017 Phys. Chem. Chem. Phys. 19 32184). We find that AHBR-mRSH generally outperforms B86R-LRC on molecular problems. To illustrate usage, we complete the OT design of an AHBR-mRSH* for nucleobases and show that it provides quasiparticle predictions that are in good agreement with both literature theory and experimental values for adenine, thymine, cytosine, and guanine.

This study employs density functional theory and non-equilibrium Green’s function methods to investigate the thermoelectric and thermal spin transport properties of four molecular devices, which are constructed by four different DNA base molecules, adenine (A), guanine (G), cytosine (C), thymine (T), adsorbing on graphene nanoribbon (GNR). The research reveals that the Device-G and Device-C adsorption turn on a spin-down electron transport channel, resulting in a strongly spin-polarized current. When a temperature difference is applied at GNR electrodes, the values of thermoelectric both charge current and spin current follows the device sequence A < T < C < G. Further analysis indicates that the adsorption of base molecules on graphene substrates effectively enhances electronic conductance, with the thermoelectric performance of adsorbed G and C significantly surpassing those of A and T. This research provides insights into the potential of thermoelectric method for DNA bases recognition.

The electron–electron interaction (EEI), weak localization and Kondo effect are known to correct low-temperature (low-T) resistivity in metals and semimetals. However, the impact of EEI on the anomalous Hall effect (AHE) by EEI remains a subject of debate. In this study, we investigate the EEI corrections to both the low-T longitudinal and AH resistivities in van der Waals ferromagnetic Fe3GaTe2 single crystals with a high Curie temperature. Our findings reveal that the longitudinal resistivity is well-described by the EEI theory developed by Altshuler et al, while the AH resistivity deviates from this theory. We found that the AH resistivity follows a T temperature dependence, and its relative rate of change is 2.6 times that of the longitudinal resistivity. These results demonstrate that EEI significantly influences the low-T AH resistivity under intrinsic mechanism in Fe3GaTe2. This observation challenges the conventional understanding that EEI does not contribute to the AHE in systems with mirror symmetry, as suggested by skew scattering and side jump models. This work opens avenues for further exploration of EEI effect in disordered magnetic materials.

Predicting magnetic phase transitions traditionally relies on a Hamiltonian model to capture key magnetic interactions. Recent advances in machine learning present an opportunity to develop a unified approach that can handle diverse magnetic systems without designing new Hamiltonians for each case. To this end, we employ message-passing neural network (MPNN) potentials to investigate magnetic phase transitions of two-dimensional chrominium trihalides CrX3 (X = I, Br, Cl) . We achieve this by introducing a specialized MPNN with the ability to incorporate the magnetic degrees of freedom. This magnetic MPNN (MMPNN) incorporates atomic magnetic moments directly into the message-passing process, enabling accurate modeling of potential energy surfaces in magnetic materials. This approach improves on our previous work, with the same aim, but using Behler-Parrinello (BP) neural network that relies on hand-crafted descriptors as the underlying universal magnetic Hamiltonian. It also adds the capability to treat magnetic degrees of freedom and atom displacement in a unified way. Using two-dimensional CrX3 as examples and combining the MPNN with the Landau-Lifshitz-Gilbert (LLG) equation, we simulate ferromagnetic (FM) and antiferromagnetic (AFM) phase transitions as a function of temperature. These results highlight the potential of message-passing neural networks for advancing research in magnetic materials.

We report x-ray diffraction and resonant elastic x-ray scattering studies on two α-RuCl3 crystals with distinct magnetic transition temperatures: TN = 7.3 K and 6.5 K. We find that the sample with TN = 6.5 K exhibits a high degree of stacking faults and structural twinning at low temperature, whereas the TN = 7.3 K sample primarily comprises a single domain of R 3¯. Notwithstanding, both samples exhibit an identical zigzag magnetic structure, with magnetic moments pointing away from the honeycomb plane by α=31(2)∘. We argue that the identical ordered moment directions in these samples suggest that the intralayer magnetic interactions remain mostly unchanged regardless of TN.

Dynamical Mean Field Theory (DMFT) is one of the powerful computational approaches to study electron correlation effects in solid-state materials and molecules. Its practical applicability is, however, limited by the quantity of numerical resources required for the solution of the underlying auxiliary Anderson impurity model. Here, the one-to-one mapping between electronic orbitals and the state of a qubit register suggests a significant computational advantage for the use of a Quantum Computer (QC) for solving this task. In this work we present a QC approach to solve a two-site DMFT model based on the Variational Quantum Eigensolver (VQE) algorithm. We analyse the propagation of stachastic and device errors through the algorithm and their effects on the calculated self-energy. Therefore, we systematically compare results obtained on simulators with calculations on the IBMQ Ehningen QC hardware. We suggest a means to overcome unphysical features in the self-energy which already result from purely stochastic noise. Based heron, we demonstrate the feasibility to obtain self-consistent results of the two-site DMFT model based on VQE simulations with a finite number of shots.