Low Dimensional Systems

We examine the behaviour of 2 electrons on a 2 x 2 square lattice sites. The Hubbard model was used to model the system and was diagonalized using the configuration interaction method, which is essentially a variational method. Variations of the ground state energy () t E , the ground state double occupied sites D and the ground state kinetic energy t E kin with the interaction strength t u (u < 0 and u > 0) were examined. The functions D t E , and t E kin were found to be symmetric functions of t u. This suggests that superconductivity is driven by both electron and hole doping.

After overviewing argentine Condensed Matter Physics outside the Metropolitan area I will focus on the Loschmidt Echo [LE], a concept developed and pursed at Córdoba. It is the recovered fraction of a localized excitation after a spreading period followed by an imperfect time reversal procedure . In Solid State NMR, the LE has allowed us to quantify the decoherence and irreversibility induced by an uncontrolled environment. Notably complex many-body dynamics makes the system particularly sensitive to environmental disturbances presenting a decoherence rate that becomes perturbation independent beyond some small threshold. These experiments and the theoretical analysis based on the Feynman's path integral, summarized at a tutorial level, fueled the field of dynamical quantum chaos [4]. The quest for a perturbation independent decoherence as an emergent phenomenon in thermodynamic limit, lead us to discuss other dynamical observables that depend non-analytically on the environment strength, i.e. that undergo a quantum dynamical phase transition QDPT . GPU based high performance computing boosts the evaluation of the LE [3], allowing us to asses thermalization and how the Metal-Insulator transition (also a QDPT) emerges in interacting many-body systems.

I will focus on the Loschmidt Echo [LE], a concept developed and pursed at Córdoba. It is the recovered fraction of a localized excitation after a spreading period followed by an imperfect time reversal procedure . In Solid State NMR, the LE has allowed us to quantify the decoherence and irreversibility induced by an uncontrolled environment. Notably complex many-body dynamics makes the system particularly sensitive to environmental disturbances presenting a decoherence rate that becomes perturbation independent beyond some small threshold. These experiments and the theoretical analysis based on the Feynman's path integral, summarized at a tutorial level, fueled the field of dynamical quantum chaos. The quest for a perturbation independent decoherence as an emergent phenomenon in thermodynamic limit, lead us to discuss other dynamical observables that depend non-analytically on the environment strength, i.e. that undergo a quantum dynamical phase transition QDPT . GPU based high performance computing boosts the evaluation of the LE [3], allowing us to assess thermalization and how the Metal-Insulator transition (also a QDPT) emerges in interacting many-body systems.

A suitable NMR experiment in a one-dimensional dipolar coupled spin system allows one to reduce the natural many-body dynamics into effective one-body dynamics. We verify this in a polycrystalline sample of hydroxyapatite ͑HAp͒ by monitoring the excitation of NMR many-body superposition states: the multiplequantum coherences. The observed effective one-dimensionality of HAp relies on the quasi-one-dimensional structure of the dipolar coupled network that, as we show here, is dynamically enhanced by the quantum Zeno effect. Decoherence is also probed through a Loschmidt echo experiment, where the time reversal is implemented on the double-quantum Hamiltonian, H DQ ϰ I i + I j + + I i -I j -. We contrast the decoherence of adamantane, a standard three-dimensional system, with that of HAp. While the first shows an abrupt Fermi-type decay, HAp presents a smooth exponential law.

We present a rigorous mathematical framework for modeling unconventional superconductivity beyond the standard Bardeen-Cooper-Schrieffer (BCS) theory. While BCS theory successfully explains conventional superconductors through phonon-mediated electron pairing, it fails to capture key phenomena in high-temperature and strongly correlated superconducting systems. In this work, we construct a non-BCS theoretical model rooted in advanced mathematical formalisms, incorporating non-trivial symmetries, non-local interactions, and topological considerations. The model is developed from first principles, without reliance on empirical fits or experimental parameters. We derive a new class of equations governing the superconducting order parameter and explore their implications through analytical techniques and graph-based representations. Our results suggest the emergence of superconducting states with properties incompatible with BCS-type behavior, offering insights into possible mechanisms behind high-temperature or exotic superconductors. This framework provides a foundation for further theoretical exploration and may guide future experimental inquiries into non-phononic superconductivity.

Twisted skyrmions, whose helicity angles are different from those of Bloch and Néel skyrmions, have recently been demonstrated in experiments. In this work, we first discuss the origin and the topological properties of twisted skyrmions. Following that, we investigate the current-induced motion of twisted skyrmions by using micromagnetic simulations. It is found that the skyrmion Hall angle of twisted skyrmions driven by the spin Hall effect (SHE) varies continuously with the helicity, which means that the skyrmion Hall angle depends significantly upon the helicity in addition to the dissipative force tensor and the Gilbert damping. More importantly, we demonstrate that the trajectory of the twisted skyrmion can be controlled in a two-dimensional plane with a Gilbert damping gradient, which makes it possible to achieve the SHE-induced motion of twisted skyrmions with zero skyrmion Hall angle. At last, the simulation results demonstrate that the dynamics of twisted skyrmions driven b...

We theoretically examine equilibrium properties of the harmonically trapped ideal Bose and Fermi gases in the quantum degeneracy regime. We analyze thermodynamic characteristics of gases with a finite number of atoms by means of the known semiclassical approach and perform comparison with exact numerical results. For a Fermi gas, we demonstrate deviations in the Fermi energy values originating from a discrete level structure and show that these are observable only for a small number of particles. For a Bose gas, we observe characteristic softening of phase transition features, which contrasts to the semiclassical predictions and related approximations. We provide a more accurate methodology of determining corrections to the critical temperature due to finite number of particles.

We investigate the first sound of a normal dilute and ultracold twocomponent Fermi gas in a harmonic microtube, i.e. a cylinder with harmonic transverse radial confinement in the length-scale of microns. We show that the velocity of the sound that propagates along the axial direction strongly depends on the dimensionality of the system. In particular, we predict that the first-sound velocity display shell effects: by increasing the density, that is by inducing the crossover from one-dimension to three-dimensions, the first-sound velocity shows jumps in correspondence with the filling of harmonic modes. The experimental achievability of these effects is discussed by considering 40 K atoms.

With angle-resolved photoemission spectroscopy, we studied the electronic structure of TaFe 1.23 Te 3 , which is a two-leg spin ladder compound with a novel antiferromagnetic ground state. Quasi-two-dimensional Fermi surface is observed, indicating sizable inter-ladder hopping, which would facilitate the in-plane ferromagnetic ordering through double exchange interactions. Moreover, an energy gap is not observed at the Fermi surface in the antiferromagnetic state. Instead, the shifts of various bands have been observed. Combining these observations with density-functional-theory calculations, we propose that the large scale reconstruction of the electronic structure, caused by the interactions between the coexisting itinerant electrons and local moments, is most likely the driving force behind the magnetic transition. TaFe 1.23 Te 3 thus provides a simpler system that contains similar ingredients as the parent compounds of iron-based superconductors, which yet could be readily modeled and understood.

We present a new framework for modeling the statistical behavior of both fully developed turbulence and short-term dynamics of financial markets based on the nonextensive thermostatistics proposed by Tsallis. We also show that intermittency -strong bursts in the energy dissipation or clusters of high price volatility -and nonextensivity -anomalous scaling of usually extensive properties like entropy -are naturally linked by a single parameter q, from the nonextensive thermostatistics.

The charge density and pair correlation function of three interacting electrons confined within a two-dimensional disc-like hard wall quantum dot are calculated by full numerical diagonalization of the Hamiltonian. The formation of a Wigner-molecule in the form of equilateral triangular configuration for electrons is observed as the size of the dot is increased.

The charge density and pair correlation function of three interacting electrons confined within a two-dimensional disc-like hard wall quantum dot are calculated by full numerical diagonalization of the Hamiltonian. The formation of a Wigner-molecule in the form of equilateral triangular configuration for electrons is observed as the size of the dot is increased.

Motivated by recent progress on synthesizing two-dimensional magnetic van der Waals systems, we propose a setup for detecting the topological Berezinskii-Kosterlitz-Thouless (BKT) phase transition in spin-transport experiments on such structures. We demonstrate that the spatial correlations of injected spin-currents into a pair of metallic leads can be used to measure the predicted universal jump of 2/π in the ferromagnet spin-stiffness as well as its predicted universal square root dependence on temperature as the transition is approached from below. Our setup provides a simple route to measuring this topological phase transition in two-dimensional magnetic systems, something which up to now has proven elusive. It is hoped that this will encourage experimental efforts to investigate critical phenomena beyond the standard Ginzburg-Landau paradigm in low-dimensional magnetic systems with no local order parameter.

We investigate the effects of Rashba spin-orbit interaction on the electronic energy dispersion and zero-temperature ballistic conductance of double quantum wire under the influence of perpendicular magnetic field. The wire system is represented by a symmetric, double quartic-well confinement potential. Numerical results reveal that competing effects between spin-orbit interaction and magnetic field modify strongly the energy subband structure and introduce anticrossings between subbands. Moreover, it is found that the conductance character of a quasi-one-dimensional ballistic conductor, which is closely related to the energy-dispersion spectrum, is very sensitive to the shape of potential profile, magnetic field and Rashba spin-orbit coupling.

Applying the generalization of the model for chain formation in break-junctions (Di Napoli et al 2012 J. Phys.: Condens. Matter 24 135501), we study the effect of light impurities on the energetics and elongation properties of Pt and Ir chains. Our model enables us to develop a tool ideal for detailed analysis of impurity-assisted chain formation, in which zigzag bonds play an important role. In particular we focus on H (s-like) and O (p-like) impurities and assume, for simplicity, that the presence of impurity atoms in experiments results in a ..M-X-M-X-... (M: metal, X: impurity) chain structure in between the metallic leads. Feeding our model with material-specific parameters from systematic full-potential first-principles calculations, we find that the presence of such impurities strongly affects the binding properties of the chains. We find that, while both types of impurities enhance the probability of chains being elongated, the s-like impurities lower the chain's stabili...

The present work investigates the resonant tunneling of electrons in symmetric triangular double barrier triodes composed of GaAs-Ga 1-y Al y As nanostructures under a step bias voltage. This work employs the complex energy method to compute the resonant tunneling energy and the associated lifetimes. In the mathematical analysis of this work, the matching conditions are taken at specific points on both lateral sides of the triangular barrier. Results showed decreasing the resonant tunneling energies for both the lowest and excited states by applying step bias voltage and disappearing the lowest energy states at a specific applied bias voltage. The resonant tunneling lifetimes of the present structure exhibited nearly constant behavior at constant values of both well half-width and barrier halfthickness although the enhancement of the bias voltage. Moreover, the lifetimes of both the lowest and the first excited states increased nearly non-linearly by increasing the aluminum concentration, with the enhancement of the lowest resonant lifetimes over those values associated with the first excited states. The results showed considerable agreement with the data published in the literature for both magnitude and tendency. The present work highlights the importance of employing the massmismatch condition in studying heterostructures. It is found from the present study that resonant tunneling energies and their related lifetimes are more affected by the variations of the aluminum concentration in the barrier region, barrier thickness, and well width, which can be adjusted to improve the performance of the resonant tunneling triangular triodes and other nanostructure devices.

Using variational matrix product states, we analyze the finite temperature behavior of a halffilled periodic Anderson model in one dimension, a prototypical model of a Kondo insulator. We present an extensive analysis of single-particle Green's functions, two-particle Green's functions, and transport functions creating a broad picture of the low-temperature properties. We confirm the existence of energetically low-lying spin excitations in this model and study their energy-momentum dispersion and temperature dependence. We demonstrate that charge-charge correlations at the Fermi energy exhibit a different temperature dependence than spin-spin correlations. While energetically low-lying spin excitations emerge approximately at the Kondo temperature, which exponentially depends on the interaction strength, charge correlations vanish already at high temperatures. Furthermore, we analyze the charge and thermal conductivity at finite temperatures by calculating the timedependent current-current correlation functions. While both charge and thermal conductivity can be fitted for all interaction strengths by gapped systems with a renormalized band gap, the gap in the system describing the thermal conductivity is generally smaller than the system describing the charge conductivity. Thus, two-particle correlations affect the charge and heat conductivities in a different way resulting in a temperature region where the charge conductivity of this one-dimensional Kondo insulator is already decreasing while the heat conductivity is still increasing.

We study the low-temperature thermodynamics of weakly-interacting uniform liquids in one-dimensional attractive Bose-Bose mixtures. The Bogoliubov approach is used to simultaneously describe quantum and thermal fluctuations. First, we investigate in detail two different thermal mechanisms driving the liquid-togas transition, the dynamical instability and the evaporation, and we draw the phase diagram. Then, we compute the main thermodynamic quantities of the liquid, such as the chemical potential, the Tan's contact, the adiabatic sound velocity and the specific heat at constant volume. The strong dependence of the thermodynamic quantities on the temperature may be used as a precise temperature probe for experiments on quantum liquids.

α-RuCl 3 is considered to be the top candidate material for the experimental realization of the celebrated Kitaev model, where ground states are quantum spin liquids (QSL) with interesting fractionalized excitations. It is however known that additional interactions beyond the Kitaev model trigger in α-RuCl 3 , a long-range zigzag antiferromagnetic ground state. In this work, we investigate a nanoflake of α-RuCl 3 through guarded high impedance measurements aimed at reaching through electronic transport, the regime where the system turns into a zigzag antiferromagnet. We investigated a variety of temperatures (1.45 K-175 K) and out-of-plane magnetic fields ranging up to 11 T. We found a clear signature of a structural phase transition at ≈ 160 K as reported for thin crystals of α-RuCl 3 , as well as a thermally activated behavior at temperatures above ≈ 30 K with a characteristic activation energy significantly smaller than the energy gap that we observe for α-RuCl 3 bulk crystals through our Angle Resolved Photoemission Spectroscopy (ARPES) experiments. Additionally we found that below ≈ 30 K, transport is ruled by Efros-Shklovskii (ES) VRH. These observations point to the presence of Coulomb impurities in our thin crystals. Most importantly, our data shows that below the magnetic ordering transition known for bulk α-RuCl 3 (≈ 7 K), there is a clear deviation from VRH or thermal activation transport mechanisms. Our work demonstrates the possibility of reaching through specialized high impedance measurements, the thrilling ground states predicted for α-RuCl 3 at low temperatures in the frame of the Kitaev model, and informs about the transport mechanisms in this material in a wide temperature range as well as on important characteristic quantities such as the localization length of the impurities in a thin α-RuCl 3 crystal.

The understanding of the dynamical properties of skyrmion is a fundamental aspect for the realization of a competitive skyrmion based technology beyond CMOS. Most of the theoretical approaches are based on the approximation of a rigid skyrmion. However, thermal fluctuations can drive a continuous change of the skyrmion size via the excitation of thermal modes. Here, by taking advantage of the Hilbert-Huang transform, we demonstrate that at least two thermal modes can be excited which are non-stationary in time. In addition, one limit of the rigid skyrmion approximation is that this hypothesis does not allow for correctly describing the recent experimental evidence of skyrmion Hall angle dependence on the amplitude of the driving force, which is proportional to the injected current. In this work, we show that, in an ideal sample, the combined effect of field-like and damping-like torques on a breathing skyrmion can indeed give rise to such a current dependent skyrmion Hall angle. While here we design and control the breathing mode of the skyrmion, our results can be linked to the experiments by considering that the thermal fluctuations and/or disorder can excite the breathing mode. We also propose an experiment to validate our findings.

A strategy for a scalable synchronization of an array of spin-Hall oscillators (SHOs) is illustrated. In detail, we present the micromagnetic simulations of two and five SHOs realized by means of couples of triangular golden contacts on the top of a Pt/CoFeB/Ta trilayer. The results highlight that the synchronization occurs for the whole current region that gives rise to the excitation of self-oscillations. This is linked to the role of the magnetodipolar coupling, which is the phenomenon driving the synchronization when the distance between oscillators is not too large. Synchronization also turns out to be robust against geometrical differences of the contacts, simulated by considering variable distances between the tips ranging from 100 nm to 200 nm. Besides, it entails an enlargement of the radiation pattern that can be useful for the generation of spin-waves in magnonics applications. Simulations performed to study the effect of the interfacial Dzyaloshinskii-Moriya interaction ...

We have studied the vibrational frequencies and atom displacements of one-dimensional hybrid systems formed by combinations of periodic and quasiregular (Fibonacci) blocks. The materials are described by nearest-neighbor force constants and the corresponding masses. It is found that the hybrid system exhibits a frequency spectrum with important differences as regards those corresponding to their periodic and quasiregular constituents. In this way we find a separate confinement of the atom displacements in the different parts of the hybrid structure for given frequency ranges.

Using variational matrix product states, we analyze the finite temperature behavior of a half-filled periodic Anderson model in one dimension, a prototypical model of a Kondo insulator. We present an extensive analysis of single-particle Green’s functions, two-particle Green’s functions, and transport functions creating a broad picture of the low-temperature properties. We confirm the existence of energetically low-lying spin excitations in this model and study their energy-momentum dispersion and temperature dependence. We demonstrate that charge-charge correlations at the Fermi energy exhibit a different temperature dependence than spin-spin correlations. While energetically low-lying spin excitations emerge approximately at the Kondo temperature, which exponentially depends on the interaction strength, charge correlations vanish already at high temperatures. Furthermore, we analyze the charge and thermal conductivity at finite temperatures by calculating the time-dependent curren...

Using the density-matrix renormalization group in combination with the Chebyshev polynomial expansion technique, we study the two-hole excitation spectrum of the one-dimensional Hubbard model in the entire filling range from the completely occupied band (n = 2) down to half-filling (n = 1). For strong interactions, the spectra reveal multiplon physics, i.e., relevant final states are characterized by two (doublon), three (triplon), four (quadruplon) and more holes, potentially forming stable compound objects or resonances with finite lifetime. These give rise to several satellites in the spectra with largely different spectral weights as well as to different two-hole, doublon-hole, two-doublon etc. continua. The complex multiplon phenomenology is analyzed by interpreting not only local and k-resolved two-hole spectra but also three-and four-hole spectra for the Hubbard model and by referring to effective low-energy models. In addition, a filter-operator technique is presented and applied which allows to extract specific information on the final states at a given excitation energy. While multiplons composed of an odd number of holes do neither form stable compounds nor well-defined resonances unless a nearest-neighbor density interaction V is added to the Hamiltonian, the doublon and the quadruplon are well-defined resonances. The k-resolved fourhole spectrum at n = 2 represents an interesting special case where a completely stable quadruplon turns into a resonance by merging with the doublon-doublon continuum at a critical wave vector. For all fillings with n > 1, the doublon lifetime is strongly k-dependent and is even infinite at the Brillouin zone edges as demonstrated by k-resolved two-hole spectra. This can be traced back to the "hidden" charge-SU(2) symmetry of the model which is explicitly broken off half-filling and gives rise to a massive collective excitation, even for arbitrary higher-dimensional but bipartite lattices.

The spin-1/2 Heisenberg orthogonal-dimer chain is considered within the perturbative strong-coupling approach, which is developed from the exactly solved spin-1/2 Ising-Heisenberg orthogonal-dimer chain with the Heisenberg intradimer and the Ising interdimer couplings. Although the spin-1/2 Ising-Heisenberg orthogonal-dimer chain exhibits just intermediate plateaux at zero, one-quarter and one-half of the saturation magnetization, the perturbative treatment up to second order stemming from this exactly solvable model additionally corroborates the fractional one-third plateau as well as the gapless Luttinger spin-liquid phase. It is evidenced that the approximate results obtained from the strong-coupling approach are in an excellent agreement with the state-of-the-art numerical data obtained for the spin-1/2 Heisenberg orthogonal-dimer chain within the exact diagonalization and density-matrix renormalization group method. The nature of individual quantum ground states is comprehensiv...

⎯In previous works [1, 2], the 2-dimensional charge transport with parallel (in plane) magnetic field was considered from the theoretical point of view showing explicitly that the specific form of the emergent equation enforces the respective field solution to fulfil the Majorana condition. In this paper we review, explain and analyze these important results in the context of the generated physical effects, namely, the quantum ring as spin filter, the quantum Hall effect and a new one of pure topological origin (as the described by the Aharonov-Casher theorems). The link with supersymmetrical models is briefly discussed.

Thermally activated processes are key to understanding the dynamics of physical systems. Thermal diffusion of (quasi-)particles for instance not only yields information on transport and dissipation processes but is also an exponentially sensitive tool to reveal emergent system properties and enable novel applications such as probabilistic computing. Here we probe the thermal dynamics of topologically stabilized magnetic skyrmion quasi-particles. We demonstrate in a specially tailored low pinning multilayer material system pure 2 skyrmion diffusion that dominates the dynamics. Finally, we analyse the applicability to probabilistic computing by constructing a device, which uses the thermally excited skyrmion dynamics to reshuffle a signal. Such a skyrmion reshuffler is the key missing component for probabilistic computing and by evaluating its performance, we demonstrate the functionality of our device with high fidelity thus enabling probabilistic computing.

Surfactant templated silica mesophases belong to the class of self-assembled materials that exhibit long range ordered two-dimensional (2D) hexagonal, three-dimensional (3D) hexagonal, or 3D cubic mesostructures when the composition of the initial deposited solution and its aging time have been optimized. Thin films of such mesophases with a thickness typically less than 300 nm are now routinely obtained by dip coating. In this study a reference solution was used with a chemical composition leading to the formation of thin films with a 3D hexagonal (P6 3 /mmc) mesostructure by dip coating. Thick films (about 10 µm thick) were alternatively prepared by a evaporation-controlled self-assembly (ECSA) process and studied with grazing incidence small-angle X-ray scattering (GISAXS). In the ECSA process, the mesostructure was developed under slower evaporation conditions than for dip-coated films by finely tuning the ethanol/H 2 O evaporation rate of the reference solution horizontally deposited on a silicon wafer. It is shown that the evaporation rate of the solvent is one of the key parameters that control the final mesostructure and can, under certain conditions, promote the formation of the cubic mesophase. The ability to precisely control such a structural arrangement on the mesoscale is of major interest for making sensor arrays, nanoreactors, photonic and fluidic devices, and low dielectric constant films.

Thermally activated processes are key to understanding the dynamics of physical systems. Thermal diffusion of (quasi-)particles for instance not only yields information on transport and dissipation processes but is also an exponentially sensitive tool to reveal emergent system properties and enable novel applications such as probabilistic computing. Here we probe the thermal dynamics of topologically stabilized magnetic skyrmion quasi-particles. We demonstrate in a specially tailored low pinning multilayer material system pure skyrmion diffusion that dominates the dynamics. Finally, we analyse the applicability to probabilistic computing by constructing a device, which uses the thermally excited skyrmion dynamics to reshuffle a signal. Such a skyrmion reshuffler is the key missing component for probabilistic computing and by evaluating its performance, we demonstrate the functionality of our device with high fidelity thus enabling probabilistic computing.

Submonolayer coverages of C 60 deposited on KBr and NaCl are characterized by noncontact atomic force microscopy. Island shapes are described both qualitatively and quantitatively and their dependence on growth parameters and substrate is discussed. At room temperature, both compact and branched island morphologies are observed to coexist. An analysis of the island areas shows a distinct transition from compact to branched morphology with increasing island area. High-resolution imaging reveals differing coincident epitaxy at steps and on open terraces, despite consistent morphology for islands at both substrate positions. Molecular dewetting is proposed as a mechanism for the formation of branched islands.

A central idea in strongly correlated systems is that doping a Mott insulator leads to a superconductor by transforming the resonating valence bonds (RVBs) into spin-singlet Cooper pairs. Here, we argue that a spin-triplet RVB (tRVB) state, driven by spatially, or orbitally anisotropic ferromagnetic interactions can provide the parent state for triplet superconductivity. We apply this idea to the iron-based superconductors, arguing that strong onsite Hund's interactions develop intraatomic tRVBs between the t2g orbitals. On doping, the presence of two iron atoms per unit cell allows these inter-orbital triplets to coherently delocalize onto the Fermi surface, forming a fully gapped triplet superconductor. This mechanism gives rise to a unique staggered structure of onsite pair correlations, detectable as an alternating π phase shift in a scanning tunnelling Josephson microscope.

The VCA ground state of the 2D Hubbard model is examined for possible phase separation under hole doping manifested by spatial inhomogeneities of coexisting different electron densities at equilibrium. Phase separation is accompanied by spectral weight loss and first Brillouin zone boundary deformation. Such instability is observed in square structures and it is absent in honeycomb lattices. To our knowledge, no previous publications have revealed relationship between Fermi surface instability and phase separation. Our VCA calculations provide strong support for spontaneous instability, driven by electron correlations in specific lattice geometries, proposed in our earlier publications using exact quantum cluster calculations.

͑1998͔͒, we presented a formalism suitable to describe the thermal properties of the phonon gas in ultrathin membranes. We extend here the formalism to the case of narrow objects, such as wires or ''bridges,'' and to the case of small nanoscopical objects. This will allow us to see crossovers between three-, two-, one-and zero-dimensional distribution of the phonon gas. ͓S0163-1829͑99͒10915-9͔

This open access document is published as a preprint in the Beilstein Archives with doi: 10.3762/bxiv.2019.67.v1 and is considered to be an early communication for feedback before peer review. Before citing this document, please check if a final, peer-reviewed version has been published in the Beilstein Journal of Nanotechnology. This document is not formatted, has not undergone copyediting or typesetting, and may contain errors, unsubstantiated scientific claims or preliminary data.

The MPX3 family of magnetic van-der-Waals materials (M denotes a first row transition metal and X either S or Se) are currently the subject of broad and intense attention for low-dimensional magnetism and transport and also for novel device and technological applications, but the vanadium compounds have until this point not been studied beyond their basic properties. We present the observation of an isostructural Mott insulator–metal transition in van-der-Waals honeycomb antiferromagnet V0.9PS3 through high-pressure x-ray diffraction and transport measurements. We observe insulating variable-range-hopping type resistivity in V0.9PS3, with a gradual increase in effective dimensionality with increasing pressure, followed by a transition to a metallic resistivity temperature dependence between 112 and 124 kbar. The metallic state additionally shows a low-temperature upturn we tentatively attribute to the Kondo effect. A gradual structural distortion is seen between 26 and 80 kbar, but ...

A generalized Hubbard model with correlated hoppings is studied at half-filling using exact diagonalization methods. For certain values of the hopping parameters our results for several static properties, the Drude weight and the single-particle spectral function, suggest the occurrence of a

A generalized Hubbard model with correlated hoppings is studied at half-filling using exact diagonalization methods. For certain values of the hopping parameters our results for several static properties, the Drude weight and the single-particle spectral function, suggest the occurrence of a

We report discovery of new metallic and magnetic phases in the van-der-Waals antiferromagnets MPS3, where M = Transition Metal, form an ideal playground for tuning both low-dimensional magnetic and electronic properties[1-4]. These are layered honeycomb antiferromagnetic Mott insulators, long studied as near-ideal 2D magnetic systems with a rich variety of magnetic and electric properties across the family.

We propose the ΘΦ (Theta-Phi) package which addresses two of the most important extensions of the essentially single-particle mean-field paradigm of the computational solid state physics: the admission of the Bardeen-Cooper-Schrieffer electronic ground state and allowance of the magnetically ordered states with an arbitrary superstructure (pitch) wave vector. Both features are implemented in the context of multi-band systems which paves the way to an interplay with the solid state quantum physics packages eventually providing access to the first-principles estimates of the relevant matrix elements of the model Hamiltonians derived from the standard DFT calculations. Several examples showing the workability of the proposed code are given.

Magnetic solitons are promising for applications due to their intrinsic properties such as small size, topological stability, ultralow power manipulation and potentially ultrafast operations. To date, research has focused on the manipulation of skyrmions, domain walls, and vortices by applied currents. The discovery of new methods to control magnetic parameters, such as the interfacial Dzyaloshinskii-Moriya interaction (DMI) by strain, geometry design, temperature gradients, and applied voltages promises new avenues for energetically efficient manipulation of magnetic structures. The latter has shown significant progress in 2d material-based technology. In this work, we present a comprehensive study using numerical and analytical methods of the stability and motion of different magnetic textures under the influence of DMI gradients. Our results show that under the influence of linear DMI gradients, Néel and Bloch-type skyrmions and radial vortex exhibit motion with finite skyrmion Hall angle, while the circular vortex undergoes expulsion dynamics. This work provides a deeper and crucial understanding of the stability and gradient-driven dynamics of magnetic solitons, and paves the way for the design of alternative low-power sources of magnetization manipulation in the emerging field of 2d materials.