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Island formation in strain-free heteroepitaxial deposition of thin films is analyzed using kinetic Monte Carlo simulations of two minimal lattice models and scaling approaches. The transition from layer-by-layer (LBL) to island (ISL) growth is driven by a weaker binding strength of the substrate which, in the kinetic model, is equivalent to an increased diffusivity of particles on the substrate compared to particles on the film. The LBL-ISL transition region is characterized by particle fluxes between layers 1 and 2 significantly exceeding the net flux between them, which sets a quasi-equilibrium condition. Deposition on top of monolayer islands weakly contributes to second layer nucleation, in contrast with the homoepitaxial growth case. A thermodynamic approach for compact islands with one or two layers predicts the minimum size in which the second layer is stable. When this is linked to scaling expressions for submonolayer island deposition, the dependence of the ISL-LBL transition point on the kinetic parameters qualitatively matches the simulation results, with quantitative agreement in some parameter ranges. The transition occurs in the equilibrium regime of partial wetting and the convergence of the transition point upon reducing the deposition rate is very slow and practically unattainable in experiments.

At ambient pressure, HfTe$_{5}$ is a material at the boundary between a weak and a strong topological phase, which can be tuned by changes in its crystalline structure or by the application of high magnetic fields. It exhibits a Lifshitz transition upon cooling, and three-dimensional (3D) quantum Hall effect (QHE) plateaus can be observed at low temperatures. Here, we have investigated the electrical transport properties of HfTe$_{5}$ under hydrostatic pressure up to 3 GPa. We find a pressure-induced crossover from a semimetallic phase at low pressures to an insulating phase at about 1.5 GPa. Our data suggest the presence of a pressure-induced Lifshitz transition at low temperatures within the insulating phase around 2 GPa. The quasi-3D QHE is confined to the low-pressure region in the semimetallic phase. This reveals the importance of the semimetallic groundstate for the emergence of the QHE in HfTe$_{5}$ and thus favors a scenario based on a low carrier density metal in the quantum limit for the observed signatures of the quasi-quantized 3D QHE.

We studied random resistor networks produced with regular structure and random distribution of edge conductances. These networks are intended to mimic crack-template-based transparent conductive films as well some random networks produced using nano-imprinting technology. Applying an effective medium theory, we found out that the electrical conductance of such networks is $\approx 0.5852 \sqrt{n_E}$, where $n_E$ is the number density of conductive edges. This dependence is in agreement with numerical calculations in Voronoi networks, although the effective conductances are approximately 15\% larger., Comment: 7 pages, 4 figures, 1 table, 68 references

Here, we present a study of the influence of microstructure on the magnetic properties of polycrystalline samples of the La1.5Sr0.5CoMnO6 double perovskite, with primary attention to the spontaneous exchange bias effect, a fascinating recently discovered phenomena for which some materials exhibit unidirectional magnetic anisotropy after being cooled in zero magnetic fields. By sintering La1.5Sr0.5CoMnO6 at different temperatures, we obtained samples with distinct average grain sizes, ranging from 1.54 to 6.65 mu_m. A detailed investigation of the material's structural, morphologic, electronic, and magnetic properties using X-ray powder diffraction, powder neutron diffraction, X-ray absorption near edge structure spectroscopy, scanning electron microscopy, and AC and DC magnetometry has revealed a systematic enhancement of the exchange bias effect with increasing the average grain size. This evolution is discussed in terms of changes in the material's porosity and grain morphology and its influence on the exchange couplings at the magnetic interfaces., Comment: 10 pages, 6 figures

Topological superconductors have long been sought for their potential use in quantum computing. The type-II Weyl semimetal MoTe$_{2}$ is an obvious candidate, exhibiting a superconducting state below 500 mK at ambient pressure, but the question remains whether the pairing is conventional $s^{++}$ or topological $s^{+-}$. The application of external pressure favors the superconducting state in MoTe$_{2}$ and suppresses the structural transition from $1T'$ to $T_{d}$. The competition between the two structures leads to a mixed phase that strongly enhances the disorder present in the system, remarkably without affecting the superconducting transition temperature, in contrast to the expectation of $s^{+-}$ pairing superconductivity. Our thorough analysis of the electrical and Hall resistivities as a function of pressure yields the most accurate temperature-pressure phase diagram available to date for MoTe$_{2}$ and a detailed view of the relationship between disorder and superconductivity, supporting a conventional $s^{++}$ pairing symmetry.

Halide perovskite has attracted intense research interest owing to its multifaceted and versatile applications in optoelectronics. This intrigue is further fueled by their propensity to undergo intricate structural modifications under extreme conditions, thereby instigating property changes. Within this context, our study delves deep into the intricate interplay of structural and vibrational attributes within the inorganic-metal halide perovskite-like CsCuCl3. Our approach employs Raman spectroscopy and Synchrotron Powder X-Ray Diffraction (SPXRD) techniques harnessed under the dual conditions of low temperatures and high pressures. We have observed a distinct spin-phonon coupling mechanism by employing Raman spectroscopy at low temperatures; this coupling has been manifested as a renormalization phonon phenomenon that occurs notably at T* = 15 K. The correlation between spin and phonon dynamics becomes pronounced through a notable hardening of phonon temperature dependence, a behavior intricately linked to the material antiferromagnetic transition at TN = 10.7 K. The SPXRD under high pressure showed a first-order structural phase transition (SPT) at the critical pressure Pc = 3.69 GPa, leading to the transformation from the hexagonal P6522 to a base-centered monoclinic cell. Notably, the coexistence of both phases is discernible within the pressure range from 2.79 to 3.57 GPa, indicating that the SPT involves the reorganization of the internal [Cu2Cl9]5- dimer unit, with the Cl-Cu-Cl bending contributing more than stretching modes. Furthermore, we demonstrate that the SPT is reversible, but residual strain pressure influences the modification of the critical pressure Pc value upon pressure decrease., Comment: 27 pages, 8 figures

Two level credibility-limited revision is a non-prioritized revision operation. When revising by a two level credibility-limited revision, two levels of credibility and one level of incredibility are considered. When revising by a sentence at the highest level of credibility, the operator behaves as a standard revision, if the sentence is at the second level of credibility, then the outcome of the revision process coincides with a standard contraction by the negation of that sentence. If the sentence is not credible, then the original belief set remains unchanged. In this paper, we propose a construction for two level credibility-limited revision operators based on Grove's systems of spheres and present an axiomatic characterization for these operators., Comment: In Proceedings TARK 2023, arXiv:2307.04005

LuFe$_4$Ge$_2$ crystallizes in the ZrFe$_4$Si$_2$-type structure, hosting chains of Fe-tetrahedra giving rise to geometric frustration and low-dimensionality. The compound orders antiferromagnetically at around 36 K accompanied by a simultaneous structural transition from a tetragonal to an orthorhombic phase. The hydrostatic pressure dependence of the magnetic and structural transitions is investigated using electrical-transport, ac magnetic-susceptibility, ac calorimetry, M$\ddot{\rm o}$ssbauer, muon-spin relaxation ($\mu$SR), and x-ray diffraction measurements. External pressure suppresses the first-order transition to the antiferromagnetic phase (AFM1) around 1.8 GPa. The structural transition is largely unaffected by pressure and remains between 30 to 35 K for pressures up to 2 GPa. A second antiferromagnetic phase (AFM2) is observed at higher pressures. The transition from the paramagnetic to the AFM2 phase is of second-order nature and appears to be connected to the structural transition. The magnetic volume fraction obtained from $\mu$SR and M$\ddot{\rm o}$ssbauer measurements reveal that the entire sample undergoes magnetic ordering in both magnetic phases. In addition, similar low-temperature muon-precession frequencies in AFM1 and AFM2 phases point at similar ordered moments and magnetic structures in both phases. Our results further indicate enhanced magnetic fluctuations in the pressure induced AFM2 phase. The experimental observations together with density functional theory calculations suggest that the magnetic and structural order parameters in LuFe$_4$Ge$_2$ are linked by magnetic frustration, causing the simultaneous magneto-structural transition., Comment: 9 pages, 8 figures

In this paper we present spin-to-charge current conversion properties in the Weyl semimetal TaP by means of the inverse Rashba-Edelstein effect (IREE) with the integration of this quantum material with the ferromagnetic metal Permalloy $(Py=Ni_{81}Fe_{19})$. The spin currents are generated in the Py layer by the spin pumping effect (SPE) from microwave-driven ferromagnetic resonance and are detected by a dc voltage along the TaP crystal, at room temperature. We observe a field-symmetric voltage signal without the contamination of asymmetrical lines due to spin rectification effects observed in studies using metallic ferromagnets. The observed voltage is attributed to spin-to-charge current conversion based on the IREE, made possible by the spin-orbit coupling induced intrinsically by the bulk band structure of Weyl semimetals. The measured IREE coefficient ${\lambda}_{IREE}=(0.30 \pm{0.01})$ nm is two orders of magnitude larger than in graphene and is comparable to or larger than the values reported for some metallic interfaces and for several topological insulators., Comment: 15 pages, 4 figures

We report on a linear Langevin model that describes the evolution of the roughness of two interfaces that move towards each other and are coupled by a diffusion field. This model aims at describing the closing of the gap between two two-dimensional material domains during growth, and the subsequent formation of a rough grain boundary. We assume that deposition occurs in the gap between the two domains and that the growth units diffuse and may attach to the edges of the domains. These units can also detach from edges, diffuse, and re-attach elsewhere. For slow growth, the edge roughness increases monotonously and then saturates at some equilibrium value. For fast growth, the roughness exhibits a maximum just before the collision between the two interfaces, which is followed by a minimum. The peak of the roughness can be dominated by statistical fluctuations or by edge instabilities. A phase diagram with three regimes is obtained: slow growth without peak, peak dominated by statistical fluctuations, and peak dominated by instabilities. These results reproduce the main features observed in Kinetic Monte Carlo simulations., Comment: 18 pages, 16 Figures

Grain boundary roughness can affect electronic and mechanical properties of two-dimensional materials. This roughness depends crucially on the growth process by which the two-dimensional material is formed. To investigate the key mechanisms that govern the roughness, we have performed kinetic Monte Carlo simulations of a simple model that includes particle attachment, detachment, and diffusion. We have studied the closure of the gap between two flakes during growth, and the subsequent formation of the grain boundary (GB) for a broad range of model parameters. The well known near-equilibrium (attachment-limited) and unstable (diffusion-limited) growth regimes are identified, but we also observe a third regime when the precursor flux is sufficiently high to fully cover the gap between the edges. This high coverage regime forms GBs with spatially uncorrelated roughness, which quickly relax to smoother configurations. Extrapolating the numerical results (with support from a theoretical approach) to edge lengths and gap widths of some micrometers, we confirm the advantage of this regime to produce GBs with minimal roughness faster than near-equilibrium conditions. This suggests an unexpected route towards efficient growth of two-dimensional materials with smooth GBs.

Recent studies revealed an important interplay between the detailed structure of fibration symmetric circuits and the functionality of biological and non-biological networks within which they have be identified. The presence of these circuits in complex networks are directed related to the phenomenon of cluster synchronization, which produces patterns of synchronized group of nodes. Here we present a fast, and memory efficient, algorithm to identify fibration symmetries over information-processing networks. This algorithm is specially suitable for large and sparse networks since it has runtime of complexity $O(M\log N)$ and requires $O(M+N)$ of memory resources, where $N$ and $M$ are the number of nodes and edges in the network, respectively. We propose a modification on the so-called refinement paradigm to identify circuits symmetrical to information flow (i.e., fibers) by finding the coarsest refinement partition over the network. Finally, we show that the presented algorithm provides an optimal procedure for identifying fibers, overcoming the current approaches used in the literature., Comment: 13 pages, 7 figures

For the development of porous materials with improved transport properties, a key missing ingredient is to determine the relations between growth kinetics, structure, and transport parameters. Here, we address these relations by studying solute diffusion through three-dimensional porous films produced by simple deposition models with controlled thickness and porosity. We simulate growing films with competitive aggregation rules that incorporate lateral aggregation (relative rate proportional to $p$), which leads to pore formation, and surface relaxation ($1-p$) that favors compaction. By connecting a solute source at the basis and a drain at the top outer surface of the films, we extract the effective diffusion coefficients from steady-state simulations. We find that for a given film thickness, the larger the $p$, the larger the effective porosity and diffusivity, but the smaller the tortuosity. Keeping constant growth conditions (i.e., same $p$), the increase of thickness always leads to an increase of effective porosity, but a nontrivial behavior in the diffusivity occurs: for $p\leq 0.7$, the diffusion coefficient is larger in thicker films; this is accompanied by a decrease of the tortuosity with the thickness, thus indicating that growth continuously improves pore structure for diffusion. Microscopically, such a result is associated with narrower distributions of local solute currents at higher points of films. Particularly for $p\geq 0.9$, in which film porosity is $\sim 0.65-0.7$, the tortuosity is between $1.3$ and $2$, increases with the thickness, and has maximal changes near $25\%$. Pairs of values of porosity and tortuosity that we obtain here, for the thickest films, agree with those experimentally measured in some porous electrodes. Noteworthy, the increase of film thickness is generally favorable for diffusion in their pores, and exceptions have small losses in tortuosity., Comment: Main: 37 pages, 11 figures, 2 tables. Suppl. Mat.: 7 pages, 4 figures. Paper written by F. Reis

This study analysed a series of live cattle spot and futures prices from the Boi Gordo Index (BGI) in Brazil. The objective was to develop a model that best portrays this commodity's behaviour to estimate futures prices more accurately. The database created contained 2,010 daily entries in which trade in futures contracts occurred, as well as BGI spot sales in the market, from 1 December 2006 to 30 April 2015. One of the most important reasons why this type of risk needs to be measured is to set loss limits. To identify patterns in price behaviour in order to improve future transactions' results, investors must analyse fluctuations in assets' value for longer periods. Bibliographic research revealed that no other study has conducted a comprehensive analysis of this commodity using this approach. Cattle ranching is big business in Brazil given that in 2017, this sector moved 523.25 billion Brazilian reals (about 130.5 billion United States dollars). In that year, agribusiness contributed 22% of Brazil's total gross domestic product. Using the proposed risk modelling technique, economic agents can make the best decision about which options within these investors' reach produce more effective risk management. The methodology was based on Holt-Winters exponential smoothing algorithm, autoregressive integrated moving average (ARIMA), ARIMA with exogenous inputs, generalised autoregressive conditionally heteroskedastic and generalised autoregressive moving average (GARMA) models. More specifically, 5 different methods were applied that allowed a comparison of 12 different models as ways to portray and predict the BGI commodity's behaviour. The results show that GARMA with order c(2,1) and without intercept is the best model.

In this paper, we adapt the classic Cram\'er-Lundberg collective risk theory model to a perturbed model by adding a Wiener process to the compound Poisson process, which can be used to incorporate premium income uncertainty, interest rate fluctuations and changes in the number of policyholders. Our study is part of a Master dissertation, our aim is to make a short overview and present additionally some new approximation methods for the infinite time ruin probabilities for the perturbed risk model. We present four different approximation methods for the perturbed risk model. The first method is based on iterative upper and lower approximations to the maximal aggregate loss distribution. The second method relies on a four-moment exponential De Vylder approximation. The third method is based on the first-order Pad\'e approximation of the Renyi and De Vylder approximations. The last method is the second order Pad\'e-Ramsay approximation. These are generated by fitting one, two, three or four moments of the claim amount distribution, which greatly generalizes the approximations. We test the precision of approximations using a combination of light and heavy tailed distributions for the individual claim amount. We assess the ultimate ruin probability and present numerical results for the exponential, gamma, and mixed exponential claim distributions, demonstrating the high accuracy of these four methods. Analytical and numerical methods are used to highlight the practical implications of our findings., Comment: Master dissertation work, 18 pages, 4 figures, 8 numerical tables

In this manuscript we consider the dual risk model with financial application, where the random gains occur under a renewal process. We particularly work the Erlang(n) case for common distribution of the inter-arrival times, from there it is easy to understand that our method or procedures can be generalised to other cases under the matrix-exponential family case. We work several and different problems involving future dividends and ruin. We also show that our results are valid even if the usual income condition is not satisfied. In most known works under the dual model, the main target under study have been the calculation of expected discounted future dividends and optimal strategies, where the dividend calculation have been done on aggregate. We can find works, at first using the classical compound Poisson model, then some examples of other renewal Erlang models. Knowing that ruin is ultimately achieved, we find important that dividends should be evaluated on an individual basis, where the early dividend contribution for the aggregate are of utmost importance. From our calculations we can really see how much important is the contribution of the first dividend. Afonso et al. (2013) had worked similar problems for the classical compound Poisson dual model. Besides that we find explicit formulae for both the probability of getting a dividend and the distribution of the amount of a single dividend. We still work the probability distribution of the number of gains to reach a given upper target (like a constant dividend barrier) as well as for the number of gains down to ruin. We complete the study working some illustrative numerical examples that show final numbers for the several problems under study., Comment: 37 pages, 7 figures, 21 tables

Using kinetic Monte Carlo simulations, we develop a framework to relate morphological properties and microscopic dynamics during island growth, coalescence, and initial formation of continuous heteroepitaxial films. The average island width is controlled by adatom mobility on the substrate. Subsequent evolution strongly depends on the Ehrlich-Schw\"{o}ebel energy barrier $E_{ES}$ of the deposited material. As $E_{ES}$ decreases, islands becomes taller and their coalescence is delayed. For small islands and large $E_{ES}$, the global roughness increases as $W\sim{\text{thickness}}^{1/2}$ and the local roughness increases at short scales (apparent anomalous scaling) before and after island coalescence. If the islands are wide, $W$ may have a plateau for large $E_{ES}$ and has a maximum for small $E_{ES}$ when the islands coalesce. This framework is applied to atomic-force microscopy data of the initial stages of CdTe deposition on Kapton: a maximum of $W$ during island coalescence indicates negligible ES barrier, consistently with scaling properties of much thicker films, and the diffusion coefficient ${10}^{-7}{\text{--}}{10}^{-5}{\text{cm}}^2/{\text s}$ on the Kapton surface at $150\,^{\circ}\mathrm{C}$ is estimated. Applications of the framework to other materials are suggested, in which the expected roles of ES barriers are highlighted.

Brazil is the 5th largest country in the world, despite of having a ``High Human Development'' it is the 9th most unequal country. The existing Brazilian micro pension programme is one of the safety nets for poor people. To become eligible for this benefit, each person must have an income that is less than a quarter of the Brazilian minimum monthly wage and be either over 65 or considered disabled. That minimum income corresponds to approximately $2$ dollars per day. This paper analyses quantitatively some aspects of this programme in the Public Pension System of Brazil. We look for the impact of some particular economic variables on the number of people receiving the benefit, and seek if that impact significantly differs among the 27 Brazilian Federal Units. We search for heterogeneity. We perform regression and spatial cluster analysis for detection of geographical grouping. We use a database that includes the entire population that receives the benefit. Afterwards, we calculate the amount that the system spends with the beneficiaries, estimate values \textit{per capita} and the weight of each UF, searching for heterogeneity reflected on the amount spent \textit{per capita}. In this latter calculation we use a more comprehensive database, by individual, that includes all people that started receiving a benefit under the programme in the period from 2nd of January 2018 to 6th of April 2018. We compute the expected discounted benefit and confirm a high heterogeneity among UF's as well as gender. We propose achieving a more equitable system by introducing `age adjusting factors' to change the benefit age.

The spread of COVID-19 caused by the recently discovered SARS-CoV-2 virus has become a worldwide problem with devastating consequences. To slow down the spread of the pandemic, mass quarantines have been implemented globally, provoking further social and economic disruptions. Here, we implement a comprehensive contact tracing network analysis to find an optimized quarantine protocol to dismantle the chain of transmission of coronavirus with minimal disruptions to society. We track billions of anonymized GPS human mobility datapoints from a compilation of hundreds of mobile apps deployed in Latin America to monitor the evolution of the contact network of disease transmission before and after the confinements. As a consequence of the lockdowns, people's mobility across the region decreases by $\sim$53\%, which results in a drastic disintegration of the transmission network by $\sim$90\%. However, this disintegration did not halt the spreading of the disease. Our analysis indicates that superspreading k-core structures persist in the transmission network to prolong the pandemic. Once the k-cores are identified, an optimized strategy to break the chain of transmission is to quarantine a minimal number of 'weak links' with high betweenness centrality connecting the large k-cores. As countries built contact tracing apps to fight the pandemic, our results could turn into a valuable resource to help deploy quarantine protocols with minimized disruptions., Comment: 7 pages, 4 figures

The infiltration of a solute in a fractal porous medium is usually anomalous, but chemical reactions of the solute and that material may increase the porosity and affect the evolution of the infiltration. We study this problem in two- and three-dimensional lattices with randomly distributed porous sites at the critical percolation thresholds and with a border in contact with a reservoir of an aggressive solute. The solute infiltrates that medium by diffusion and the reactions with the impermeable sites produce new porous sites with a probability $r$, which is proportional to the ratio of reaction and diffusion rates at the scale of a lattice site. Numerical simulations for $r\ll1$ show initial subdiffusive scaling and long time Fickean scaling of the infiltrated volumes or areas, but with an intermediate regime with time increasing rates of infiltration and reaction. The anomalous exponent of the initial regime agrees with a relation previously applied to infinitely ramified fractals. We develop a scaling approach that explains the subsequent time increase of the infiltration rate, the dependence of this rate on $r$, and the crossover to the Fickean regime. The exponents of the scaling relations depend on the fractal dimensions of the critical percolation clusters and on the dimensions of random walks in those clusters. The time increase of the reaction rate is also justified by that reasoning. As $r$ decreases, there is an increase in the number of time decades of the intermediate regime, which suggests that the time increasing rates are more likely to be observed is slowly reacting systems., Comment: 14 pages, 13 figures

We study the statistics of the number of executed hops of adatoms at the surface of films grown with the Clarke-Vvedensky (CV) model in simple cubic lattices. The distributions of this number, $N$, are determined in films with average thicknesses close to $50$ and $100$ monolayers for a broad range of values of the diffusion-to-deposition ratio $R$ and of the probability $\epsilon$ that lowers the diffusion coefficient for each lateral neighbor. The mobility of subsurface atoms and the energy barriers for crossing step edges are neglected. Simulations show that the adatoms execute uncorrelated diffusion during the time in which they move on the film surface. In a low temperature regime, typically with $R\epsilon\lesssim 1$, the attachment to lateral neighbors is almost irreversible, the average number of hops scales as $\langle N\rangle \sim R^{0.38\pm 0.01}$, and the distribution of that number decays approximately as $\exp\left[-\left({N/\langle N\rangle}\right)^{0.80\pm 0.07}\right]$. Similar decay is observed in simulations of random walks in a plane with randomly distributed absorbing traps and the estimated relation between $\langle N\rangle$ and the density of terrace steps is similar to that observed in the trapping problem, which provides a conceptual explanation of that regime. As the temperature increases, $\langle N\rangle$ crosses over to another regime when $R\epsilon^{3.0\pm 0.3}\sim 1$, which indicates high mobility of all adatoms at terrace borders. The distributions $P\left( N\right)$ change to simple exponential decays, due to the constant probability for an adatom to become immobile after being covered by a new deposited layer. At higher temperatures, the surfaces become very smooth and $\langle N\rangle \sim R\epsilon^{1.85\pm 0.15}$, which is explained by an analogy with submonolayer growth.

We show that logic computational circuits in gene regulatory networks arise from a fibration symmetry breaking in the network structure. From this idea we implement a constructive procedure that reveals a hierarchy of genetic circuits, ubiquitous across species, that are surprising analogues to the emblematic circuits of solid-state electronics: starting from the transistor and progressing to ring oscillators, current-mirror circuits to toggle switches and flip-flops. These canonical variants serve fundamental operations of synchronization and clocks (in their symmetric states) and memory storage (in their broken symmetry states). These conclusions introduce a theoretically principled strategy to search for computational building blocks in biological networks, and present a systematic route to design synthetic biological circuits.

After their re-emergence in the last decades, dengue fever and other vector-borne diseases are a potential threat to the lives of millions of people. Based on a data set of dengue cases in the Brazilian city of Fortaleza, collected from 2011 to 2016, we study the spatio-temporal characteristics of dengue outbreaks to characterize epidemic and non-epidemic years. First, we identify regions that show a high prevalence of dengue cases and mosquito larvae in different years and also analyze their corresponding correlations. Our results show that the characteristic correlation length of the epidemic is of the order of the system size, suggesting that factors such as citizen mobility may play a major role as a drive for spatial spreading of vector-borne diseases. Inspired by this observation, we perform a mean-field estimation of the basic reproduction number and find that our estimated values agree well with the values reported for other regions, pointing towards similar underlying spreading mechanisms. These findings provide insights into the spreading characteristics of dengue in densely populated areas and should be of relevance for the design of improved disease containment strategies., Comment: 25 pages, 8 figures

We report on the pressure evolution of the giant anomalous Hall effect (AHE) in the chiral antiferromagnet Mn$_3$Ge. The AHE originating from the non-vanishing Berry curvature in Mn$_3$Ge can be continuously tuned by application of hydrostatic pressure. At room temperature, the Hall signal changes sign as a function of pressure and vanishes completely at $p=1.53$ GPa. Even though the Hall conductivity changes sign upon increasing pressure, the room-temperature saturation value of 23 ${\rm \Omega^{-1}cm^{-1}}$ at 2.85 GPa is remarkably high and comparable to the saturation value at ambient pressure of about 40 ${\rm \Omega^{-1}cm^{-1}}$. The change in the Hall conductivity can be directly linked to a gradual change of the size of the in-plane components of the Mn moments in the non-collinear triangular magnetic structure. Our findings, therefore, provide a route for tuning of the AHE in the chiral antiferromagnetic Mn$_3$Ge., Comment: 5 pages, 4 figures

In limited mobility (LM) models of thin film deposition, the final position of each atom or molecule is chosen according to a set of stochastic rules before the incidence of another atom or molecule. Here we investigate the possibility of a LM model to reproduce features of a more realistic approach that represents the interplay of collective adatom diffusion and the external flux. In the LM model introduced here, each adatom may execute $G$ hops to neighboring columns of the deposit, but a hop attempt from a site with $n$ lateral neighbors has probability $P^n$, with $P<1$. These rules resemble those of the Clarke-Vvedensky (CV) model without energy barriers at step edges, whose main parameters are the diffusion-to-deposition ratio $R$ on terraces and the detachment probability $\epsilon$ per lateral neighbor. At short times, the roughness of the LM model can be written in terms of a scaling function of $G$ and $P$ and the growth exponent is consistent with the Villain-Lai-Das Sarma universality class. The evolution of the surface roughness and of the autocorrelation function of the CV model is reproduced with reasonable accuracy by the LM model with suitable choices of parameters. The increase of the parameters $G$ and $R$ of those models produces smoother film surfaces, while the increase of $P$ and $\epsilon$ smoothen the terrace boundaries at short lengthscales. However, the detachment probabilities of the two models have very different effects on the surface roughness: in the LM model, for fixed $G$, the surface roughness increases as $P$ increases; in the CV model, the surface smoothens as $\epsilon$ increases, for fixed $R$. This result is related to the non-Markovian nature of the LM model, since the diffusivity of an adatom depends on its history at the film surface and may be severely reduced after a detachment from a terrace step., Comment: Preprint for a publication in Physica A

We perform a kinetic Monte Carlo simulation study of a model of thin film deposition of a two-component mixture in which the activation energy for diffusion of an adatom is additive over its nearest neighbors and in which the interactions between adatoms of the same species are stronger than those between adatoms of different species. The film morphology is investigated for broad ranges of values of the ratios between terrace diffusivity and atomic flux, of the probabilities of detachment from lateral neighbors, and of probabilities of crossing terrace edges. First, we consider a symmetric case in which the interactions of adatoms of the same species are the same for the two components. For low and intermediate temperatures, we show the formation of narrow domains, whose widths are $3$-$30$ lattice constants, which meander in the layers parallel to the substrate, and are connected through very long distances. The domain width depends on the diffusivity-flux ratio of the same species, but it is weakly affected by interactions of different species, so rough estimates of that width can be obtained by using tabulated properties of films with a single component. At high temperatures, the separation of domains is enhanced, but their long distance connectivity is lost, which shows that the formation of the long meandering domains is restricted to a certain range of temperature and flux. Similar morphological features are obtained when the intra-species interactions are different and the adatom diffusion coefficients on terraces of the same species differ up to two orders of magnitude. An approximate scaling relation for the domain width is obtained, but the species with the largest mobility constrains the temperature range in which the long connected domains are found., Comment: Preprint accepted for publication by Journal of Alloys and Compounds

At ambient pressure and zero field, tetragonal CeAuSb$_{2}$ hosts stripe antiferromagnetic order at $T_{N} = 6.3$ K. Here we first show via bulk thermodynamic probes and x-ray diffraction measurements that this magnetic order is connected with a structural phase transition to a superstructure which likely breaks $C_{4}$ symmetry, thus signaling nematic order. The temperature-field-pressure phase diagram of CeAuSb$_{2}$ subsequently reveals the emergence of additional ordered states under applied pressure at a multicritical point. Our phenomenological model supports the presence of a vestigial nematic phase in CeAuSb$_{2}$ akin to iron-based high-temperature superconductors; however, superconductivity, if present, remains to be discovered.

We investigated the pressure evolution of the electrical transport in the almost compensated Weyl semimetal TaP. In addition, we obtained information on the modifications of the Fermi-surface topology with pressure from the analysis of pronounced Shubnikov-de Haas (SdH) quantum oscillations present in the Hall-effect and magnetoresistance data. The simultaneous analysis of the Hall and longitudinal conductivity data in a two-band model revealed an only weak decrease in the electron- and hole charge-carrier densities up to 1.2 GPa, while the mobilities are essentially pressure independent along the a-direction of the tetragonal crystal structure. Only weak changes in the SdH frequencies for B||a and B||c point at a robust Fermi-surface topology. In contrast to the stability of the Fermi-surface topology and of the density of charge carriers, our results evidence a strong pressure variation of the magnitude of transverse magnetoresistance for B||a contrary to the results for B||c. We can relate the former to an increase in the charge-carrier mobilities along the crystallographic c-direction., Comment: 6 pages, 5 figures

We study a random walk infiltration (RWI) model, in homogeneous and in fractal media, with localized sources at their boundaries. The particles released at a source, which is maintained at a constant density, execute unbiased random walks over a lattice; it represents solute infiltration by diffusion into a medium in contact with a reservoir. A scaling approach shows that the infiltrated length, area, or volume evolves in time as the number of distinct sites visited by a single random walker in the same medium. This is consistent with simulations of the lattice model and exact and numerical solutions of the corresponding diffusion equation. In a Sierpinski carpet, the infiltrated area is expected to evolve as t^{D_F/D_W} (Alexander-Orbach relation), where D_F is the fractal dimension of the medium and D_W is the random walk dimension; the numerical integration of the diffusion equation supports this relation and improves results of lattice random walk simulations. In a Menger sponge in which D_F>D_W (a fractal with a dimension close to 3), a linear time increase of the infiltrated volume is predicted and confirmed numerically. Thus, no evidence of fractality can be observed in infiltrated volumes or masses in media where random walks are not recurrent, although the tracer diffusion is anomalous. We compare our results with a fluid infiltration model in which the pressure head is constant at the source and the front displacement is driven by the local gradient of that head. Exact or numerical solutions in two and three dimensions and in a carpet show that this type of fluid infiltration is in the same universality class of RWI, with an equivalence between the head and the particle concentration. These results set a relation between different infiltration processes with localized sources and the recurrence properties of random walks in the same media., Comment: 11 pages, 12 figures included

We study a model for thin film electrodeposition in which instability development by preferential adsorption and reduction of cations at surface peaks competes with surface relaxation by diffusion of the adsorbates. The model considers cations moving in a supported electrolyte, adsorption and reduction when they reach the film surface, and consequent production of mobile particles that execute activated surface diffusion, which is represented by a sequence of random hops to neighboring lattice sites with a maximum of G hop attempts (G>>1), a detachment probability epsilon<1 per neighboring particle, and a no-desorption condition. Computer simulations show the formation of a compact wetting layer followed by the growth of branched deposits. The maximal thickness z_c of that layer increases with G, but is weakly affected by epsilon. A scaling approach describes the crossover from smooth film growth to unstable growth and predicts z_c ~ G^gamma, with gamma = 1/[2(1-nu)] = 0.43, where nu=0.30 is the inverse of the dynamical exponent of the Villain-Lai-Das Sarma equation that describes the initial roughening. Using previous results for related deposition models, the thickness z_c can be predicted as a function of an activation energy for terrace surface diffusion and the temperature, and the small effects of the parameter epsilon are justified. These predictions are confirmed by the numerical results with good accuracy. We discuss possible applications, with a particular focus on the growth of multifuncional structures with stacking layers of different porosity., Comment: Two-column format with 12 pages, 7 figures included

We provide a theoretical framework to analyze the properties of frontal collisions of two growing interfaces considering different short range interactions between them. Due to their roughness, the collision events spread in time and form rough domain boundaries, which defines collision interfaces in time and space. We show that statistical properties of such interfaces depend on the kinetics of the growing interfaces before collision, but are independent of the details of their interaction and of their fluctuations during the collision. Those properties exhibit dynamic scaling with exponents related to the growth kinetics, but their distributions may be non-universal. These results are supported by simulations of lattice models with irreversible dynamics and local interactions. Relations to first passage processes are discussed and a possible application to grain boundary formation in two-dimensional materials is suggested., Comment: Paper with 12 pages and 2 figures; supplemental material with 4 pages and 3 figures

We investigate by numerical simulation and finite-size analysis the impact of long-range shortcuts on a spatially embedded transportation network. Our networks are built from two-dimensional ($d=2$) square lattices to be improved by the addition of long-range shortcuts added with probability $P(r_{ij})\sim r_{ij}^{-\alpha}$ [J. M. Kleinberg, Nature 406, 845 (2000)]. Considering those improved networks, we performed numerical simulation of multiple discrete package navigation and found a limit for the amount of packages flowing through the network. Such limit is characterized by a critical probability of creating packages $p_{c}$, where above this value a transition to a congested state occurs. Moreover, $p_{c}$ is found to follow a power-law, $p_{c}\sim L^{-\gamma}$, where $L$ is the network size. Our results indicate the presence of an optimal value of $\alpha_{\rm min}\approx1.7$, where the parameter $\gamma$ reaches its minimum value and the networks are more resilient to congestion for larger system sizes., Comment: 7 pages, 5 figures

La3Co4Sn13 is a superconducting material with transition temperature at Tc = 2.70 K, which presents a superlattice structural transition at T* ~ 150 K, a common feature for this class of compounds. However, for this material, it is not clear that at T* the lattice distortions arise from a charge density wave (CDW) or from a distinct microscopic origin. Interestingly, it has been suggested in isostructural non-magnetic intermetallic compounds that T* can be suppressed to zero temperature, by combining chemical and external pressure, and a quantum critical point is argued to be observed near these critical doping/pressure. Our study shows that application of pressure on single-crystalline La3Co4Sn13 enhances Tc and decreases T*. We observe thermal hysteresis loops for cooling/heating cycles around T* for P > 0.6 GPa, in electrical resistivity measurements, which are not seen in x-ray diffraction data. The hysteresis in electrical measurements may be due to the pinning of the CDW phase to impurities/defects, while the superlattice structural transition maintains its ambient pressure second-order transition nature under pressure. From our experiments we estimate that T* vanishes at around 5.5 GPa, though no quantum critical behavior is observed up to 2.53 GPa., Comment: 6 pages, 5 figures

Probabilistic shaping (PS) is a promising technique to approach the Shannon limit using typical constellation geometries. However, the impact of PS on the chain of signal processing algorithms of a coherent receiver still needs further investigation. In this work we study the interplay of PS and phase recovery using the blind phase search (BPS) algorithm, which is widely used in optical communications systems. We first investigate a supervised phase search (SPS) algorithm as a theoretical upper bound on the BPS performance, assuming perfect decisions. It is shown that PS influences the SPS algorithm, but its impact can be alleviated by moderate noise rejection window sizes. On the other hand, BPS is affected by PS even for long windows because of correlated erroneous decisions in the phase recovery scheme. The simulation results also show that the capacity-maximizing shaping is near to the BPS worst-case situation for square-QAM constellations, causing potential implementation penalties., Comment: Accepted for publication in the next available issue of the IEEE/OSA Journal of Lightwave Technology (https://ieeexplore.ieee.org/document/8457202/)