Showing 1–50 of 217 results for author: Souza, M

A few remarks on hyperstatistics and some applications

Authors: Lucas Squillante, Samuel M. Soares, Guilherme Lepski, Mariano de Souza

Abstract: In a recent paper [arXiv:2604.24783 (2026)], we have proposed a general approach to treat systems with inherent non-Boltzmann-Gibbsian behaviour. Given the extremely high accuracy of our approach, we have adopted the term hyperstatistics. We have applied such a statistical mechanics approach, i.e., hyperstatistics, to the discharge of a capacitor in a RC series circuit, pumping of $^4$He of a clos… ▽ More In a recent paper [arXiv:2604.24783 (2026)], we have proposed a general approach to treat systems with inherent non-Boltzmann-Gibbsian behaviour. Given the extremely high accuracy of our approach, we have adopted the term hyperstatistics. We have applied such a statistical mechanics approach, i.e., hyperstatistics, to the discharge of a capacitor in a RC series circuit, pumping of $^4$He of a closed cycle cryostat, midrapidity data of $p$-Pb collisions at the LHC, as well as for the distribution of accelerations in turbulent systems. Here, we discuss into more details the ground of hyperstatistics. We demonstrate the versatility of hyperstatistics upon applying it to the velocity autocorrelation function in Brownian motion and also regarding its potential to describe brain dynamics. △ Less

Submitted 15 July, 2026; v1 submitted 17 June, 2026; originally announced June 2026.

Comments: 12 pages, 2 figures, 2 tables, typos fixed

Thermodynamic and magnetocaloric properties of a triangular spin-1/2 cluster with Dzyaloshinskii-Moriya interaction

Authors: Jordana Torrico, Romulo A. Silva, S. M. de Souza, Onofre Rojas

Abstract: We present a theoretical investigation of the magnetic and thermodynamic properties of the triangular spin-1/2 cluster with Dzyaloshinskii-Moriya (DM) interaction, described by a spin-1/2 Heisenberg Hamiltonian with antisymmetric exchange interactions. The energy spectrum and ground-state phase diagram reveal the presence of ferromagnetic (FM), ferrimagnetic (FI), and frustrated (FR) phases, stron… ▽ More We present a theoretical investigation of the magnetic and thermodynamic properties of the triangular spin-1/2 cluster with Dzyaloshinskii-Moriya (DM) interaction, described by a spin-1/2 Heisenberg Hamiltonian with antisymmetric exchange interactions. The energy spectrum and ground-state phase diagram reveal the presence of ferromagnetic (FM), ferrimagnetic (FI), and frustrated (FR) phases, strongly influenced by the total spin and the DM interaction. We analyze magnetization and susceptibility, showing that at low temperatures the system exhibits a characteristic 1/3 magnetization plateau, while thermal fluctuations suppress magnetic order at higher temperatures. The entropy and specific heat display residual entropies due to ground-state degeneracies, Schottky-type anomalies at intermediate temperatures, and additional low-temperature features related to phase transitions. Particular attention is given to the magnetocaloric effect (MCE), characterized by both direct and inverse regimes depending on the magnetic field variation. We find that the DM interaction enhances the complexity of the MCE, leading to nontrivial entropy variations as a function of the magnetic field. These results provide insights into the role of frustration and anisotropy in tuning the MCE of properties triangular spin clusters, with relevance to \mathrm{Cu}_{3}-based molecular magnets. △ Less

Submitted 9 July, 2026; v1 submitted 28 May, 2026; originally announced May 2026.

Comments: 12 pages, 12 figures

Journal ref: J. Magn. Magn. Mater. 655, 174365 (2026)

Hyperstatistics

Authors: Lucas Squillante, Samuel M. Soares, Constantino Tsallis, Mariano de Souza

Abstract: We propose a general approach, named by us hyperstatistics, to treat complex systems, in which Boltzmann-Gibbs statistics breaks down in domains of the system. Hyperstatistics preserves the concavity of nonadditive $q$-entropy. We obtain analytical closed-form expressions for the here proposed $(q, n)$-generalized Boltzmann factor $B^n_q$ considering uniform, $γ$, Log-normal, F, and the $q$-$γ$ pr… ▽ More We propose a general approach, named by us hyperstatistics, to treat complex systems, in which Boltzmann-Gibbs statistics breaks down in domains of the system. Hyperstatistics preserves the concavity of nonadditive $q$-entropy. We obtain analytical closed-form expressions for the here proposed $(q, n)$-generalized Boltzmann factor $B^n_q$ considering uniform, $γ$, Log-normal, F, and the $q$-$γ$ probability distribution functions. Remarkably, for all investigated distribution functions, $B^n_q$ reduces to a $q$-exponential-type function. To demonstrate the applicability of hyperstatistics, we use a table top experiment of the discharge of a capacitor considering $γ$-distributed relaxation times, the pressure decay over time associated with the pumping of $^4$He lines of a closed cycle cryostat, midrapidity data for $p$-Pb collisions at the LHC, as well as data set for acceleration distribution in turbulent systems. Furthermore, we deduce the power-law-like dielectric response using the $q$-$γ$-distribution function. Our proposal is applicable to systems with inherent non-Boltzmann-Gibbsian statistics in domains of the system. △ Less

Submitted 6 August, 2026; v1 submitted 23 April, 2026; originally announced April 2026.

Comments: 26 pages, 5 figures, 1 table. Supplementary material upon request

Hierarchical localization in disordered Apollonian networks

Authors: Eduardo M. K. Souza, Francisco A. B. F. de Moura, Guilherme M. A. Almeida

Abstract: We investigate localization properties of the Apollonian network (AN) in the presence of diagonal and off-diagonal disorder. By employing a site-resolved localization measure, we show that the localization degree is strongly dependent on the energy and tied to the hierarchical topology of the network. At the spectral edges, eigenstates are strongly localized on highly connected sites originating f… ▽ More We investigate localization properties of the Apollonian network (AN) in the presence of diagonal and off-diagonal disorder. By employing a site-resolved localization measure, we show that the localization degree is strongly dependent on the energy and tied to the hierarchical topology of the network. At the spectral edges, eigenstates are strongly localized on highly connected sites originating from previous generations, a behavior that persists under both disorder mechanisms. In contrast, around zero energy localization is associated with the lowest-degree sites. As disorder breaks the underlying C3 symmetry of the AN, it promotes spatial reconfiguration of these states while preserving their support on low-degree nodes. For diagonal disorder, localization is enhanced over a broad range of negative energies, whereas off-diagonal disorder induces weakening of localization in this region. Finally, we show that the hub dominates the spectral edges but has negligible contribution near the band center, indicating that its associated localized states are robust against disorder. These results highlight how topology and disorder jointly shape localization in complex networks. △ Less

Submitted 12 April, 2026; originally announced April 2026.

Stability of Supported Pd-based Ethanol Oxidation Reaction Electrocatalysts in Alkaline Media

Authors: Tuani C. Gentil, Maria Minichova, Valentín Briega-Martos, Victor S. Pinheiro, Felipe M. Souza, João Paulo C. Moura, Júlio César M. Silva, Bruno L. Batista, Mauro C. Santos, Serhiy Cherevko

Abstract: This study evaluates the dissolution of the supported electrocatalysts Pd/C, PdSn/C, PdNb/C, and PdFe3O4/C during ethanol oxidation reaction for ADLFC applications. A scanning flow cell (SFC) coupled to an inductively coupled mass spectrometry (online ICP-MS) is used to assess the dissolution stability in a broad potential window. Accelerated stress tests with and without ethanol are developed usi… ▽ More This study evaluates the dissolution of the supported electrocatalysts Pd/C, PdSn/C, PdNb/C, and PdFe3O4/C during ethanol oxidation reaction for ADLFC applications. A scanning flow cell (SFC) coupled to an inductively coupled mass spectrometry (online ICP-MS) is used to assess the dissolution stability in a broad potential window. Accelerated stress tests with and without ethanol are developed using a rotating disk electrode (RDE) with dissolution products analysis by ex-situ ICP-MS. Potential profiles simulating those experienced by the catalyst during regular fuel cell operation were used. Sn and Fe catalysts demonstrate improved activity and stability compared with the material with Pd alone. For these reasons, PdSn/C and PdFe3O4/C are suitable for ADLFC applications. Severe Nb dissolution destabilizes Pd, increasing its leaching. This work demonstrates that while additional metals and oxides can improve the alcohol oxidation kinetics of Pd, these additives' dissolution stability must already be considered at the catalyst design stage. △ Less

Submitted 8 April, 2026; originally announced April 2026.

Universal and non-universal facets of quantum critical phenomena unveiled along the Schmidt decomposition theorem

Authors: Samuel M. Soares, Lucas Squillante, Henrique S. Lima, Constantino Tsallis, Mariano de Souza

Abstract: Critical phenomena have been extensively investigated both theoretically and experimentally in many fields, such as condensed matter physics, biology, e.g., brain criticality, and cosmology. In particular, the behaviour of response functions right at critical points (CPs) is highly topical. It turns out that in the frame of Boltzmann-Gibbs-von Neumann-Shannon approach, the extensive character of e… ▽ More Critical phenomena have been extensively investigated both theoretically and experimentally in many fields, such as condensed matter physics, biology, e.g., brain criticality, and cosmology. In particular, the behaviour of response functions right at critical points (CPs) is highly topical. It turns out that in the frame of Boltzmann-Gibbs-von Neumann-Shannon approach, the extensive character of entropy breaks down at CPs. The latter implies diverging susceptibilities, which is at odds with experimental observations. Here, we investigate the influence of the spin magnitude $S$ on the quantum Grüneisen parameter $Γ^{0\text{K}}_{q}$ right at CPs for the 1D Ising model under a transverse magnetic field. Our findings are fourfold: $\textit{i}$) for higher $S$, $Γ^{0\text{K}}_{q}$ is increased, but remains finite, reflecting the enhancement of the Hilbert space dimensionality; $\textit{ii}$) the Schmidt decomposition theorem recovers the extensivity of the nonadditive $q$-entropy $S_q$ only for a $\textit{special}$ value of the entropic index $q$; $\textit{iii}$) the universality class in the frame of $S_q$ depends only on the symmetry of the system; $\textit{iv}$) we propose an experimental setup to explore finite-size effects in connection with the Hilbert space occupation at CPs. Our findings unveil both universal and non-universal aspects of quantum criticality in terms of $Γ^{0\text{K}}_{q}$ and $S_q$. △ Less

Submitted 9 January, 2026; v1 submitted 11 December, 2025; originally announced December 2025.

Comments: 14 pages, 4 figures, supplementary material upon request

Thermodynamic constraints and pseudotransition behavior in a one-dimensional water-like system

Authors: F. F. Braz, S. M. de Souza, M. L. Lyra, Onofre Rojas

Abstract: We investigate a one-dimensional water-like lattice model with Van der Waals and hydrogen-bond interactions, allowing for particle number fluctuations through a chemical potential. The model, defined on a chain with periodic boundary conditions, exhibits three ground-state phases: gas, bonded liquid, and dense liquid, separated by sharp phase boundaries in the chemical potential and temperature pl… ▽ More We investigate a one-dimensional water-like lattice model with Van der Waals and hydrogen-bond interactions, allowing for particle number fluctuations through a chemical potential. The model, defined on a chain with periodic boundary conditions, exhibits three ground-state phases: gas, bonded liquid, and dense liquid, separated by sharp phase boundaries in the chemical potential and temperature plane. Using the transfer matrix method, we derive exact analytical results within the grand-canonical ensemble and examine the finite-temperature behavior. The system exhibits clear pseudotransition features, including sharp but analytic changes in entropy, density, and internal energy, along with finite peaks in specific heat and correlation length. To assess the role of thermodynamic constraints, we consider the behavior under fixed density through a Legendre transformation. This constrained analysis reveals smoother anomalies, such as entropy kinks and finite jumps in specific heat, contrasting with the sharper grand-canonical signatures. These results underscore the ensemble dependence of pseudotransitions and show how statistical constraints modulate critical-like behavior. We also verify that the residual entropy continuity criterion holds in the grand-canonical ensemble but is violated when the system is constrained. Our findings illustrate how even a simple one-dimensional model can mimic water-like thermodynamic anomalies. △ Less

Submitted 16 October, 2025; v1 submitted 17 September, 2025; originally announced September 2025.

Comments: 101 pages, 9 figures

Journal ref: Phys. Rev. E 112, 044144 (2025)

Magnetostriction as the origin of the magnetodielectric effect in La2CoMnO6

Authors: M. Boldrin, A. Bagri, D. Barlettani, E. Teather, L. Squillante, M. de Souza, R. B. Pontes, A. G. Silva, T. J. A. Mori, R. Perry, R. Lora-Serrano, E. Granado, E. M. Bittar, L. S. I. Veiga, L. Bufaiçal

Abstract: The La2CoMnO6 (LCMO) perovskite has received a lot of attention due to its near room temperature magnetodielectric effect. Despite the recent efforts, the mechanism ruling the correlation between its magnetic and dielectric properties is not yet fully understood. In order to address this issue, we conducted a detailed investigation of the coupling between the structural, electronic and magnetic pr… ▽ More The La2CoMnO6 (LCMO) perovskite has received a lot of attention due to its near room temperature magnetodielectric effect. Despite the recent efforts, the mechanism ruling the correlation between its magnetic and dielectric properties is not yet fully understood. In order to address this issue, we conducted a detailed investigation of the coupling between the structural, electronic and magnetic properties of a polycrystalline LCMO sample. Using magnetic field-dependent x-ray powder diffraction and measurements with a capacitive dilatometer, we show that applying an external magnetic field decreases the unit cell volume, thereby modifying the octahedral distortions. Experiments involving temperature and field-dependent x-ray absorption spectroscopy at the Co-L2,3 edges provide further evidence that the spin-orbit interaction of outermost Co 3d-orbital and the field-induced enhancement of covalence effects are the key contributors to the magnetostrictive effects. From a detailed analysis using multiplet and density functional theory calculations, we propose that the field-induced modulations of the orbital hybridization and the ligand-to-metal charge transfer are responsible for the changes in the dielectric response of LCMO, thus enabling a direct coupling between magnetic, elastic and dielectric properties in this material. △ Less

Submitted 9 September, 2025; originally announced September 2025.

Comments: 11 pages, 7 figures

Journal ref: Physical Review Materials 9, 094403 (2025)

Resonant cavity-QED with chiral flat bands

Authors: E. M. Broni, A. M. C. Souza, M. L. Lyra, F. A. B. F. de Moura, G. M. A. Almeida

Abstract: Flat bands exhibit high degeneracy and intrinsic localization, offering a promising platform for enhanced light-matter interactions. Here, we investigate the resonant interaction between a two-level emitter and a chiral flat band hosted by a photonic lattice. In the weak coupling regime, the emitter undergoes Rabi oscillations with a lifted photonic mode whose spatial structure reflects the nature… ▽ More Flat bands exhibit high degeneracy and intrinsic localization, offering a promising platform for enhanced light-matter interactions. Here, we investigate the resonant interaction between a two-level emitter and a chiral flat band hosted by a photonic lattice. In the weak coupling regime, the emitter undergoes Rabi oscillations with a lifted photonic mode whose spatial structure reflects the nature of compact localized states and the onset of Anderson localization. We show that weak hopping disorder induces a delocalization of the lifted mode whereas the effective emitter-field coupling strength, and the associated mode volume experienced by the emitter, remains protected against structural fluctuations. We illustrate our approach using selected flat band lattices. Our findings provide a route to flat band state preparation via quench dynamics and robust cavity-QED control. △ Less

Submitted 24 March, 2026; v1 submitted 14 May, 2025; originally announced May 2025.

Comments: 9 pages, 6 figures

Journal ref: Phys. Rev. A 113, 043727 (2026)

Electrocatalytic Hydrogen Peroxide Generation Using WO$_3$ Nanoparticle-Decorated Sodium Niobate Microcubes

Authors: Vanessa S Antonin, Felipe M Souza, Victor S Pinheiro, João PC Moura, Aline B Trench, Caio Machado Fernandes, Marcos RV Lanza, Mauro C Santos

Abstract: The current work studies the electrocatalytic performance of NaNbO$_3$ microcubes decorated with WO$_3$ nanoparticles on Printex L6 at varying concentrations (1%, 3%, 5%, and 10% by weight) for H$_2$O$_2$ electrogeneration aiming for future use in electrochemical advanced oxidation processes for organic pollutant degradation H$_2$O$_2$ electrogeneration was studied using oxygen reduction reaction… ▽ More The current work studies the electrocatalytic performance of NaNbO$_3$ microcubes decorated with WO$_3$ nanoparticles on Printex L6 at varying concentrations (1%, 3%, 5%, and 10% by weight) for H$_2$O$_2$ electrogeneration aiming for future use in electrochemical advanced oxidation processes for organic pollutant degradation H$_2$O$_2$ electrogeneration was studied using oxygen reduction reaction (ORR) with the rotating ring-disk electrode (RRDE) technique. Electrochemical results revealed an improvement in H$_2$O$_2$ electrogeneration for the NaNbO$_3$@WO$_3$/C materials compared to that achieved with Printex L6 carbon. Notably, the 5% NaNbO$_3$@WO$_3$/C electrocatalyst exhibited a higher ring current for oxygen reduction reaction and promoted a 2.1-electron transfer, facilitating a higher rate of H$_2$O$_2$ electrogeneration through the 2-electron mechanism. Also, enhancing oxygen-containing functional groups has shown the capability to thoroughly adjust characteristics and enhance active sites, increasing H$_2$O$_2$ electrogeneration. These findings suggest that 5% NaNbO$_3$@WO$_3$/C electrocatalysts hold promise for in situ hydrogen peroxide electrogeneration. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Spin-Exchange Induced Spillover on Poor Man's Majoranas in Minimal Kitaev Chains

Authors: J. E. Sanches, L. T. Lustosa, L. S. Ricco, H. Sigurðsson, M. de Souza, M. S. Figueira, E. Marinho Jr., A. C. Seridonio

Abstract: The "Poor Man's Majoranas" (PMMs) [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection can "spill over" from one edge into another of the minimal Kitaev chain when perturbed electrostatically. As aftermath, this leads to a delocalized Majorana fermion (MF) at both the edges. Additionally, according to recent differential conductance measurements in a pair of superconducting and spinle… ▽ More The "Poor Man's Majoranas" (PMMs) [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection can "spill over" from one edge into another of the minimal Kitaev chain when perturbed electrostatically. As aftermath, this leads to a delocalized Majorana fermion (MF) at both the edges. Additionally, according to recent differential conductance measurements in a pair of superconducting and spinless quantum dots (QDs), such a PMM picture was brought to reality [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. Based on this scenario, we propose the spillover of the PMM when its QD is exchange coupled to a quantum spin $S$. We show that if this QD is perturbed by the exchange coupling $J$, solely the half $2S+1$ $(2S+2)$ of the fine structure stays explicit for a fermionic (bosonic) $S.$ Concurrently, the other half squeezes itself as the delocalized MF zero-mode. Particularly, turning-off the superconductivity the multiplicity $2S+1$ holds regardless the spin statistics. Meanwhile, the PMM spillover induced by $J$ becomes a statistics dependent effect. Hence, our findings contribute to the comprehension of spin-phenomena interplay with superconductivity in minimal Kitaev chains, offering insights for future quantum computing devices hosting PMMs. △ Less

Submitted 28 April, 2025; originally announced April 2025.

Journal ref: Journal of Physics: Condensed Matter, Volume 37, Number 20, 205601 (2025)

Impact of Broken Inversion Symmetry on Molecular States in multi-Weyl fermions

Authors: W. C. Silva, J. E. Sanches, D. S. Rojo, L. Squillante, M. de Souza, M. S. Figueira, I. A. Shelykh, E. Marinho Jr., A. C. Seridonio

Abstract: We study inversion-symmetry (IS) breaking in impurity dimers coupled to topological multi-Weyl systems in the low-energy dispersion domain. In the IS-preserved multi-Weyl semimetal phase, Hubbard bands split into symmetric and antisymmetric molecular-like subbands. Breaking IS induces a transition to a multi-Weyl metal, lifting the degeneracy of the Weyl node and closing the pseudogap. This causes… ▽ More We study inversion-symmetry (IS) breaking in impurity dimers coupled to topological multi-Weyl systems in the low-energy dispersion domain. In the IS-preserved multi-Weyl semimetal phase, Hubbard bands split into symmetric and antisymmetric molecular-like subbands. Breaking IS induces a transition to a multi-Weyl metal, lifting the degeneracy of the Weyl node and closing the pseudogap. This causes opposite energy shifts: valence-band symmetric (antisymmetric) subbands red- (blue-) shift, reversing in the conduction band until a degeneracy point. Beyond this threshold, symmetric bands flatten near band cutoffs, whereas antisymmetric bands form quasi-zero energy modes asymptotically approaching -- yet never crossing -- the Fermi level. Crucially, identical molecular symmetries maintain nondegeneracy even as energy separation vanishes with stronger IS breaking. Our results demonstrate symmetry-selective mechanisms for topological molecular states in multi-Weyl systems. △ Less

Submitted 21 August, 2025; v1 submitted 28 April, 2025; originally announced April 2025.

Journal ref: Physical Review B 112, 085134 (2025)

Quantum Otto engine mimicking Carnot near pseudotransitions in the one-dimensional extended Hubbard model in the atomic limit

Authors: Onofre Rojas, Moises Rojas, S. M. de Souza

Abstract: The one-dimensional extended Hubbard model (EHM) in the atomic limit has recently been found to exhibit a curious thermal pseudo-transition behavior, which closely resembles first and second-order thermal phase transitions. This phenomenon, occurring at half-filling, is influenced by the quantum phase transition between the alternating pair (AP) and paramagnetic (PM) phases at zero temperature. In… ▽ More The one-dimensional extended Hubbard model (EHM) in the atomic limit has recently been found to exhibit a curious thermal pseudo-transition behavior, which closely resembles first and second-order thermal phase transitions. This phenomenon, occurring at half-filling, is influenced by the quantum phase transition between the alternating pair (AP) and paramagnetic (PM) phases at zero temperature. In this study, we leverage this anomalous behavior to investigate the performance of quantum many-body machines, using the EHM as the working substance. Our analysis reveals that the quantum Otto engine, when operating in the anomalous region, closely mimics the ideal Carnot engine. In this region, both the work output and thermal efficiency of the Otto engine increase, approaching the performance of a Carnot engine. This highlights the potential of many-body systems, such as the EHM, in enhancing quantum thermodynamic performance. Our findings demonstrate that, although the second law of thermodynamics prevents engines from surpassing Carnot efficiency, the Otto engine can operate remarkably close to this limit in the anomalous region, offering insights into new directions for future research on quantum thermodynamic cycles and working substances. △ Less

Submitted 13 April, 2025; v1 submitted 4 April, 2025; originally announced April 2025.

Comments: 12 pages, 9 figures

Journal ref: Phys. Rev. E 111 044121 (2025)

Quantum geometry and the electric magnetochiral anisotropy in noncentrosymmetric polar media

Authors: Pierpaolo Fontana, Victor Velasco, Chang Niu, Peide D. Ye, Pedro V. Lopes, Kaio E. M. de Souza, Marcus V. O. Moutinho, Caio Lewenkopf, Marcello B. Silva Neto

Abstract: The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, ${\bf I}$, can be controlled by an external magnetic field, ${\bf B}$. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description o… ▽ More The electric magnetochiral anisotropy is a nonreciprocal phenomenon accessible via second harmonic transport in noncentrosymmetric, time-reversal invariant materials, in which the rectification of current, ${\bf I}$, can be controlled by an external magnetic field, ${\bf B}$. Quantum geometry, which characterizes the topology of Bloch electrons in a Hilbert space, provides a powerful description of the nonlinear dynamics in topological materials. Here, we demonstrate that the electric magnetochiral anisotropy in noncentrosymmetric polar media owes its existence to the quantum metric, arising from the spin-orbit coupling, and to large Born effective charges. In this context, the reciprocal magnetoresistance $β{\bf B}^2$ is modified to $R( I,P,B)=R_0[1+βB^2 + γ^{\pm}{\bf I}\cdot({\bf P}\times{\bf B})]$, where the chirality dependent $γ^{\pm}$ is determined by the quantum metric dipole and the polarization ${\bf P}$. We predict a universal scaling $γ^{\pm}(V)\sim V^{-5/2}$ which we verified by phase sensitive, second harmonic transport measurements on hydrothermally grown 2D tellurium films under applied gate voltage, $V$. The control of rectification by varying ${\bf I}$, ${\bf P}$, ${\bf B}$, and $V$, demonstrated in this work, opens up new avenues for the building of ultra-scaled CMOS circuits. △ Less

Submitted 13 February, 2025; originally announced February 2025.

Comments: 6 pages, 4 figures + 10 pages, 4 figures of Supplemental Material

Journal ref: Phys. Rev. Lett. 135, 106602 (2025)

Enhancement of Electric Drive in Silicon Quantum Dots with Electric Quadrupole Spin Resonance

Authors: Philip Y. Mai, Pedro H. Pereira, Lucas Andrade Alonso, Ross C. C. Leon, Chih Hwan Yang, Jason C. C. Hwang, Daniel Dunmore, Julien Camirand Lemyre, Tuomo Tanttu, Wister Huang, Kok Wai Chan, Kuan Yen Tan, Jesús D. Cifuentes, Fay E. Hudson, Kohei M. Itoh, Arne Laucht, Michel Pioro-Ladrière, Christopher C. Escott, Andrew Dzurak, Andre Saraiva, Reinaldo de Melo e Souza, MengKe Feng

Abstract: Quantum computation with electron spin qubits requires coherent and efficient manipulation of these spins, typically accomplished through the application of alternating magnetic or electric fields for electron spin resonance (ESR). In particular, electrical driving allows us to apply localized fields on the electrons, which benefits scale-up architectures. However, we have found that Electric Dipo… ▽ More Quantum computation with electron spin qubits requires coherent and efficient manipulation of these spins, typically accomplished through the application of alternating magnetic or electric fields for electron spin resonance (ESR). In particular, electrical driving allows us to apply localized fields on the electrons, which benefits scale-up architectures. However, we have found that Electric Dipole Spin Resonance (EDSR) is insufficient for modeling the Rabi behavior in recent experimental studies. Therefore, we propose that the electron spin is being driven by a new method of electric spin qubit control which generalizes the spin dynamics by taking into account a quadrupolar contribution of the quantum dot: electric quadrupole spin resonance (EQSR). In this work, we explore the electric quadrupole driving of a quantum dot in silicon, specifically examining the cases of 5 and 13 electron occupancies. △ Less

Submitted 9 October, 2025; v1 submitted 2 February, 2025; originally announced February 2025.

Comments: Main: 5 pages, 4 figures Supp: 4 pages

Non-monotonic evolution of contact area in soft contacts during incipient torsional loading

Authors: Bo Zhang, Mariana de Souza, Daniel M. Mulvihill, Davy Dalmas, Julien Scheibert, Yang Xu

Abstract: Many properties of soft contact interfaces are controlled by the contact area (e.g. friction, contact stiffness and surface charge generation). The contact area increases with the contact age at rest. In contrast, it usually reduces under unidirectional shear loading. Although the physical origin of such a reduction is still debated, it always happens in an anisotropic way because the reduction ma… ▽ More Many properties of soft contact interfaces are controlled by the contact area (e.g. friction, contact stiffness and surface charge generation). The contact area increases with the contact age at rest. In contrast, it usually reduces under unidirectional shear loading. Although the physical origin of such a reduction is still debated, it always happens in an anisotropic way because the reduction mainly occurs along the shearing direction. Whether such anisotropy is a necessary condition for shear-induced area reduction remains an open question. Here, we investigate the contact area evolution of elastomer-based sphere-plane contacts under an isotropic shear loading, i.e. torsional loading. We find that, when macroscopic sliding is reached, the contact area has undergone a net area reduction. However, the area evolves non-monotonically as the twisting angle increases, with an initial rise up to a maximum before dropping to the value during macroscopic sliding. The ratio of maximum to initial contact area is found weakly dependent on the normal load, angular velocity and dwell time (time interval between the instants when the normal load and twist motion are first applied) within the investigated ranges. We show that non-monotonic area evolution can also be found under unidirectional shear loading conditions under large normal force. These observations challenge the current descriptions of shear-induced contact area evolution and are expected to serve as a benchmark for future modelling attempts in the field. △ Less

Submitted 30 October, 2024; originally announced October 2024.

Unveiling the interdisciplinary character of negative pressure

Authors: Francisco F. Barbosa, Lucas Squillante, Luciano Ricco, Roberto E. Lagos-Monaco, Antonio C. Seridonio, Mariano de Souza

Abstract: We explore the concept of negative pressure and its relevance in a variety of physical contexts: the expansion of the universe, mixture theory, cavitation, and the capillary effect in plants. Using thermodynamic arguments, we discuss the intricate connection between negative pressure and negative thermal expansion. We highlight the fact that metastable states and competing phases are often associa… ▽ More We explore the concept of negative pressure and its relevance in a variety of physical contexts: the expansion of the universe, mixture theory, cavitation, and the capillary effect in plants. Using thermodynamic arguments, we discuss the intricate connection between negative pressure and negative thermal expansion. We highlight the fact that metastable states and competing phases are often associated with the emergence of negative pressure. We also propose a new link between the effective Grüneisen parameter and nucleation theory. △ Less

Submitted 14 October, 2024; originally announced October 2024.

Comments: 15 pages, 5 figs, comments are welcome

Higgs-like stiffness and fractons on the verge of phase transitions

Authors: Lucas Squillante, Antonio C. Seridonio, Roberto E. Lagos-Monaco, Mariano de Souza

Abstract: In condensed matter Physics, massive longitudinal Higgs modes emerge from fluctuations of the order parameter. A few years ago, the Higgs mode was \emph{caught} experimentally in the vicinity of an insulator-to-superconductor quantum phase transition [Nat. Phys. $\textbf{11}$, 188 (2015)]. Here, we propose, in analogy to the Higgs mode, the concept of Higgs-like stiffness (HLS), which emerges clos… ▽ More In condensed matter Physics, massive longitudinal Higgs modes emerge from fluctuations of the order parameter. A few years ago, the Higgs mode was \emph{caught} experimentally in the vicinity of an insulator-to-superconductor quantum phase transition [Nat. Phys. $\textbf{11}$, 188 (2015)]. Here, we propose, in analogy to the Higgs mode, the concept of Higgs-like stiffness (HLS), which emerges close to both classical and quantum phase transitions as a universal manifestation of matter. We build up a Landau free energy for the dielectric response function to demonstrate that \emph{any} complex physical quantity can be used to infer the presence of the HLS. Our analysis is corroborated by experimental results of the quasi-static dielectric constant for the (TMTTF)$_2$SbF$_6$ Fabre salt. Yet, we discuss the appearance of fractons in connection with the locking of particular molecular rotational degrees of freedom. △ Less

Submitted 28 September, 2024; originally announced September 2024.

Comments: 8 pages, 2 figures. Comments are welcome

Cellular Griffiths-like phase

Authors: Lucas Squillante, Isys F. Mello, Luciano S. Ricco, Marcos F. Minicucci, Aniekan Magnus Ukpong, Antonio C. Seridonio, Roberto E. Lagos-Monaco, Mariano de Souza

Abstract: Protein compartmentalization in the frame of a liquid-liquid phase separation is a key mechanism to optimize spatiotemporal control of biological systems. Such a compartmentalization process reduces the intrinsic noise in protein concentration due to stochasticity in gene expression. Employing Flory-Huggins solution theory, Avramov/Casalini's model, and the Grüneisen parameter, we unprecedentedly… ▽ More Protein compartmentalization in the frame of a liquid-liquid phase separation is a key mechanism to optimize spatiotemporal control of biological systems. Such a compartmentalization process reduces the intrinsic noise in protein concentration due to stochasticity in gene expression. Employing Flory-Huggins solution theory, Avramov/Casalini's model, and the Grüneisen parameter, we unprecedentedly propose a cellular Griffiths-like phase (CGLP), which can impact its functionality and self-organization. The here-proposed CGLP is key ranging from the understanding of primary organisms' evolution to the treatment of diseases. Our findings pave the way for an alternative Biophysics approach to investigate coacervation processes. △ Less

Submitted 25 September, 2024; originally announced September 2024.

Comments: 13 pages, 2 figures, suppl. material upon request

Journal ref: Heliyon 10, e34622 (2024)

Exploring the expansion of the universe using the Grüneisen parameter

Authors: Lucas Squillante, Gabriel O. Gomes, Isys F. Mello, Guilherme Nogueira, Antonio C. Seridonio, Roberto E. Lagos-Monaco, Mariano de Souza

Abstract: For a perfect fluid, pressure $p$ and energy density $ρ$ are related via the equation of state (EOS) $ω= p/ρ$, where $ω$ is the EOS parameter, being its interpretation usually constrained to a numerical value for each universe era. Here, based on the Mie-Grüneisen EOS, we show that $ω$ is recognized as the effective Grüneisen parameter $Γ_{eff}$, whose singular contribution, the so-called Grüneise… ▽ More For a perfect fluid, pressure $p$ and energy density $ρ$ are related via the equation of state (EOS) $ω= p/ρ$, where $ω$ is the EOS parameter, being its interpretation usually constrained to a numerical value for each universe era. Here, based on the Mie-Grüneisen EOS, we show that $ω$ is recognized as the effective Grüneisen parameter $Γ_{eff}$, whose singular contribution, the so-called Grüneisen ratio $Γ$, quantifies the barocaloric effect. Our analysis suggests that the negative $p$ associated with dark-energy implies a metastable state and that in the dark-energy-dominated era $ω$ is time-dependent, which reinforces recent proposals of a time-dependent cosmological constant. Furthermore, we demonstrate that $Γ_{eff}$ is embodied in the energy-momentum stress tensor in the Einstein field equations, enabling us to analyse, in the frame of an imperfect fluid picture, anisotropic effects of the universe expansion. We propose that upon going from decelerated- to accelerated-expansion, a phase transition-like behavior can be inferred. Yet, our analysis in terms of entropy, $Γ$, and a by us adapted version of Avramov/Casalini's model to Cosmology unveil hidden aspects related to the expansion of the universe. Our findings pave the way to interpret cosmological phenomena in connection with concepts of condensed matter Physics via $Γ_{eff}$. △ Less

Submitted 25 September, 2024; originally announced September 2024.

Comments: 11 pages, 1 figure, comments are welcome

Journal ref: Results in Physics 57, 107344 (2024)

Universally non-diverging Grüneisen parameter at critical points

Authors: Samuel M. Soares, Lucas Squillante, Henrique S. Lima, Constantino Tsallis, Mariano de Souza

Abstract: According to Boltzmann-Gibbs (BG) statistical mechanics, the thermodynamic response, such as the isothermal susceptibility, at critical points (CPs) presents a divergent-like behavior. An appropriate parameter to probe both classical and quantum CPs is the so-called Grüneisen ratio $Γ$. Motivated by the results reported in Phys. Rev. B $\textbf{108}$, L140403 (2023), we extend the quantum version… ▽ More According to Boltzmann-Gibbs (BG) statistical mechanics, the thermodynamic response, such as the isothermal susceptibility, at critical points (CPs) presents a divergent-like behavior. An appropriate parameter to probe both classical and quantum CPs is the so-called Grüneisen ratio $Γ$. Motivated by the results reported in Phys. Rev. B $\textbf{108}$, L140403 (2023), we extend the quantum version of $Γ$ to the non-additive $q$-entropy $S_q$. Our findings indicate that using $S_q$ at the unique value of $q$ restoring the extensivity of the entropy, $Γ$ is universally non-diverging at CPs. We unprecedentedly introduce $Γ$ in terms of $S_q$, being BG recovered for $q \rightarrow 1$. We thus solve a long-standing problem related to the $\textit{illusory}$ diverging susceptibilities at CPs. △ Less

Submitted 17 September, 2024; originally announced September 2024.

Comments: 5 pages, 3 figs, comments are welcome

Squeezed state protection of fine structure in "Poor Man's Majorana" via quantum spin coupling

Authors: J. E. Sanches, L. T. Lustosa, L. S. Ricco, H. Sigurðsson, M. de Souza, M. S. Figueira, E. Marinho Jr., A. C. Seridonio

Abstract: The "Poor Man's Majorana" [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection has been theoretically predicted to rely on the minimal Kitaev chain. Afterward, a pair of superconducting and spinless quantum dots turned the proposal practicable and differential conductance pinpointed consistent fingerprints with such a scenario [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. In th… ▽ More The "Poor Man's Majorana" [Phys. Rev. B 86, 134528 (2012)] devoid of topological protection has been theoretically predicted to rely on the minimal Kitaev chain. Afterward, a pair of superconducting and spinless quantum dots turned the proposal practicable and differential conductance pinpointed consistent fingerprints with such a scenario [Nature 614, 445 (2023) and Nature 630, 329 (2024)]. In this work, we propose a model wherein the "Poor Man's Majorana" presents protection when one of the dots is exchange coupled to a quantum spin. If this quantum dot is perturbed by tuning the exchange coupling, the well-known spill over-like behavior of this Majorana surprisingly remains unchanged, and solely half of the fine structure is unexpectedly viewed. As a matter of fact, the "Poor Man's Majorana" zero mode consists in squeezing of the other half at zero frequency, which imposes its pinning there and prevents the mixing of the mode with the explicit fine structure. We claim that if the supposed unavoidable split of the zero mode by the fine structure is unexpectedly absent, then the "Poor Man's Majorana" can be considered robust against the quantum spin. In this way, it becomes protected and the lack of topological protection paradigm of the "Poor Man's Majorana" has been revisited, pushing this seemingly well-established issue into a new direction. △ Less

Submitted 27 August, 2024; originally announced August 2024.

Unusual low-temperature behavior in the half-filled band of the one-dimensional extended Hubbard model in atomic limit

Authors: Onofre Rojas, S. M. de Souza, J. Torrico, L. M. Verissimo, M. S. S. Pereira, M. L. Lyra, Oleg Derzhko

Abstract: Recently, a kind of finite-temperature pseudo-transition was observed in several quasi-one-dimensional models. In this work, we consider a genuine one-dimensional extended Hubbard model in the atomic limit, influenced by an external magnetic field and with the arbitrary number of particles controlled by the chemical potential. The one-dimensional extended Hubbard model in the atomic limit was init… ▽ More Recently, a kind of finite-temperature pseudo-transition was observed in several quasi-one-dimensional models. In this work, we consider a genuine one-dimensional extended Hubbard model in the atomic limit, influenced by an external magnetic field and with the arbitrary number of particles controlled by the chemical potential. The one-dimensional extended Hubbard model in the atomic limit was initially studied in the seventies and has been investigated over the past decades, but it still surprises us today with its fascinating properties. We rigorously analyze its low-temperature behavior using the transfer matrix technique and provide accurate numerical results. Our analysis confirms that there is an anomalous behavior in the half-filled band, specifically occurring between the alternating pair (AP) and paramagnetic (PM) phases at zero temperature. Previous investigations did not deeply identify this anomalous behavior, maybe due to the numerical simplicity of the model, but from analytical point of view this is not so easy to manipulate algebraically because one needs to solve an algebraic cubic equation. In this study, we explore this behavior and clearly distinguish the pseudo-transition, which could easily be mistaken with a real phase transition. This anomalous behavior mimics features of both first- and second-order phase transitions. However, due to its nature, we cannot expect a finite-temperature phase transition in this model. △ Less

Submitted 7 September, 2024; v1 submitted 3 June, 2024; originally announced June 2024.

Comments: 12 pages, 10 figures

Journal ref: Phys. Rev. E 110, 024130 (2024)

Random Apollonian networks with tailored clustering coefficient

Authors: Eduardo M. K. Souza, Guilherme M. A. Almeida

Abstract: We introduce a family of complex networks that interpolates between the Apollonian network and its binary version, recently introduced in [Phys. Rev. E \textbf{107}, 024305 (2023)], via random removal of nodes. The dilution process allows the clustering coefficient to vary from $C=0.828$ to $C=0$ while maintaining the behavior of average path length and other relevant quantities as in the determin… ▽ More We introduce a family of complex networks that interpolates between the Apollonian network and its binary version, recently introduced in [Phys. Rev. E \textbf{107}, 024305 (2023)], via random removal of nodes. The dilution process allows the clustering coefficient to vary from $C=0.828$ to $C=0$ while maintaining the behavior of average path length and other relevant quantities as in the deterministic Apollonian network. Robustness against the random deletion of nodes is also reported on spectral quantities such as the ground-state localization degree and its energy gap to the first excited state. The loss of the $2π/ 3$ rotation symmetry as a tree-like network emerges is investigated in the light of the hub wavefunction amplitude. Our findings expose the interplay between the small-world property and other distinctive traits exhibited by Apollonian networks, as well as their resilience against random attacks. △ Less

Submitted 27 March, 2024; originally announced March 2024.

Comments: 6 pages, 7 figures

Journal ref: Physical Review E 109, 054311 (2024)

A Cooper-pair beam splitter as a feasible source of entangled electrons

Authors: B. Sharmila, F. M. Souza, H. M. Vasconcelos, L. Sanz

Abstract: We investigate the generation of an entangled electron pair emerging from a system composed of two quantum dots attached to a superconductor Cooper pair beam splitter. We take into account three processes: Crossed Andreev Reflection, cotuneling, and Coulomb interaction. Together, these processes play crucial roles in the formation of entangled electronic states, with electrons being in spatially s… ▽ More We investigate the generation of an entangled electron pair emerging from a system composed of two quantum dots attached to a superconductor Cooper pair beam splitter. We take into account three processes: Crossed Andreev Reflection, cotuneling, and Coulomb interaction. Together, these processes play crucial roles in the formation of entangled electronic states, with electrons being in spatially separated quantum dots. By using perturbation theory, we derive an analytical effective model that allows a simple picture of the intricate process behind the formation of the entangled state. Several entanglement quantifiers, including quantum mutual information, negativity, and concurrence, are employed to validate our findings. Finally, we define and calculate the covariance associated with the detection of two electrons, each originating from one of the quantum dots with a specific spin value. The time evolution of this observable follows the dynamics of all entanglement quantifiers, thus suggesting that it can be a useful tool for mapping the creation of entangled electrons in future applications within quantum information protocols. △ Less

Submitted 24 June, 2024; v1 submitted 29 January, 2024; originally announced January 2024.

Comments: To be published in Physical Review A

Journal ref: Physical Review A 109, 062439 (2024)

Topological speckles

Authors: Yure M. I. A. Rodrigues, Matheus F. V. Oliveira, Andre M. C. Souza, Marcelo L. Lyra, Francisco A. B. F. de Moura, Guilherme M. A. Almeida

Abstract: The time evolution of a topological Su-Schrieffer-Heeger chain is analyzed through the statistics of speckle patterns. The emergence of topological edge states dramatically affects the dynamical fluctuations of the wavefunction. The intensity statistics is found to be described by a family of noncentral chi-squared distributions, with the noncentrality parameter reflecting on the degree of edge-st… ▽ More The time evolution of a topological Su-Schrieffer-Heeger chain is analyzed through the statistics of speckle patterns. The emergence of topological edge states dramatically affects the dynamical fluctuations of the wavefunction. The intensity statistics is found to be described by a family of noncentral chi-squared distributions, with the noncentrality parameter reflecting on the degree of edge-state localization. The response of the speckle contrast with respect to the dimerization of the chain is explored in detail as well as the role of chiral symmetry-breaking disorder, number of edge states, their energy gap, and the locations between which the transport occurs. In addition to providing a venue for speckle customization, our results appeal to the use of speckle patterns for characterization of nontrivial topological properties. △ Less

Submitted 31 October, 2023; originally announced October 2023.

Comments: 6 pages, 4 figures

Magnetocaloric effect in $\mathrm{Cu}_{3}$-type compounds using the Heisenberg antiferromagnetic model in a triangular ring

Authors: G. A. Antonio, J. Torrico, A. S. da Mata, S. M. de Souza, Onofre Rojas

Abstract: In this work we present a theoretical investigation into an antiferromagnetically coupled spin system, specifically ${\rm Cu}_{3}-X$ ($\mathrm{X=As,Sb}$), which exhibits an isosceles triangular configuration or slightly distorted equilateral triangular configuration, as previously identified in reference {[}Phys. Rev. Lett. \textbf{96}, 107202 (2006){]}. This system can be effectively represented… ▽ More In this work we present a theoretical investigation into an antiferromagnetically coupled spin system, specifically ${\rm Cu}_{3}-X$ ($\mathrm{X=As,Sb}$), which exhibits an isosceles triangular configuration or slightly distorted equilateral triangular configuration, as previously identified in reference {[}Phys. Rev. Lett. \textbf{96}, 107202 (2006){]}. This system can be effectively represented by the Heisenberg model on a triangular structure, taking into account the exchange interaction, the Dzyaloshinskii-Moriya interaction, g-factors and external magnetic field, as delineated in the aforementioned reference. By using numerical approach we explore both zero-temperature and finite-temperature behaviors of a ${\rm Cu}_{3}$-like antiferromagnetically coupled spin system. At zero temperature, the system displays a 1/3 quasi-plateau magnetization, when the magnetic field is varied. Moreover, we place particular emphasis on magnetic properties including magnetization, magnetic susceptibility, entropy, and specific heat at finite temperatures. Furthermore, we investigate the magnetocaloric effect as a function of an externally imposed magnetic field, oriented both parallel and perpendicular to the plane of the triangular structure. Interestingly, these configurations demonstrate remarkably similar behavior for both orientations of the magnetic field. Our investigation also includes an analysis of the adiabatic curve, the Grüneisen parameter, and the variation in entropy when applied or removed the magnetic field. The magnetocaloric effect is found to be more prominent in low the temperature region, typically at $T\sim1$K, for both parallel and perpendicular magnetic fields at $\sim4.5$T and $\sim5$T, respectively. △ Less

Submitted 10 October, 2023; v1 submitted 27 September, 2023; originally announced September 2023.

Comments: 9 pages, 8 figures

Journal ref: Phys. Rev. B 108, 134415 (2023)

Grüneisen parameter as an entanglement compass and the breakdown of the Hellmann-Feynman theorem

Authors: Lucas Squillante, Luciano S. Ricco, Aniekan Magnus Ukpong, Roberto E. Lagos-Monaco, Antonio C. Seridonio, Mariano de Souza

Abstract: The Grüneisen ratio $Γ$, i.e., the singular part of the ratio of thermal expansion to the specific heat, has been broadly employed to explore both finite-$T$ and quantum critical points (QCPs). For a genuine quantum phase transition (QPT), thermal fluctuations are absent and thus the thermodynamic $Γ$ cannot be employed. We propose a quantum analogue to $Γ$ that computes entanglement as a function… ▽ More The Grüneisen ratio $Γ$, i.e., the singular part of the ratio of thermal expansion to the specific heat, has been broadly employed to explore both finite-$T$ and quantum critical points (QCPs). For a genuine quantum phase transition (QPT), thermal fluctuations are absent and thus the thermodynamic $Γ$ cannot be employed. We propose a quantum analogue to $Γ$ that computes entanglement as a function of a tuning parameter $λ$ and show that QPTs take place only for systems in which the ground-state energy depends on $λ$ non-linearly. Furthermore, we demonstrate the breakdown of the Hellmann-Feynman theorem in the thermodynamic limit at any QCP. We showcase our approach using the quantum 1D Ising model with transverse field and Kane's quantum computer. The slowing down of the dynamics and thus the "creation of mass" close to any QCP/QPT is also discussed. △ Less

Submitted 25 September, 2024; v1 submitted 1 June, 2023; originally announced June 2023.

Comments: 5 pages, 3 figures, comments are wellcome!

Journal ref: Physical Review B 108, L140403 (2023)

Analogue of atomic collapse for adatoms on rhombohedral multilayer graphene

Authors: W. C. Silva, J. E. Sanches, A. M. Freitas, L. T. Lustosa, M. de Souza, A. C. Seridonio

Abstract: We propose that a multi-graphene of ABC-type stacking yields virtual bound states lying within the Coulomb insulating gap of an Anderson-like adatom. Wondrously, a virtual state constitutes the counterpart of the atomic collapse phenomenon proposed in relativistic atomic Physics, while the second emerges as its particle-hole symmetric, analogous to a positron state. Thus, we introduce the effect a… ▽ More We propose that a multi-graphene of ABC-type stacking yields virtual bound states lying within the Coulomb insulating gap of an Anderson-like adatom. Wondrously, a virtual state constitutes the counterpart of the atomic collapse phenomenon proposed in relativistic atomic Physics, while the second emerges as its particle-hole symmetric, analogous to a positron state. Thus, we introduce the effect as the adatomic collapse, which occurs due to a flat band with a dispersionless state and a divergent density of states $\sim|\varepsilon-\varepsilon_{F}|^{2/J-1}$ near the Fermi energy $\varepsilon_{F}$ for $J\geq3,$ where $Jπ$ is the Berry phase. We conclude this scenario based on the Kramers-Kronig transformation of the quasiparticle broadening, from where we observe that the aforementioned van Hove singularity induces virtual bound states. Counterintuitively, near the singularity, we find these states above and below the Fermi energy correlated to the existence of the bottom and top edges of the Coulomb insulating region, respectively. As such a behavior rises without a twist, the system is known as Moiréless and the phenomenon emerges also assisted by the adatom Coulomb correlations. Similarly to Science 340, 734 (2013) we find the effective critical atomic number $\mathcal{Z}_{c}\sim0.96$ in contrast to an ultra-heavy nucleus. Thus, we point out that multi-graphene is a proper playground for testing a predicted phenomenon of the relativistic atomic Physics in the domain of the condensed matter Physics. △ Less

Submitted 11 December, 2023; v1 submitted 5 April, 2023; originally announced April 2023.

Towards a quasiphase transition in the single-file chain of water molecules: Simple lattice model

Authors: Maksym Druchok, Volodymyr Krasnov, Taras Krokhmalskii, Tatiana Cardoso e Bufalo, Sergio Martins de Souza, Onofre Rojas, Oleg Derzhko

Abstract: Recently, X.Ma et al. [Phys. Rev. Lett. 118, 027402 (2017)] have suggested that water molecules encapsulated in (6,5) single-wall carbon nanotube experience a temperature-induced quasiphase transition around 150 K interpreted as changes in the water dipoles orientation. We discuss further this temperature-driven quasiphase transition performing quantum chemical calculations and molecular dynamics… ▽ More Recently, X.Ma et al. [Phys. Rev. Lett. 118, 027402 (2017)] have suggested that water molecules encapsulated in (6,5) single-wall carbon nanotube experience a temperature-induced quasiphase transition around 150 K interpreted as changes in the water dipoles orientation. We discuss further this temperature-driven quasiphase transition performing quantum chemical calculations and molecular dynamics simulations and, most importantly, suggesting a simple lattice model to reproduce the properties of the one-dimensionally confined finite arrays of water molecules. The lattice model takes into account not only the short-range and long-range interactions but also the rotations in a narrow tube and the both ingredients provide an explanation for a temperature-driven orientational ordering of the water molecules, which persists within a relatively wide temperature range. △ Less

Submitted 18 February, 2023; originally announced February 2023.

Comments: 15 pages, 10 figures

Journal ref: J. Chem. Phys. 158, 104304 (2023)

Fractionalization of Majorana-Ising-type quasiparticles

Authors: J. E. Sanches, L. T. Lustosa, L. S. Ricco, I. A. Shelykh, M. de Souza, M. S. Figueira, A. C. Seridonio

Abstract: We theoretically investigate the spectral properties of a quantum impurity (QI) hosting the here proposed {Majorana-Ising-type quasiparticle (MIQ) excitation}. It arises from the coupling between a finite topological superconductor (TSC) based on a chain of magnetic adatoms-superconducting hybrid system and an integer large spin $S$ flanking the QI. Noteworthy, the spin $S$ couples to the QI via t… ▽ More We theoretically investigate the spectral properties of a quantum impurity (QI) hosting the here proposed {Majorana-Ising-type quasiparticle (MIQ) excitation}. It arises from the coupling between a finite topological superconductor (TSC) based on a chain of magnetic adatoms-superconducting hybrid system and an integer large spin $S$ flanking the QI. Noteworthy, the spin $S$ couples to the QI via the Ising-type exchange interaction. As the Majorana zero-modes (MZMs) at the edges of the TSC chain are overlapped, we counterintuitively find a regime wherein the Ising term modulates the localization of a fractionalized and resonant MZM at the QI site. Interestingly enough, the fermionic nature of this state is revealed as purely of electron tunneling-type and most astonishingly, it has the Andreev conductance completely null in its birth. Therefore, we find that a resonant edge state appears as a zero-mode and discuss it in terms of a poor man's Majorana[Nature 614, 445 (2023)]. △ Less

Submitted 11 December, 2023; v1 submitted 9 January, 2023; originally announced January 2023.

Valence state and lattice incorporation of Ni in Zn/Co-based magnetic oxides

Authors: V. Ney, B. Henne, M. de Souza, W. Jantsch, K. M. Johansen, F. Wilhelm, A. Rogalev, A. Ney

Abstract: Ni incorporation has been studied in a comprehensive range of Zn/Co-based magnetic oxides to elucidate it valence state and lattice incorporation. The resulting structural and magnetic properties are studied in detail. To the one end Ni in incorporated by in-diffusion as well as reactive magnetron co-sputtering in wurtzite ZnO where only the Ni-diffused ZnO exhibits significant conductivity. This… ▽ More Ni incorporation has been studied in a comprehensive range of Zn/Co-based magnetic oxides to elucidate it valence state and lattice incorporation. The resulting structural and magnetic properties are studied in detail. To the one end Ni in incorporated by in-diffusion as well as reactive magnetron co-sputtering in wurtzite ZnO where only the Ni-diffused ZnO exhibits significant conductivity. This is complemented by Ni and Co codoping of ZnO leading. To the other end, the ZnCo$_2$O$_4$ spinel is co-doped with varying amounts of Ni. In the wurtzite oxides Ni is exclusively found on tetrahedral lattice sites in its formal 2+ oxidation state as deep donor. It behaves as an anisotropic paramagnet and a limited solubility of Ni about 10\% is found. Due to its smaller magnetic moment it can induce partial uncompensation of the Co magnetic moments due to antiferromagnetic coupling. In the spinel Ni is found to be incorporated in its formal 3+ oxidation state on octahedral sites and couples antiferromagnetically to the Co moments leading again to magnetic uncompensation of the otherwise antiferromagnetic ZnCo$_2$O$_4$ spinel and to ferrimagnetism at higher Ni concentrations. Increasing Ni even further leads to phase separation of cubic NiO resulting in an exchange-biased composite magnetic oxide. △ Less

Submitted 9 August, 2022; originally announced August 2022.

Comments: 15 pages, 13 figures

Binary Apollonian networks

Authors: Eduardo M. K. Souza, Guilherme M. A. Almeida

Abstract: There is a well-known relationship between the binary Pascal's triangle and Sierpinski triangle in which the latter obtained from the former by successive modulo 2 additions on one of its corners. Inspired by that, we define a binary Apollonian network and obtain two structures featuring a kind of dendritic growth. They are found to inherit the small-world and scale-free property from the original… ▽ More There is a well-known relationship between the binary Pascal's triangle and Sierpinski triangle in which the latter obtained from the former by successive modulo 2 additions on one of its corners. Inspired by that, we define a binary Apollonian network and obtain two structures featuring a kind of dendritic growth. They are found to inherit the small-world and scale-free property from the original network but display no clustering. Other key network properties are explored as well. Our results reveal that the structure contained in the Apollonian network may be employed to model an even wider class of real-world systems. △ Less

Submitted 28 June, 2022; originally announced June 2022.

Journal ref: Phys. Rev. E 107, 024305 (2023)

Topological charge Fano effect in multi-Weyl semimetals

Authors: W. C. Silva, W. N. Mizobata, J. E. Sanches, L. S. Ricco, I. A. Shelykh, M. de Souza, M. S. Figueira, E. Vernek, A. C. Seridonio

Abstract: We theoretically analyze the Fano interference in a single impurity multi-Weyl semimetal hybrid system and show the emergence of the topological charge Fano effect in the bulk local density of states. In multi-Weyl semimetals, the number of Fermi arcs at the system boundaries is determined by the topological charge $J$, a direct consequence of the "bulk-boundary" correspondence principle. Analogou… ▽ More We theoretically analyze the Fano interference in a single impurity multi-Weyl semimetal hybrid system and show the emergence of the topological charge Fano effect in the bulk local density of states. In multi-Weyl semimetals, the number of Fermi arcs at the system boundaries is determined by the topological charge $J$, a direct consequence of the "bulk-boundary" correspondence principle. Analogously, we find that $J$ also modulates the bulk Fano profile of the system with an embedded quantum impurity. Thus, by increasing $J$, the Fano lineshape evolves from resonant, typical for $J=1$ (single Weyl), towards antiresonant, extrapolating to the so-called hyper Weyl semimetals with $J\gg1$. Specially for the maximum case protected by the rotational symmetry $C_{2J=6}$, namely the $J=3$ (triple Weyl), which acquires asymmetric Fano profile, the Fano parameter absolute value is predicted to be $\tan(C_{2J=6})$, where $C_{2J}\equiv(360^{\circ}/2J)$ defines the rotational angle. Hence, the Fano discretization in the $J$ term introduces the topological charge Fano effect in multi-Weyl semimetals. We also suggest a transport device where we expect that the proposed Fano effect could be detected. △ Less

Submitted 24 June, 2022; v1 submitted 27 March, 2022; originally announced March 2022.

Non-Gaussian Effects of the Saha's Ionization in the Early Universe

Authors: L. L. Sales, F. C. Carvalho, E. P. Bento, H. T. C. M. Souza

Abstract: Tsallis' thermostatistical has received increasing attention due to its success in describing phenomena that manifest unusual thermodynamic properties. In this context, the generalized Saha equation must follow a condition of generalized thermal equilibrium of matter and radiation. The present work aims to explore the non-Gaussian effects on Saha's ionization via Tsallis statistics. To accomplish… ▽ More Tsallis' thermostatistical has received increasing attention due to its success in describing phenomena that manifest unusual thermodynamic properties. In this context, the generalized Saha equation must follow a condition of generalized thermal equilibrium of matter and radiation. The present work aims to explore the non-Gaussian effects on Saha's ionization via Tsallis statistics. To accomplish this, we generalized the number density taking into account a non-Gaussian Fermi-Dirac distribution, and then set out the Saha equation for the cosmological recombination. As a result, we highlight two new non-Gaussian effects: $i$) two generalized chemical equilibrium conditions, one for the relativistic regime and the other for the non-relativistic one; and $ii$) the hydrogen binding $q$-energy. We demonstrated that to yields smooth shifts in the binding energy, the $a$-parameter must be very small. We also showed that binding $q$-energy exhibits symmetrical behavior around the value of the standard binding energy. Besides, we used the $q$-energy in order to access other hydrogen energy levels, and we ascertained the values of the $a$-parameter that access those levels and their relationship to temperature. Finally, we employed these results to examine the non-Gaussian effects of the deuterium bottleneck, recombination and the particle anti-particle excess. △ Less

Submitted 19 January, 2022; originally announced January 2022.

Comments: 9 pages, 2 figures

Journal ref: Eur. Phys. J. C (2022) 82:54

Atomic frustration-based twistronics

Authors: W. N. Mizobata, J. E. Sanches, M. Penha, W. C. Silva, C. A. Carvalho, M. S. Figueira, M. de Souza, A. C. Seridonio

Abstract: We theoretically investigate atomic frustrated states in diatomic molecules hosted by the bilayer graphene setup twisted by the first magic angle and with broken inversion symmetry in the Dirac cones of the system mini Brillouin zones. Such states show local spectral features typically from uncoupled atoms, but counterintuitively, they also exhibit nonlocal molecular correlations, which turn them… ▽ More We theoretically investigate atomic frustrated states in diatomic molecules hosted by the bilayer graphene setup twisted by the first magic angle and with broken inversion symmetry in the Dirac cones of the system mini Brillouin zones. Such states show local spectral features typically from uncoupled atoms, but counterintuitively, they also exhibit nonlocal molecular correlations, which turn them into atomically frustrated. By considering a particle-hole symmetric molecule in the Moiré superlattice length-scale, we reveal distinctly from the metallic Weyl counterparts, a molecular zero mode atomically frustrated at the spectral densities of the dimer's atoms. To this end, a strong metallic phase with a plateau in the density of states established by the broken inversion symmetry, together with pronounced blue and red shifts in the molecular levels, due to the magic angle condition, should occur synergistically with atomic Coulomb correlations. Consequently, an entire collapse of these molecular peaks into a single one atomically frustrated, taking place exactly at the Fermi energy, becomes feasible just by tuning properly opposite gate voltages attached to the graphene monolayers. Therefore, we propose that unusual molecular bindings can be engineered via the twistronics of the bilayer graphene system, in particular, if its metallic phase is fully established. △ Less

Submitted 10 October, 2021; originally announced October 2021.

Journal ref: 2D Materials 8, 045038 (2021)

Fine-Tuning the Polarizable CL&Pol Force Field for the Deep Eutectic Solvent Ethaline

Authors: Rafael Maglia de Souza, Mikko Karttunen, Mauro Carlos Costa Ribeiro

Abstract: Polarizable force fields are gradually becoming a common choice for ionic soft matter, in particular for molecular dynamics (MD) simulations of ionic liquids (ILs) and deep eutectic solvents (DESs). The CL&Pol force field introduced in 2019 is the first general, transferable and polarizable force field for MD simulations of different types of DESs. The original formulation contains, however, some… ▽ More Polarizable force fields are gradually becoming a common choice for ionic soft matter, in particular for molecular dynamics (MD) simulations of ionic liquids (ILs) and deep eutectic solvents (DESs). The CL&Pol force field introduced in 2019 is the first general, transferable and polarizable force field for MD simulations of different types of DESs. The original formulation contains, however, some problems that appear in simulations of ethaline and may also have a broader impact. First, the originally proposed atomic diameter parameters are unbalanced, resulting in too weak interactions between the chlorides and the hydroxyl groups of the ethylene glycol molecules. This, in turn, causes an artificial phase separation in long simulations. Second, there is an overpolarization of chlorides due to strong induced dipoles that give rise to the presence of peaks and antipeaks at very low $q$-vector values (\SI{2.4}{\per\nano\meter}) in the partial components of the structure factors. In physical terms, this is equivalent to overestimated spatial nano-scale heterogeneity. To correct these problems, we adjusted the chloride-hydroxyl radial distribution functions against \textit{ab initio} data and then extended the use of the Tang-Toennis damping function for the chlorides' induced dipoles. These adjustments correct the problems without losing the robustness of the CL\&Pol force field. The results were also compared with the non-polarizable version, the CL&P force field. We expect that the corrections will facilitate reliable use of the CL&Pol force field for other types of DESs. △ Less

Submitted 28 September, 2021; originally announced September 2021.

Anomalous thermodynamics in a mixed spin-1/2 and spin-1 hexagonal nanowire system

Authors: R. A. Pimenta, O. Rojas, S. M. de Souza

Abstract: The mixed spin-1/2 Ising model and spin-1 Blume-Capel model in an hexagonal nanowire structure under the presence of crystal field is considered. The free energy is obtained through the transfer matrix technique, which is solved numerically. Our main result lies in the presence of pseudo-transition in low temperature region near the ferrimagnetic/ferromagnetic boundary, due to the influence of a c… ▽ More The mixed spin-1/2 Ising model and spin-1 Blume-Capel model in an hexagonal nanowire structure under the presence of crystal field is considered. The free energy is obtained through the transfer matrix technique, which is solved numerically. Our main result lies in the presence of pseudo-transition in low temperature region near the ferrimagnetic/ferromagnetic boundary, due to the influence of a crystal field. The evidence of a pseudo-transition is observed in several quantities. Free energy first derivative quantities like entropy and internal energy show an abrupt but continuous jump, whereas quantities associated with second derivatives of the free energy like the specific heat exhibit a strong sharp peak, quite similar to a second order phase transition. We also investigate magnetization patterns and do not find evidence of spontaneous magnetization. Nevertheless, assuming a small magnetic field, we can induce a magnetization which resembles a spontaneous magnetization at a pseudo-critical temperature. △ Less

Submitted 3 August, 2021; originally announced August 2021.

Comments: 13 pages, 15 figures

Controlling the atom-sphere interaction with an external electric field

Authors: P. P. Abrantes, V. Pessanha, Reinaldo de Melo e Souza, C. Farina

Abstract: We investigate the system constituted by a polarizable atom near a nanosphere under the influence of an external electrostatic field, showing that the attractive dispersive force between them can be overcome by the electrostatic interaction. Therefore, in addition to the advantageous possibility of actively tuning the resultant force with an external agent without the requirement of physical conta… ▽ More We investigate the system constituted by a polarizable atom near a nanosphere under the influence of an external electrostatic field, showing that the attractive dispersive force between them can be overcome by the electrostatic interaction. Therefore, in addition to the advantageous possibility of actively tuning the resultant force with an external agent without the requirement of physical contact, this force may also become repulsive. We analyze this situation in different physical regimes of distance and explore the interaction of different atoms with both metallic and dielectric spheres, discussing which cases are easier to control. Furthermore, our results reveal that these repulsive forces can be achieved with feasible field intensities in the laboratory. △ Less

Submitted 25 August, 2021; v1 submitted 9 July, 2021; originally announced July 2021.

Journal ref: Phys. Rev. A 104, 022820 (2021)

Zone refining of ultra-high purity sodium iodide for low-background detectors

Authors: Burkhant Suerfu, Frank Calaprice, Michael Souza

Abstract: There has been a growing interest in ultra-high purity, low-background NaI(Tl) crystals for dark matter direct searches. Past research indicates that zone refining is an efficient and scalable way to purify NaI. In particular, K and Rb -- two elements with radioisotopes that can cause scintillation backgrounds -- can be efficiently removed by zone refining. However, zone refining has never been de… ▽ More There has been a growing interest in ultra-high purity, low-background NaI(Tl) crystals for dark matter direct searches. Past research indicates that zone refining is an efficient and scalable way to purify NaI. In particular, K and Rb -- two elements with radioisotopes that can cause scintillation backgrounds -- can be efficiently removed by zone refining. However, zone refining has never been demonstrated for ultra-high purity NaI which became commercially available recently. In this article, we show that many common metallic impurities can be efficiently removed via zone refining. A numerical model for predicting the final impurity distribution was developed and used to fit the ICP-MS measurement data to determine the segregation coefficient and the initial concentration. Under this scheme, the segregation coefficient for K is estimated to be 0.57, indicating that zone refining is still effective in removing K from ultra-high purity NaI. As zone refining tends to move the impurities to one end, elements with concentrations too low to be measured directly in the unprocessed powder can potentially be detected in the end due to the enrichment. We also present an analysis technique to estimate the initial concentrations of impurities with partial data, which effectively enhances the sensitivity of the spectrometer. Using this technique, the initial concentration of $^{85}$Rb is estimated to be between 5 ppt and 14 ppt at 90% CL, at least 14 times lower than the detection limit of ICP-MS and 7 times lower than the current most stringent limit set by the DAMA collaboration by direct counting of radioactive $^{87}$Rb. These results imply that zone refining is a key technique in developing next-generation, NaI-based crystal scintillators for dark matter direct detection. △ Less

Submitted 13 May, 2021; originally announced May 2021.

Journal ref: Phys. Rev. Applied 16, 014060 (2021)

Low temperature pseudo-phase transition in an extended Hubbard diamond chain

Authors: Onofre Rojas, Jordana Torrico, L. M. Veríssimo, M. S. S. Pereira, S. M. de Souza, M. L. Lyra

Abstract: We consider the extended Hubbard diamond chain with an arbitrary number of particles driven by chemical potential. The interaction between dimer diamond chain and nodal couplings is considered in the atomic limit (no hopping), while the dimer interaction includes the hopping term. We demonstrate that this model exhibits a pseudo-transition effect in the low-temperature regime. Here, we explore the… ▽ More We consider the extended Hubbard diamond chain with an arbitrary number of particles driven by chemical potential. The interaction between dimer diamond chain and nodal couplings is considered in the atomic limit (no hopping), while the dimer interaction includes the hopping term. We demonstrate that this model exhibits a pseudo-transition effect in the low-temperature regime. Here, we explore the pseudo-transition rigorously by analyzing several physical quantities. The internal energy and entropy depict sudden, although continuous, jumps which closely resembles discontinuous or first-order phase transition. At the same time, the correlation length and specific heat exhibit astonishing strong sharp peaks, quite similar to a second-order phase transition. We associate the ascending and descending part of the peak with power-law \textquotedbl pseudo-critical\textquotedbl exponents. We determine the pseudo-critical exponents in the temperature range where these peaks are developed, namely $ν=1$ for the correlation length and $α=3$ for the specific heat. We also study the behavior of the electron density and isothermal compressibility around the pseudo-critical temperature. △ Less

Submitted 20 February, 2021; originally announced February 2021.

Comments: 14 pages, 12 figures

Journal ref: Phys. Rev. E 103, 042123 (2021)

Spin-Polarized Initialization and Readout for Single-Qubit State Tomography

Authors: M. B. Sambú, L. Sanz, F. M. Souza

Abstract: We propose a theoretical protocol for reconstructing the density matrix of a single-electron spin qubit using spin-polarized transport. The system consists of a quantum dot coupled to ferromagnetic reservoirs and subject to a magnetic field lying in the $xy$ plane of the Bloch sphere. Spin-dependent tunneling events measured along the $x\pm$, $y\pm$, and $z\pm$ quantization axes give rise to proba… ▽ More We propose a theoretical protocol for reconstructing the density matrix of a single-electron spin qubit using spin-polarized transport. The system consists of a quantum dot coupled to ferromagnetic reservoirs and subject to a magnetic field lying in the $xy$ plane of the Bloch sphere. Spin-dependent tunneling events measured along the $x\pm$, $y\pm$, and $z\pm$ quantization axes give rise to probability distributions that encode the quantum state of the qubit. The open-system dynamics are described using a Lindblad master equation, which captures the time evolution of the spin under continuous coupling to the reservoirs. By counting tunneling events for four different magnetic alignments, we formulate a scheme for reconstructing the full density matrix of the qubit. The resulting simulation data are analyzed using machine-learning techniques to process the measured probability distributions and infer the corresponding density matrix elements. The proposed model enables complete access to the open-system density matrix, including both population probabilities and relative phase information. Successful state reconstruction demonstrates the validity and robustness of the approach, highlighting its applicability to experimentally accessible spin-transport platforms. △ Less

Submitted 30 March, 2026; v1 submitted 26 January, 2021; originally announced January 2021.

Comments: revised version, 9 pages, 4 figures

Magnetoelastic properties of a spin-1/2 Ising-Heisenberg diamond chain in vicinity of a triple coexistence point

Authors: N. Ferreira, J. Torrico, S. M. de Souza, O. Rojas, J. Strečka

Abstract: We study magnetoelastic properties of a spin-1/2 Ising-Heisenberg diamond chain, whose elementary unit cell consists of two decorating Heisenberg spins and one nodal Ising spin. It is assumed that each couple of the decorating atoms including the Heisenberg spins harmonically vibrates perpendicularly to the chain axis, while the nodal atoms involving the Ising spins are placed at rigid positions w… ▽ More We study magnetoelastic properties of a spin-1/2 Ising-Heisenberg diamond chain, whose elementary unit cell consists of two decorating Heisenberg spins and one nodal Ising spin. It is assumed that each couple of the decorating atoms including the Heisenberg spins harmonically vibrates perpendicularly to the chain axis, while the nodal atoms involving the Ising spins are placed at rigid positions when ignoring their lattice vibrations. An effect of the magnetoelastic coupling on a ground state and finite-temperature properties is particularly investigated close to a triple coexistence point depending on a spring-stiffness constant ascribed to the Heisenberg interaction. The magnetoelastic nature of the Heisenberg dimers is reflected through a non-null plateau of the entropy emergent in a low-temperature region, whereas the specific heat displays an anomalous peak slightly below the temperature region corresponding to the entropy plateau. The magnetization also exhibits a plateau in the same temperature region at almost saturated value before it gradually tends to zero upon increasing of temperature. The magnetic susceptibility displays within the plateau region an inverse temperature dependence, which slightly drops above this plateau, whereas an inverse temperature dependence is repeatedly recovered at high enough temperatures. △ Less

Submitted 18 January, 2021; originally announced January 2021.

Comments: 12 pages, 5 figures

Journal ref: Condens. Matter Phys., 2020, vol. 23, No. 4, 43713

Experimental Validation of Fully Quantum Fluctuation Theorems Using Dynamic Bayesian Networks

Authors: Kaonan Micadei, John P. S. Peterson, Alexandre M. Souza, Roberto S. Sarthour, Ivan S. Oliveira, Gabriel T. Landi, Roberto M. Serra, Eric Lutz

Abstract: Fluctuation theorems are fundamental extensions of the second law of thermodynamics for small systems. Their general validity arbitrarily far from equilibrium makes them invaluable in nonequilibrium physics. So far, experimental studies of quantum fluctuation relations do not account for quantum correlations and quantum coherence, two essential quantum properties. We here experimentally verify det… ▽ More Fluctuation theorems are fundamental extensions of the second law of thermodynamics for small systems. Their general validity arbitrarily far from equilibrium makes them invaluable in nonequilibrium physics. So far, experimental studies of quantum fluctuation relations do not account for quantum correlations and quantum coherence, two essential quantum properties. We here experimentally verify detailed and integral fully quantum fluctuation theorems for heat exchange using two quantum-correlated thermal spins-1/2 in a nuclear magnetic resonance setup. We confirm, in particular, individual integral fluctuation relations for quantum correlations and quantum coherence, as well as for the sum of all quantum contributions. These refined formulations of the second law are important for the investigation of fully quantum features in nonequilibrium thermodynamics. △ Less

Submitted 24 March, 2022; v1 submitted 11 December, 2020; originally announced December 2020.

Journal ref: Phys. Rev. Lett. 127, 180603 (2021)

PFG NMR time-dependent diffusion coefficient analysis of confined emulsion: post drainage phase conformation

Authors: B. Chencarek, M. Nascimento, A. M. Souza, R. S. Sarthour, B. Coutinho, M. D. Correia, I. S. Oliveira

Abstract: In this work, we present a characterization of phase configuration in water-saturated sintered glass bead samples after oil injection, through the analysis of time-dependent diffusion coefficients obtained from sets of one-dimensional pulsed field gradient nuclear magnetic resonance (PFG NMR) measurements, pre and post drainage. Estimates of samples surface-to-volume ratio and permeability from pr… ▽ More In this work, we present a characterization of phase configuration in water-saturated sintered glass bead samples after oil injection, through the analysis of time-dependent diffusion coefficients obtained from sets of one-dimensional pulsed field gradient nuclear magnetic resonance (PFG NMR) measurements, pre and post drainage. Estimates of samples surface-to-volume ratio and permeability from pre drainage PFG measurements in a water-saturated sample were compared with analytical and reported values, respectively, and a fair agreement was found in both cases. Short-time analysis of diffusion coefficients extracted from PFG measurements was used to quantify the increase in surface-to-volume ratio probed by the wetting phase after drainage. Analysis of water and oil diffusion coefficients from post drainage PFG experiments were carried out using a bi-Gaussian model, and two distinct scenarios were considered to describe fluids conformation within pores. For the case where non-wetting phase was considered to exhibit a poorly connected geometry, an analysis assuming the formation of oi-in-water droplets within pores was performed, and a Gaussian distribution of droplets radii was determined. △ Less

Submitted 27 November, 2020; originally announced November 2020.

Dynamic generation of GHZ states with coupled charge qubits

Authors: J. Nogueira, P. A. Oliveira, F. M. Souza, L. Sanz

Abstract: In this paper, we present a proof-of-principle of the formation of pure maximally entangled states from the Greenberger-Horne-Zeilinger class, in the experimental context of charged quantum dots. Each qubit must be identified as a pair of quantum dots, sharing an excess electron, coupled by tunneling. The electron-electron interaction is accounted for and is responsible for the coupling between th… ▽ More In this paper, we present a proof-of-principle of the formation of pure maximally entangled states from the Greenberger-Horne-Zeilinger class, in the experimental context of charged quantum dots. Each qubit must be identified as a pair of quantum dots, sharing an excess electron, coupled by tunneling. The electron-electron interaction is accounted for and is responsible for the coupling between the qubits. The interplay between coherent tunneling events and many-body interaction gives rise to the formation of highly entangled states. We begin by treating the problem of encoding three-qubits in a system with three pairs of quantum dots, and the numerical analysis of the exact quantum dynamics to find the conditions for the generation of the GHZ states. An effective two-level model sheds light on the role of a high-order tunneling process behind the dynamics. The action of the main decoherence process, the charge dephasing, is quantified in the process. We then evaluate the physical requirements for the dynamical generation of GHZ states in a $N$ qubit scenario, and its challenges. △ Less

Submitted 12 March, 2021; v1 submitted 9 September, 2020; originally announced September 2020.

Comments: To be published in Physical Review A

Journal ref: Phys. Rev. A 103, 032438 (2021)

Dynamical decoupling in interacting systems: applications to signal-enhanced hyperpolarized readout

Authors: A. Ajoy, R. Nirodi, A. Sarkar, P. Reshetikhin, E. Druga, A. Akkiraju, M. McAllister, G. Maineri, S. Le, A. Lin, A. M. Souza, C. A. Meriles, B. Gilbert, D. Suter, J. A. Reimer, A. Pines

Abstract: Methods that preserve coherence broadly impact all quantum information processing and metrology applications. Dynamical decoupling methods accomplish this by protecting qubits in noisy environments but are typically constrained to the limit where the qubits themselves are non-interacting. Here we consider the alternate regime wherein the inter-qubit couplings are of the same order as dephasing int… ▽ More Methods that preserve coherence broadly impact all quantum information processing and metrology applications. Dynamical decoupling methods accomplish this by protecting qubits in noisy environments but are typically constrained to the limit where the qubits themselves are non-interacting. Here we consider the alternate regime wherein the inter-qubit couplings are of the same order as dephasing interactions with the environment. We propose and demonstrate a multi-pulse protocol that protects transverse spin states by suitably Hamiltonian engineering the inter-spin coupling while simultaneously suppressing dephasing noise on the qubits. We benchmark the method on 13C nuclear spin qubits in diamond, dipolar coupled to each other and embedded in a noisy electronic spin bath, and hyperpolarized via optically pumped NV centers. We observe effective state lifetimes of 13C nuclei $T_2^{\prime}\approx$2.5s at room temperature, an extension of over 4700-fold over the conventional $T_2^{\ast}$ free induction decay. The spins are continuously interrogated during the applied quantum control, resulting in 13C NMR line narrowing and an $>$500-fold boost in SNR due to the lifetime extension. Together with hyperpolarization spin interrogation is accelerated by $>10^{11}$ over conventional 7T NMR. This work suggests strategies for the dynamical decoupling of coupled qubit systems with applications in a variety of experimental platforms. △ Less

Submitted 19 August, 2020; originally announced August 2020.

Comments: 6+6 pages. Originally submitted to peer-review on 04 May 2020

Low-temperature thermodynamics of the two-leg ladder Ising model with trimer rungs: A mystery explained

Authors: Taras Hutak, Taras Krokhmalskii, Onofre Rojas, Sergio Martins de Souza, Oleg Derzhko

Abstract: Recently, a surprising low-temperature behavior has been revealed in a two-leg ladder Ising model with trimer rungs (Weiguo Yin, arXiv:2006.08921). Motivated by these findings, we study this model from another perspective and demonstrate that the reported observations are related to a critical phenomenon in the standard Ising chain. We also discuss a related curiosity, namely, the emergence of a p… ▽ More Recently, a surprising low-temperature behavior has been revealed in a two-leg ladder Ising model with trimer rungs (Weiguo Yin, arXiv:2006.08921). Motivated by these findings, we study this model from another perspective and demonstrate that the reported observations are related to a critical phenomenon in the standard Ising chain. We also discuss a related curiosity, namely, the emergence of a power-law behavior characterized by quasicritical exponents. △ Less

Submitted 9 August, 2020; originally announced August 2020.

Comments: 5 pages, 4 figures

Journal ref: Physics Letters A, Volume 387, 28 January 2021, 127020

Theoretical and experimental comparative study of nonlinear properties of imidazolium cation based ionic liquids

Authors: Vinícius Castro Ferreira, Letícia Zanchet, Wesley Formentin Monteiro, Letícia Guerreiro da Trindade, Michèle Oberson de Souza, Ricardo Rego Bordalo Correia

Abstract: This work describes the experimental and theoretical study of the nonlinear optical properties of the imidazolium cation based ionic liquids and the corresponding thermo-optical parameters. Experimental results of nonlinear optical properties, such as nonlinear refractive index and thermo-optical properties are determined by Z-scan and EZ-scan techniques with a femtosecond laser source. Theoretica… ▽ More This work describes the experimental and theoretical study of the nonlinear optical properties of the imidazolium cation based ionic liquids and the corresponding thermo-optical parameters. Experimental results of nonlinear optical properties, such as nonlinear refractive index and thermo-optical properties are determined by Z-scan and EZ-scan techniques with a femtosecond laser source. Theoretical simulations of linear and nonlinear optical properties performed by density functional theory (DFT) are discussed, in terms of polarizability, the first and second-order of hyperpolarizability. A correlation between the theoretical and experimental results is presented, where the variation of the signals of each ionic liquid can be compared with their nonlinear optical properties. △ Less

Submitted 4 August, 2020; originally announced August 2020.

Comments: 25 pages, 5 figures, 5 tables

Atomic frustrated impurity states in Weyl metals

Authors: W. N. Mizobata, Y. Marques, M. Penha, J. E. Sanches, L. S. Ricco, M. de Souza, I. A. Shelykh, A. C. Seridonio

Abstract: We theoretically analyze the effect of the inversion symmetry breaking on the structure of the impurity molecular states in Weyl metals. We show that for the case of a highly noncentrosymmetric Weyl metallic host, the standard picture of the alternating bonding and antibonding orbitals breaks down, and a qualitatively different frustrated atomic state emerges. This is a consequence of the pseudoga… ▽ More We theoretically analyze the effect of the inversion symmetry breaking on the structure of the impurity molecular states in Weyl metals. We show that for the case of a highly noncentrosymmetric Weyl metallic host, the standard picture of the alternating bonding and antibonding orbitals breaks down, and a qualitatively different frustrated atomic state emerges. This is a consequence of the pseudogap closing and related delicate Fano interplay between intra- and inter-impurity scattering channels. △ Less

Submitted 1 September, 2020; v1 submitted 11 May, 2020; originally announced May 2020.

Journal ref: Phys. Rev. B 102, 075120 (2020)