Brazilian Journal of Physics最新文献

{"title":"Parity-Selective Spin Filtering and Coherent Spin-Phase Control by a Localized Zeeman Segment in a Resonant-Tunneling Cavity","authors":"Cui Jiang,&nbsp;Jia-Yi Ye,&nbsp;Lu-Han Yu,&nbsp;Chun-Xia Li","doi":"10.1007/s13538-026-02173-w","DOIUrl":"10.1007/s13538-026-02173-w","url":null,"abstract":"<div><p>We study coherent spin transport through a one-dimensional double-barrier resonant-tunneling structure containing a finite, localized Zeeman segment in its central cavity. The Zeeman term is diagonal in spin, so the two spin channels experience opposite local potentials <span>(pm V_{1})</span> and do not mix. This simplicity exposes a spatial parity selection rule: the spin splitting of the <i>n</i>th cavity resonance is <span>(Delta E_n simeq 2V_{1}W_n)</span>, where <span>(W_n)</span> is the probability weight of the quasibound state inside the segment. A centered segment is an even-parity perturbation, so odd modes split strongly while even modes are protected by their central node; displacing the segment inverts this selectivity. The peak polarization obeys a universal scaling <span>(|P_z|simeq 2Q_n^2/(1+2Q_n^2))</span>, with <span>(Q_n=Delta E_n/Gamma _n)</span> the ratio of splitting to resonance linewidth, which collapses the dependence on Zeeman strength, segment width, and position onto a single curve. For a GaAs-like model, the first resonance reaches 93–95% polarization, while the nearly degenerate second resonance acts as a high-transmission spin-phase element with a position-tunable phase of up to 0.57 rad. The filtering contrast remains about 91% at 4 K. Localized-field position and cavity parity thus emerge as simple design parameters for combining resonant spin filtering with coherent spin-phase control.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"57 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149367401","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Topological Superconductivity and Antichiral Edge States in Two-dimensional Electron Gases","authors":"Juan Herrera Mateos,&nbsp;Gabriel F. Rodríguez Ruiz,&nbsp;Leandro Tosi,&nbsp;Liliana Arrachea,&nbsp;C. A. Balseiro","doi":"10.1007/s13538-026-02118-3","DOIUrl":"10.1007/s13538-026-02118-3","url":null,"abstract":"<div><p>A magnetic field applied parallel to a Rashba spin-orbit-coupled two-dimensional electron gas, proximized by a conventional superconductor, gives rise to a topological superconducting phase hosting antichiral edge states formed by co-propagating Majorana fermions. These modes remain robust against edge corrugations in systems with non-planar boundaries, provided that the characteristic radius of curvature of the boundary exceeds the Fermi wavelength of the two-dimensional electron gas. In this work, we revisit the properties of this phase and investigate the local density of states (LDOS) both at the edges and in the bulk. We identify distinctive spectral signatures near the Fermi energy associated with the antichiral Majorana modes, providing experimentally accessible fingerprints of the phase.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"57 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149367400","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Nonlinear Theory of Supersonic and Hypersonic Electrostatic Solitons of Acoustic-type in Three-component Warm Plasma with Nonextensive Light Particles: Gas Dynamic Approach","authors":"Alexander E. Dubinov,&nbsp;Ilya N. Kitayev","doi":"10.1007/s13538-026-02168-7","DOIUrl":"10.1007/s13538-026-02168-7","url":null,"abstract":"<div><p>The properties of nonlinear stationary waves and solitons in a warm three-component plasma were studied. A feature of the plasma under study was a special signature of charges of species, when light particles and particles of an intermediate mass have the same charge sign, and heavy particles are charged oppositely. Another feature was the chosen light particle distribution, the super-nonextensive Tsallis distribution. The study was performed within the gas dynamic approximation. A linear analysis of the waves was performed and a dispersion equation was derived. As a result, an expression for the linear velocity of sound was obtained. Normalization to this expression of soliton velocities provides the Mach number. Nonlinear analysis of waves by the Sagdeev pseudopotential method was performed. It was found that stationary subsonic periodic waves, supersonic and hypersonic solitons may exist in the plasma under study. The effect of the temperature of the fraction of light particles, their relative concentration and their parameter of non-extensiveness on the conditions for the existence of hypersonic solitons was studied. Profiles of physical quantities in supersonic and hypersonic solitons were calculated. It was shown that hypersonic solitons can have abnormally high Mach numbers, a giant amplitude of the potential, and a high degree of compression of the fraction with intermediate mass particles. An abnormal dependence of the amplitude of the concentration of intermediate mass particles in hypersonic solitons on the Mach number was found. The dependence turned out to be nonmonotonic. At the same time, the dependence of the potential amplitude in hypersonic solitons on the Mach number is increasing at least on the studied parameter intervals.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"57 1","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-11-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149367399","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Dynamical Tunneling in the Bose–Hubbard Dimer","authors":"Ted Pudlik,&nbsp;D. K. Campbell","doi":"10.1007/s13538-026-02170-z","DOIUrl":"10.1007/s13538-026-02170-z","url":null,"abstract":"<div><p>We present and discuss results on a specific simple system involving quantum tunneling: namely, the “Bose–Hubbard dimer” or “Bose–Josephson junction (BJJ)”. A physical realization of this system is provided by a Bose–Einstein condensate (BEC) in a double-well optical lattice. We show that, despite its simplicity, the system exhibits remarkable macroscopic quantum behavior that can be understood in many cases by a semiclassical “global phase space” approach but which in fact requires a fully quantum treatment in certain regions of parameter space. We compare the results of our theoretical studies with existing experimental data and predict new phenomena that should be observed in future experiments. Among these new phenomena are the existence of tunneling between two self-trapped states that are unconnected in the semiclassical approximation.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-11-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149338484","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Real-Space Renormalization-Group Study of Decoherence and Revival Following a Sudden Quench in a Finite System","authors":"F. D. Picoli,&nbsp;G. Diniz,&nbsp;L. N. Oliveira","doi":"10.1007/s13538-026-02169-6","DOIUrl":"10.1007/s13538-026-02169-6","url":null,"abstract":"<div><p>To investigate the nonequilibrium dynamics of a quantum impurity system, we examine two physical properties for the spinless resonant level model subject to sudden quenches of the hybridization between the impurity and the metal. We compute the time dependence of the impurity occupation and the survival probability (fidelity) as probes of the dephasing induced by particle-hole excitations. This dephasing reflects the entanglement between the impurity level and the metallic bath and, together with the loss of purity of this level, provides clear evidence of the loss of coherence, as discussed by Franco and Appel. For finite systems, coherence loss is only apparent, because discrete spectra lead to quasi-periodic dynamics and revivals when phases realign. We show that a hybrid linear–logarithmic discretization suppresses these finite-size artifacts by making the excitation energies incommensurate, thereby reducing revivals. Starting from the Rabi oscillations in the single-site limit of the tight-binding model describing the metal, we extend the analysis to large lattices, where damping and relaxation emerge. Our combination of analytical and numerical results offers a unified picture of the crossover from coherent oscillations to effectively irreversible decoherence.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02169-6.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149339514","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Time-dependent Trapped Plasmas: Nonlinear Dynamics, Symmetries and Invariants","authors":"Thonimar V. Alencar,&nbsp;Luiz Gustavo Ferreira Soares,&nbsp;Ronaldo Thibes","doi":"10.1007/s13538-026-02172-x","DOIUrl":"10.1007/s13538-026-02172-x","url":null,"abstract":"<div><p>We investigate the nonlinear dynamics of a single-component plasma confined in a time-dependent harmonic trap with regard to aspects of symmetry and invariant functions in a variational approximation. The system is described as a fluid in an isentropic adiabatic regime by a system of partial differential equations (pde). A convenient change of variables, along with a Gaussian ansatz for the number density distribution, allows a consistent mathematical description in terms of ordinary differential equations (ode). From this formulation, we follow up with an analysis concerning the corresponding differential operators algebraic structure and Noether symmetries in specific physical regimes. For each studied case, proper invariants are identified. As a result, the obtained conserved quantities capture an interplay between the internal plasma dynamics and the time modulation of the trap, resulting in a sharp restriction for the system evolution.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02172-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149339513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"From Macroscopic Quantum Tunneling to Circuit QED: Coherence and Dissipation in 3D Transmon Qubits","authors":"Gustavo Moreto,&nbsp;Diego Molina,&nbsp;Saulo G. Alberton,&nbsp;Denys Brito,&nbsp;Ednilson Cunha,&nbsp;Arthur Rebello,&nbsp;Daniel Benvenutti,&nbsp;Agatha Dutra,&nbsp;Beatriz Sacramento,&nbsp;Italo L. Soares Andrade,&nbsp;Lucas M. Ruela,&nbsp;Francisco Rouxinol","doi":"10.1007/s13538-026-02171-y","DOIUrl":"10.1007/s13538-026-02171-y","url":null,"abstract":"<div><p>Superconducting quantum circuits are a leading platform for quantum-information processing, but their development requires expertise spanning device design, microfabrication, cryogenic operation, microwave control, and quantum characterization. In this work, we report the realization of a flux-tunable superconducting transmon platform and present an integrated workflow encompassing design, fabrication, measurement, and numerical modeling. The device consists of an <span>(Al/AlO_x/Al)</span> transmon coupled to a three-dimensional microwave cavity operating in the circuit quantum electrodynamics (cQED) dispersive regime. Two-tone spectroscopy reveals a fundamental transition frequency of <span>(omega _{01}=5.0122~textrm{GHz})</span> and an anharmonicity of <span>(alpha /2pi =-202.4~textrm{MHz})</span>, corresponding to <span>(E_J/E_C approx 82.9)</span>. Flux spectroscopy yields a cavity-qubit coupling strength of <span>(g/2pi = 260~textrm{MHz})</span>, while the cavity linewidth gives a loaded quality factor of <span>(Q_L=6127)</span> and a Purcell limit of <span>(T_1^{textrm{Purcell}}approx 82~mu textrm{s})</span>. Time-domain measurements yield coherence times of <span>(T_1 = 17.4~mu textrm{s})</span> and <span>(T_2^* = 5.8~mu textrm{s})</span>. To investigate coherence and dissipation in the device, the experimental observations are analyzed within a Lindblad master-equation framework describing cavity photon loss and thermal excitation, qubit energy relaxation, and pure dephasing processes. Using a set of experimentally extracted parameters, the model reproduces the measured spectroscopic and time-domain observables, providing a quantitative description of the open-system dynamics of the transmon-cavity platform. The analysis shows that the measured coherence is primarily limited by pure dephasing and energy-relaxation processes, whereas thermal excitation plays a minor role under the experimental conditions. Inspired by the broader framework of quantum dissipation in macroscopic quantum systems pioneered by Caldeira and collaborators, this approach enables a quantitative analysis of relaxation and dephasing processes in superconducting quantum circuits. Beyond the characterization of a single device, the present work demonstrates the establishment of the expertise, infrastructure, and experimental workflow required for the design, fabrication, measurement, and modeling of superconducting quantum circuits, contributing to the development of quantum technologies in Brazil and related applications.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s13538-026-02171-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149235062","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Mechanistic Study of Crack Propagation and Anisotropic Fracture Behavior in TH-Graphyne Nanosheets via Molecular Dynamics Simulations","authors":"Guangjie Xie,&nbsp;Tao Ji,&nbsp;Bowen Wei","doi":"10.1007/s13538-026-02166-9","DOIUrl":"10.1007/s13538-026-02166-9","url":null,"abstract":"<div><p>This study investigates the mechanical behavior of two-dimensional TH-graphyne nanosheets using molecular dynamics simulations. The pristine nanosheet exhibits significant mechanical anisotropy, with Young’s moduli of 204.77 GPa and 270.19 GPa and ultimate tensile strengths of 51.03 GPa and 92.73 GPa along the x- and y-directions, respectively. The influence of crack orientation (0°–90°) shows up to a 54.5% reduction in stiffness and a 75.6% drop in strength. Temperature increases from 200 K to 1000 K results in modulus reductions of over 65% and decreases fracture toughness (K_IC) by approximately 78%. Crack length variations from 30 Å to 60 Å lead to stiffness reductions of up to 71.7% and a drop in toughness by as much as 84.5%. The fracture process is characterized by brittle failure initiated at the crack tip, with minimal plastic deformation observed during propagation.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149234438","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Effect of Electron Spin Polarization on Laser-Assisted Semirelativistic Excitation of Atomic Hydrogen from the Metastable 2s State to the 4s State in a Circularly Polarized Laser Field","authors":"C. Hajjaj,&nbsp;M. Ouali,&nbsp;S. Taj,&nbsp;B. Manaut,&nbsp;M. El Idrissi","doi":"10.1007/s13538-026-02162-z","DOIUrl":"10.1007/s13538-026-02162-z","url":null,"abstract":"<div><p>This paper presents a semirelativistic theoretical study of a laser-assisted inelastic electron-atom scattering. Specifically, we investigate the laser-assisted excitation of atomic hydrogen from the metastable 2s state to the 4s state, induced by electron impact with particular emphasis upon spin-dependent effects. The analysis is carried out within the framework of the first Born approximation, while the interaction of the incident and scattered electrons with the laser field is described using Dirac–Volkov states. An analytical expression for the spin-unpolarized differential cross section is derived, providing a reference for assessing the consistency and reliability of the adopted theoretical approach. In addition, the spin-flip and spin–non-flip differential cross sections are investigated. The numerical results show that the spin-flip contribution is negligible compared with the spin–non-flip contribution over the range of parameters considered, indicating that spin-conserving transitions dominate the excitation process.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149189380","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A DFT Study on the Influence of Sulfur Vacancy and Oxygen Doping on Bandgap Engineering of 2H WS2 Nanolayers","authors":"B. Bhattacharjee,&nbsp;G. Pradhan","doi":"10.1007/s13538-026-02165-w","DOIUrl":"10.1007/s13538-026-02165-w","url":null,"abstract":"<div><p>This study is an extension of our experimental work on synthesis of WS₂ nanolayers; by varying laser energy in pulsed laser deposition, indicating sulfur deficient nanolayers. Hence, we further investigated the influence of number and different vacancy configurations within the non-periodic supercell, appearing to be at the edge or at the center, of sulfur vacancy (SV) and oxygen doping (OD), on the band structure, bandgap and density of states of the monolayers (ML) and bilayers (BL) of 2 H WS₂ polymorph, using Density functional theory. The (001) slab model of the WS₂ ML &amp; BL was made with an array of 3 × 3 × 1 and 3 × 3 × 2 supercells, respectively. The number of SV &amp; OD was varied from 1 to 3 and 1 to 2, respectively. For edge appearing SV WS₂ ML, the bandgap narrows rapidly with increase of SV and closes for 3 SV; having S/W ratio of 1.66. For center appearing SV, the bandgap also narrows slowly with increase of SV and remains slightly open for 3 SV. In WS₂ BL, the bandgap remains open for edge and center appearing 3 SV. The 1 O atom (5.55% doping) doped pristine ML, shows 0.5% to 1.99% bandgap opening, as compared to pristine ML. The 2 O atom (11.11%) doped pristine ML, shows 5.5% to 9.95% bandgap narrowing. This work indicates the feasibility of the bandgap engineering of WS₂ nanolayers by controlled SV and O doping.</p></div>","PeriodicalId":499,"journal":{"name":"Brazilian Journal of Physics","volume":"56 6","pages":""},"PeriodicalIF":1.8,"publicationDate":"2026-10-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"149189379","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}