Condensed Matter Physics最新文献

{"title":"Dynamics of Bose-Einstein condensates under anharmonic trap","authors":"H. Al-Jibbouri","doi":"10.5488/CMP.25.23301","DOIUrl":"https://doi.org/10.5488/CMP.25.23301","url":null,"abstract":"The dynamics of weakly interacting three-dimensional Bose-Einstein condensates (BECs), trapped in external axially symmetric plus anharmonic distortion potential are studied. Within a variational approach and time-dependent Gross-Pitaevskii equation, the coupled condensate width equations are derived. By modulating anharmonic distortion of the trapping potential, nonlinear features are studied numerically and illustrated analytically, such as mode coupling of oscillation modes, and resonances. Furthermore, the stability of attractive interaction BEC in both repulsive and attractive anharmonic distortion is examined. We demonstrate that a small repulsive and attractive anharmonic distortion is effective in reducing (extending) the condensate stability region since it decreases (increases) the critical number of atoms in the trapping potential.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"35 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-06-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73434531","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":"Phase transitions in ferroelectric domain walls","authors":"E. Eliseev, M. Glinchuk, L. Yurchenko, P. Maksymovych, A. Morozovska","doi":"10.5488/CMP.25.43706","DOIUrl":"https://doi.org/10.5488/CMP.25.43706","url":null,"abstract":"Despite multiple efforts, there exist many unsolved fundamental problems related with detection and analysis of internal polarization structure and related phase transitions in ferroelectric domain walls. Their solution can be very important for the progress in domain wall nanoelectronics and related applications in advanced memories and other information technologies. Here, we theoretically study the features of phase transitions in the domain walls, which are potentially detectable by the scanning probe capacitance microwave microscopy. The finite element modelling based on the Landau-Ginzburg-Devonshire theory is performed for the capacitance changes related with the domain wall motion in a multiaxial ferroelectric BaTiO3.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"8 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-06-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79197031","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":"Quantum fluctuations approach to the nonequilibrium GW approximation","authors":"Erik Schroedter, Jan‐Philip Joost, M. Bonitz","doi":"10.5488/CMP.25.23401","DOIUrl":"https://doi.org/10.5488/CMP.25.23401","url":null,"abstract":"The quantum dynamics of fermionic or bosonic many-body systems following external excitation can be successfully studied using two-time nonequilibrium Green's functions (NEGF) or single-time reduced density matrix methods. Approximations are introduced via a proper choice of the many-particle self-energy or decoupling of the BBGKY hierarchy. These approximations are based on Feynman's diagram approaches or on cluster expansions into single-particle and correlation operators. Here, we develop a different approach where, instead of equations of motion for the many-particle NEGF (or density operators), single-time equations for the correlation functions of fluctuations are analyzed. We present a derivation of the first two equations of the alternative hierarchy of fluctuations and discuss possible decoupling approximations. In particular, we derive the polarization approximation (PA) which is shown to be equivalent to the single-time version [following by applying the generalized Kadanoff-Baym ansatz (GKBA)] of the nonequilibrium GW approximation with exchange effects of NEGF theory, for weak coupling. The main advantage of the quantum fluctuations approach is that the standard ensemble average can be replaced by a semiclassical average over different initial realizations, as was demonstrated before by Lacroix and co-workers [see e.g. D. Lacroix et al., Phys. Rev. B, 2014, 90, 125112]. Here, we introduce the stochastic GW (SGW) approximation and the stochastic polarization approximation (SPA) which are demonstrated to be equivalent to the single-time GW approximation without and with exchange, respectively, in the weak coupling limit. In addition to the standard stochastic approach to sample initial configurations, we also present a deterministic approach. Our numerical tests confirm that our approach has the same favorable linear scaling with the computation time as the recently developed G1-G2 scheme [Schluenzen et al., Phys. Rev. Lett., 2020, 124, 076601]. At the same time, the SPA and SGW approaches scale more favorably with the system size than the G1-G2 scheme, allowing to extend nonequilibrium GW calculations to bigger systems.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"34 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-04-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90830245","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":"Theoretical analysis of magnetic properties and the magnetocaloric effect using the Blume-Capel model","authors":"Samuel de Oliveira, R. Morais, J. P. Santos, F. Barreto","doi":"10.5488/CMP.25.13702","DOIUrl":"https://doi.org/10.5488/CMP.25.13702","url":null,"abstract":"This work investigates the magnetic properties and the magnetocaloric effect in the spin-1 Blume-Capel model. The study was carried out using the mean-field theory from the Bogoliubov inequality to obtain the expressions of free energy, magnetization and entropy. The magnetocaloric effect was calculated from the variation of the entropy obtained by the mean-field theory. Due to the dependence on the external magnetic field and the anisotropy included in the model, the results for the magnetocaloric effect provided the system with first-order and continuous phase transitions. To ensure the results, the Maxwell relations were used in the intervals where the model presents continuous variations in magnetization and the Clausius-Clapeyron equation in the intervals where the model presents discontinuity in the magnetization. The methods and models for the analysis of a magnetic entropy change and first-order and continuous magnetic phase transitions, such as mean-field theory and the Blume-Capel model, are useful tools in understanding the nature of the magnetocaloric effect and its physical relevance.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"15 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82320905","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":"Electronic structure of short-period ZnSe/ZnTe superlattices based on DFT calculations","authors":"M. Caid, Y. Rached, D. Rached, O. Cheref, H. Rached, S. Benalia, M. Merabet","doi":"10.5488/CMP.25.13701","DOIUrl":"https://doi.org/10.5488/CMP.25.13701","url":null,"abstract":"In the present study we discuss the effect of variation in the number of monolayers n on the electronic and optical properties of superlattices (SLs) (ZnSe)n/(ZnTe)n. The total energies were calculated by the full-potential linear muffin-tin orbital (FP-LMTO) method, and the exchange-correlation energy was applied in the local density approximation (LDA). First, the calculations show a decrease in the derivative of bulk modulus and electronic bandgap with an increase in the number of monolayers n. Second, the radiation energies up to 15 eV, the dielectric function ε(ω), the refractive index n(ω), and the reflectivity R(ω) are studied. These calculations may be beneficial to understand the properties of short-period superlattices (ZnSe)n/(ZnTe)n.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"433 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78129832","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":"Resonance pressure of electromagnetic radiation on metal nanoparticle","authors":"N. I. Grigorchuk","doi":"10.5488/CMP.25.13703","DOIUrl":"https://doi.org/10.5488/CMP.25.13703","url":null,"abstract":"The influence of the electromagnetic irradiation pressure on a spheroidal metallic nanoparticle at the frequencies close to the surface plasmon vibrations has been considered. With the action of the radiation pressure, the polarizability of metal nanoparticle becomes a tensor quantity. The expressions for the resonance pressure components for the cases of plane-polarized and circularly polarized light have been derived. We have demonstrated that the resonance pressure can substantially depend on the shape of a non-spherical nanoparticle and its orientation with respect to the direction of light propagation and the light polarization.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"4 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79160567","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":"Investigation of the stability and charge states of vacancy in clusters Si29 and Si38","authors":"A. Normurodov, A. Mukhtarov, F. Umarova, M. Tashmetov, S. Makhkamov, N. Sulaymonov","doi":"10.5488/CMP.25.13301","DOIUrl":"https://doi.org/10.5488/CMP.25.13301","url":null,"abstract":"Stability and charge states of vacancy in Si29 and Si38 clusters have been calculated by non-conventional tight-binding method and molecular dynamics. Based on the theoretical calculations, it was shown that the vacancy in pure dimerized clusters is unstable, while in hydrogenated Si29H24 and Si38H30 clusters it is stable, but leads to a distortion of its central part with the transition of symmetry from Td to C3v and a change in the forbidden gap. The charges of cluster atoms in the presence of a vacancy are distributed so that all silicon atoms acquire a stable negative charge, which occurs due to the outflow of electrons of the central atom to the neighboring spheres.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"32 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72700585","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":"Equilibrium properties of the lattice fluid with the repulsion between the nearest neighbors on the two-level lattice with nonrectangular geometry","authors":"Y. Groda","doi":"10.5488/CMP.25.13501","DOIUrl":"https://doi.org/10.5488/CMP.25.13501","url":null,"abstract":"The equilibrium properties of the lattice fluid with the repulsion between the nearest neighbors on the two-level planar triangular lattice are investigated. The numerical results obtained from the analytical expressions are compared with the Monte Carlo simulation data. It is shown that the previously proposed diagrammatic approximation makes it possible to determine the equilibrium characteristics of the lattice fluid with the repulsion between the nearest neighbors on a two-level lattice with an accuracy comparable to the accuracy of modelling the system using the Monte Carlo method in the entire range of thermodynamic parameters. It was found that, in contrast to a similar one-level system, a lattice fluid with the repulsion between the nearest neighbors undergoes a first-order phase transition.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"43 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81097961","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":"Non-extensive thermodynamics of the radiation in heterogeneous thermal plasmas","authors":"G. Dragan, V. Kutarov, A. Bekshaev","doi":"10.5488/CMP.25.13502","DOIUrl":"https://doi.org/10.5488/CMP.25.13502","url":null,"abstract":"Thermodynamic characteristics of the radiation of condensed combustion products presented in the form of agglomerates of metal-oxide nanoparticles demonstrate deviations from the classical Planck’s law. We propose to interpret these deviations in terms of the non-additive entropy of the photon system interacting with the heterogeneous combustion products, which makes it possible to use the non-extensive Tsallis thermodynamics for their description. It is assumed that the non-additive character of the radiation entropy in heterogeneous plasma can be explained by the influence of long-range interactions and non-equilibrium physicochemical processes. An expression is obtained for the energy-dependent distribution of the photon density, based on the phenomenological parameter of non-extensiveness q which, in the first approximation, does not depend on the energy. In this case, the \"non-extensive\" Planck’s law can be reduced to the \"usual\" Planck distribution by introducing the \"effective temperature\" that exceeds the real temperature. Numerical modelling has shown that the spectral density of photons, the position and magnitude of its maximum depend on the value of the parameter q, which can be used for its experimental determination and revelation of its physical nature and origin.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"1 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-03-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79808350","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":"Does the second critical-point of water really exist in nature?","authors":"F. Hirata","doi":"10.5488/CMP.25.23601","DOIUrl":"https://doi.org/10.5488/CMP.25.23601","url":null,"abstract":"In the past decade, a literary phrase “No man's land” has been flooded in the scientific papers. The expression is used to describe a meta-stable region in the phase-diagram that cannot be accessed by experiments. It has been claimed based on the molecular dynamics (MD) simulation that there is a critical point, or the second critical point (SCP), in the “no man's land,” and it has created a big dispute in the field of science. It is proved in the present paper that the hypothesis of SCP is completely against the rigorous theorem of thermodynamics, referred as the Gibbs phase rule. The reason why the simulations have found SCP erroneously is merely because the method violates the requirement which all the statistical-mechanics treatments should satisfy to reproduce the thermodynamics. That is the thermodynamic limit. It is clarified what is the identity of the ``liquid-liquid phase transition'' and SCP in pure liquids, discovered by the simulations and by some experiments. In order to explain the physics of liquid-liquid phase transition observed experimentally in single component liquids, a new concept is proposed.","PeriodicalId":10528,"journal":{"name":"Condensed Matter Physics","volume":"23 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2022-01-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81559520","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}