HỘi nghị VẬt lý LÝ thuyết toàn quốc lần thứ 37 The 37th National Conference on Theoretical Physics

Người trình bày: Võ Văn Ớn (Trường Đại học Thủ Dầu Một)

Người trình bày: Hoàng Thanh Phi Hùng (Quảng Bình)

Nguyen Van Hieu and Nguyen Bich Ha

Newly emerging and being rapidly developed, plasmonics is a very perspective direction of research in nanoscience and nanotechnology. Numerous experimental works on a large variety of photonic processes in which the plasmons play substantial roles were done, but there were only few theoretical works on these processes, and they are mainly phenomenological. In the present article we propose an approach based on the functional integral formalism, which would be able to be applied to the theoretical study of all physical processes with the participation of plasmons. After the presentation of the basics of functional integral technique, this technique is applied to the study of systems of interacting electrons in nanomaterials. Dynamical equation of plasmon was derived and quantum plasmonic field was introduced. In the case of homogeneous and isotropic electron gas in three-dimensional space, this dynamical equation gives rise to the plasmon dispersion exactly coinciding with that derived from the conventional theories. However, the proposed calculation method, based on functional integral technique, can be effectively applied to the study of plasmons in nanostructures with complicated shapes, while the conventional theories are not able to be applied.

Alexander Povolotsky

The Totally Asymmetric Simple Exclusion Process (TASEP) is the paradigmatic model of non-equilibrium statistical physics. Being exactly solvable, it allows a calculation of correlation functions of particle currents and positions. At the same time, its large scale behaviour is specific for a wide variety of phenomena unified under concept of Kardar-Parisi-Zhang (KPZ) universality class, such as growing interfaces, traffic models and polymers in random media. In the talk we review the derivation of universal correlation functions of KPZ class using the exact solution of the TASEP.

Phan Van Nham(1), Holger Fehske(2), Klaus Becker(3)

We explore the spontaneous formation of an excitonic insulator state at the semimetal-semiconductor transition of mixed-valence materials in the framework of the spinless Falicov-Kimball model with direct f-f electron hopping. Adapting the projector-based renormalization method, the existence of excitonic insulator phase at low temperature on both sides of the semiconductor-semimetal transition is addressed, whereas on the semiconductor side with high temperature the excitonic bound states is typified. To this end we calculate the imaginary part of the dynamical electron-hole pair susceptibility and analyze the wave vector and energy dependence of excitonic resonances emerging in the band gap. We thereby confirm the existence of the exciton insulator and its exciton environment within a generic two-band lattice model with local Coulomb attraction

Irina Pirozhenko

We calculate electromagnetic vacuum energy in the presence of bodies with nontrivial dielectric and magnetic properties. First we consider the sphere-plate system in scattering approach and estimate the limits of possible Casimir repulsion. Second we study Fluctuation induced quantum interactions in the background of the media described by Maxwell fish-eye model. The research is of possible interest for the design of micro(nano)-electromechanical systems.

Nguyen Thi Hong Van

Searching for the standard model Higgs boson (or shortly, Higgs) plays a key role in the Large Hadron Collider (LHC) program. Higgs productions and methods of the Higgs search at the LHC will be presented. The Higgs can be searched directly via its decay modes or via precision electroweak measurements which can give results sensitive to the Higgs mass. Finally, the latest search for the Higgs using datasets produced by proton-proton collisions at sqrt(s) = 7 TeV (in 2011) and sqrt(s) = 8 TeV (in 2012) and collected by the ATLAS detector of the LHC will be summarized.

Nguyen Quang Hung

Pairing reentrance phenomena of hot rotating nuclei is studied within the Bardeen-Cooper-Schrieffer (BCS)-based approach, taking into account the effect of thermal fluctuations on the pairing field and coupling to the quasiparticle-pair vibrations at finite temperature and angular momentum within the pairing model plus noncollective rotating along the symmetry axis. The numerical calculations are performed within a doubly-folded equidistant multilevel model as well as several realistic nuclei such as O$^{20}$, Ne$^{22}$, Ca$^{44}$, Ni$^{60}$, and Ge$^{72}$. The results obtained for the pairing gaps, total energies, heat capacities, and level densities show that the thermal fluctuations smooth out the superfluid-normal phase transition and leads to the appearance of a thermally assisted pairing or pairing reentrance in hot rotating nuclei, which can be clearly seen in the behavior of pairing gaps obtained at finite temperature and angular momentum [1]. Moreover, in addition to the pairing gap, the heat capacity also serve as a good observable to detect the appearance of the pairing reentrance, whereas such a signature in the level density is rather weak [2]. The formalism is applied to not only nuclear but also any finite hot rotating Fermi systems.

Mai Suan Li

The basic concepts and methods used in the computer-aided drug design such as docking, MM-PBSA and steered molecular dynamics (SMD) will be discussed. The main idea of using SMD to screen out potential leads is based on the hypothesis that the larger is the force needed to unbind a ligand from a receptor the higher its binding affinity. Instead of binding free energy, the rupture force defined as the maximum on the force-time/displacement profile, is employed as a score function. The particular attention will be drawn to recent results obtained by SMD for top-leads for influenza viruses.

Aggregation of beta amyloid peptides is believed to be associated with the Alzheimer's disease. Therefore, one of possible therapeutic approaches is to prevent fibril formation of these peptides. Applying the virtual screening to data base of about 40000 compounds from Eastern herbs we have found several very promising leads for treatment of the Alzheimer's disease. General structural properties of ligands that may control their binding affinity will be discussed.

Wieslaw Leoński and Cao Long Van

Problems of quantum-optical states engineering have attracted remarkable interest in last years. Various concepts of such states and methods of their production and manipulation have been presented in numerous papers. They have diverse applications in atomic and molecular, solid-state and nanosystem physics, and also in the quantum information theory. The latter have recently given a stimulating pulse for the investigation of the states defined in finite-dimensional Hilbert space. In this communication we present a method referred as to nonlinear quantum scissors[1], that allow for generation such a states. The method is based on the interaction of quantum nonlinear Kerr-like oscillators with external electromagnetic field [2,3]. We show that under some special conditions, the system's evolution remains closed within a finite set of n-photon Fock states. In consequence, finite-dimensional coherent, squeezed or even maximally entangled states can be generated [1] (and the references quoted therein). 1. W. Leoński and A. Kowalewska-Kudłaszyk, Progress in Optics, Ed. E. Wolf, 56 (2011) 131. 2. W. Leoński and R. Tanaś, Phys. Rev. A 49 (1994) R20. 3. Miranowicz Adam; W. Leoński, J. Phys. B:At. Mol. Opt. Phys. 39 (2006) 1683..

Nguyen Ngoc Ty, Le Van Hoang

The laser with pulse duration of a few femto-second is available nowadays that gives us new tools to investigate the molecular structures. We review some main results in this direction such as the development of the methods of HHG calculations, the molecular imaging by tomography method, the discovery of the electron interference effect in the HHG spectra, and the affect of the molecular vibration to the HHG spectra. We also discuss about how to extract the molecular structures from HHG spectra based on the newest publications including results of our group.

Nguyen Thi Trang, Nguyen Van Chinh, Nguyen Tat Thang, Bach Thanh Cong

The Ising model with spin ½ and random competing ferromagnetic (FM), antiferromagnetic (AF) exchange interactions is used for studying on the First Order Magnetization Process (FOMP) in some magnetic systems. Dependence of the magnetization on the temperature, field, and occurrence probability of interaction was obtained during the effective field approximation. It was shown by numerical calculation that the FOMP depends strongly on the strength and occurrence probability of AF exchange interaction. The developed theory is applied for analyzing of FOMP in some magnetic systems.

Le Van Tan and Cao Huy Thien

The spin dependent compressibility for 2D semiconductor system is calculated with including both the exchange and correlation effects. The influence of temperature, carrier density and spin polarization on the inverse compressibility is reported.

Dinh Nhu Thao(1), Nguyen Hong Quang(2)

The many electron system interacting with a magnetic ion in two dimensional semiconductor quantum dots is studied by unrestricted Hartree-Fock method. The electron-ion magnetic exchange interaction and its influence on the electronic properties and light absorption of charged excitons in dilute magnetic quantum dots are investigated in details in the dependence of the ion location and charging effect.

Nguyen Ngoc Tuan

The close relation between superconductivity and magnetism in cuprates allowed one to propose a new pairing mechanism for Cooper pair: pairing with non-zero momentum that equals to nesting vector of magnetic order. The features of the Meissner effect in superconductors with a finite pairing momentum are analyze within linear response theory.

T. Bui Dinh(1), V. Cao Long(1), Wieslaw Leoński(1) and K. Dinh Xuan(2)

Exactly as in the optical case [1], existence of localized or solitary waves in a rod is provided by a balance between nonlinearity and dispersion. In our paper [1] we considered the effect of higher orders of dispersion in creating solitons. We consider now the higher orders of nonlinearity. The leading nonlinearity for longitudinal waves is quadratic which provides to the double dispersion equation (DDE) of Porubov’s type [2,3]. In this paper, using the F-expansion method described in [4], we obtain an interesting class of traveling solitary waves for both cases: without cubic nonlinearity and with its presence. As a byproduct, we regain the results obtained previously by other authors [2,3]. Moreover, our analytical solutions describe very well the results obtained by numerical simulations [5]. REFERENCES [1] T. Bui Dinh, V. Cao Long, B. Nguyen Huy, S. Vu Ngoc, Optical solitons in presence of higher-order effects, Photonics Lett. of Poland 2(2) (2010) 97-99. [2] A.V. Porubov, Amplification of nonlinear strain waves in solids. World Scientific, Singapore (2003). [3] V.I. Erofeev, N.V. Erofeeva, Solitons and nonlinear periodic strain waves in rods, plates and shells (a review), Acoust. Phys. 48 (2002) 643-655. [4] S. Zhang, W. Wang, and J. L. Tong, Exact Non-traveling Wave and Coefficient Function Solutions for (2+1)-Dimensional Dispersive Long Wave Equations, Electronic Journal of Theoretical Physics EJTP 5, No. 19 (2008) 177–190. [5] T. Bui Dinh, V. Cao Long, K. Dinh Xuan, K. W. Wojciechowski, Computer simulation of solitary waves in a common or auxetic elastic rod with both quadratic and cubic nonlinearities, Phys. Status Solidi B, 1-7(2012)/DOI 10.1002/pssb.201084221.

Dinh Xuan Khoa, and Nguyen Huy Bang

In this tall, we focus on our recent studies in nonlinear optics and laser spectroscopy of alkali-metal diatomic molecules. The former area concerning to investigation of coherent effects in atomic media under optical excitations, such as Electromagnetically Induced transparency (EIT) [1], EIT enhanced Kerr nonlinearity [2, 3]. The later area concerning to application of polarization labeling spectroscopy technique [4] to investigate structure of alkali-metal diatomic molecules [5]. Spectroscopic characterization of excited electronic states is described in several aspects, such as molecular constants [5], potential energy curve [6] and intensity distribution [7]. Some prospects of our researches are discussed.

References

[1] Dinh Xuan Khoa et al., EIT Four-level lambda scheme of cold Rubidium atoms., Computational Methods in Science and Technology (Poland), ISSN 1505-0602, Special Issue 2 (2010) 13-16.

[2] Le Van Doai et al., EIT enhanced Kerr nonlinearity in the five-level cascade system of Rb85 atoms, paper at this conference.

[3] Le Van Doai et al., EIT enhanced Kerr nonlinearity in the four-level cascade system of Rb85 atoms, paper at this conference.

[4] Le Canh Trung et al., First rotational observation of the 21Π state of NaLi, paper at this conference; Nguyen Tien Dung et al., Polarization labeling Spectroscopy for NaLi, Comm. in Phys., 21(N4) (2011) 359-364.

[5] Nguyen Huy Bang et al., Spectroscopy of mixed alkali dimers by the polarisation labelling technique: application to NaLi and NaRb molecules", Optical Materials 31 (2009) 527-531; Dinh Xuan Khoa et al., Experimental determination of molecular constants for the 21Π state of NaLi, Paper at this conference.

[6] Nguyen Tien Dung et al., Construction of potential curve for the 31П state of NaLi molecule by the IPA and DPOTFIT methods, paper at this conference.

[7] Nguyen Tien Dung et al., Calculation of vibrational intensity distribution for the 41Π←11Σ+ band system of NaLi”. Computational Methods in Science and Technology (Poland), ISSN 1505-0602, Special Issue 2 (2010) 17-20; Nguyen Tien Dung et al., Population density distribution of vibrational levels in the 21П state of NaLi molecule, paper at this conference.

Chu Van Bien(1) and Ho Quang Quy(2)

Trên cơ sở tính chất phi tuyến của bộ liên kết và khả năng khuếch đại của sợi quang, hệ nén xung đa vòng đã được đề xuất. Sử dụng các biểu thức của hệ số truyền qua bộ liên kết và biểu thức gần đúng của biên độ sóng khuếch đại, quá trình nén xung đã được mô phỏng. Kết quả cho thấy, hệ số nén xung phụ thuộc vào cường độ xung vào, hệ số truyền qua sợi phi tuyến, độ rộng xung vào. Sau mỗi vòng khuếch đại, hệ số nén tăng lên đáng kể. Chúng tôi, đã tìm ra một bộ tham số mà sau quá trình nén được kết quả tối ưu.

Tran Minh Hien and Ho Trung Dung

We consider the emission pattern of a three-dimensional pointlike dipole situated near a left-handed-medium slab. Unlike earlier work, we focus on the direction normal to the slab surface. It is shown that the evanescent field may help to narrow the major peak of the image created by the propagating field.We point out that care has to be taken when applying Snell's law to the superlens problem. In particular, it cannot explain why the focus is shifted away from the ideal position when material absorption decreases below some threshold value.

P.K.Hung and N.T.T.Ha

Diffusion rate for particles in disordered system is influenced by two disorder types: the energetic and geometric disorder. Several previous studies shows that the energetic disorder is mainly responsible for diffusion in disordered lattice which has been quantified by the correlation coefficient. This effect may be important for diffusion in fluids, but still not studied yet. In present paper we focus on how the correlation effect exhibits for dynamics in the alumina liquid and what it connects to the motion of particles in the liquid. The models consisting of 2000 particles have been constructed at temperature from 2400 to 4000 K and upon pressure from 0 to 20 GPa. We found that the transitions AlOx -> AlOx±1 are not randomly proceed through cations, but strongly localized in some small regions. It means that they are correlated spatially. The correlation coefficient determined here is strongly depends on the temperature and pressure. In particular, the localization leads to existence of large cluster of non-exchanging units AlOx. The percolation of domains with high and low frequent transitions is also analyzed and discussed here.

Nguyen Thuy Trang

Surface-related properties and influence of solvent play important roles in lead sulfide nanocomposites which has been attracted numerous researches due to their wide range of applications from optoelectronics to biology. This paper represents our ab initio study on geometry and electronic structure of PbS surface. Here the influence of solvent was statically included using the conductor-like screening model (COSMO). The results show that the screening charges from solvent enhance the surface rumpling and crystal bonding of the surface but suppress the surface relaxation. However such solvent effects tend to saturate when the dielectric constant increases.