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| 2. |
- Firat, Coskun, et al.
(författare)
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Characterization of density oscillations in confined and degenerate Fermi gases
- 2018
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Ingår i: Modern physics letters B. - 0217-9849. ; 32:32
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Tidskriftsartikel (refereegranskat)abstract
- Friedel oscillations appear in density of Fermi gases due to Pauli exclusion principle and translational symmetry breaking nearby a defect or impurity. In confined Fermi gases, this symmetry breaking occurs also near to boundaries. Here, density oscillations of a degenerate and confined Fermi gas are considered and characterized. True nature of density oscillations are represented by analytical formulas for degenerate conditions. Analytical characterization is first done for completely degenerate case, then temperature effects are also incorporated with a finer approximation. Envelope functions defining the upper and lower bounds of these oscillations are determined. It is shown that the errors of obtained expressions are negligible as long as the system is degenerate. Numbers, amplitudes, averages and spatial coordinates of oscillations are also given by analytical expressions. The results may be helpful to efficiently predict and easily calculate the oscillations in density and density-dependent properties of confined electrons at nanoscale.
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| 3. |
- Johannesson, Henrik, 1953, et al.
(författare)
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Two-Impurity Kondo Model: Spin-Orbit Interactions and Entanglement
- 2011
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Ingår i: Modern Physics Letters B. - 0217-9849. ; 25
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Konferensbidrag (refereegranskat)abstract
- Motivated by proposals to employ RKKY-coupled spins as building blocks in a solid-state quantum computer, we analyze how the RKKY interaction in a 2D electron gas is influenced by spin-orbit interactions. Using a two-impurity Kondo model with added Dresselhaus and Rashba spin-orbit interactions we find that spin-rotational invariance of the RKKY interaction — essential for a well-controllable two-qubit gate — is restored when tuning the Rashba coupling to have the same strength as the Dresselhaus coupling. We also discuss the critical properties of the two-impurity Kondo model in the presence of spin-orbit interactions, and extract the leading correction to the block entanglement scaling due to these interactions.
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| 4. |
- Liang, D., et al.
(författare)
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Structural, electronic, vibrational and optical properties of Bi-n clusters
- 2017
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Ingår i: Modern Physics Letters B. - : World Scientific Pub Co Pte Lt. - 0217-9849 .- 1793-6640. ; 31:28
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Tidskriftsartikel (refereegranskat)abstract
- The neutral, anionic and cationic bismuth clusters with the size n up to 14 are investigated by using B3LYP functional within the regime of density functional theory and the LAN2DZ basis set. By analysis of the geometries of the Bin (n = 2-14)clusters, where cationic and anionic bismuth clusters are largely similar to those of neutral ones, a periodic effect by adding units with one to four atoms into smaller cluster to form larger cluster is drawn for the stable structures of bismuth clusters. An even odd alteration is shown for the properties of the clusters, such as the calculated binding energies and dissociation energies, as well as frontier orbital energies, electron affinities, ionization energies. All the properties indicate that the Bi-4 cluster is the most possible existence in bismuth-containing materials, which supports the most recent experiment. The orbital compositions, infrared and Raman activities and the ultraviolet absorption of the most possible tetramer bismuth cluster are given in detail to reveal the periodic tendency of adding bismuth atoms and the stability of tetramer bismuth cluster.
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| 5. |
- Lu, P. F., et al.
(författare)
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Electronic and optical properties of InGaAs/GaAs quantum dots with tunable aspect-ratio
- 2014
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Ingår i: Modern Physics Letters B. - : World Scientific Pub Co Pte Lt. - 0217-9849 .- 1793-6640. ; 28:9
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, a combined approach of finite element method (FEM) and quadratic programming optimization method is proposed to investigate the nonuniform equilibrium composition profile of InGaAs/GaAs quantum dots (QDs) in the framework of Gibbs energy optimization (GEO). The proposed QDs are varied with aspect ratio from 0.3 to 0.5. The wave functions of electron and heavy hole are predicted by using the k . p method. The changes of wave functions before and after optimization can be observed by using composition optimization. Both the eigenvalues and transition energy change obviously with the increasing aspect ratio. The linear optical absorption coefficients corresponding to the interband ground state transition are obtained via the density matrix approach and perturbation expansion method. The numerical results reveal that the aspect ratio and composition profile play significant roles in determining the electronic and optical properties.
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| 6. |
- Mamontov, Eugen, 1955, et al.
(författare)
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The nonzero minimum of the diffusion parameter and the uncertainty principle for a Brownian particle
- 2002
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Ingår i: Modern physics letters B. - : World Scientific. - 0217-9849. ; 16:13, s. 467-471
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Tidskriftsartikel (refereegranskat)abstract
- The limits of applicability of many classical (non-quantum-mechanical) theories are not sharp. These theories axe sometimes applied to the problems which axe, in their nature, not very well suited for that. Two of the most widely used classical approaches are the theory of diffusion stochastic process and Itos stochastic differential equations. It includes the Brownian-motion treatment as the basic particular case. The present work shows that, for quantum-mechanical reasons, the diffusion parameter of a Brownian paxticle cannot be arbitrarily small since it has a nonzero minimum value. This fact leads to the version of Heisenbergs uncertainty principle for a Brownian particle which is obtained in the precise mathematical form of a limit inequality. These quantitative results can help to,properly apply the theories associated with Brownian-particle modelling. The consideration also discusses a series of works of other authors.
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| 7. |
- Melgaard, Michael
(författare)
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Quantum collisions in semi-constrained structures
- 2007
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Ingår i: Modern physics letters B. - 0217-9849. ; 21:13, s. 767-779
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Tidskriftsartikel (refereegranskat)abstract
- The problem of a quantum particle moving in a narrow, bent two-dimensional channel is used to illustrate features of collisions in systems with semi-constrained structures. The collision theory of such systems is developed and, under certain general restrictions on the geometry, the following properties are rigorously established: (1) The (localized) Moller wave operator exist and the S operator is unitary in the scattering channels. (2) The singular spectrum is discrete in intervals away from the continuum thresholds. The discussion is based on a time-dependent approach.
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| 8. |
- Mingbo, Sun, et al.
(författare)
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A Modified Sub-Cell-Fix Method for Re-Initialization of Level-Set Distance Function and Its Dependence Tests on Grid Stretching
- 2010
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Ingår i: Modern Physics Letters B. - 0217-9849. ; 24:15, s. 1615-1629
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Tidskriftsartikel (refereegranskat)abstract
- The sub-cell-fix (SCF) method proposed by Russo and Smereka(3) computes the distance function of the cells adjacent to the zero level-set without disturbing the original zero level-set. A modified sub-cell-fix scheme independent of local curvature is developed in this paper, which makes use of a combination of the points adjacent to zero level-set surfaces and preserves the interface in a second-order accuracy. The new sub-cell-fix scheme is capable of handling large local curvature, and as a result it demonstrates satisfactory performance on several challenging test cases. The limitations of the modified scheme on stretched grids are tested and it is found that the highly stretched grid causes large numerical errors, and needs further assessment and modification.
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| 9. |
- Nika, Grigor
(författare)
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A gradient system for a higher-gradient generalization of Fourier’s law of heat conduction
- 2023
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Ingår i: Modern physics letters B. - : World Scientific. - 0217-9849 .- 1793-6640. ; 37:11, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- We derive a generalized heat conduction problem for a rarefied gas at slip regime from a gradient system where the driving functional is the entropy. Specifically, we construct an Onsager system (X,S,Kheat) such that the associated evolution of the system is given by ∂tu=+Kheat(u)DS(u), where the Onsager operator, Kheat(u), contains higher-gradients of the absolute temperature u. Moreover, through Legendre-Fenchel theory we write the Onsager system as a classical gradient system (X,S,G) with an induced gradient flow equation, ∂tu=∇GDS(u). We demonstrate the usefulness of the approach by modeling scale-size thermal effects in periodic media that have been recently observed experimentally.
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| 10. |
- Shen, Jian Qi
(författare)
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Isotropic negatively-refracting atomic-vapor medium
- 2007
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Ingår i: Modern physics letters B. - 0217-9849. ; 21:12, s. 717-728
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Tidskriftsartikel (refereegranskat)abstract
- A new scenario to realize negative refraction with a photonic-resonant vapor material that can exhibit both electric and magnetic responses via multilevel quantum coherence is suggested. Compared with the previous method of artificial composite metamaterial, where the mechanism was considered by means of classical electromagnetic theory and the materials produced have anisotropic millimetre-scale composite structures, the present scheme suggested within the framework of quantum optics can be used to design and fabricate isotropic negatively-refracting materials with atomic-scale microscopic structure units. Such an advantage may lead to a potentially important application in the techniques of superlens and perfect imaging.
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