The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Young-dae Jung - One of the best experts on this subject based on the ideXlab platform.
-
Temperature effects on the nonstationary Karpman-Washimi ponderomotive magnetization in quantum plasmas
Physics of Plasmas, 2009Co-Authors: Sang-chul Na, Young-dae JungAbstract:The Temperature effects on the nonstationary Karpman–Washimi ponderomotive magnetization are investigated in quantum Fermi plasmas. The cyclotron frequency due to the ponderomotive force of the electromagnetic wave has been obtained as a function of the Fermi Debye length and quantum wavelength. It is found that the Karpman–Washimi ponderomotive magnetization decreases with increasing Fermi Temperature. The maximum position of the Fermi Debye length is found to be increased with an increase in the frequency in the small Fermi Debye length domain. It is also shown that the Fermi ponderomotive magnetization decreases with increasing frequency in the large Fermi Debye length domain. In addition, it is shown that the frequency dependence on the ponderomotive magnetization diminishes with increasing Fermi Temperature.
-
Temperature effects on the nonstationary Karpman–Washimi ponderomotive magnetization in quantum plasmas
Physics of Plasmas, 2009Co-Authors: Young-dae JungAbstract:The Temperature effects on the nonstationary Karpman–Washimi ponderomotive magnetization are investigated in quantum Fermi plasmas. The cyclotron frequency due to the ponderomotive force of the electromagnetic wave has been obtained as a function of the Fermi Debye length and quantum wavelength. It is found that the Karpman–Washimi ponderomotive magnetization decreases with increasing Fermi Temperature. The maximum position of the Fermi Debye length is found to be increased with an increase in the frequency in the small Fermi Debye length domain. It is also shown that the Fermi ponderomotive magnetization decreases with increasing frequency in the large Fermi Debye length domain. In addition, it is shown that the frequency dependence on the ponderomotive magnetization diminishes with increasing Fermi Temperature.
Christoph Ortner - One of the best experts on this subject based on the ideXlab platform.
-
Point defects in tight binding models for insulators
Mathematical Models and Methods in Applied Sciences, 2020Co-Authors: Christoph Ortner, Jack ThomasAbstract:We consider atomistic geometry relaxation in the context of linear tight binding models for point defects. A limiting model as Fermi-Temperature is sent to zero is formulated, and an exponential rate of convergence for the nuclei configuration is established. We also formulate the thermodynamic limit model at zero Fermi-Temperature, extending the results of [H. Chen, J. Lu and C. Ortner, Thermodynamic limit of crystal defects with finite Temperature tight binding, Arch. Ration. Mech. Anal. 230 (2018) 701–733]. We discuss the non-trivial relationship between taking zero Temperature and thermodynamic limits in the finite Fermi-Temperature models.
-
Locality of Interatomic Forces in Tight Binding Models for Insulators
ESAIM: Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Christoph Ortner, Jack Thomas, Huajie ChenAbstract:The tight binding model is a minimalistic electronic structure model for predicting properties of materials and molecules. For insulators at zero Fermi-Temperature we show that the potential energy surface of this model can be decomposed into exponentially localised site energy contributions, thus providing qualitatively sharp estimates on the interatomic interaction range which justifies a range of multi-scale models. For insulators at finite Fermi-Temperature we obtain locality estimates that are uniform in the zero-Temperature limit. A particular feature of all our results is that they depend only weakly on the point spectrum. Numerical tests confirm our analytical results. This work extends and strengthens (Chen, Ortner 2016) and (Chen, Lu, Ortner 2018) for finite Temperature models.
-
Point Defects in Tight Binding Models for Insulators
arXiv: Mathematical Physics, 2020Co-Authors: Christoph Ortner, Jack ThomasAbstract:We consider atomistic geometry relaxation in the context of linear tight binding models for point defects. A limiting model as Fermi-Temperature is sent to zero is formulated, and an exponential rate of convergence for the nuclei configuration is established. We also formulate the thermodynamic limit model at zero Fermi-Temperature, extending the results of [H. Chen, J. Lu, C. Ortner. Arch. Ration. Mech. Anal., 2018]. We discuss the non-trivial relationship between taking zero Temperature and thermodynamic limits in the finite Fermi-Temperature models.
-
locality of interatomic forces in tight binding models for insulators
Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Christoph Ortner, Jack Thomas, Huajie ChenAbstract:The tight binding model is a minimalistic electronic structure model for predicting properties of materials and molecules. For insulators at zero Fermi-Temperature we show that the potential energy surface of this model can be decomposed into exponentially localised site energy contributions, thus providing qualitatively sharp estimates on the interatomic interaction range which justifies a range of multi-scale models. For insulators at finite Fermi-Temperature we obtain locality estimates that are uniform in the zero-Temperature limit. A particular feature of all our results is that they depend only weakly on the point spectrum. This work extends and strengthens (Chen, Ortner 2016) and (Chen, Lu, Ortner 2018) for finite Temperature models.
-
thermodynamic limit of crystal defects with finite Temperature tight binding
Archive for Rational Mechanics and Analysis, 2018Co-Authors: Huajie Chen, Jianfeng Lu, Christoph OrtnerAbstract:We consider a tight binding model for localised crystalline defects with electrons in the canonical ensemble (finite Fermi Temperature) and nuclei positions relaxed according to the Born–Oppenheimer approximation. We prove that the limit model as the computational domain size grows to infinity is formulated in the grand-canonical ensemble for the electrons. The Fermi-level for the limit model is fixed at a homogeneous crystal level, independent of the defect or electron number in the sequence of finite-domain approximations. We quantify the rates of convergence for the nuclei configuration and for the Fermi-level.
Rembert A. Duine - One of the best experts on this subject based on the ideXlab platform.
-
magnons versus electrons in thermal spin transport through metallic interfaces
Journal of Physics D, 2018Co-Authors: Maarten Beens, Yaroslav Tserkovnyak, Rembert A. Duine, Joseph P. HeremansAbstract:We develop a theory for spin transport in magnetic metals that treats the contribution of magnons and electrons on equal footing. As an application, we consider thermally-driven spin injection across an interface between a magnetic metal and a normal metal, i.e. the spin-dependent Seebeck effect. We show that the ratio between magnonic and electronic contribution scales as , with the Fermi Temperature T F and the Curie Temperature T C . Since, typically, , the magnonic contribution may dominate the thermal spin injection, even though the interface is more transparent for electronic spin current.
Deborah Jin - One of the best experts on this subject based on the ideXlab platform.
-
Spin Excitations in a Fermi Gas of Atoms
Physical review letters, 2002Co-Authors: Brian Demarco, Deborah JinAbstract:We have experimentally investigated a spin excitation in a quantum degenerate Fermi gas of atoms. In the hydrodynamic regime the damping time of the collective excitation is used to probe the quantum behavior of the gas. At Temperatures below the Fermi Temperature we measure up to a factor of 2 reduction in the excitation damping time compared to the classical expectation. In addition, we observe a strong excitation energy dependence for this quantum statistical effect.
-
Evaporative Cooling of a Two-Component Degenerate Fermi Gas
Physical Review A, 2000Co-Authors: Murray Holland, Brian Demarco, Deborah JinAbstract:We derive a quantum theory of evaporative cooling for a degenerate Fermi gas with two constituents and show that the optimum cooling trajectory is influenced significantly by the quantum statistics of the particles. The cooling efficiency is reduced at low Temperatures due to Pauli blocking of available final states in each binary collision event. We compare the theoretical optimum trajectory with experimental data on cooling a quantum degenerate cloud of potassium-40, and show that Temperatures as low as 0.3 times the Fermi Temperature can now be achieved.
-
Onset of Fermi degeneracy in a trapped atomic Gas
Science (New York N.Y.), 1999Co-Authors: Brian Demarco, Deborah JinAbstract:An evaporative cooling strategy that uses a two-component Fermi gas was employed to cool a magnetically trapped gas of 7 x 10(5) (40)K atoms to 0.5 of the Fermi Temperature T(F). In this Temperature regime, where the state occupation at the lowest energies has increased from essentially zero at high Temperatures to nearly 60 percent, quantum degeneracy was observed as a barrier to evaporative cooling and as a modification of the thermodynamics. Measurements of the momentum distribution and the total energy of the confined Fermi gas directly revealed the quantum statistics.
Huajie Chen - One of the best experts on this subject based on the ideXlab platform.
-
Locality of Interatomic Forces in Tight Binding Models for Insulators
ESAIM: Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Christoph Ortner, Jack Thomas, Huajie ChenAbstract:The tight binding model is a minimalistic electronic structure model for predicting properties of materials and molecules. For insulators at zero Fermi-Temperature we show that the potential energy surface of this model can be decomposed into exponentially localised site energy contributions, thus providing qualitatively sharp estimates on the interatomic interaction range which justifies a range of multi-scale models. For insulators at finite Fermi-Temperature we obtain locality estimates that are uniform in the zero-Temperature limit. A particular feature of all our results is that they depend only weakly on the point spectrum. Numerical tests confirm our analytical results. This work extends and strengthens (Chen, Ortner 2016) and (Chen, Lu, Ortner 2018) for finite Temperature models.
-
locality of interatomic forces in tight binding models for insulators
Mathematical Modelling and Numerical Analysis, 2020Co-Authors: Christoph Ortner, Jack Thomas, Huajie ChenAbstract:The tight binding model is a minimalistic electronic structure model for predicting properties of materials and molecules. For insulators at zero Fermi-Temperature we show that the potential energy surface of this model can be decomposed into exponentially localised site energy contributions, thus providing qualitatively sharp estimates on the interatomic interaction range which justifies a range of multi-scale models. For insulators at finite Fermi-Temperature we obtain locality estimates that are uniform in the zero-Temperature limit. A particular feature of all our results is that they depend only weakly on the point spectrum. This work extends and strengthens (Chen, Ortner 2016) and (Chen, Lu, Ortner 2018) for finite Temperature models.
-
thermodynamic limit of crystal defects with finite Temperature tight binding
Archive for Rational Mechanics and Analysis, 2018Co-Authors: Huajie Chen, Jianfeng Lu, Christoph OrtnerAbstract:We consider a tight binding model for localised crystalline defects with electrons in the canonical ensemble (finite Fermi Temperature) and nuclei positions relaxed according to the Born–Oppenheimer approximation. We prove that the limit model as the computational domain size grows to infinity is formulated in the grand-canonical ensemble for the electrons. The Fermi-level for the limit model is fixed at a homogeneous crystal level, independent of the defect or electron number in the sequence of finite-domain approximations. We quantify the rates of convergence for the nuclei configuration and for the Fermi-level.