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3 Interfaces
Published in Jiabao Yi, Sean Li, Functional Materials and Electronics, 2018
Zhiqi Liu, Anil Annadi, Ariando
However, it is still puzzling that the Kondo temperature is so high and close to 100 K as the conventional Kondo effect found in metal doped with magnetic elements has a typical Kondo temperature of ~10 K. The reason could be that the Kondo effect in strongly correlated oxides is largely different from that in metals. On the other hand, the resistance minimum was argued to be due to the weak localization in a two-dimensional system [28]. Whether it is due to the Kondo effect or weak localization is still an open issue up to now as no systematical temperature- and field-dependent resistance data in the light of the Kondo model or the weak localization model have been reported to clarify this issue.
Computational Modeling of Nanoparticles
Published in Sarhan M. Musa, ®, 2018
This equation is called the Landauer formula for the conductance [32]. It implies that the conductance of a thin wire stays infinite even for small values of the length L. The conductance increases to infinity, meaning zero resistance, if we have a large device for which the number of conducting modes is infinite. However, a very large number of conducting modes means a large device that is no longer considered to be a nanodevice. This kind of quantization of the electron conductance is seen in many systems, for example, in quantum wires and in atomic chains. Transport properties of nanostructures are modeled using different quantum-mechanical methods approximating different properties of the structure. In some simulations electron interactions are included carefully so that many-particle effects are included. These models include, for example, the Kondo model and the Anderson impurity model [33]. Nanostructures in these models do not have any specific geometry; they are just considered as discrete electron states. Other groups of models consider the specific shape of the nanostructure. The discrete atomic structure can also be included. This means that it is possible to get information about the effects of structural changes of the system. Typically, the electron–electron interactions are then included in a mean-field manner. This means that some many-particle effects cannot be seen. The DFT is a mean field theory, which is successfully used in computational materials physics and chemistry obtaining results in good quantitative agreement with measurements. In order to model transport properties the nanostructure is connected to the electrodes. This means that the size of the system is infinite. In practice, we have to define the calculation volume Ω to be infinite. In order to handle the finite-size effects we use the scattering formalism.
Role of Ce 4f-conduction band on-site hybridisation in the nature of magnetism in Ce5MGe2, where M is d-electron-type metal
Published in Philosophical Magazine, 2020
It is generally accepted that at low temperature limit, a narrow band of heavy electrons gives rise to the large specific-heat coefficient γ and originates from renormalised hybridisation of the f−c states. The essence of low-temperature physical properties is grasped properly by the periodic Anderson model. Within the periodic Anderson model, Doradziński and Spałek [13] calculated the mean-field magnetic phase diagram (DS), which includes the Kondo polarisation effect. It was documented that the stability of the magnetic/nonmagnetic ground state in the Kondo-lattice limit is strongly dependent on the on-site hybridisation magnitude , the bare f-level position in the conduction band, the number of electrons per site and on the intersite Coulomb interaction U between the f-electron states. The DS phase diagram on the plane has been shown to provide a qualitative account of experimental results on the series of Ce-ternary intermetallics [14,15]. For the series of CeGe compounds, DS diagram predicts for each of them a strongly ferromagnetic (SFM) T=0 phase and accompanying a weak Kondo coupling in the plane for roughly estimated eV from XPS and . If intrasite Kondo effect is expressed by Kondo temperature ( eV is a bandwidth of bare s and d states), one expects local Kondo temperature K. On the basis of two-level Kondo model [16], magnetic entropy predicts for the series CeGe larger value of . Despite the large approximations in the estimate of the and quantities, the DS model predicts the magnetic state of the system in agreement with the experimental data.