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Effective mass (solid-state physics)

About: Effective mass (solid-state physics) is a research topic. Over the lifetime, 12539 publications have been published within this topic receiving 295485 citations.


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Journal ArticleDOI
01 Aug 1991-Nature
TL;DR: In this paper, the muon-spin-relaxation measurements of the magnetic-field penetration depth λ in K3C60 have been obtained, which indicates that the superconducting energy gap is isotropic, without nodes or zero points.
Abstract: THE discovery1–3 of superconductivity in C60 doped with the alkali metals potassium and rubidium has introduced a new family of three-dimensional molecular superconductors4. The potassium-doped compound3 K3C60 has a relatively high transition temperature (Tc = 19.3K), a very high upper critical field (Hc2 (T⇒ 0)≈50T) and a short superconducting coherence length5 (£ = 26 A), in common with the copper oxide superconductors. Here we report muon-spin-relaxation measurements of the magnetic-field penetration depth λ in K3C60. The temperature dependence of λ and of the muon spin relaxation rate indicate that the superconducting energy gap is isotropic, without nodes or zero points. The low-temperature penetration depth λ (T⇒ 0) is about 4,800 A, which implies a ratio of superconducting carrier density to effective mass to be n2/(m*/me) = 1.2 x 1020 cm-3 if one assumes the 'clean limit'. Combining this result with the value of e, we estimate the Fermi temperature TF = 470 K. In the relationship between TF and Tc, K3C60 conforms to the trend exhibited by 'exotic' superconductors6,7 such as the Chevrel phase compounds, the copper oxides and the organic BEDT systems.

161 citations

Journal ArticleDOI
TL;DR: In this article, a general theory for quantum simulation of cubic semiconductor n-type metal-oxide-semiconductor field effect transistors is presented within the effective mass equation approach.
Abstract: The general theory for quantum simulation of cubic semiconductor n-type metal-oxide-semiconductor field-effect transistors is presented within the effective-mass equation approach. The full three-dimensional transport problem is described in terms of coupled transverse subband modes which arise due to quantum confinement along the body thickness direction. Couplings among the subbands are generated for two reasons: due to spatial variations of the confinement potential along the transport direction and due to nonalignment of the device coordinate system with the principal axes of the constant energy conduction-band ellipsoids. The problem simplifies considerably if the electrostatic potential is separable along the transport and confinement directions, and further if the potential variations along the transport direction are slow enough to prevent dipolar coupling (Zener tunneling) between subbands. In this limit, the transport problem can be solved by employing two unitary operators to transform an arbit...

160 citations

Journal ArticleDOI
TL;DR: In this article, the authors derived the radiative recombination lifetimes due to direct and indirect transitions and applied them to Ge and Si, respectively, and showed that in Ge at room temperature, while the density of filled states in the conduction band at k=0 is very low, the rate of recombination by direct transitions is nevertheless somewhat greater than that by indirect transitions.
Abstract: The mechanisms by which electrons and holes recombine with the emission of radiation are examined. Expressions are derived for the radiative recombination lifetimes due to direct and indirect transitions and are applied to Ge and Si. Matrix elements in the transition probability for direct and indirect transitions are obtained from analyses of the cyclotron resonance effective mass data and the optical absorption data close to the band edge, respectively. For indirect transitions the calculated lifetimes were of the order of seconds and agreed within a factor of 3 with lifetimes calculated by the method of Van Roosbroeck and Shockley. It is shown that in Ge at room temperature, while the density of filled states in the conduction band at k=0 is very low, the rate of recombination by direct transitions is nevertheless somewhat greater than that by indirect transitions. This is consistent with the findings of Haynes. The role of radiative recombination in the observed lifetimes of excess carriers is questioned. It is concluded that for those semiconductors which have a rather high absorption constant close to the band edge (InSb), an emitted photon is usually reabsorbed before it can escape from the crystal, producing another hole-electron pair, without contributing to the macroscopically observed lifetime. In the limit of a very high absorption constant, this emission and absorption of photons acts as an additional mechanism for the diffusion of hole-electron pairs.

160 citations

Journal ArticleDOI
TL;DR: In this article, the effect of shell thickness, impurity, and dielectric environment on the absorption coefficients and refractive index changes associated with intersubband transitions in ZnO/ZnS core shell quantum dot (CSQD) and inverted CSQD was investigated.
Abstract: In the present work, we investigated theoretically the linear, nonlinear, and total absorption coefficients and refractive index changes associated with intersubband transitions in ZnO/ZnS core shell quantum dot (CSQD) and ZnS/ZnO inverted CSQD (ICSQD), emphasizing on the influence of the shell thickness, impurity, and dielectric environment. The effect of the polarization charges due to the possible existence of the dielectric mismatch between the system and its surrounding matrix is considered. The electronic structures are numerically calculated by employing the potential morphing method in the framework of effective mass approximation. We find that in both impurity-free CSQD and ICSQD, increasing the shell thickness red shifts significantly the threshold energy and enhances drastically the nonlinear absorption coefficients and all the refractive index changes, independently on the dielectric environments. Similar behaviour has also been observed in most of the cases studied when the impurity is displaced from the core center to the shell center. In contrast, comparing to a dielectrically homogeneous system, dispersing the systems into a matrix with a lower dielectric constant blue shifts all the peak positions of the absorption coefficients and refractive index changes. However, the corresponding magnitudes (in absolute value) are substantially reduced. Finally, we find that the nonlinear properties are more sensitive to the external perturbations, while at a weak radiation intensity, the variation of the total quantities is generally dominated by that of the corresponding linear terms.

160 citations

Journal ArticleDOI
TL;DR: In this paper, the HgTe•CdTe superlattice was found to exhibit properties superior to those of the (Hg, Cd)Te alloy as an infrared detector material.
Abstract: The HgTe‐CdTe superlattice is found to exhibit properties superior to those of the (Hg, Cd)Te alloy as an infrared detector material. A calculation shows that the superlattice tunneling length is shorter than that of the alloy with the same band gap. For a given cutoff wavelength tolerance, we find that less fractional precision is needed in the superlattice control parameter (layer thicknesses) than in the alloy control parameter (composition). Also, p‐side diffusion currents are expected to be reduced due to the larger superlattice electron effective mass.

159 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202215
2021410
2020421
2019395
2018362
2017412