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.

Low-energy electrodynamics of SmB 6

Abstract: We have performed direct measurements of the low-temperature dynamical conductivity and dielectric permittivity of single crystalline ${\mathrm{SmB}}_{6}$ in the spectral range from 0.6 to 4.5 meV, i.e., below the hybridization gap. The obtained results together with the data of Hall-effect and infrared reflection measurements give evidence for a 19-meV energy gap in the density of states and an additional narrow donor-type band lying only 3 meV below the bottom of the upper conduction band. It is shown that at temperatures $5\mathrm{K}lTl20\mathrm{K}$ the electrodynamic response and the dc conductivity of ${\mathrm{SmB}}_{6}$ are determined by quasifree carriers thermally excited in the conduction band. We evaluate the microscopic parameters of these carriers: the spectral weight, the concentration, the effective mass, the scattering rate, and the mobility. Below 8 K the concentration of carriers in the conduction band freezes out exponentially and finally the electronic properties of ${\mathrm{SmB}}_{6}$ are determined by the localized carriers in the narrow band with the typical signature of hopping conductivity.

Experimental study of quantum size effects in thin metal films by electron tunneling

Abstract: Periodic structure in the electron tunneling spectra of Pb, Mg, Au, and Ag has been observed. Such spectra represent in fact a direct observation of size-dependent electronic states in thin metal films. Films with thicknesses from 100 to 1000 \AA{} were studied and the effect on the electronic standing-wave energies was measured. The physical model for these effects and their observability involve the existence of so-called commensurate states. The spacing of the quantized energy levels provides a direct measurement of the electron group velocity while their location in energy determines the position of band edges and other critical energy states in the band structure of the metals. In some cases, the effective mass can also be determined. A qualitative theoretical picture is sufficient to understand all of the sailient features of the observations. A number of experiments including alloying, strain, and electric field modulation are also described.

High precision quantum control of single donor spins in silicon

Abstract: The Stark shift of the hyperfine coupling constant is investigated for a P donor in Si far below the ionization regime in the presence of interfaces using tight-binding and band minima basis approaches and compared to the recent precision measurements. In contrast with previous effective mass-based results, the quadratic Stark coefficient obtained from both theories agrees closely with the experiments. It is also shown that there is a significant linear Stark effect for an impurity near the interface, whereas, far from the interface, the quadratic Stark effect dominates. This work represents the most sensitive and precise comparison between theory and experiment for single donor spin control. Such precise control of single donor spin states is required particularly in quantum computing applications of single donor electronics, which forms the driving motivation of this work.

Symmetry of boundary conditions of the Dirac equation for electrons in carbon nanotubes

Abstract: We consider the effective mass model of spinless electrons in single-wall carbon nanotubes that is equivalent to the Dirac equation for massless fermions. Within this framework we derive all possible energy independent hard wall boundary conditions that are applicable to metallic tubes. The boundary conditions are classified in terms of their symmetry properties and we demonstrate that the use of different boundary conditions will result in varying degrees of valley degeneracy breaking of the single-particle energy spectrum.

Bose polarons in ultracold atoms in one dimension: beyond the Fr\"ohlich paradigm

Abstract: Mobile impurity atoms immersed in Bose-Einstein condensates provide a new platform for exploring Bose polarons. Recent experimental advances in the field of ultracold atoms make it possible to realize such systems with highly tunable microscopic parameters and to explore equilibrium and dynamical properties of polarons using a rich toolbox of atomic physics. In this paper we present a detailed theoretical analysis of Bose polarons in one dimensional systems of ultracold atoms. By combining a non-perturbative renormalization group approach with numerically exact diffusion Monte Carlo calculations we obtain not only detailed numerical results over a broad range of parameters but also qualitative understanding of different regimes of the system. We find that an accurate description of Bose polarons requires the inclusion of two-phonon scattering terms which go beyond the commonly used Frohlich model. Furthermore we show that when the Bose gas is in the strongly interacting regime, one needs to include interactions between the phonon modes. We use several theoretical approaches to calculate the polaron energy and its effective mass. The former can be measured using radio-frequency spectroscopy and the latter can be studied experimentally using impurity oscillations in a harmonic trapping potential. We compare our theoretical results for the effective mass to the experiments by Catani et al. [PRA 85, 023623 (2012)]. In the weak-to-intermediate coupling regimes we obtain excellent quantitative agreement between theory and experiment, without any free fitting parameter. We supplement our analysis by full dynamical simulations of polaron oscillations in a shallow trapping potential. We also use our renormalization group approach to analyze the full phase diagram and identify regions that support repulsive and attractive polarons, as well as multi-particle bound states.