Carrier transport in broken-gap heterostructures tuned by a magnetic field

Abstract

We have performed an eight-band k · p model calculation on the current-voltage ͑I-V͒ curves associated with interband magnetotransport in a double-barrier broken-gap heterostructure using the Burt-Foreman multiband envelope function theory and the scattering matrix approach. In a sample with very thin barriers, the broadening ⌫ 0 of a virtual bound state with energy E 0 can be very large. Depending on the relative values of ⌫ 0 and ͉E 0 − E F ͉, where E F is the Fermi energy, the behavior of the I-V curve can be either of Ohmic type or of resonant-tunneling type, and can be tuned from one to the other by changing the applied magnetic-field strength.

The 4He total photo-absorption cross section with two- plus three-nucleon interactions from chiral effective field theory

“…We find an overall good agreement with the photo-disintegration data from bremsstrahlung photons [16], which are consistent with the indirect measurements of Ref. [40], while we [16] multiplied by a factor of 2, the total cross section measurements of Shima et al [15], the total photo-absorption at the peak derived from Compton scattering via dispersion relations from Wells et al [40]; (lower panel) the EIHH predictions for AV18, AV18+UIX [20] and UCOM [21]. The widths of the χEFT NN and χEFT NN+NNN curves reflect the uncertainties in the calculations (see text).…”

“…With the exception of [17], early evaluations of the 4 He photo-disintegration [18,19,14] showed better agreement with the high-peaked experiments, and, ultimately, with those of Ref. [16]. The inability of these calculations to reproduce a suppressed cross section at low energy was often imputed to the semirealistic nature of the Hamiltonian and, in particular, to the absence of the NNN force.…”

“…[13,14,15]). The latest examples date back to the past two years [15,16]. Of particular controversy is the height of the cross section at the peak, alternatively found to be either pronounced or suppressed with differences up to a factor of 2 between different experimental data.…”

“…We compare to experimental data in the region ω < 40 MeV, where corrections to the unretarded dipole approximation are expected to be largely negligible and the relative uncertainty of our calculations is minimal. The data sets from Nilsson et al [16] and Shima et al [15] are chosen here as the latest examples of controversial experiments characterizing the 4 He photo-effect since the 50's (see reviews of available data in Refs. [13,14] and [15]).…”

“…4, we estimate the total cross section from the 4 He(γ, n) measurements of Ref. [16] by assuming σ γ (ω) ≃ 2σ γ,n (ω). The latter assumption, which relies on the similarity of the (γ, p) and (γ, n) cross sections, provides a sufficiently safe estimate of the total cross section below the three-body break-up threshold (ω = 26.1 MeV).…”