We develop a unified numerical approach for modeling semiconductor-superconductor heterostructures. Our approach takes into account on equal footing important key ingredients: proximity-induced superconductivity, orbital and Zeeman effect of an applied magnetic field, spin-orbit coupling as well as the electrostatic environment. As a model system, we consider indium arsenide (InAs) nanowires with epitaxial aluminum (Al) shell and demonstrate qualitative agreement of the obtained results with the existing experimental data. Finally, we characterize the topological superconducting phase emerging in a finite magnetic field and calculate the corresponding topological phase diagram.
We present a flexible figure-9 Yb: fiber-laser and investigate the impact of intra-cavity group delay dispersion on amplitude/phase noise. We show that the free-running carrier-envelope-offset frequency short-term linewidth can range from several MHz to <10 kHz.
We present our results for simultaneous measurement of the refractive indices of gallium arsenide (GaAs) and aluminum gallium arsenide $({\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\text{\ensuremath{-}}x}\mathrm{As})$ in the spectral region from $2.0\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{m}\phantom{\rule{0.16em}{0ex}}\mathrm{to}\phantom{\rule{0.16em}{0ex}}7.1\phantom{\rule{0.16em}{0ex}}\textmu{}\mathrm{m}$ $(5000\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{to}\phantom{\rule{0.16em}{0ex}}1400\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1})$. We obtain these values from a monocrystalline superlattice Bragg mirror of excellent purity (background doping $\ensuremath{\le}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}\phantom{\rule{0.16em}{0ex}}/\phantom{\rule{0.16em}{0ex}}{\mathrm{cm}}^{3}\phantom{\rule{0.16em}{0ex}}$), grown via molecular beam epitaxy. To recover the refractive indices over such a broad wavelength range, we fit a dispersion model for each material. In a novel combination of well-established methods, we measure both a photometrically accurate transmittance spectrum of the Bragg mirror via Fourier-transform infrared spectrometry and the individual physical layer thicknesses of the structure via scanning electron microscopy. To infer the uncertainty of the refractive index values, we estimate relevant measurement uncertainties and propagate them via a Monte Carlo method. This highly-adaptable approach conclusively yields propagated relative uncertainties on the order of ${10}^{\ensuremath{-}4}$ over the measured spectral range for both GaAs and ${\mathrm{Al}}_{0.929}{\mathrm{Ga}}_{0.071}\mathrm{As}$. The fitted model can also approximate the refractive index for MBE-grown ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\text{\ensuremath{-}}x}\mathrm{As}$ for $0\ensuremath{\le}x\ensuremath{\le}1$. Both these updated values and the measurement approach will be essential in the design, fabrication, and characterization of next-generation active and passive optical devices in a spectral region that is of high interest in many fields, e.g., laser design and cavity-enhanced spectroscopy in the mid-infrared.
In this comment, we show that the model introduced in Hess et al. Phys. Rev. Lett. {\bf 130}, 207001 (2023) fails the topological gap protocol (TGP) (Pikulin et al., arXiv:2103.12217 and M. Aghaee et al., Phys. Rev. B 107, 245424 (2023)). In addition, we discuss this model in the broader context of how the TGP has been benchmarked.
Superconductor proximitized one-dimensional semiconductor nanowires with strong spin-orbit interaction (SOI) are at this time the most promising candidates for the realization of topological quantum information processing. In current experiments the SOI originates predominantly from extrinsic fields, induced by finite size effects and applied gate voltages. The dependence of the topological transition in these devices on microscopic details makes scaling to a large number of devices difficult unless a material with dominant intrinsic bulk SOI is used. Here we show that wires made of certain ordered alloys InAs$_{1-x}$Sb$_x$ have spin-splittings up to 20 times larger than those reached in pristine InSb wires. In particular, we show this for a stable ordered CuPt-structure at $x = 0.5$, which has an inverted band ordering and realizes a novel type of a topological semimetal with triple degeneracy points in the bulk spectrum that produce topological surface Fermi arcs. Experimentally achievable strains can drive this compound either into a topological insulator phase, or restore the normal band ordering making the CuPt-ordered InAs$_{0.5}$Sb$_{0.5}$ a semiconductor with a large intrinsic linear in $k$ bulk spin splitting.
Recent experiments on Majorana fermions in semiconductor nanowires [S. M. Albrecht, A. P. Higginbotham, M. Madsen, F. Kuemmeth, T. S. Jespersen, J. Nyg\aa{}rd, P. Krogstrup, and C. M. Marcus, Nature (London) 531, 206 (2016)] revealed a surprisingly large electronic Land\'e $g$ factor, several times larger than the bulk value---contrary to the expectation that confinement reduces the $g$ factor. Here we assess the role of orbital contributions to the electron $g$ factor in nanowires and quantum dots. We show that an $\mathbf{L}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{S}$ coupling in higher subbands leads to an enhancement of the $g$ factor of an order of magnitude or more for small effective mass semiconductors. We validate our theoretical finding with simulations of InAs and InSb, showing that the effect persists even if cylindrical symmetry is broken. A huge anisotropy of the enhanced $g$ factors under magnetic field rotation allows for a straightforward experimental test of this theory.
The nucleus of 229Thorium presents a unique isomer state of very low energy and long lifetime, current estimates are around 7.8 eV and seconds to hours respectively. This nuclear transitions therefore is a promising candidate for a novel type of frequency standard and several groups worldwide have set out to investigate this system. Our aim is to construct a solid state nuclear clock, i.e. a frequency standard where Thorium ions are implanted into Calciumfluoride crystals transparent in vacuum ultraviolet range. As a first step towards an accurate determination of the exact energy and lifetime of this isomer state we perform low-resolution fluorescent spectroscopic measurements.
The electronic structure of surfaces and interfaces plays a key role in the properties of quantum devices. Here, we study the electronic structure of realistic Al/InAs/Al heterojunctions using a combination of density functional theory (DFT) with hybrid functionals and state-of-the-art quasi-particle $GW$ (QS$GW$) calculations. We find a good agreement between QS$GW$ calculations and hybrid functional calculations which themselves compare favourably well with ARPES experiments. Our study confirm the need of well controlled quality of the interfaces to obtain the needed properties of InAs/Al heterojunctions. A detailed analysis of the effects of spin-orbit coupling on the spin-splitting of the electronic states show a linear scaling in $k$-space, related to the two-dimensional nature of some interface states. The good agreement by QS$GW$ and hybrid functional calculations open the door towards trust-able use of an effective approximation to QS$GW$ for studying very large heterojunctions.
A method for generating a single-cavity dualcomb or multicomb for laser spectroscopy, the method comprising the steps of providing a laser system comprising a pump source, a gain medium, and a resonator having a spectral filter; spectrally filtering, by the spectral filter, light in the resonator and attenuating, in particular blocking, by the spectral filter, one or more wavelength bands at least one of which being located completely within the gain bandwidth of the laser system such that two or more at least partially separated spectral regions are provided; mode-locking the two or more at least partially separated spectral regions.
