arXiv subjects

G. W. Winkler

Publications and source records attributed to G. W. Winkler.

4 recordsLinked to original sources

arXiv2024

Self-consistent quasi-particle $GW$ and hybrid functional calculations for Al/InAs/Al heterojunctions: band offset and spin-orbit coupling effects

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.

cond-mat.mes-hall↗

arXiv2021

Full parity phase diagram of a proximitized nanowire island

We measure the charge periodicity of Coulomb blockade conductance oscillations of a hybrid InSb-Al island as a function of gate voltage and parallel magnetic field. The periodicity changes from $2e$ to $1e$ at a gate-dependent value of the magnetic field, $B^*$, decreasing from a high to a low limit upon increasing the gate voltage. In the gate voltage region between the two limits, which our numerical simulations indicate to be the most promising for locating Majorana zero modes, we observe correlated oscillations of peak spacings and heights. For positive gate voltages, the $2e$-$1e$ transition with low $B^*$ is due to the presence of non-topological states whose energy quickly disperses below the charging energy due to the orbital effect of the magnetic field. Our measurements demonstrate the importance of a careful exploration of the entire available phase space of a proximitized nanowire as a prerequisite to define future topological qubits.

cond-mat.mes-hall↗

arXiv2020

Andreev Modes from Phase Winding in a Full-shell Nanowire-based Transmon

We investigate transmon qubits made from semiconductor nanowires with a fully surrounding superconducting shell. In the regime of reentrant superconductivity associated with the destructive Little-Parks effect, numerous coherent transitions are observed in the first reentrant lobe, where the shell carries 2π winding of superconducting phase, and are absent in the zeroth lobe. As junction density was increased by gate voltage, qubit coherence was suppressed then lost in the first lobe. These observations and numerical simulations highlight the role of winding-induced Andreev states in the junction.

cond-mat.mes-hall↗

arXiv2018

Topological superconductivity in full shell proximitized nanowires

We consider a new model system supporting Majorana zero modes based on semiconductor nanowires with a full superconducting shell. We demonstrate that, in the presence of spin-orbit coupling in the semiconductor induced by a radial electric field, the winding of the superconducting order parameter leads to a topological phase supporting Majorana zero modes. The topological phase persists over a large range of chemical potentials and can be induced by a predictable and weak magnetic field piercing the cylinder. The system can be readily realized in semiconductor nanowires covered by a full superconducting shell, opening a pathway for realizing topological quantum computing proposals.

cond-mat.supr-con↗