ith their experimental verification in 2007, topological insulators (TIs) render a new and fascinating class of materials 1 . A band inversion in the bulk of three-dimensional (3D) TIs creates a 2D metallic subspace at the physical surface of these 3D crystals. The charge carriers of the 2D metal (Dirac electrons) have their spin locked to the momentum, which leads to a topological protection of the subspace 2-4 . This intrinsic quantumspin texture enables the realization of novel technologies, which range from spintronics to quantum computing. Particularly in combination with superconductors (S), TIs promise new quantum devices. Networks of TI nanostructures in proximity to superconductive islands have been predicted to host non-Abelian Majorana modes at the ends and at the crossing points of the networks [5][6][7][8] . Braiding of these elusive modes, that is, exchanging the position of Majorana modes in a 2D plane (Supplementary Fig. 2), resembles topologically protected quantum operations in the Majorana platform. Topological quantum bits (qubits), which use Majorana modes 9,10 to store and process quantum information, are expected to compute fault tolerantly with minimal need for error correction [11][12][13][14] .Topological qubits require high-quality (multi-terminal) Josephson junctions (JJs) 12,15,16 . The simplest type of such a JJ is a two-terminal S-TI-S device (Fig. 1). The Josephson effect 17 allows for an electrical current to conduct dissipationlessly across a lateral junction of two close-by superconductive electrodes separated by a weak link of non-superconductive material. In conventional lateral JJs, the supercurrent is mediated by Andreev bound states (ABS), which effectively transport Cooper pairs across the weak link 18 . In S-TI-S junctions the Dirac system forms a weak link. The quantum spin texture of the Dirac system causes an additional transport channel, known as Majorana bound states (MBS), which adds to conventional ABS 19 . In contrast to ABS, MBS facilitate single-electron transport across the weak link 20 . The contribution of MBS to a supercurrent can be detected via Shapiro response measurements 19,[21][22][23][24] . MBS manifest themselves by a suppression of odd Shapiro steps in low-temperature transport experiments under radio frequency (RF) radiation, due to their 4π-periodic energy-phase dependency 25 .To create and preserve MBS in S-TI-S junctions, the Dirac system in between the superconductive electrodes needs to be conserved (Fig. 1b). Surface oxidation 26,27 and reactions with water molecules at ambient conditions 28 can lead to additional non-topological states at the surface of (Bi,Sb)-based TIs. These superimpose locally with the Dirac system, and thus allow for additional scattering events that could destroy the MBS. To avoid surface degradation in (Bi,Sb)-based TIs, an in situ deposited protective AlO x capping layer on top of the topological surface is often employed 29,30 . Although such capping layers protect the topological surface states for ex situ fabricat...

Inverters based on uniaxially tensile strained Si (sSi) nanowire (NW) tunneling field-effect transistors (TFETs) are fabricated. Tilted dopant implantation using the gate as a shadow mask allows self-aligned formation of p-i-n TFETs. The steep junctions formed by dopant segregation at low temperatures improve the band-to-band tunneling, resulting in higher oncurrents of n- and p-TFETs of >10 μA/μm at VDS = 0.5 V. The subthreshold slope for n-channel TFETs reaches a minimum value of 30 mV/dec, and is <60 mV/dec over one order of magnitude of drain current. The first sSi NW complementary TFET inverters show sharp transitions and fairly high static gain even at very low VDD = 0.2 V. The first transient response analysis of the inverters shows clear output voltage overshoots and a fall time of 2 ns at VDD = 1.0 V

We report tunneling spectroscopy experiments on a bilayer graphene double quantum dot device that can be tuned by all-graphene lateral gates. The diameter of the two quantum dots are around 50 nm and the constrictions acting as tunneling barriers are 30 nm in width. The double quantum dot features addition energies on the order of 20 meV. Charge stability diagrams allow us to study the tunable interdot coupling energy as well as the spectrum of the electronic excited states on a number of individual triple points over a large energy range. The obtained constant level spacing of 1.75 meV over a wide energy range is in good agreement with the expected single-particle energy spacing in bilayer graphene quantum dots. Finally, we investigate the evolution of the electronic excited states in a parallel magnetic field.Keywords: graphene, bilayer graphene, quantum dot, double quantum dot, excited states Graphene quantum dots (QDs) are interesting candidates for spin qubits with long coherence times [1]. The suppressed hyperfine interaction and weak spin-orbit coupling [2, 3] make graphene and flat carbon structures in general, promising for future quantum information technology [4]. Significant progress has been made recently in the fabrication and understanding of graphene quantum devices. A "paper-cutting" technique enables the fabrication of graphene nanoribbons [5][6][7][8][9][10][11][12][13], quantum dots [14][15][16][17][18][19], and double quantum dot devices [20][21][22][23], where a disorder-induced energy gap allows confinement of individual carriers in graphene. These devices allowed the experimental investigation of excited states [16,21], spin states [19] and the electron-hole crossover [17]. However, all of these studies were based on single-layer graphene and showed a number of device limitations related to the presence of disorder, vibrational excitations and to the fact that the missing band gap makes it difficult to realize soft confinement potentials and "well-behaving" tunneling barriers. In particular, it has been shown that intrinsic ripples and corrugations in single-layer graphene can lead to unintended vibrational degrees of freedom [24] and to a coherent electron-vibron coupling in graphene QDs [25]. Bilayer graphene is a promising candidate to overcome some of these limitations. In particular it allows to open a band gap by an out-of-plane electric field [26][27][28], which may enable a soft confinement potential and may reduce the influence of localized edge states. More importantly, it has been shown that ripples and substrate-induced disorder are reduced in bilayer graphene [29], which increases the mechanical stability and suppresses unwanted vibrational modes.Here, we present a bilayer graphene double quantum dot (DQD) device, with a number of lateral gates. These local gates allow to tune transport from hole to electron dominated regimes and they enable to access different device configurations. We focus on the DQD configuration and show characteristic honeycomb-like charge stability dia...

Electron and hole Bloch states in bilayer graphene exhibit topological orbital magnetic moments with opposite signs, which allows for tunable valley-polarization in an out-of-plane magnetic field. This property makes electron and hole quantum dots (QDs) in bilayer graphene interesting for valley and spin-valley qubits. Here, we show measurements of the electron–hole crossover in a bilayer graphene QD, demonstrating opposite signs of the magnetic moments associated with the Berry curvature. Using three layers of top gates, we independently control the tunneling barriers while tuning the occupation from the few-hole regime to the few-electron regime, crossing the displacement-field-controlled band gap. The band gap is around 25 meV, while the charging energies of the electron and hole dots are between 3 and 5 meV. The extracted valley g -factor is around 17 and leads to opposite valley polarization for electrons and holes at moderate B -fields. Our measurements agree well with tight-binding calculations for our device.