Thematic Sessions
1Early diagnostics of diseases, chaired by dr.ir. Loes Segerink & prof.dr.ir. Albert van den Berg
2Unconventional electronics, chaired by prof.dr.ir. Wilfred van der Wiel & prof.dr.ing. Guus Rijnders
3Storage and conversion of renewable energy, chaired by prof.dr. Guido Mul & dr.ir. Mark Huijben
4Water, chaired by prof.dr.ir. Rob Lammertink & dr.ir. Wiebe de Vos
Chairs: prof.dr.ir. Wilfred van der Wiel (NanoElectronics) & prof.dr.ing. Guus Rijnders (Inorganic Materials Science)
One of the greatest successes of the 20th century has been the development of digital computers. Conventional computation is based on Turing’s abstract model of a machine, now referred to as the Turing machine. Based on the ideas of Turing, Von Neumann proposed a computer architecture, which forms the foundation for all digital computing. In this computational paradigm, physical components are constructed into logic gates, from which the Von Neumann architecture is built. During the last decades computers have become more and more powerful by integrating increasingly many and smaller components on chips. It is becoming very hard and extremely expensive to continue this miniaturisation. Current transistors consist of only a handful of atoms. It is a major challenge to produce chips in which the millions of transistors have the same characteristics, and thus to make the chips operate properly. Another drawback is that their energy consumption is reaching unacceptable levels. It is obvious that we have to look for alternative, unconventional directions.
In this session, we will address questions as Have we reached the end of the Digital Age? Can we use molecular selfassembly for future electronics? and Can we exploit the computational power of nanoscale materials to realize revolutionary new computer architectures? The audience is invited to participate in a lively discussion following the four short presentations.
14.00 
Introduction by Wilfred van der Wiel 
14.15 
Jorrit de Boer (QTM) Majorana bound states in Weyl semimetals 
14.30 
Matthias Brauns (NE) Hole spins in GeSi nanowires 
14.45 
Paul Kelly (CMS) Giant room temperature interface spin Hall and inverse spin Hall effects 
15.00 
Ray Hueting (SC) NegativeCapacitance FieldEffect Transistor: The Balancing Act 
15.15 
Discussion 

Majorana bound states in Weyl semimetals
Jorrit de Boer MSc. (Quantum Transport in Matter)
Observation of a 4πPeriodic supercurrent in 3D Dirac/Weyl semimetal based Josephson junctions
3D Dirac semimetals are a class of materials with a 3dimensional linear dispersion in the bulk. When either time reversal symmetry or inversion symmetry is broken, a 3D Dirac semimetal can turn into a Weyl semimetal. One Dirac cone splits into two Weyl cones with opposite chirality at opposite momenta k_{0} and k_{0}. Such a 3D Dirac semimetal can be found in Bibased materials at the transition point from a band insulator to a topological insulator. For Sbdoped Bi, the phase diagram is well known and the transition point is ~3%.
By mechanical exfoliation and standard ebeam lithography, we fabricated various devices on Bi_{0.97}Sb_{0.03} flakes. The high field results of Hall bar shaped samples consistently show a negative longitudinal magnetoresistance (LMR) with B parallel to I. This AdlerBellJackiw anomaly is a strong indication of a Weyl semimetal.
We investigated the Nb/Bi_{0.97}Sb_{0.03}/Nb junctions in different regimes by making junctions with different lengths. We observed normal Fraunhofer patterns and Shapiro steps in long junctions, and irregular Fraunhofer patterns and a missing n=1 Shapiro step at low RF in short junctions. The missing n=1 Shapiro step is considered to be one of the major indications of the presence of Majorana bound states.
Hole spins in GeSi nanowires
Dipl.Phys. Matthias Brauns (NanoElectronics)
We grow monocrystalline and nearly defectfree GeSi coreshell nanowires, which we use to fabricate devices with ohmic contacts to the nanowire and local gates. The low defect density allows us to electrostatically define quantum dots of various lengths in the wires. We can control quantum dot lengths from ~50 to ~400 nm and the longer dots can be split into a double dot in a controlled way from strong to very weak interdot tunnel coupling, indicating a very clean system.
Using these devices for spintronics experiments, we observe a strongly anisotropic gfactor in excitedstate magnetospectroscopy measurements on single quantum dots. Forming a double quantum dot, we also observe Pauli spin blockade, a key ingredient for spinbased quantum computation. These findings demonstrate that GeSi nanowires are an ideal platform for experiments leading to quantum computation applications using spinorbit states as well as Majorana bound states.
Giant room temperature interface spin Hall and inverse spin Hall effects
Prof.dr. Paul Kelly (Computational Materials Science)
The spin Hall angle (SHA) is a measure of the efficiency with which a transverse spin current is generated from a charge current by the spinorbit coupling and disorder in the spin Hall effect (SHE). In a study of the SHE for a PtPy (Py=Ni_{80}Fe_{20}) bilayer using a firstprinciples scattering approach, we find a SHA that increases monotonically with temperature and is proportional to the resistivity for bulk Pt. By decomposing the room temperature SHE and inverse SHE currents into bulk and interface terms, we discover a giant interface SHA that dominates the total inverse SHE current with potentially major consequences for applications.
To study bulk Pt, we set up a scattering geometry consisting of two crystalline semiinfinite Pt leads sandwiching a scattering region of length L_{Pt} of disordered Pt with atoms displaced from their equilibrium positions by populating phonon modes. For the resistivity and spinflip diffusion length, this approach has been shown to yield essentially perfect agreement with experiment. We study the SHE by calculating local longitudinal and transverse charge and spin current densities in the scattering region so that both intrinsic and extrinsic contributions are naturally included. To study interface effects, we model a PyPt bilayer by matching 9x9 interface unit cells of Py to 37x37 unit cells of Pt [3] including both lattice and spin disorder in Py. This presentation will review the computational procedures that make these calculations possible.
NegativeCapacitance FieldEffect Transistor: The Balancing Act
Dr.ir. Ray Hueting (Semiconductor Components)
In many electronics devices, in particular portable electronics (e.g. tablets and smartphones), reducing the power consumption has been quite cumbersome. Part of this can be attributed to the operation of the conventional transistor, the key component of the microchip. Recently there has been a wide interest from both the industry and academics in adopting the socalled negativecapacitance fieldeffect transistor (NCFET) for tackling this issue. In this talk, the basic background of this NCFET will be explained and a brief overview will be given.