(Click on the speaker's name to read the abstract)
|8:30||Arne Laucht||Annica Black-Schaffer||Ingrid D. Barcelos||Paulo V. Santos|
|9:20||Sergey A. Dvoretsky||Contributed 5||Vladimir Falko||Contributed 15|
|9:45||Contributed 6||Contributed 16||Contributed 23|
|10:10||Contributed 1||Contributed 7||Contributed 13||Contributed 17||Contributed 24|
|10:35||Coffee break||Coffee break||
|Coffee break||Coffee break|
|11:00||Felix von Oppen||70 years of the transistor (1947-2017)
|Leandro Malard Moreira||Gian Salis||Andrew Mitchell|
|11:50||Sven Höfling||Contributed 8||Contributed 14||Contributed 18||Contributed 25|
|12:15||Contributed 9||Social Program||Contributed 19||Closing|
|14:20||Tutorial 1: Spintronics
J. Carlos Egues
|Tutorial 2: 2D materials
Christiano de Matos
|Tutorial 3: MBE growth
|15:35||Werner Wegscheider||Sergio Ulloa||Vanessa Sih|
|16:25||Coffee break||Coffee break||Coffee break|
|16:50||Contributed 2||Contributed 10||Contributed 20|
|17:15||Contributed 3||Contributed 11||Contributed 21|
|17:40||Contributed 4||Contributed 12||Contributed 22|
- Day 1 | Sunday - August 13, 2017
- Day 2 | Monday - August 14, 2017
The investigations of development of HgCdTe hetero- and nanostructures growth on GaAs substrates are presented. Multi-chamber MBE installation for growth of HgCdTe epilayers on GaAs and Si substrates up to 4” in diameter with precise control of films quality in situ allows to solve many problems connected with the producing high uniformity MCT layer composition over the surface area and control the MCT composition throughout the thickness. The defects formation mechanisms, its nature, the parameters characterization allows are presented.The growth of HgCdTe heterostructures with different composition distribution throughout the thickness allows to prepare material with unique properties that lead to simplification of fabricating high quality IR detectors on their basis.
The new fields of science are connected with different new physical phenomena studied on HgCdTe nanostructures such as single or multilayer quantum wells (QW). The results of HgCdTe based QW mostly HgTe QW growth with ellipsomentric control and parameters measurement are presented. The application of HgCdTe heterostructures for different IR detector type is presented. We presented the results of study of different HgTe QW in field of carrier transport, interaction with THz radiation, for laser radiation, 2D and 3D TI etc.
This work were partially supported by grants RBFR “15-52-16017 NTSIL_a”, “15-52-16008 NTSIL_a” and “Volkswagen Stiftung”.
Topological superconductivity and Majorana bound states in chains of magnetic adatoms
Recent experiments provide possible evidence for Majorana bound states in chains of magnetic adatoms on a conventional superconductor. The formation of topological superconductivity in this system relies on ferromagnetic order of the magnetic moments and spin-orbit coupling of the substrate superconductor.
In this talk, I will discuss the physical picture underlying these experiments which starts with the physics of individual magnetic adatoms and includes a possible explanation of the unexpectedly strong localization of the observed end states.
The greatest advantage over the QCL is the low threshold power. Lasing at a temperature of 25 °C could be achieved at an input power as low as 29 mW which is especially beneficial for battery powered sensing systems. In the talk wavelength dependent performance characteristics will be discussed as well as different technologies that enable operation on a single longitudinal mode.
In collaboration with: C. Reichl, T. Tschirky, C. Lehner, S. Fält, M. Berl. W. Dietsche, L. Tiemann, K. Ensslin, T Ihn, S. Müller, M. Karalic, C. Mittag, V. Pribiag, L. Kouwenhoven
- Day 3 | Tuesday - August 15, 2017
With the current slow-down of Moore's law and the abolition of the ITRS roadmap, there is a pressing need to explore various material, architectural and physical solutions for low-power electronics, ranging from spintronics to 2D materials to subthermal switching. I will summarize the opportunities and challenges for various material, device and circuit level solutions in addressing the future of electronics. Digital electronics is based on the control of charge current. Over the last decade or two, we have made enormous progress both in understanding the quantum flow of charge in nano-structures at their molecular scales, as well as translating this understanding into practical, predictive simulation tools. I will start with a multiscale model that couples bandstructure and quantum transport for physics based compact models for charge, spin and heat flow, ranging from ballistic to diffusive, quantum to classical, non-interacting to many-body. I will then show how we can convert these into 'first principles' simulation platforms that take into account details of the interfacial chemistry, bonding, spin and topological indices to provide atomistic insights into non-equilibrium properties. Finally, I will show how we can use these tools to explore emerging low-power devices ranging from nano-magnetic switches for all spin logic, to metal insulator transitions in complex oxides, to 'phase transition switches' such as relays, tunnelFETs and 2D chiral tunneling FETs that attempt to bypass the fundamental Boltzmann tyranny limiting today's silicon devices. I will also outline possible architectural solutions such as neuromorphic and approximate computing schemes that maybe able to utilize existing CMOS hardware in innovative ways.
I will describe how states at the edges of crystallites or lateral interfaces of 2D materials result in unusually long-range RKKY and DM interactions between MIs adsorbed or hybridized in these regions. We use a tight-binding description of the materials and study differences between different boundary geometries. The boundary states are shown to mediate interactions between MIs that may give rise to interesting magnetic phases. The combination of long range interactions and DM terms leads to helical and strongly frustrated impurity interactions in chains of MIs, with remarkable phase transitions as the range and relative signs of the different interactions is varied. We show that the magnetic configurations depend on the impurity concentration and doping levels in the host, opening an interesting experimental approach to study these phase transitions.
- Day 4 | Wednesday - August 16, 2017
Study of structural properties of heterostructures formed from twodimensional materials
We present the analysis of electronic band structure of InSe and (other III-VI semiconductors) films, from the stoichiometric mono-layer to N-layer films, and we describe the resulting optical properties of these 2D materials [1,2]. This study is based on the ab initio DFT and related multi-orbital tight-binding model analysis of the electronic band structure and wave functions in the two-dimensional N-layer InSe crystals, and it is compared to the results of luminescence spectroscopy of this material. We show [1-3] that the band gap in InSe (and GaSe) strongly depend on the number of layers, with a strong (more than twice) reduction from the monolayer to crystals with N>6. We find that the conduction-band-edge electron mass in few-layer InSe is quite light (comparable to Si), which suggests opportunities for high-mobility devices and the development of nanocircuits. In contrast, the valence band in mono-, bi- and trilayer InSe is flat, opening possibilities for strongly correlated hole gases in p-doped films. We also propose a model to describe electronic properties of misaligned layers of InSe. Using the band structure and wave functions, we analyse optical transitions in thin films of InSe, identify their polarisation and compare the results of modelling to the measurements performed on hBN-encapsulated atomically thin InSe crystals.
In this work we will show our recent developments on the understanding of electron relaxation pathways and the non-linear optical properties of novel 2D materials. By using two-color pump probe scheme, we have studied the photo-excited electronic cooling in graphene in presence of controlled defect densities. We clearly observe an inverse linear dependence of the electron scattering rate with the mean distance between defects in the samples . This dependence can be explained the defect assisted acoustic phonon supercollision model in graphene. The disorder- assisted scattering process allows for large phonon recoil momentum values and the entire thermal distribution of acoustic phonons can contribute to the scattering process, resulting in efficient carrier energy dissipation. Also we have used both Second Harmonic Generation (SHG) and Coherent Anti Stokes Raman Scattering (CARS) to study the nonlinear optical properties of mono- and few-layers of molybdenum disulfide (MoS_2) and graphene respectively. In the case of the molybdenum disulfide we have observed efficient SHG from odd number of layers due to the absence of inversion symmetry . By using different laser excitation energies, we could probe the resonant effect in the SHG due to the presence of different optical transitions in MoS_2. By analyzing the resonant profile of SHG we can observe the different types of excitons in this material, which are compared with recent theoretical results in the literature. Because graphene have inversion symmetry, the SHG is almost absent, however third order nonlinearities are greatly enhanced in this material due its peculiar band structure. We have studied four wave mixing process in graphene, and in particular we will discuss the CARS process in graphene .
We acknowledge FAPEMIG, CNPq, Finep and CAPES.
 T. V. Alencar et al., Nano Letters 14, 5621 (2014).
 L. M. Malard et al., Phys. Rev. B 87, 201401 (2013).
 L. Lafetá L., arXiv1701.09023 (2017).
- Day 5 | Thursday - August 17, 2017
Drift and diffusion of spin polarization in a semiconductor two-dimensional electron gas is strongly influenced by spin precession in the effective spin-orbit magnetic field. The non-commuting spin rotations that occur between subsequent scattering events typically lead to rapid spin dephasing, which can be lifted by engineering the spin-orbit interaction to a persistent spin helix (PSH) symmetry , or by laterally confining the electron gas to a length scale smaller than the spin-orbit length . If the spin-orbit interaction is linear in momentum, the average precession angle only depends on the distance the electrons travel, irrespective of whether transport occurs by diffusion or by drift. We show that for cubic Dresselhaus spin-orbit interaction, drift and diffusion by same distances lead to spin precession angles that differ by a factor of two. We have measured spin dynamics in a GaAs-based two-dimensional electron gas tuned to the PSH symmetry using spatially and time-resolved Kerr rotation measurements. Spin polarization is locally injected using a focused circularly polarized laser pulse. In absence of an external magnetic field, the spin polarization measured at a fixed position with respect to the injection point is found to precess with time. The precession frequency depends linearly on the drift velocity and can be explained within a simple model [3,4]. This finding highlights the role of nonlinear SOI in spin transport and is relevant for spintronics applications that require spin manipulation in absence of an external magnetic field.
 J. Schliemann, J. C. Egues, and D. Loss, Phys. Rev. Lett. 90, 146801 (2003).
 P. Altmann, M. Kohda, C. Reichl, W. Wegscheider and G. Salis, Phys. Rev. B 92, 235304 (2015)
 P. Altmann, F. G. G. Hernandez, G. J. Ferreira, M. Kohda, C. Reichl, W. Wegscheider and G. Salis, Phys. Rev. Lett. 116, 196802 (2016).
 G. J. Ferreira, F. G. G. Hernandez, P. Altmann, and G. Salis, Phys. Rev. B 95, 125119 (2017)
In the last decades, nanotechnology has entered our daily life with one of the representatives being semiconductor technology in its various forms. Beside the ability to scale processes down to nanometer sizes, semiconductor technology and science is driven by the capacity to form semiconductor junctions and combinations. This idea, known as heterostructure, was created in the late 50s, after the invention of the transistor in the late 40s. It took some two decades before its realization by a major technological breakthrough – the invention of molecular beam epitaxy (MBE). By now, heterostructures and heterostructure based devices are the backbone of internet communication, mobile telephones and other advanced electronics – many grown by MBE. In this tutorial, I would like to give an overview of MBE - a technique that is important for basic science providing samples for quantum mechanical studies - like the quantum hall effect, single photon sources or Kondo effect – to device structures including high efficient solar cells, quantum cascade lasers or high mobility transistors embedded in cell phones. I will cover the basics of epitaxial growth, do an introduction, what a heterostructure is and its possibilities for band structure design. To illustrate these possibilities, I will take about photoluminescence from heterostructures like quantum wells and quantum dots and discuss, how a 2D electron gas emerge at heterostructure boundaries. I will provide examples from our research to explain basic growth phenomena from flat layer to pattern substrates and luminescence from semiconductor nanostructures fabricated in our labs.
Electrical generation and manipulation of electron and nuclear spin polarization in semiconductors
 B. M. Norman, C. J. Trowbridge, D. D. Awschalom, and V. Sih, "Current-Induced Spin Polarization in Anisotropic Spin-Orbit Fields," Phys. Rev. Lett. 112, 056601 (2014).
 C. J. Trowbridge, B. M. Norman, Y. K. Kato, D. D. Awschalom, and V. Sih, "Dynamic nuclear polarization from current-induced electron spin polarization," Phys. Rev. B 90, 085122 (2014).
 M. Luengo-Kovac et al, in preparation (2017).
- Day 6 | Friday - August 18, 2017
Here, we present measurements of the spin relaxation rate W in a gate defined single-electron GaAs quantum dot at electron temperatures down to 60 mK as a function of both direction as well as strength of magnetic field, spanning an unprecedented range from 0.6 T to 14 T applied in the plane of the 2D electron gas. Due to the interplay of Rashba and Dresselhaus SO contributions, W shows strong anisotropy when varying the direction of the applied in-plane magnetic field B with a piezoelectric rotator. Along the crystal axis where SOI coupling is weak, a spin relaxation time T1 of 57+/-10 s has been obtained at a magnetic field of 0.6 T. However, quite surprisingly, this is still more than one order of magnitude shorter than the expected value based on SO mediated spin relaxation. Further, W shows a B3 dependence and becomes isotropic at the lowest magnetic fields. These observations thus indicate hyperfine interaction mediated spin relaxation (non flip-flop) via phonons at the lowest magnetic fields used here.
Command of the dot orbitals, control of the B-field direction and low-B-field measurements -- made possible by a low electron temperature -- reveal hyperfine spin relaxation and allow comprehensive modeling, giving excellent agreement between experiment and theory.
 Z. Iftikhar et al, Nature 526, 233 (2015)
 A. K. Mitchell et al, Phys. Rev. Lett. 116, 157202 (2016)
To be announced