# Program

(Click on the speaker's name to read the abstract)

**Day 1 | Sunday - August 13, 2017**

**Day 2****| Monday - August 14, 2017**

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”.

*Electronic transport in the quantum spin Hall state due to the presence of adatoms in graphene*

*Long-range exchange interactions between magnetic impurities in Dirac materials*

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.

*Interband Cascade Lasers: Current Status and Future Challenges*

*Molecular Beam Epitaxial Growth of the Topological Insulator $Bi_{2}Te_{3}$*

Bismuth telluride has been recently established as a simple model system for the three-dimensional topological insulator with a single Dirac cone on the surface, as determined experimentally from angle-resolved photoemission spectroscopy [1]. The conductivity measurement of the metallic surface states in $Bi_{2}Te_{3}$ is hindered by the bulk conductivity due to intrinsic defects, like vacancies and anti-sites. Counter doping (Ca, Sn or Pb) is a way to control the Fermi level and suppress the bulk contribution. Intrinsic conduction through topological surface states has been also obtained in very thin insulating $Bi_{2}Te_{3}$ epitaxial films [2].

*Topological nonsymmorphic ribbons out of symmorphic bulk*

*Energy transfer to rare earth ions in amorphous semiconductor alloys*

**Day 3****|****Tuesday - August 15, 2017**

*Topological superconductors with Majorana fermions*

Topological superconductors with Majorana fermion quasiparticles form a newly discovered class of matter. The Majorana fermion can be seen as half an electron, or more accurately, the electron wave function has split up into two separate parts. This non-local property is currently been intensively explored for implementing fault-tolerant quantum computation. I will explain where and why Majorana fermions appear, in particular focusing on systems where very standard components are combined to achieve the required non-trivial topology: spin-orbit coupled semiconductors, magnetism, and conventional s-wave superconductivity. I will also present some of our recent results in modeling topological superconductors with Majorana fermions, focusing on a simple mean to detect Majorana fermions, their robustness against disorder, and how they often appear in conjunction with spontaneous currents.

*Energy scaling and magnetic properties of sub-gap excitations in a hybrid superconductor-semiconductor nanowire quantum dot*

*Kondo effect and quantum criticality of magnetic vacancies and adatoms in graphene*

*Observation of thermally activated hysteresis in graphene/hBN devices: the role of the hBN-SiO2 interface*

*Nano-electronics and Moore’s Law - what comes next?*

Victor Lopez-Richard*A quantum dot arquitechture for memristive and memcapacitive functionalities*

The memory and dynamical functionalities of memcapacitors and memristors would enable not only high density integration but also pave the way for new computational schemes and the emulation of neural networks. We have engineered a quantum-dot based transistor with controllable counting ability based on its intrinsic memcapacitive bistability. The conductance is tuned by charging a quantum dot which was precisely positioned in the center of a narrow quantum wire. The Coulomb interaction of the localized charges with a nearby transistor channel results in a wide maximum to minimum conductance ratio. This allows producing periodic super-cycles of defined periods and predetermined reliability. Being an intrinsic behavior of our device, it may seem, at first glance, a perplexing electric response. It is not. In the two terminal configuration, our device can be set to its memristive mode. Applying voltage pulses, the input signal can be integrated in a way that the memristor state is reset with periods that depend on the amplitude or the frequency of the input signal. In general, the control of the rate solely with the input signal requires a feedback and to realize very dense artificial neural networks it would be beneficial to implement this feedback without the need of additional circuitry. Our protocol delivers a state-dependent threshold voltage for the reset with a single memristor. This memdevice can emulate key functionalities of neurons (integrate-and-fire) and synapses (synaptic plasticity). Learning rules can be reproduced by tuning the shapes of pre- and post-synaptic voltage pulses. In this case, the conductance is controlled by the time difference between the pre- and post-synaptic voltage pulses and the corresponding shapes. The presented memristor is also optically active and its state can be controlled by the pulse wavelength and width. So beyond the electrical excitation, light-sensitive synapses or optically tunable memories can also be foreseen.

*Inter-valley Auger recombination in InGaAs/InP quantum wells*

Christiano J. S. de Matos*2D materials and their application to optoelectronics and photonics*

Since the isolation of graphene in 2004, a wide range of other atomically thin (2D) materials have been obtained and studied. 2D conductors, insulators, semiconductors and even superconductors have been identified, with properties that are different from their bulk (3D) counterparts. Additionally, 2D materials can be stacked to yield 2D heterostructures, allowing for a new generation of thin and flexible electronic, optoelectronic and photonic devices. This tutorial will review the recent advances in the science and technology of 2D materials, discussing the methods to synthesise and characterise them, as well as some of their applications in optoelectronics and photonics.

*Topological superconductivity and Majorana bound states in chains of magnetic adatoms*

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.

*Optical properties of large area tungsten disulfide monolayers*

*Vacancy and magnetism in graphene: DFT modeling*

*The Effect of Growth Techniques on the Electrical Active defects in Indium doped TiO2 Thin Films*

**Day 4 | Wednesday - August 16, 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.

*Optoelectronics in a two-dimensional nanometer-sized device based on the graphene-hexagonal boron nitride heterostructure*

We acknowledge FAPEMIG, CNPq, Finep and CAPES.

[1] T. V. Alencar et al., Nano Letters 14, 5621 (2014).

[2] L. M. Malard et al., Phys. Rev. B 87, 201401 (2013).

[3] L. Lafetá L., arXiv1701.09023 (2017).

*Twist-controlled tunnelling in vertically stacked heterostructures of graphene/bilayer-graphene and boron-nitride*

*Exciton fine structure of black phosphorus quantum dots*

**Day 5****|****Thursday - August 17, 2017**

[3] J. Buller et al., Phys. Rev. B94, 125432 (2016).

*Controling the exciton dynamics in single quantum-dot embeded in a cavity*

*Giant Photoinduced Magnetic Polarons in Europium Chalcogenides*

*Time-Dependent Spin Precession Frequency in InGaAs/GaAs Quantum Wells with Mn Delta-Doped Heterostructures*

[1] J. Schliemann, J. C. Egues, and D. Loss, Phys. Rev. Lett. 90, 146801 (2003).

[2] P. Altmann, M. Kohda, C. Reichl, W. Wegscheider and G. Salis, Phys. Rev. B 92, 235304 (2015)

[3] P. Altmann, F. G. G. Hernandez, G. J. Ferreira, M. Kohda, C. Reichl, W. Wegscheider and G. Salis, Phys. Rev. Lett. 116, 196802 (2016).

[4] G. J. Ferreira, F. G. G. Hernandez, P. Altmann, and G. Salis, Phys. Rev. B 95, 125119 (2017)

Poliana Penteado*Persistent Skyrmion Lattice of Noninteracting Electrons with Spin-Orbit Coupling*

A persistent spin helix (PSH) is a robust helical spin-density pattern arising in disordered 2D electron gases with Rashba $\alpha$ and Dresselhaus $\beta$ spin-orbit (SO) tuned couplings, i.e., $\alpha=\beta$. We investigate the emergence of a persistent Skyrmion lattice (PSL) resulting from the coherent superposition of PSHs along orthogonal directions—crossed PSHs—in wells with two occupied subbands $\nu=1,2$. For realistic GaAs wells, we show that the Rashba αν and Dresselhaus βν couplings can be simultaneously tuned to equal strengths but opposite signs, e.g., $\alpha_1=\beta_1$ and $\alpha_2=-\beta_2$. In this regime, and away from band anticrossings, our noninteracting electron gas sustains a topologically nontrivial Skyrmion-lattice spin density excitation, which inherits the robustness against spin-independent disorder and interactions from its underlying crossed PSHs. We find that the spin relaxation rate due to the interband SO coupling is comparable to that of the cubic Dresselhaus term as a mechanism of the PSL decay. Near anticrossings, the interband-induced spin mixing leads to unusual spin textures along the energy contours beyond those of the Rahsba-Dresselhaus bands. Our PSL opens up the unique possibility of observing topological phenomena, e.g., topological and Skyrmion Hall effects, in ordinary GaAs wells with noninteracting electrons.

*Resonant electronic Raman scattering: A BCS-like system*

*Electrical generation and manipulation of electron and nuclear spin polarization in semiconductors*

[2] 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).

[3] M. Luengo-Kovac et al, in preparation (2017).

*Extrinsic bistability in resonant tunneling diodes*

*Direct probing the electrostatic potential inside unstrained mesoscopic GaAs structures*

*Modeling the Schottky like contatcs on nanowires InP-InGaP tunnel diodes*

**Day 6****|****Friday - August 18, 2017**

Ingrid D. Barcelos*Study of structural properties of heterostructures formed from two dimensional materials*

Large part of the technological advances that emerged from solid state physics has its origin in the manufacture of semiconductor heterostructures. They currently make up the research object of two-thirds of all research groups working in semiconductor physics. This is due to the fact that new properties arise by changes in the electronic structure of interfaces that occur to put different materials in contact. A natural tendency is the predictable search heterostructure concepts and fabrication methods using new materials. This presentation consists of single/few layer graphene foils produced by chemical vapor deposition (CVD) are rolled with selfpositioned layers of InGaAs/Cr forming compact multi-turn tubular structures that consist on successive graphene/metal/semiconductor heterojunctions on a radial superlattice. Using elasticity theory and Raman spectroscopy, we show that it is possible to produce homogeneously curved graphene with a curvature radius on the 600−1200 nm range. Additionally, the study of tubular structures also allows the extraction of values for the elastic constants of graphene that are in excellent agreement with elastic constants found in the literature. However, our process has the advantage of leading to a well-defined and nonlocal curvature. From the results described in this work, one can assume that curvature effects solely do not modify the Raman signature of graphene and that strain phenomena observed previously may be ascribed to possible stretching due to the formation of local atomic bonds. This implies that the interactions of graphene with additional materials on heterostructures must be investigated in detail prior to the development of applications and devices.

*Strain-Gradient Position Mapping of Semiconductor Quantum Dots*

*Realistic Gap and Spin-orbit splitting from hybrid-DFT: determining effective mass parameters comparable to experiments*

*Many-body electronic structure calculations of europium complexes in ZnO*

[1] Z. Iftikhar et al, Nature 526, 233 (2015)

[2] A. K. Mitchell et al, Phys. Rev. Lett. 116, 157202 (2016)

*Kondo effect in one dimension spin-orbit coupled systems*

**Social program**

To be announced