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Upcoming Conference: Mauterndorf Winterschool 2018

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20th International Winterschool on New Developments in Solid State Physics, Mauterndorf, Feb. 25 - March 2, 2018 ...  more of Upcoming Conference: Mauterndorf Winterschool 2018 (Titel)

Wir gratulieren Dr. Rinaldo Trotta zur Habilitation!

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"Zum Gral der Halbleitertechnik", in: Die Presse vom 8.4.2017

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© Johan Persson, DTU Kopenhagen ...  more of "Zum Gral der Halbleitertechnik", in: Die Presse vom 8.4.2017 (Titel)

Fritz Kohlrausch Preis der Österreichischen Physikalischen Gesellschaft an Rinaldo Trotta

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Bildquelle: Robert Herbst, POINT OF VIEW (http://pov.at). ...  more of Fritz Kohlrausch Preis der Österreichischen Physikalischen Gesellschaft an Rinaldo Trotta (Titel)

Video Online: "Embedding a Single Quantum Dot into a Photonic Crystal Cavity"

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Artikel OÖNachrichten: "Rinaldo Trotta: Der 1,5-Millionen-Euro-Forscher"

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Our recent work (Nature Comm.7, 10375, 2016) on tunable entangled photons from QDs has been recently highlighted in the Laser Focus World magazine!

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Position Indication:

Content

Workgroup Springholz
  (Narrow gap semiconductors and epitaxy of self-assembled nanostructures)

Beschreibung: Group Leader: a.Prof. Gunther Springholz

Group Members:

Research Fields:

Microcavities and IV-VI lasers for the mid-infrared spectral region
         Vertical cavity surface emitting lasers
         Microdisk Lasers

Epitaxially precipitated IV-VI quantum dots in II-VI matrices
         Optical properties of MIR emitting PbTe/CdTe quantum dots
         TEM characterisation of PbTe/CdTe quantum dots
         PbTe/CdTe light emitting diodes

Magnetic Semiconductors
         EuSe and EuTe
         GeMnTe

Growth studies of IV-VI epitaxial layers
         Strain relaxation mechanisms and dislocation patterning in PbTe on PbSe (100) heteroepitaxy
         Spiral growth of PbTe (111) in molecular beam epitaxy far from thermodynamic equilibrium

IV-VI Stranski-Krastanow quantum dots
          Vertical and lateral ordering in self-organized IV-VI quantum dot superlattices

Si-SiGe growth studies

STM movie recorded during annealing of Ge nanowires for 4 hours at T=530°C, showing the elongation and replication of nanowires into nanowire bundles. (1.2 x 1.2 µm²)

STM movie recorded during annealing of Ge nanowires for 28 hours at T=555-600°C, showing the shrinking and dissolution of nanowires. (1.5 x 1.9 µm²)

Research Highlights:

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Topological insulators constitute a new phase of matter protected by symmetries. Timereversal
symmetry protects strong topological insulators of the Z2 class, which possess an
odd number of metallic surface states with dispersion of a Dirac cone. Topological crystalline
insulators are merely protected by individual crystal symmetries and exist for an even
number of Dirac cones. Here, we demonstrate that Bi-doping of Pb1−xSnxSe (111) epilayers
induces a quantum phase transition from a topological crystalline insulator to a Z2 topological
insulator. This occurs because Bi-doping lifts the fourfold valley degeneracy and induces a
gap at Γ, while the three Dirac cones at the M points of the surface Brillouin zone remain
intact. We interpret this new phase transition as caused by a lattice distortion. Our findings
extend the topological phase diagram enormously and make strong topological insulators
switchable by distortions or electric fields.


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Negative longitudinal magnetoresistance (NLMR) is shown to occur in topological
materials in the extreme quantum limit, when a magnetic field is applied parallel
to theexcitation current. We perform pulsed and dc field measurements on
Pb1−xSnxSe epilayers where the topological state can be chemically tuned.
The NLMR is observed in the topological state, but is suppressed and becomes
positive when the system becomes trivial. In a topological material, the lowest N ¼ 0
conduction Landau level disperses down in energy as a function of increasing
magnetic field, while the N ¼ 0 valence Landau level disperses upwards.
This anomalous behavior is shown to be responsible for the observed NLMR.
Our workprovides an explanation of the outstanding question of NLMR in topological
insulators and establishes this effect as a possible hallmark of bulk conduction in
topological matter.

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Entanglement of the spin–orbit and magnetic order in multiferroic materials bears
a strong potential for engineering novel electronic and spintronic devices. Here, we
explore the electron and spin structure of ferroelectric a-GeTe thin films doped with
ferromagnetic Mn impurities to achieve its multiferroic functionality. We use bulk-sensitive
angle-resolved photoemission spectroscopy (SX-ARPES)to follow hybridization of the GeTe
valence band with the Mn dopants. We observe a gradual opening of the Zeeman gap in the
bulk Rashba bands around the Dirac point with increase of the Mn concentration, indicative
of the ferromagnetic order, at persistent Rashba splitting. Furthermore, subtle details
regarding the spin–orbit and magnetic order entanglement are deduced from spin-resolved
ARPES measurements. We identify antiparallel orientation soft-X-ray of the ferroelectric
polarization, and altering of the Rashba-type spin helicity by magnetic switching.
Our experimental results are supported by first-principles calculations of the electron
and spin structure.

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NATURE COMMUNICATIONS | 7:11623 (2016)


Commercial magnetic memories rely on the bistability of ordered spins in ferromagnetic
materials. Recently, experimental bistable memories have been realized using fully
compensated antiferromagnetic metals. Here we demonstrate a multiple-stable memory
device in epitaxial MnTe, an antiferromagnetic counterpart of common II–VI semiconductors.
Favourable micromagnetic characteristics of MnTe allow us to demonstrate a smoothly
varying zero-field antiferromagnetic anisotropic magnetoresistance (AMR) with a harmonic
angular dependence on the writing magnetic field angle, analogous to ferromagnets. The
continuously varying AMR provides means for the electrical read-out of multiple-stable
antiferromagnetic memory states, which we set by heat-assisted magneto-recording and by
changing the writing field direction. The multiple stability in our memory is ascribed to
different distributions of domains with the Ne´el vector aligned along one of the three
magnetic easy axes. The robustness against strong magnetic field perturbations combined
with the multiple stability of the magnetic memory states are unique properties of
antiferromagnets.


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Macroscopic ferroelectric order in α-GeTe with its noncentrosymmetric lattice structure
leads to a giant Rashbaspin splitting in the bulk bands due to strong spin-orbit interaction.
Direct measurements of the bulk band structure using soft x-ray angle-resolved
photoemission (ARPES) reveals the three-dimensional electronic structurewith spindle
torus shape. By combining high-resolution and spin-resolved ARPES as well as photoemission
calculations, the bulk electronic structure is disentangled from the two-dimensional surface
electronic structure by means of surface capping, which quenches the complex surface electronic
structure. This unravels the bulk Rashba-split states in the ferroelectric Rashba α-GeTe(111)
semiconductor exhibiting a giant spin splitting with Rashba parameter αR around 4.2 eV A° ,
the highest of so-far known materials.