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Seminarium Fizyki Ciała Stałego

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Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab.Wojciech Knap (CENTERA Laboratories, UNIPRESS Polish Academy of Sciences)

“Plasmonic Crystals in Graphene and GaN for Terahertz Active Devices"

Abstract(pdf file)
Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

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The seminar in the Hybrid mode
Faculty of Physics room 0.06
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr hab. Switlana Stelmach (Institute of High Pressure Physics Polish Academy of Sciences, Warsaw)

“Atomic structure of nanocrystals - diffraction studies assisted by molecular dynamics"

The tools commonly used in crystallography for diffractometric studies of crystalline materials are of limited use for studying the atomic structure of nanomaterials. Due to the large fraction of atoms located at the surface a nanocrystal must not be considered as a small single crystal. The need for a new method of structural studies of nanocrystalline materials, and creation of a sub-section of Crystallography named Nano-Crystallography is presented and justified. The essence of the new methodology is the identification of the surface and non-uniform bulk structure of nanoparticles based on experimentally measured atomic Pair Distribution Function.
Using experimental large Q diffraction data and molecular dynamics simulations the shape, the surface structure and lattice deformation in the interior of nano-size grains were identified and quantitatively described. Examples of results on CdSe quantum dots, diamond and SiC nano-crystals will be presented.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. Paweł Hawrylak (Department of Physics, University of Ottawa, Ottawa, Canada)

Interacting electrons in semiconductor and graphene quantum dots

We discuss effects of electron-electron interactions in synthetic quantum matter with semiconductor and graphene quantum dots in semiconductor nanowires, transition metal dichalcogenites (TMDCs), graphene, artificial graphene and gated bilayer graphene. We start with atomistic design of InAs quantum dots in InP nanowires for entangled photons emission. We follow with quantum dot arrays for synthetic spin one chains, paradigm of quantum matter, and synthetic Kitaev chains hosting Majorana Fermions. This is followed by graphene quantum dots and quantum simulators of strongly correlated phases in synthetic quantum Hall systems. We finish with excitons and broken symmetry valley and spin polarized phases of Dirac Fermions in voltage controlled semiconductors in bilayer graphene.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Ryszard Buczynski (Faculty of Physics, University of Warsaw, Institute of Microelectronics and Photonics, Lukasiewicz Research Network)

“Free-form nanostructured optical fibers"

Nanostructured optical fibers are a new class of optical fibers. The use of nanotechnology in the construction of optical fibers allows shaping their optical properties by means of the internal structure of the core, not by structuring the cladding or changing the geometric parameters of the fiber. In the case of nanostructured optical fibers, their dispersion, mode and polarization properties are determined by the internal discrete nanostructure of the core composed of a hexagonal lattice of nanorods made of various types of passive and active glasses. The fundamentals of their operation, manufacturing technology, selected applications and development prospects will be discussed.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Mateusz Tokarczyk (Faculty of Physics University of Warsaw)

"Two stage metalorganic vapour-phase epitaxy growth of high-quality h-BN on the wafer-scale sapphire: the role of substrate off-cut"

Hexagonal boron nitride (h-BN) is an attractive 2D material for possible applications in electronic and optoelectronic devices based on van der Waals heterostructures, but direct growth of high-quality hBN on the wafer-scale is still the bottleneck for future successful implementation of hBN in industry. Although the synthesis of h-BN by MOVPE has already been reported, there is a fundamental lack in understanding of many basic aspects of this process. In particular, the role of the substrate off-cut, although known to be of major importance for the growth of other materials, has not been fully addressed so far.
In the first part of this presentation, I will present our recent results that address the influence of the sapphire substrate off-cut angle on the final quality of h-BN obtained in a two-step growth procedure. The main process starts with a self-limiting continuous growth (CFG) of a BN buffer followed by flow-modulated epitaxy (FME) in the second step and is used to study samples with different off-cuts angles for three different CFG times. Based on results obtained by x-ray diffraction and reflectometry, Raman and Fourier-transform spectroscopy, atomic force microscopy and scanning electron microscopy (SEM), we ﬁnd that a substrate with optimal off-cut angle clearly yields the highest quality of h-BN layers. Samples with this off-cut have the lowest amount of debris on the surface, most intense x-ray diffraction signal, minimal Raman phonon linewidth and thinnest amorphous BN part.
In the second part, I will discuss the relationship between the angular arrangement of the h-BN layers and the surface of the sapphire substrate (off-cut/offset analysis).
M. Tokarczyk, et al. 2D Materials 10, 025010 (2023).

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Ryszard Zdyb (Institute of Physics, Maria Curie-Sklodowska University, Lublin, Poland)

“Epitaxial growth of ultrathin Co films on silicene"

Integration of 2D materials with ferromagnets offers a simple way for the injection, transport and detection of spin polarized current in single atom thick structures. Making such heterostructure with silicene appears to be particularly challenging due to the possible formation of silicides. In this presentation we show results of LEEM, LEED, STM and HR TEM measurements which reveal that the planar form of silicene supports epitaxial growth of ultrathin ferromagnetic Co films. The obtained heterostructure is stable at room temperature, apparently, without destruction of the silicene layer.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab.Tomasz Dietl (International Research Centre MagTop, Institute of Physics, Polish Academy of Sciences, Warsaw)

“Charge dopants control quantum spin Hall materials"

Abstract:Unlike in the quantum Hall effect and quantum anomalous Hall effect, the quantization precision in the quantum spin Hall effect depends on unavoidable background impurities and defects. However, doping with magnetic ions restores the quantization accuracy.

Semiconductors’ sensitivity to electrostatic gating and doping accounts for their widespread use in information communication and new energytechnologies. In the talk, I will present outcomes of two companion papers [1,2], inspired by experimental data accumulated in Wuerzburg and Warsaw for HgTe and (Hg,Mn)Te quantum wells and bulk crystals. Results of those papers demonstrate quantitatively and with no adjustable parameters that the presence of paramagnetic acceptor dopants elucidates a variety of hitherto puzzling properties of two-dimensional topological semiconductors at the topological phase transition and in the regime of the quantum spin Hall effect. The concepts of resonant states, charge correlation, Coulomb gap, exchange interaction between conducting electrons and holes localized on acceptors, strong coupling limit of the Kondo effect, the Luttinger correlations, and bound magnetic polaron explain a short topological protection length, high hole mobilities compared with electron mobilities, and different temperature dependence of the spin Hall resistance in HgTe and (Hg,Mn)Te quantum wells. A new concept of precessional dephasing of a carrier spin by a dense bath of localized spins is put forward. It is concluded that while electrostatic gating is widely used to reveal the unique properties of quantum materials, the obtained results demonstrate that charge dopants play an important and unanticipated role in the physics and applications of topological semiconductors.

[1] T. Dietl, "Effects of charge dopants in quantum spin Hall materials", Phys. Rev. Lett. 130, 086202 (2023).
[2] T. Dietl, “Quantitative theory of backscattering in topological HgTeand (Hg,Mn)Te quantum wells: Acceptor states, Kondo effect, precessionaldephasing, and bound magnetic polaron", Phys. Rev. B 107, 085421 (2023)[Editors’ Suggestion].

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Mateusz Tokarczyk (Faculty of Physics University of Warsaw)

“Two stage metalorganic vapour-phase epitaxy growth of high-quality h-BN on the wafer-scale sapphire: the role of substrate off-cut"

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Tomasz Tokarczyk (Faculty of Physics University of Warsaw)

“Two stage metalorganic vapour-phase epitaxy growth of high-quality h-BN on the wafer-scale sapphire: the role of substrate off-cut"

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Mateusz Tokarczyk (Faculty of Physics room 0.06)

“Two stage metalorganic vapour-phase epitaxy growth of high-quality h-BN on the wafer-scale sapphire: the role of substrate off-cut"

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

mgr Joanna Wincukiewicz (Faculty of Physics, University of Warsaw)

“Influence of extrinsic properties on magnetism and magnetotransport in Mn doped Bi2Te3 topological insulator with self-organized MnBi2Te4 layers"

Abstract(pdf file)

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

mgr Aleksander Bogucki (Wydział Fizyki UW)

The influence of strain on the magnetic ion's spin relaxation in semiconductor nanostructures

The spin-lattice interaction is a critical factor influencing the potential use of a given magnetic ion in information processing and storage. This work presents results on spin relaxation rates obtained with the optically detected paramagnetic resonance technique (ODMR). In particular, the influence of the strain occurring directly in the surrounding of a magnetic ion placed in a quantum well will be considered. Furthermore, the results of measurements at different magnetic fields and temperatures will be presented. Finally, a model will be shown that well describes the observed relationship.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Michał Baranowski (Politechnika Wrocławska)

Excitons in 2D perovskites an old quasiparticle at the new playground

Optical properties of low-dimensional semiconductor nanostructures are often driven by excitons – a quasi-particle composed of a photo-created electron and hole bound by the Coulomb attraction. Excitonic effects are particularly strong in two-dimensional (2D) van der Waals semiconductors, in which simultaneous quantum and dielectric confinement enhance the binding energy of the electron-hole pair to values as large as hundreds of meV. A prominent example is the 2D Ruddlesden–Popper metal-halide perovskites (2DP), in which exciton binding energies reach a few hundred milli-electronvolts. Additionally, the soft, polar, and low symmetry lattice creates a unique background for electron-hole interaction in 2DP, providing a fascinating playground for studying the exciton physics which in some aspects remain challenging for our understanding our understanding.Here I will discuss certain aspects of excitonic physics in 2D perovskites related to their energy structure, and unique behaviours (probably) resulting from the particularly strong coupling of electronic excitation with lattice vibration. This aspect includes a variation of exciton binding energy with temperature and the possibility to observe exciton fine structure splitting of phonon replica. I will also show that the van der Waals nature of 2DP allows to easily combine them with other 2D materials, in particular transition metal dichalcogenide. The nontrivial band alignment of such a stack provides conditions for the charge transfer, resulting in the formation of interlayer excitons. Simultaneously strong excitonic effects in both types of materials facilitate energy transfer between the layers that can be tuned by an appropriate alignment of the excitonic states.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Jarosław Domagała (IF PAN)

High Resolution X-ray Diffraction – a basic tool for microstructural characterisation of bulk crystals and epi-wafers

In the seminar I will show what information about microstructure of bulk crystals and epi-structures can be drawn from the High Resolution X-ray Diffraction. In the first part of my talk I will present basics of the experimental set-up and ways of the data interpretation. In the second part, I will show a member of examples: GaAs and GaN crystals, and epilayers: InGaN, GaMnAs, InSe, TaAs.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Valentine V. Volobuev (Polish Academy of Sciences, National Technical University “KhPI”, Kharkiv, Ukraine.)

"Epitaxial films of topological materials."

Topological materials are promising candidates for future electronics and spintronics as well as of great interest for fundamental condensed matter physics.
In this talk, we will discuss epitaxial films of topological materials produced by molecular beam epitaxy in form or orientation which is difficult to achieve in bulk. The results of growth, structural characterization, transport properties and angular resolved photoemission spectroscopy investigations will be presented.
In the first part of the talk, we will consider (111)-oriented topological crystalline insulator films based on IV–VI semiconductors, their band and spin structure, transport and magnetism.
In the second part, we will focus on Dirac and Weyl semimetal phases in gray tin (α-Sn) epitaxial films synthesized on (001) insulating CdTe/GaAs substrates.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali B2.38, ul. Pasteura 5 o godzinie 11:15

dr Carlos Antón Solanas (Depto. de Física de Materiales, Instituto Nicolás Cabrera, Universidad Autónoma de Madrid, 28049 Madrid, Spain Instituto de Física de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain)

Single-photon light sources: from semiconductor quantum dots to two-dimensional crystal quantum dots

An optimal single-photon source fulfils the following triple benchmark: (I) Brightness: it delivers a single-photon Fock state deterministically “at the push of a button” (and never vacuum cid:clip_image002.png); (II) Purity: it always generates a photon number Fock state cid:clip_image004.png (and never multi-photon Fock states cid:clip_image006.png); (III) Indistinguishability: all the emitted single-photon Fock states are identical, and thus, they perfectly interfere as bosons (displaying the Hong-Ou-Mandel effect).

In the first part of this talk, I will discuss the state-of-the-art on near-optimal single-photon emitters [1], based on semiconductor quantum dots in cavities. In this context, I will discuss my recent results on this platform to generate other kinds of quantum states of light beyond single-photon Fock states, such as superposition and scalable multipartite time-entanglement in the photon number basis [2,3].

In the second part of this talk, I will discuss another platform to generate single-photons based on atomically thin WSe2 monolayers. The local strain in these monolayers produces a potential capable to trap single excitons and so produce single-photon emission [4]. These quantum dots can be coupled to optical cavities, enhancing their performance towards competitive single-photon sources. First quantum communication testbed-applications with atomically thin WSe2 quantum dots are being implemented [5], promising a “bright future” for these novel emitters.

References

[1] N. Tomm et al., A Bright and Fast Source of Coherent Single Photons, Nat. Nanotechnol. 16, 399 (2021).
[2] J. C. Loredo et al., Generation of Non-Classical Light in a Photon-Number Superposition, Nat. Photonics 13, 803 (2019).
[3] S. C. Wein et al., Photon-Number Entanglement Generated by Sequential Excitation of a Two-Level Atom, Nat. Photon. 16, 5 (2022).
[4] O. Iff et al., Strain-Tunable Single Photon Sources in WSe 2 Monolayers, Nano Lett. 19, 6931 (2019).
[5] T. Gao, M. v Helversen, C. Anton-Solanas, C. Schneider, and T. Heindel, Atomically-Thin Single-Photon Sources for Quantum Communication, ArXiv:2204.06427 [Cond-Mat, Physics:Quant-Ph] (2022).

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Dr. Alexander Lau (International Centre for Interfacing Magnetism and Superconductivity with Topological Matter - MagTop , Institute of Physics, Polish Academy of Sciences)

“ An investigation of flat bands in two and three dimensions"

The recent discovery of unconventional superconductivity in a stacked, twisted pair of graphene sheets is a famous consequence of what is known as a flat energy band, in which the kinetic energy of the electrons becomes negligible and their mutual interactions dominate. Materials with flat energy bands give rise to enhanced correlation effects, exotic phases of matter, and unexpected properties. In this talk, I will present our recent results on flat bands in two and three dimensions.
I will start with the celebrated example of magic-angle twisted bilayer graphene. This material exhibits flat low-energy bands with Van Hove singularities close to the Fermi level. In our study, we compute four-terminal conductance in mesoscopic, ballistic samples of small-angle twisted bilayer graphene with up to one million lattice sites. We establish a correspondence between features in the wide-junction conductance and the presence of Van Hove singularities in the density of states. Moreover, we identify additional transport features, such as a large, pressure-tunable minimal conductance and conductance peaks coinciding with non-singular band crossings. Our results suggest that twisted bilayer graphene close the magic angle is a unique system featuring simultaneously large conductance due to the quasi-flat bands, strong quantum nonlinearity due to the Van Hove singularities and high sensitivity to external parameters [1].
In the second part of my talk, I will lift the study of electronic flat bands into the third dimension. I will show theoretically how to use strain engineering to generate flat three-dimensional energy bands in topological nodal-line semimetals, which are materials whose valence and conduction bands cross to form closed loops. I will unravel the underlying mechanism and present the competition of the arising superconducting and magnetic orders. The required strain profile can be realized, for instance, by bending the sample, which allows for in situ tuning of the emerging correlated phases and the transition temperatures. Finally, I will introduce rhombohedral graphite and CaAgP as promising material candidates to realize this proposal [2].
[1] A. S. Ciepielewski, J. Tworzydło, T. Hyart, and A. Lau, Phys. Rev. Research 4, 043145 (2022)
[2] A. Lau, T. Hyart, C. Autieri, A. Chen, and D. I. Pikulin, Phys. Rev. X 11, 031017 (2021),

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr hab. Michał Bejger, Prof CAMK PAN (Nicolaus Copernicus Center of the Polish Academy of Sciences)

Origin of the elements in the Universe

Chemical elements are the fundamental building blocks of life, as well as necessary components of our technology and civilization.
I will summarise the knowledge of the origin of the elements from an astronomer's perspective: from the early Universe big bang, life of stars to the fate of their remnants.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Piotr Perlin (Institute of High Pressure Physics “Unipress”, Polish Academy of Sciences, Warsaw, Poland TOP-Gan Corp. Warsaw, Poland)

“Laser diodes based on nitride semiconductors for applications in quantum technologies, challenges and solutions."

III-N semiconductors (AlInGaN) are critical materials for modern optoelectronics. Light emitters based on these semiconductors (laser diodes and LEDs) can be adapted to operate at various wavelengths covering the visible and ultraviolet part of the spectrum. At the same time, group III nitrides are the first widely used semiconductors that combine a wide band gap and a non-cubic crystallographic structure. This situation forced the industry to face several new phenomena, such as the presence of a strong internal electric field in quantum structures, the problem of effective doping, and finally the presence of high dislocation density. As part of this presentation, I would like to show that with the increasing maturity of technology, some problems have been solved, some have turned out to be beneficial rather than problematic, but some remain unresolved. The emergence of efficient, visible light sources coincides with the demand for emerging quantum technologies. Using the example of optical atomic clocks, I will show the path of development of optical elements, such as laser diodes with adjustable wavelength of visible light and semiconductor optical amplifiers. Finally, I will discuss the challenges of building a nitride-based photonic integrated circuit.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Piotr Kapuściński (Laboratoire National des Champs Magnétiques Intenses, Grenoble, Francja)

Electronic excitations in Raman scattering magneto-spectroscopy of transition metal dichalcogenide monolayers

Whereas Raman scattering spectroscopy has been widely applied to study the monolayers (ML) of transition metal dichalcogenides (TMD) no electronic excitations in these emerging 2D semiconductors have been observed with this technique. Here, we report the inelastic light scattering magneto-spectroscopy under quasi-resonant conditions on lightly doped WSe2 and MoSe2 monolayers and reveal a series of inter Landau level excitations. Data analysis allows us to determine the single particle effective masses in the systems studied. Those relevant band structure parameters are of primary importance for modeling the advanced ML-TMD properties, though they are barely estimated from other, more conventional measurements.

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Anna Kaleta (Institute of Physics Polish Academy of Sciences)

“Strain-mediated high TC of GaAs:MnAs granular system – microscopic studies of Mn segregation in WZ-(Ga,Mn)As by in-situ transmission electron microscopy"

Thermal decomposition of (Ga,Mn)As, the canonical dilute ferromagnetic semiconductor, leads to the formation of ferromagnetic α-MnAs (of hexagonal crystal structure) nanocrystals (NCs) being incoherent with the surrounding zinc-blende GaAs crystalline matrix. On the other hand, wurtzite (WZ) (Ga,Mn)As, sharing similar symmetry with hexagonal α-MnAs, can be obtained if (Ga,Mn)As is grown as shells of WZ GaAs nanowire cores. We have shown that annealing of the WZ (Ga,Mn)As at 450 °C results in tensely strained MnAs NCs embedded semi-coherently in WZ-GaAs matrix and stabilizes ferromagnetic α-MnAs phase to above 127 °C (bulk α-MnAs TC = 40 °C) [1].
I will present structural changes in WZ-(Ga,Mn)As NW shell at high spatial resolution occurring under annealing by employing in-situ scanning transmission electron microscopy (STEM). I will also show how to control the granular GaAs:MnAs system to achieve the desired size and distribution of MnAs NCs by designing the core-shell nanowire system and selecting the appropriate annealing conditions. In this context, I will present the role of the (Ga,Al)As shell and the importance of the anisotropy of the WZ GaAs crystal structure in the process of manganese diffusion and the movement of MnAs NCs in the nanowires.
[1] A. Kaleta, S. Kret, K. Gas, B. Kurowska, S. Kryvyi, B. Rutkowski,N.G. Szwacki, M. Sawicki, J. Sadowski, Nano Lett. 19, 7324 (2019)

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr hab. Yaroslav Zhydachevskyy, prof. IF PAN (Institute of Physics Polish Academy of Sciences)

“Chemical tuning and band gap engineering of Mn4+ luminescent properties in complex oxides"

The possibility of tuning of luminescent properties including the band gap engineering by adjusting the chemical composition will be demonstrated for the Mn4+-doped Al2O3-Ga2O3 solid solutions and RAlO3 (R = Y, La, Gd, Yb, Lu) perovskites. In particular, spectroscopic features of the Mn4+ deep red emission in Al2O3-Ga2O3 alloys, including the temperature-dependent emission efficiency and decay time, as well as the possibility of their tuning through chemical and hydrostatic pressure will be shown. The possibility of band gap engineering in RAlO3:Mn4+ perovskites in the context of trap depths of intrinsic point defects and their effect on thermoluminescent properties of the material will be demonstrated using both experimental and theoretical approaches.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

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The seminar in the Hybrid mode
Faculty of Physics room 0.06
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Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Robert Kudrawiec (Department of Semiconductor Materials Engineering, Faculty of Fundamental Problems of Technology, Wroclaw University of Science and Technology)

“Van der Waals crystals and monolayers under hydrostatic pressure – conclusions for piezo-reflectance spectroscopy"

Abstract(pdf file)

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
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Attention
The seminar in the Hybrid mode
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instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Czesław Skierbiszewski (Institute of High Pressure Physics PAS, Unipress)

“How tunnel junctions changed our perception of III-N optoelectronic devices"

Abstract(pdf file)

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Artur Slobodeniuk (Faculty of Mathematics and Physics, Charles University, Praga)

Coulomb and many-body effects in the coherent optical response of 2D semiconductors

The Coulomb interaction in transition metal dichalcogenide monolayersresults in strongly bound excitons which dominate the optical responseof these materials. Despite a large number of studies, an understandingof how Coulomb and many-body correlation effects affect the excitonicresonances on a femtosecond time scale is still lacking. In order toclarify this question, we consider the excitonic shifts induced by theintense circularly-polarized non-resonant pump pulse applied normally tothe monolayer. We observe experimentally valley-selective (optical Starkand Bloch-Siegert) transient blue shifts of both 1s A and B excitontransitions. We use semiconductor Bloch equations for the theoreticaldescription of the shifts. The solutions of these equations are obtainedwith a modified perturbation technique, which takes into accountmany-body and Coulomb interaction effects. These solutions allow us toexplain the polarization dependence of the observed shifts and calculatetheir values analytically.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

mgr Mateusz Król (Faculty of Physics, University of Warsaw)

“Non-Hermitian effects in microcavities filled with liquid crystals: annihilation of exceptional points "

In quantum mechanics, the assumed hermicity of the Hamiltonian ensures that the probability of finding a particle is constant over time. The description of dissipation or gain in a system typically requires introduction of non-Hermitian terms. The resulting non-Hermitian Hamiltonian can exhibit properties unavailable for typical Hermitian systems. The most striking example of such behavior is the existence of so-called Exceptional Points (EP), points in parameter space where both eigenvalues and eigenvectors coalesce (are degenerate).
In this work, we introduce the basics of non-Hermitian physics with special emphasis on the properties of EPs. Specifically, we consider a planar optical microcavity filled with a birefringent liquid crystal. We show how polarization dependent losses in such a system lead to emergence of EPs. We demonstrate, both theoretically and experimentally, how owing to the sensibility of the liquid crystal to an external electric field, it is possible to change the position of the EPs. In particular, we show how EPs can be removed (annihilated) from the system when two of them are brought into a single position.
M. Król, I. Septembre et al., Annihilation of exceptional points from different Dirac valleys in a 2D photonic system, Nat. Commun. 13, 5340 (2022).

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr Łukasz Kubiszyn (VIGO Photonics S.A.)

“MBE growth and characterization of antimonide superlattice-based heterostructures for IR detection at VIGO Photonics"

During the last 7 years, VIGO has been developing the technology of antimonide superlattices (SLs) grown on GaAs substrates, in particular InAs/InAsSb (the so-called Ga-free) SLs. The optimization of growth and processing resulted in MWIR and LWIR heterostructural devices whose detectivity is approaching the level of mercury-cadmium telluride (MCT) detectors offered in the VIGO catalogue. We are constantly developing new devices aiming at the replacement of MCT for some applications. During the seminar, the overall progress of the technology and device architecture will be presented. Greater focus will be put on recent results concerning interband cascade LWIR detectors whose aim is to reach high detectivity in conditions where the conventional IR photodiodes suffer from a very low quantum efficiency and extremely low resistances. The challenges of the technology and plans for future improvements will be also discussed.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :
instruction: (pdf file)

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

prof. dr hab. Andrzej Golnik (Faculty of Physics, University of Warsaw)

Prof. Leonard Sosnowski and 75 years of Solid State Physics Division at University of Warsaw

On 1 September 1947 dr. Leonard Sosnowski was hired as a deputy professor on the Chair of Electronics and Radiology of the University of Warsaw. This date is commonly treated as a foundation of the Solid State Physics Division at the University. I would like to remind you some facts from the beginnings of the Division as well as to sketch some trends of its development.

Uwaga
Seminarium w trybie Hybrydowym
Faculty of Physics room 0.06
link to remote mode:
https://zoom.us/j/7218838148
szczegóły patrz instrukcja :
instrukcja: (pdf file)

Attention
The seminar in the Hybrid mode
Faculty of Physics room 0.06
for details see instruction :

Zapraszamy do sali 0.06, ul. Pasteura 5 o godzinie 10:15

dr hab. inż. Paweł Scharoch, university professor (Wroclaw University of Science and Technology Department of Semiconductor Materials Engineering)

“Semiconductor materials engineering from the perspective of DFT calculations”

As long as semiconductors are fundamental materials for high technologies, their engineering has become indispensable. Engineering means not only formation but also tuning the properties, which is a subject of extended worldwide research. The role of ‘ab initio’ computational methods based on Density Functional Theory (DFT) cannot be overvalued. They not only provide theoretical evidence which helps to interpret experimental results but also, due to their ‘ab initio’ character, the properties of materials can be predicted with high credibility. The examples of extended, systematic studies of the whole groups of materials will be presented, focusing on various ways of the properties modification, like alloying (within group IV materials), alternative crystal structures (group III-V in wurtzite structure), or strains (group IV). It will be also shown how the DFT may be used in device modelling, via providing a reference for adjusting the parameters of simpler methods, like kp. Chosen examples of DFT calculations referred to optical measurements done within the Department of Semiconductor Materials Engineering, at Wroclaw University of Science and Technology will be presented.