Semiconductor Nanostructures “Lendület” Research Group

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Introduction

Welcome to the Adam Gali group at Wigner Research Centre for Physics Our group’s research focuses on theoretical and experimental characterization of point defects in semiconductors and semiconductor nanostructures. We are developing and implementing new techniques for introducing dopants and defects in semiconductor (nano)structures, and studying their properties by experimental and theoretical spectroscopy tools.

We are looking for an experienced and ambitious researcher with a background in optically detected magnetic resonance (ODMR) techniques to study solid state qubits. This is a Postdoc job that can be turned to tenure track position for qualified researchers. Email your CV to Adam Gali!


We combine heat combustion, ion or neutron irradiation, colloid chemistry and related techniques to fabricate semiconductor nanostructures. Our focus is on silicon carbide to realize ultimate in vivo bioimaging agents. We are active in the field of computational materials science and has a large experience in using density functional theory (DFT) based methods in solids and nanostructures. The group leader started to apply advanced hybrid density functional theory methods on defects in bulk and nanostructured semiconductors already from 2002. From 2005 the GW method was also applied. Advanced time-dependent DFT (TDDFT) has been employed to determine the absorption spectrum of nanoclusters since 2008. These theories were utilized directly to defect engineering in bulk semiconductors and in their oxide interface, biomarkers, solid state quantum bits and spintronics, solar cells and related topics.


Projects

Publications: https://vm.mtmt.hu/search/slist.php?inited=1&co_on=&ty_on=1&la_on=&LanguageID=&abs_on=&sp_on=&st_on=&url_on=1&cite_type=2&orderby=3D1a&Scientific=1&Independent=&top10=&lang=1&location=mtmt&debug=&stn=1&AuthorID=10002866&DocumentID=&tipus=&besorolas=&jelleg=1Mtmt Publications Scholar.pngScholar Publications Scopus.pngScopus

Facilities & Support

People

Group meeting in 2017 December
Group leader
Adam Gali
Postdoc fellows
Zoltán Bodrog
Dávid Beke
Viktor Ivády
Bálint Somogyi
Gergő Thiering
Péter Udvarhelyi
András Csóré
Anton Pershin
Hanen Hamdi
Vladimir Verkhovlyuk
Graduate students
Gyula Károlyházy
Naina Mukesh
Péter Rózsa
Undergraduate students
János Tamási
Mihály Mátyás Rudolf
Laboratory Assistants
István Balogh
Ádám Viszoki
Szabolcs Czene

Former members

  • Márton Vörös (industry)
  • Tamás Hornos (industry)
  • Hugo Pinto (now PostDoc at Adam Foster group)
  • Thomas Chanier (now PostDoc at Namur University)
  • Tamás Demján (industry)
  • Attila Szállás (industry)
  • Elisa Londero (now staff at Observatory of Trieste)
  • Krisztián Szász (now Postdoc at Budapest University of Technology and Economics)
  • Jyh-Pin Chou (now assistant professor at National Changhua University of Education, Taiwan)
  • Emilie Bruyer (industry)
  • Balázs Juhász (industry)
  • Philipp Auburger

Research partners around the world

Highlights

Our group member, Gergő Thiering, has been honored by receiving the János Bolyai Research Grant from the Hungarian Academy of Sciences. (2020) Congratulations!


Our group member, Dávid Beke, has been honored by receiving the János Bolyai Research Grant from the Hungarian Academy of Sciences. (2019) Congratulations!


Our group member, Viktor Ivády, has been honored by receiving the Premium Postdoctoral Fellowship from the Hungarian Academy of Sciences. (2018) Congratulations!


2021 PRL.png

In collaboration with the [Nathalie P. de Leon Research group] we report the realization of optically detected magnetic resonance and coherent control of SiV(0), enabled by efficient optical spin polarization via previously unreported higher-lying Rydberg-like excited states. We assign these states as bound exciton states using group theory and density functional theory. These bound exciton states enable new control schemes for SiV(0) as well as other emerging defect systems.

Phys. Rev. Lett. 125, 237402 (2021). DOI:10.1103/PhysRevLett.125.237402



2021 JPCL.gif

In this paper, we analyze the numerical aspects of the inherent multireference density matrix renormalization group (DMRG) calculations on top of the periodic Kohn–Sham density functional theory using the complete active space approach. The potential of the framework is illustrated by studying hexagonal boron nitride nanoflakes embedding a charged single boron vacancy point defect by revealing a vertical energy spectrum with a prominent multireference character. We investigate the consistency of the DMRG energy spectrum from the perspective of sample size, basis size, and active space selection protocol. Results obtained from standard quantum chemical atom-centered basis calculations and plane-wave based counterparts show excellent agreement. Furthermore, we also discuss the spectrum of the periodic sheet which is in good agreement with extrapolated data of finite clusters. These results pave the way toward applying the DMRG method in extended correlated solid-state systems, such as point defect qubit in wide band gap semiconductors.

J. Chem. Theory Comput. 17, 2, 1143–1154 (2021). DOI:10.1021/acs.jctc.0c00809


2020 Stabilization.png

Defect-based quantum systems in wide bandgap semiconductors are strong candidates for scalable quantum-information technologies. However, these systems are often complicated by charge-state instabilities and interference by phonons, which can diminish spin-initialization fidelities and limit room-temperature operation. Here, we identify a pathway around these drawbacks by showing that an engineered quantum well can stabilize the charge state of a qubit. Using density-functional theory and experimental synchrotron X-ray diffraction studies, we construct a model for previously unattributed point defect centers in silicon carbide as a near-stacking fault axial divacancy and show how this model explains these defects’ robustness against photoionization and room temperature stability. These results provide a materials-based solution to the optical instability of color centers in semiconductors, paving the way for the development of robust single-photon sources and spin qubits.

Nature Communications 10, 5607 (2019). DOI:10.1038/s41467-019-13495-6



2019 PRODJT.png

The product Jahn–Teller effect may occur for such coupled electron–phonon systems in solids where single electrons occupy double degenerate orbitals. We propose that the excited state of the neutral XV split-vacancy complex in diamond, where X and V labels a group-IV impurity atom of X = Si, Ge, Sn, Pb and the vacancy, respectively, is such a system with eg and eu double degenerate orbitals and Eg quasi-localized phonons. We develop and apply ab initio theory to quantify the strength of electron–phonon coupling for neutral XV complexes in diamond, and find a significant impact on the corresponding optical properties of these centers. Our results show good agreement with recent experimental data on the prospective SiV(0) quantum bit, and reveals the complex nature of the excited states of neutral XV color centers in diamond.

npj Comput Mater 5, 18 (2019). DOI:10.1038/s41467-019-13495-6


2018 PhysRevX.png

We use density-functional theory calculations to see if other group-IV elements—namely, germanium, tin, and lead—in a vacancy center exhibit similar optical properties to silicon but with improved spin properties that permit an economical cooling system. We develop a new theory for understanding the interaction of light and magnetic fields with these color centers, and we explore how the dynamical motion of the atoms strongly affects the magneto-optical properties of the color center. By combining our theory with density-functional theory calculations, we find that lead-vacancy color centers should have favorable optical and spin properties for operating at room temperature.

Phys. Rev. X 8, 021063 (2018). DOI:10.1103/PhysRevX.8.021063


2017 PRX.png

Our ab initio simulations determined the magneto-optical properties of the neutral divacancy in silicon carbide that contributed to understanding its qubit operation carried out by Prof. David D. Awschalom group.

Phys. Rev. X 7, 021046 (2017). DOI:10.1103/PhysRevX.7.021046


Nanoletters2017.png

Our ab initio study identified the nitrogen terminated (111) diamond surface to host shallow nitrogen-vacancy centers for quantum sensing. In cooperation with Alex Retzker we showed, that special quantum simulations can be carried out with the nitrogen nuclear spins in this system

Nano Letters 17 (4), pp 2294-2298. (2017) DOI:10.1021/acs.nanolett.6b05023


Adamant cover.png

We investigated the electron-phonon coupling in small diamond cages called diamondoids. These quantum systems are mostly modelled within the Born-Oppenheimer approximations, where the coupling between the electrons and vibration modes is not fully taken into account. In our study we shown that the severe electron-phonon coupling is a key point to properly describe the overall lineshape of the experimental photoemission spectrum. Our method goes beyond the typical Born-Oppenheimer approximation, where the electrons are pure electron-like quasi-particles. In our model, we deduced a link between the many-body perturbation approach of the electron-phonon coupling and the well-known Jahn-Teller effect.

Nature Communications 7: 11327. (2016). DOI:10.1038/ncomms11327