arXiv subjects

Peter Deák

Publications and source records attributed to Peter Deák.

9 recordsLinked to original sources

arXiv2026

Single-photon emitters and spin-photon interfaces in silicon

Single photons enable the distribution of quantum information over large distances and thus play a major role in quantum technologies such as communication and computing. Solid-state emitters are practical and efficient sources of single photons that can be manufactured in large numbers. When combined with a spin, the resulting spin-photon interfaces can store quantum states for extended periods and serve as the basis for quantum networks and repeaters. Among the many host materials explored over the past few decades, silicon stands out for its advanced nanofabrication, the maturity of its integrated photonics and microelectronics, and its high isotopic purity, which leads to exceptionally long spin coherence. These properties position silicon single-photon emitters and spin-photon interfaces among the most promising hardware platforms for implementing quantum networks and distributed quantum information processors. This review summarizes the current state of the art and open challenges towards coherent single-photon sources and scalable spin-photon interfaces based on color centers and erbium dopants in nanophotonic silicon structures.

quant-ph↗

arXiv2024

All epitaxial self-assembly of vertically-confined silicon color centers using ultra-low temperature epitaxy

Silicon-based color-centers (SiCCs) have recently emerged as quantum-light sources that can be combined with telecom-range Si Photonics platforms. Unfortunately, using current SiCC fabrication, deterministic control over the vertical emitter position is impossible due to ion-implantation's stochastic nature. To overcome this bottleneck towards high-yield integration, we demonstrate a radically innovative creation method for various SiCCs, solely relying on epitaxial growth of Si and C-doped Si at atypically-low temperatures in a ultra-clean growth environment. These telecom emitters can be confined within sub-1nm thick layers embedded at arbitrary vertical positions within a highly crystalline Si matrix. Tuning growth conditions and doping, different SiCC types, e.g., W-centers, T-centers, G-centers, or derivatives like G'-centers can be created, which are particularly promising as Si-based single-photon sources and spin-photon interfaces. The zero-phonon emission from G'-centers can be conveniently tuned by the C-concentration, leading to a systematic wavelength shift and linewidth narrowing towards low emitter densities.

cond-mat.mes-hall↗

arXiv2024

Quantum bit with telecom wave-length emission from a simple defect in Si

Spin-to-photon interfaces from defects in silicon hold great promise towards realizing quantum repeaters with the combination of advanced semiconductor and photonics technologies. Recently, controlled creation and erasure of simple carbon interstitial defects have been successfully realised in silicon. This defect has a stable structure near room temperature and emits in the wave-length where the signal loss is minimal in optical fibres used in communication technologies. Our in-depth theoretical characterization confirms the assignment of the observed emission to the neutral charge state of this defect. We find that the emission is due to the recombination of a bound exciton. We also discovered a metastable triplet state that could be applied as a quantum memory. Based on the analysis of the electronic structure of the defect and its similarities to a known optically detected magnetic resonance centre in silicon, we propose that a carbon interstitial can act as a quantum bit and may realize a spin-to-photon interface in CMOS-compatible platforms.

quant-ph↗

arXiv2020

A Koopmans-compliant screened exchange potential with correct asymptotic behavior for semiconductors

The performance of density functional theory depends largely on the approximation applied for the exchange functional. We propose here a novel screened exchange potential for semiconductors, with parameters based on the physical properties of the underlying microscopic screening and obeying the requirements for proper asymptotic behavior. We demonstrate that this functional is Koopmans-compliant and reproduces a wide range of band gaps. We also show, that the only tunable parameter of the functional can be kept constant upon changing the cation or the anion isovalently, making the approach suitable for treating alloys.

cond-mat.mtrl-sci↗

arXiv2020

Self-consistent potential correction for charged periodic systems

Supercell models are often used to calculate the electronic structure of local perturbations from the ideal periodicity in the bulk or on the surface of a crystal or in wires. When the defect or adsorbent is charged, a jellium counter charge is applied to maintain overall neutrality, but the interaction of the artificially repeated charges has to be corrected, both in the total energy and in the one-electron eigenvalues and eigenstates. This becomes paramount in slab or wire calculations, where the jellium counter charge may induce spurious states in the vacuum. We present here a self-consistent potential correction scheme and provide successful tests of it for bulk and slab calculations.

cond-mat.mtrl-sci↗

arXiv2019

Computational identification of Ga-vacancy related electron paramagnetic resonance centers in $β$-Ga$_2$O$_3$

A combined experimental/theoretical study of the EPR in irradiated $β$-Ga$_2$O$_3$ is presented. Four EPR spectra, two $S=1/2$ and two $S=1$, are observed after high-energy proton or electron irradiation. One of the S=1/2 spectra (EPR1) can be observed at room temperature and below and is characterized by the spin Hamiltonian parameters $g_b=2.0313$, $g_c=2.0079$, $g_{a*}=2.0025$ and a quasi isotropic hyperfine interaction with two equivalent Ga neighbors of $~\sim$14 G on $^{69}$Ga. The second (EPR2) is observed after photoexcitation (with threshold 2.8 eV) at low temperature and is characterized by $g_b=2.0064$, $g_c=2.0464$, $g_{a*}=2.0024$ and a quasi isotropic hyperfine interaction with two equivalent Ga neighbors of 10 G. A spin $S=1$ spectrum with a similar g-tensor and a 50\% reduced hyperfine splitting accompanies each of these, which is indicative of a defect of two weakly coupled $S=1/2$ centers. DFT calculations of the magnetic resonance fingerprint of a wide variety of native defect models are carried out to identify these EPR centers in terms of specific defect configurations. The EPR1 center is proposed to correspond to a complex of two tetrahedral $V_\mathrm{Ga1}$ with an interstitial Ga in between them. This model was previously shown to have lower energy than the simple tetrahedral Ga vacancy and has a $2-/3-$ transition level higher than other $V_\mathrm{Ga}$ related models, which would explain why the other ones are already in their diamagnetic $3-$ state and are thus not observed if the Fermi level is pinned approximately at this level. The EPR2 spectra are proposed to correspond to the octahedral $V_\mathrm{Ga2}$. Models based on self-trapped holes and oxygen interstitials are ruled out because they would have hyperfine interaction with more than two Ga nuclei and because they can not support a corresponding $S=1$ center.

cond-mat.mtrl-sci↗

arXiv2018

Proton Irradiation Induced Defects in \b{eta}-Ga2O3: a combined EPR and Theory Study

Proton irradiation of both n-type and semi-insulating bulk samples of \b{eta}-Ga2O3 leads to the formation of one paramagnetic defect with spin S=1/2, monoclinic point symmetry, a g-tensor with principal values of gb=2.0313, gc=2.0079, ga*= 2.0025 and quasi isotropic superhyperfine interaction of 13G with two equivalent Ga neigbours. Its high introduction rate indicates it to be a primary irradiation induced defect. At low temperature, photoexcitation transforms this defect into a different metastable S=1/2 center with principal g-values of gb=2.0064, gc=2.0464, ga*= 2.0024 and a reduced hyperfine interaction of 9G. This metastable defect is stable up to T=100K, when it switches back to the previous configuration. Density functional theory calculations of the Spin Hamiltonian parameters of various intrinsic defects are carried out using the Gauge Including Projector Augmented Wave method in order to determine the microscopic structure of these defects.Our results do not support the intuitive model of the isolated octahedral or tetrahedral gallium vacancy, VGa2-, but favor the model of a gallium vacancy complex VGa-Gai-VGa.

cond-mat.mtrl-sci↗

arXiv2014

Observation of vacancy-related polaron states at the surface of anatase and rutile TiO2 by high-resolution photoelectron spectroscopy

Defects in the surface region of a reducible oxide, as TiO2, have a profound effect on applications, while their nature is very much influenced by the possibility of small polaron formation. Here, we probe rutile (110) and anatase (101) single crystals via high-resolution ultraviolet photoelectron spectroscopy and resolve multiple components of the well-known defect state in the band gap. In rutile, we find two at VBM+2.1 eV and VBM+1.4 eV, which we assign to subsurface polaron traps and vacancy-bound states, respectively, confirming the predicted partial suppression of polaron formation at high vacancy concentration. New defects are created in situ on the anatase surface by the synchrotron beam. We assign a component at VBM+2.3 eV, which can be removed by annealing, to polaron states associated with surface oxygen vacancies. We also identify a second component at VBM+1.6 eV, which can not be removed by annealing, and is too deep to be associated with oxygen vacancies.

cond-mat.mtrl-sci↗

arXiv2013

Calculation ofthe transitions and migration of nitrogen and vacancy related defects,with implications on the formation of NV centers in bulk diamond

Formation and excitation energies as well charge transition levels, are determined forthe substitutional nitrogen (Ns),the vacancy (V) and related point defects (NV, NVH, N2, N2V and V2) by screened non-local hybrid density functional supercell plane wave calculations in bulk diamond. In additionthe activation energy for V and NV diffusion is calculated.We find good agreement between theory and experiment for the previously well-establisheddata, and predict missing ones. Based on the calculated properties of these defects, the formation of the negatively charged nitrogen-vacancy center is studied, which is a prominent candidate for application in quantum information processing and for nanosensors. We find that the concentration of NV defects are limited in natural diamonds due to the relatively high formation energy of NV. Our results imply that NV defects dominantly form just in the early stage of annealing in N-doped and irradiated diamonds. We find that the amphoteric divacancy defect with multiple acceptor states may significantly influence the charge state and photo-stability of NV in irradiated diamond samples.

cond-mat.mtrl-sci↗