arXiv subjects

Joel Davidsson

Publications and source records attributed to Joel Davidsson.

At least 19 recordsLinked to original sources

arXiv2026

Color Centers in Cubic Boron Nitride

Cubic boron nitride (c-BN) is a wide-bandgap semiconductor (WBGS) with potential applications in both power electronics and quantum technologies. Color centers in WBGS can be used as single photon emitters and quantum sensors. Several zero phonon lines have been measured in c-BN experiment but not yet identified. To systematically probe the combinatorially complex chemical space of defects, we generate a large-scale point defect data set for c-BN. We apply density functional theory calculation implemented in a high-throughput workflow Automatic Defect Analysis and Qualification (ADAQ) to broadly screen for point defect complexes containing s- or p-elements. More than 8000 defects have been calculated in different charge and spin states. The calculated properties are stored in defect database and are then filtered to find defects with properties similar to the NV-center in diamond. More accurate calculations using hybrid functionals are then performed on a selected set of promising defects to further assess their suitability for quantum technology. In particular, we reexamined the ONVB defect which likely explains the GC-2 line. The hybrid calculations also suggest other defect candidates with bright emission, such as two carbon defects and the NaB- defect.

cond-mat.mtrl-sci↗

arXiv2025

Demonstration of the ODMR activity of the telecom range ClV center in SiC: a wavefunction theory analysis

Recently, density functional theory-based high-throughput screening of point defects in 4H-SiC revealed the positively charged chlorine-vacancy (ClV) defect to be a promising quantum bit candidate emitting at telecom wavelengths, with an electronic structure analogous to the well-known NV center in diamond. Furthermore, recent infrared photoluminescence (PL) measurements on chlorine-implanted 4H-SiC have revealed new PL lines associated with the ClV defect. While the defect possesses a high-spin ground state, there is a lack of evidence of optically detected magnetic resonance (ODMR), a key ingredient for optical spin initialization and readout. In this Letter, we employ a multireference wavefunction-based quantum chemistry method, specifically, second-order perturbation theory (NEVPT2) on top of a defect-localized many-body wavefunction (CASSCF), to explore the many-body electronic structure of the ClV center. We estimate photoluminescence, internal conversion, and intersystem crossing rates to investigate the possibility of spin polarization and ODMR activity. Our findings establish the ClV center in 4H-SiC as an optically addressable spin qubit with fiber optics compatibility in the technologically mature 4H-SiC host material, enabling the development of large-scale quantum networks.

cond-mat.mtrl-sci↗

arXiv2025

NV-like Defects More Common Than Four-Leaf Clovers: A Perspective on High-Throughput Point Defect Data

Point defects for quantum technologies is an emerging research area, with the nitrogen-vacancy (NV) center in diamond at the forefront. However, how rare are defects with NV-like properties? In this perspective, I highlight the results of NV-like defects across 33 different materials, revealing that they are more common than finding four-leaf clovers. I also discuss expanding the search criteria to identify other defects relevant to quantum technologies. Utilizing point defect databases will be instrumental in assisting researchers in discovering previously unexplored defects suitable for quantum technologies.

cond-mat.mtrl-sci↗

arXiv2025

High-Throughput Exploration of NV-like Color Centers Across Host Materials

Point defects in semiconductors offer a promising platform for advancing quantum technologies due to their localized energy states and controllable spin properties. Prior research has focused on a limited set of defects within materials such as diamond, silicon carbide, and hexagonal boron nitride. We present a high-throughput study to systematically identify and evaluate point defects across a diverse range of host materials, aiming to uncover previously unexplored defects in novel host materials suitable for use in quantum applications. A range of host materials are selected for their desirable properties, such as appropriate bandgaps, crystal structure, and absence of d- or f-electrons. The Automatic Defect Analysis and Qualification (ADAQ) software framework is used to generate vacancies, substitutions with s- and p-elements, and interstitials in these materials and use density functional theory to calculate key properties such as Zero-Phonon Lines (ZPLs), ionic displacements, Transition Dipole Moments (TDMs), and formation energies. Special attention is given to charge correction methods for materials with dielectric anisotropy. We uncover new defect-host combinations with advantageous properties for quantum applications: 28 defects across 11 isotropic and 2 anisotropic host materials show properties similar to the nitrogen-vacancy (NV) center in diamond. Beryllium (Be) substitutional defects in SrS, MgS, and SrO emerge as particularly promising. These findings contribute to diversifying and enhancing the materials available for quantum technologies.

cond-mat.mtrl-sci↗

arXiv2025

Native defects and impurities in talcum quasi-2D layers

Layered semiconductors have recently emerged as capable host materials for novel quantum applications ranging from phonics to sensing. Most studies have focused on artificial layered materials, while natural layered materials, such as talc and other silicates, have remained largely unexplored despite their desirable properties, e.g, wide direct bandgap, low concentration of optically active defects, and low abundance of nuclear spins. In this article, we carry out a comprehensive computational study of pristine and defective talc layers and discuss their potential applications. After investigating bulk properties, such as lattice parameters, band structure, and dielectric constant, we study the electronic structure, charge states, spin and optical properties of vacancy defects, metal, metalloid, and non-metallic impurities. Our results establish the basis for identifying color centers, electron paramagnetic resonance centers, potential spin quantum bits, and p and n-type dopants. These findings mature the theory of talc and point toward potential applications in quantum technologies.

cond-mat.mtrl-sci↗

arXiv2025

Comparative study of divacancies in 3C-, 4H- and 6H-SiC

The divacancy comprising two neighboring vacant sites in the SiC lattice is a promising defect for applications in quantum technology. So far, most work is concerned with the divacancy in 4H-SiC, whereas the divacancies in 6H- and 3C-SiC have received much less attention. Here, we outline arguments showing that the neutral charge state of the divacancies in the latter two polytypes is intrinsically stable, in contrast to that in 4H-SiC where the photoluminescence quenches in most materials for certain excitation energies (below approximately 1.3 eV). Divacancies in 6H- and 3C-SiC are anticipated to remain stable even with resonant excitation. We provide new ab initio calculation results for the charge transfer levels of divacancies in 6H- and 3C-SiC. Using the temperature dependence of the divacancy emission in 3C-SiC, we estimate the energy position of the (+|0) charge transfer level of the divacancy within the bandgap of this polytype and compare with theoretical results.

quant-ph↗

arXiv2025

An NV- center in magnesium oxide as a spin qubit for hybrid quantum technologies

Recent predictions suggest that oxides, such as MgO and CaO, could serve as hosts of spin defects with long coherence times and thus be promising materials for quantum applications. However, in most cases specific defects have not yet been identified. Here, by using a high-throughput first-principles framework and advanced electronic structure methods, we identify a negatively-charged complex between a nitrogen interstitial and a magnesium vacancy in MgO with favorable electronic and optical properties for hybrid quantum technologies. We show that this NV- center has stable triplet ground and excited states, with singlet shelving states enabling optical initialization and spin-dependent readout. We predict several properties, including absorption, emission, and zero-phonon line energies, as well as zero-field splitting tensor, and hyperfine interaction parameters, which can aid in the experimental identification of this defect. Our calculations show that due to a strong pseudo-Jahn Teller effect and low frequency phonon modes, the NV- center in MgO is subject to a substantial vibronic coupling. We discuss design strategies to reduce such coupling and increase the Debye-Waller factor, including the effect of strain and the localization of the defect states. We propose that the favorable properties of the NV- defect, along with the technological maturity of MgO, could enable hybrid classical-quantum applications, such as spintronic quantum sensors and single qubit gates.

cond-mat.mtrl-sci↗

arXiv2025

Theoretical characterization of NV-like defects in 4H-SiC using ADAQ with the SCAN and r2SCAN meta-GGA functionals

Kohn-Sham density functional theory (DFT) is widely used for screening color centers in semiconductors. While the Perdew-Burke-Ernzerhof (PBE) functional is efficient, it often lacks precision in describing defects. The Heyd-Scuseria-Ernzerhof (HSE) functional is more accurate but computationally expensive, making it impractical for large-scale screening. However, third-rung functionals of "Jacob's ladder" remain largely under explored in this context. This study evaluates the Strongly Constrained and Appropriately Normed (SCAN) family of meta-GGA functionals as potential alternatives to PBE for characterizing NV-like color centers in 4H-SiC using the Automatic Defect Analysis and Qualification (ADAQ) framework. We examine nitrogen, oxygen, fluorine, sulfur, and chlorine vacancies in 4H-SiC, focusing on applications in quantum technology. Our results show that SCAN and r2SCAN achieve greater accuracy than PBE, approaching HSE's precision at a lower computational cost. This suggests that the SCAN family offers a practical improvement for screening new color centers, with computational demands similar to PBE.

cond-mat.mtrl-sci↗

arXiv2024

Temperature dependence of the AB-lines and Optical Properties of the Carbon-Antisite Vacancy Pair in 4H-SiC

Defects in semiconductors have in recent years been revealed to have interesting properties in the venture towards quantum technologies. In this regard, silicon carbide has shown great promise as a host for quantum defects. In particular, the ultra-bright AB photoluminescence lines in 4H-SiC are observable at room temperature and have been proposed as a single-photon quantum emitter. These lines have been previously studied and assigned to the carbon antisite-vacancy pair (CAV). In this paper, we report on new measurements of the AB-lines' temperature dependence, and carry out an in-depth computational study on the optical properties of the CAV defect. We find that the CAV defect has the potential to exhibit several different zero-phonon luminescences with emissions in the near-infrared telecom band, in its neutral and positive charge states. However, our measurements show that the AB-lines only consist of three non-thermally activated lines instead of the previously reported four lines, meanwhile our calculations on the CAV defect are unable to find optical transitions in full agreement with the AB-line assignment. In the light of our results, the identification of the AB-lines and the associated room temperature emission require further study.

cond-mat.mtrl-sci↗

arXiv2024

Discovery of Atomic Clock-Like Spin Defects in Simple Oxides from First Principles

Virtually noiseless due to the scarcity of spinful nuclei in the lattice, simple oxides hold promise as hosts of solid-state spin qubits. However, no suitable spin defect has yet been found in these systems. Using high-throughput first-principles calculations, we predict spin defects in calcium oxide with electronic properties remarkably similar to those of the NV center in diamond. These defects are charged complexes where a dopant atom -- Sb, Bi, or I -- occupies the volume vacated by adjacent cation and anion vacancies. The predicted zero phonon line shows that the Bi complex emits in the telecommunication range, and the computed many-body energy levels suggest a viable optical cycle required for qubit initialization. Notably, the high-spin nucleus of each dopant strongly couples to the electron spin, leading to many controllable quantum levels and the emergence of atomic clock-like transitions that are well protected from environmental noise. Specifically, the Hanh-echo coherence time increases beyond seconds at the clock-like transition in the defect with \ch{^{209}Bi}. Our results pave the way to designing quantum states with long coherence times in simple oxides, making them attractive platforms for quantum technologies.

cond-mat.mtrl-sci↗

arXiv2024

Na in Diamond: High Spin Defects Revealed by the ADAQ High-Throughput Computational Database

Color centers in diamond are at the forefront of the second quantum revolution. A handful of defects are in use, and finding ones with all the desired properties for quantum applications is arduous. By using high-throughput calculations, we screen 21607 defects in diamond and collect the results in the ADAQ database. Upon exploring this database, we find not only the known defects but also several unexplored defects. Specifically, defects containing sodium stand out as particularly relevant because of their high spins and predicted improved optical properties compared to the NV center. Hence, we studied these in detail, employing high-accuracy theoretical calculations. The single sodium substitutional (Na$\mathrm{_C}$) has various charge states with spin ranging from 0.5 to 1.5, ZPL in the near-infrared, and a high Debye-Waller factor, making it ideal for biological quantum applications. The sodium vacancy (NaV) has a ZPL in the visible region and a potential rare spin-2 ground state. Our results show sodium implantation yields many interesting spin defects that are valuable additions to the arsenal of point defects in diamond studied for quantum applications.

cond-mat.mtrl-sci↗

arXiv2024

ADAQ-SYM: Automated Symmetry Analysis of Defect Orbitals

Quantum technologies like single photon emitters and qubits can be enabled by point defects in semiconductors, with the NV-center in diamond being the most prominent example. There are many different semiconductors, each potentially hosting interesting defects. The symmetry properties of the point defect orbitals can yield useful information about the behavior of the system, such as the interaction with polarized light. We have developed a tool to perform symmetry analysis of point defect orbitals obtained by plane-wave density functional theory simulations. The software tool, named ADAQ-SYM, calculates the characters for each orbital, finds the irreducible representations, and uses selection rules to find which optical transitions are allowed. The capabilities of ADAQ-SYM are demonstrated on several defects in diamond and 4H-SiC. The symmetry analysis explains the different zero phonon line (ZPL) polarization of the hk and kh divacancies in 4H-SiC.

cond-mat.mtrl-sci↗

arXiv2023

Selection rules in the excitation of the divacancy and the nitrogen-vacancy pair in 4H- and 6H-SiC

In this study, we address the selection rules with respect to the polarization of the optical excitation of two colour centres in 4H-SiC and 6H-SiC with potential for applications in quantum technology, the divacancy and the nitrogen-vacancy pair. We show that the photoluminescence (PL) of the axial configurations of higher symmetry (C3v) than the basal ones (C1h) can be cancelled using any excitation (resonant or non-resonant) with polarization parallel to the crystal axis (EL||c). The polarization selection rules are determined using group-theoretical analysis and simple physical arguments showing that phonon-assisted absorption with EL||c is prohibited despite being formally allowed by group theory. A comparison with the selection rules for the silicon vacancy, another defect with C3v symmetry, is also carried out. Using the selection rules, we demonstrate selective excitation of only one basal divacancy configuration in 4H-SiC, the P3 line and discuss the higher contrast and increased Debye-Waller factor in the selectively excited spectrum.

quant-ph↗

arXiv2023

The Chlorine Vacancy in 4H-SiC: An NV-like Defect With Telecom Emission

The diamond nitrogen vacancy (NV) center remains an ever increasing topic of interest. At present, it is considered an ideal example of a solid-state qubit applicable in quantum communication, computing, and sensing alike. With its success, the search for defects that share or improve upon its advantageous features is an ongoing endeavor. By performing large-scale high-throughput screening of 52600 defects in 4H silicon carbide (SiC), we identify a collection of NV-like color-centers of particular interest. From this list, the single most promising candidate consists of a silicon vacancy and chlorine substituted on the carbon site, and is given the name of the chlorine vacancy (ClV) center. Through high-accuracy first-principle calculations, we confirm that the ClV center is similar to the NV center in diamond in its local structure and shares many qualitative and quantitative features in the electronic structure and spin properties. In contrast to the NV center, however, the ClV center in SiC exhibits emission in the telecom range near the C-band.

cond-mat.mtrl-sci↗

arXiv2023

Absorption $\textit{versus}$ Adsorption: High-Throughput Computation of Impurities in 2D Materials

Doping of a two-dimensional (2D) material by impurity atoms occurs \textit{via} two distinct mechanisms: absorption of the dopants by the 2D crystal or adsorption on its surface. To distinguish the relevant mechanism, we systematically dope 53 experimentally synthesized 2D monolayers by 65 different chemical elements in both absorption and adsorption sites. The resulting 17,598 doped monolayer structures were generated using the newly developed ASE \texttt{DefectBuilder} -- a Python tool to set up point defects in 2D and bulk materials -- and subsequently relaxed by an automated high-throughput density functional theory (DFT) workflow. We find that interstitial positions are preferred for small dopants with partially filled valence electrons in host materials with large lattice parameters. On the contrary, adatoms are favored for dopants with a low number of valence electrons due to lower coordination of adsorption sites compared to interstitials. The relaxed structures, characterization parameters, defect formation energies, and magnetic moments (spins) are available in an open database to help advance our understanding of defects in 2D materials.

cond-mat.mtrl-sci↗

arXiv2022

Exhaustive characterization of modified Si vacancies in 4H-SiC

The negatively charged silicon vacancy ($\mathrm{V_{Si}^-}$) in silicon carbide is a well-studied point defect for quantum applications. At the same time, a closer inspection of ensemble photoluminescence and electron paramagnetic resonance measurements reveals an abundance of related but so far unidentified signals. In this study, we search for defects in 4H-SiC that explain the above magneto-optical signals in a defect database generated by Automatic Defect Analysis and Qualification (ADAQ) workflows. This search reveals only one class of atomic structures that exhibit silicon-vacancy-like properties in the data: a carbon antisite ($\mathrm{C_{Si}}$) within sub-nanometer distances from the silicon vacancy only slightly alters the latter without affecting the charge or spin state. Such a perturbation is energetically bound. We consider the formation of $\mathrm{V_{Si}^-+C_{Si}}$ up to 2 nm distance and report their zero phonon lines and zero field splitting values. In addition, we perform high-resolution photoluminescence experiments in the silicon vacancy region and find an abundance of lines. Comparing our computational and experimental results, several configurations show great agreement. Our work demonstrates the effectiveness of a database with high-throughput results in the search for defects in quantum applications.

cond-mat.mtrl-sci↗

arXiv2021

ADAQ: Automatic workflows for magneto-optical properties of point defects in semiconductors

Automatic Defect Analysis and Qualification (ADAQ) is a collection of automatic workflows developed for high-throughput simulations of magneto-optical properties of point defect in semiconductors. These workflows handle the vast number of defects by automating the processes to relax the unit cell of the host material, construct supercells, create point defect clusters, and execute calculations in both the electronic ground and excited states. The main outputs are the magneto-optical properties which include zero-phonon lines, zero-field splitting, and hyperfine coupling parameters. In addition, the formation energies are calculated. We demonstrate the capability of ADAQ by performing a complete characterization of the silicon vacancy in silicon carbide in the polytype 4H (4H-SiC).

cond-mat.mtrl-sci↗

arXiv2020

Theoretical polarization of zero phonon lines in point defects

In quantum technologies, point defects in semiconductors are becoming more significant. Understanding the frequency, intensity, and polarization of the zero phonon line is important. The last two properties are the subject of this paper. I present a method for calculating these properties and show the importance of using wave functions from both the ground and excited state. The validity of this method is demonstrated on the divacancy in 4H-SiC. Here, the calculated polarization and lifetimes are in excellent agreement with experimental measurements. In general, this method can help to identify point defects and estimate suitable applications.

cond-mat.mtrl-sci↗