University of Oulu

Shang, Z., Hashemi, A., Berencén, Y., Komsa, H.-P., Erhart, P., Zhou, S., … Astakhov, G. V. (2020). Local vibrational modes of Si vacancy spin qubits in SiC. Physical Review B, 101(14).

Local vibrational modes of Si vacancy spin qubits in SiC

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Author: Shang, Z.1; Hashemi, A.2; Berencén, Y.1;
Organizations: 1Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, Dresden, Germany
2Department of Applied Physics, Aalto University, Espoo, Finland
3Microelectronics Research Unit, University of Oulu, Oulu, Finland
4Department of Physics, Chalmers University of Technology, Gothenburg, Sweden
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.6 MB)
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Language: English
Published: American Physical Society, 2020
Publish Date: 2020-07-13


Silicon carbide is a very promising platform for quantum applications because of the extraordinary spin and optical properties of point defects in this technologically friendly material. These properties are strongly influenced by crystal vibrations, but the exact relationship between them and the behavior of spin qubits is not fully investigated. We uncover the local vibrational modes of the Si vacancy spin qubits in as-grown 4H-SiC. We apply microwave-assisted spectroscopy to isolate the contribution from one particular type of defects, the so-called V2 center, and observe the zero-phonon line together with seven equally separated phonon replicas. Furthermore, we present first-principles calculations of the photoluminescence line shape, which are in excellent agreement with our experimental data. To boost up the calculation accuracy and decrease the computation time, we extract the force constants using machine-learning algorithms. This allows us to identify the dominant modes in the lattice vibrations coupled to an excited electron during optical emission in the Si vacancy. A resonance phonon energy of 36 meV and a Debye-Waller factor of about 6% are obtained. We establish experimentally that the activation energy of the optically induced spin polarization is given by the local vibrational energy. Our findings give insight into the coupling of electronic states to vibrational modes in SiC spin qubits, which is essential to predict their spin, optical, mechanical, and thermal properties. The approach described can be applied to a large variety of spin defects with spectrally overlapped contributions in SiC as well as in other three- and two-dimensional materials.

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Series: Physical review. B
ISSN: 2469-9950
ISSN-E: 2469-9969
ISSN-L: 2469-9950
Volume: 101
Issue: 14
Article number: 144109
DOI: 10.1103/PhysRevB.101.144109
Type of Publication: A1 Journal article – refereed
Field of Science: 114 Physical sciences
Funding: This work has been supported by the German Research Foundation (DFG) under Grant No. AS 310/5-1 and the Academy of Finland under Projects No. 286279 and No. 311058. We also thank CSC-IT Center Science Ltd., Finland, and HLRS, Stuttgart, Germany for generous grants of computer time. Z.S. thanks the China Scholarship Council (CSC File No. 201706220060) for support. The authors thank R. Narkowicz and K. Lenz for designing and characterization of the coplanar waveguides.
Academy of Finland Grant Number: 286279
Detailed Information: 286279 (Academy of Finland Funding decision)
311058 (Academy of Finland Funding decision)
Copyright information: © 2020 American Physical Society.