Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Ab initio prediction of strain-tunable spin defects in quasi-1D TiS3 and NbS3 nanowires

Jordan Chapman, Arindom Nag, Thang Pham, Vsevolod Ivanov

TL;DR

This study demonstrates that quasi-1D TiS3 and NbS3 nanowires host intrinsic sulfur vacancies and divacancies whose electronic and spin properties are highly tunable by in-plane, axis-directed strain. Using ab initio hybrid-DFT calculations, the authors show in-gap defect states with bright optical transitions and reveal strain-induced spin-state transitions: TiS3 VS can switch from triplet to singlet under mild compressive strain, while NbS3 VD can adopt a triplet ground state under tensile strain with a ZPL of 0.83 eV. The work highlights the strong anisotropy and uniaxial confinement of defect states in TMTC nanowires, enabling tunable spin-photon defects for quantum information and sensing. Overall, the findings establish TMTC nanowires as a versatile platform for strain-controlled spin defects with potential for scalable quantum technologies.

Abstract

Defects in atomically thin van der Waals materials have recently been investigated as sources of spin-photon entanglement with sensitivity to strain tuning. Unlike many two-dimensional materials, quasi-one-dimensional materials such as transition metal trichalcogenides exhibit in-plane anisotropy resulting in axis-dependent responses to compressive and tensile strains. Herein, we characterize the tunable spin and optical properties of intrinsic vacancy defects in titanium trisulfide (TiS3) and niobium trisulfide (NbS3) nanowires. Within our ab initio approach, we show that sulfur vacancies and divacancies (VS and VD , respectively) in TiS3 and NbS3 adopt strain-dependent defect geometries between in-plane strains of -3 % and 3 %. The calculated electronic structures indicate that both VS and VD possess in-gap defect states with optically bright electronic transitions whose position relative to the conduction and valence bands varies with in-plane strain. Further, our calculations predict that VS in TiS3 and VD in NbS3 exhibit transitions in their ground state spins; specifically, a compressive strain of 0.4 % along the direction of nanowire growth causes a shift from a triplet state to a singlet state for the VS defect in TiS3, whereas a tensile strain of 2.9 % along the same direction in NbS3 induces a triplet ground state with a zero-phonon line of 0.83 eV in the VD defect. Our work shows that the anisotropic geometry of TiS3 and NbS3 nanowires offers exceptional tunability of optically active spin defects that can be used in quantum applications.

Ab initio prediction of strain-tunable spin defects in quasi-1D TiS3 and NbS3 nanowires

TL;DR

This study demonstrates that quasi-1D TiS3 and NbS3 nanowires host intrinsic sulfur vacancies and divacancies whose electronic and spin properties are highly tunable by in-plane, axis-directed strain. Using ab initio hybrid-DFT calculations, the authors show in-gap defect states with bright optical transitions and reveal strain-induced spin-state transitions: TiS3 VS can switch from triplet to singlet under mild compressive strain, while NbS3 VD can adopt a triplet ground state under tensile strain with a ZPL of 0.83 eV. The work highlights the strong anisotropy and uniaxial confinement of defect states in TMTC nanowires, enabling tunable spin-photon defects for quantum information and sensing. Overall, the findings establish TMTC nanowires as a versatile platform for strain-controlled spin defects with potential for scalable quantum technologies.

Abstract

Defects in atomically thin van der Waals materials have recently been investigated as sources of spin-photon entanglement with sensitivity to strain tuning. Unlike many two-dimensional materials, quasi-one-dimensional materials such as transition metal trichalcogenides exhibit in-plane anisotropy resulting in axis-dependent responses to compressive and tensile strains. Herein, we characterize the tunable spin and optical properties of intrinsic vacancy defects in titanium trisulfide (TiS3) and niobium trisulfide (NbS3) nanowires. Within our ab initio approach, we show that sulfur vacancies and divacancies (VS and VD , respectively) in TiS3 and NbS3 adopt strain-dependent defect geometries between in-plane strains of -3 % and 3 %. The calculated electronic structures indicate that both VS and VD possess in-gap defect states with optically bright electronic transitions whose position relative to the conduction and valence bands varies with in-plane strain. Further, our calculations predict that VS in TiS3 and VD in NbS3 exhibit transitions in their ground state spins; specifically, a compressive strain of 0.4 % along the direction of nanowire growth causes a shift from a triplet state to a singlet state for the VS defect in TiS3, whereas a tensile strain of 2.9 % along the same direction in NbS3 induces a triplet ground state with a zero-phonon line of 0.83 eV in the VD defect. Our work shows that the anisotropic geometry of TiS3 and NbS3 nanowires offers exceptional tunability of optically active spin defects that can be used in quantum applications.
Paper Structure (5 sections, 1 equation, 5 figures, 1 table)

This paper contains 5 sections, 1 equation, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Methods
  3. Results and Discussion
  4. Conclusion.
  5. Acknowledgments

Figures (5)

  • Figure 1: Theoretical predictions of TMTC unit cell geometry (i) and electronic band structure (ii) for (a) TiS$_3$ and (b) NbS$_3$. Band energies are plotted relative to the Fermi energy. (c) SEM images of bent (i) TiS$_3$ and (ii) NbS$_3$ nanowires (indicated by an orange arrow). (d) Simulated scanning transmission electron microscopy (STEM) images showing common intrinsic defects (V$_S$: sulfur vacancy, V$_D$: sulfur divacancy and V$_{Ti}$: titanium vacancy) in TiS$_3$ nanowires in dark field (i) and bright field (ii) modes.
  • Figure 2: Vacancy defects in (a) TiS$_3$ and (b) NbS$_3$. V$_S$ and V$_D$ defects are shown in black and red, respectively.
  • Figure 3: Electronic structures of (a) V$_S$, (b) V$_D$ in a $4 \times 4 \times 1$ TiS$_3$ supercell, (c) V$_S$, (d) V$_D$ in a $3 \times 3 \times 1$ NbS$_3$ supercell, showing the conduction band (blue), valence band (green), localized defect states (black lines) plotted relative to the Fermi energy $E_F$ (dashed line). Up/down spin channels are shown separately in the left/right columns of each panel.
  • Figure 4: Strain response of formation energies of intrinsic vacancy defects. Formation energy as a function of $\varepsilon_y$ and the same curve with increased resolution are shown in (a) and (b), respectively, for V$_S$ in TiS$_3$ and (c) and (d) for V$_D$ in NbS$_3$. Singlet ground states are plotted with circles, while square marks correspond to triplet ground states. Defect structural polymorphs are delineated with different color curves.
  • Figure 5: Strain tunable spin states of V$_S$ in TiS$_3$ and V$_D$ in NbS$_3$. (a) Spin singlet and (b) spin triplet state wavefunctions of V$_S$ in TiS$_3$ at $\varepsilon$$_y$ = -0.4 % and (c) defect position of the HOMO level relative to the CBM. (d) Spin singlet and (e) spin triplet state wavefunctions of V$_D$ in NbS$_3$ at $\varepsilon$$_y$ = 2.9 % and (f) defect position of the HOMO level relative to the CBM. The insets of (a), (b), (d), and (f) correspond to the defect electronic structures, following the same conventions described in \ref{['e-_structures']}. The HOMO levels that are plotted in (c) and (f) are indicated with red lines.