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Many-body electronic structure, self-doped double-exchange, and Hund metallicity in 1T-CrTe2 bulk and monolayer

Dong Hyun David Lee, Hyeong Jun Lee, Taek Jung Kim, Min Yong Jeong, Myung Joon Han

Abstract

The van der Waals (vdW) ferromagnet 1T-CrTe2 is an emerging spintronics platform, notable for its high Curie temperature (Tc) and intriguing transport properties. However, the fundamental interplay between the electron correlations and magnetism underlying its high Tc still remains elusive. Here, using density functional theory plus dynamical mean-field theory (DFT+DMFT), we identify 1T-CrTe2 as a self-doped double-exchange ferromagnet with pronounced Hund metallicity. This identification is grounded in the first detailed analysis of its many-body electronic structure, which reveals a dual electronic nature of Cr-d orbitals where itinerant eg electrons coexist with localized t2g moments. The interaction between these orbitals, mediated by Hund's coupling, drives the double-exchange ferromagnetism, establishing 1T-CrTe2 as a Hund metal reminiscent of orbital-selective Mott systems. In the monolayer limit, while this physical picture persists, structural deformation, rather than reduced dimensionality, notably reduces Tc.Our findings offer a new perspective on the high-Tc ferromagnetism in 1T-CrTe2, a mechanism potentially pivotal for other correlated two-dimensional vdW metallic magnets.

Many-body electronic structure, self-doped double-exchange, and Hund metallicity in 1T-CrTe2 bulk and monolayer

Abstract

The van der Waals (vdW) ferromagnet 1T-CrTe2 is an emerging spintronics platform, notable for its high Curie temperature (Tc) and intriguing transport properties. However, the fundamental interplay between the electron correlations and magnetism underlying its high Tc still remains elusive. Here, using density functional theory plus dynamical mean-field theory (DFT+DMFT), we identify 1T-CrTe2 as a self-doped double-exchange ferromagnet with pronounced Hund metallicity. This identification is grounded in the first detailed analysis of its many-body electronic structure, which reveals a dual electronic nature of Cr-d orbitals where itinerant eg electrons coexist with localized t2g moments. The interaction between these orbitals, mediated by Hund's coupling, drives the double-exchange ferromagnetism, establishing 1T-CrTe2 as a Hund metal reminiscent of orbital-selective Mott systems. In the monolayer limit, while this physical picture persists, structural deformation, rather than reduced dimensionality, notably reduces Tc.Our findings offer a new perspective on the high-Tc ferromagnetism in 1T-CrTe2, a mechanism potentially pivotal for other correlated two-dimensional vdW metallic magnets.
Paper Structure (16 sections, 3 equations, 4 figures, 2 tables)

This paper contains 16 sections, 3 equations, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Results and discussions
  3. Discussion
  4. Summary
  5. Methods
  6. Data availability
  7. Acknowledgements
  8. Author contributions
  9. Competing interests

Figures (4)

  • Figure 1: Crystal and electronic structure of the bulk phase.a Crystal structure of bulk 1T-CrTe$_2$ (left) and a schematic diagram of the crystal field levels (right). b Upper panel: LDA+DMFT spectral functions $A(\omega)$ in the PM phase (solid lines; $T=450$ K) compared with the LDA results (shaded areas). Lower panel: Corresponding orbital-resolved $A(\omega)$ from the LDA+DMFT calculation. c Upper panel: LDA+DMFT Cr-$d$ spectral functions in the FM phase (purple solid; $T=150$ K) compared with the LSDA (red dotted) and LSDA+$U$ (blue dash-dot) results. Positive and negative values correspond to the majority (up) and minority (down) spins, respectively. Lower panel: Same as in (b), but for the FM phase. d LDA+DMFT momentum-dependent spectral function $A(\mathbf{k}, \omega)$ at $T=150$ K for the up-spin (left panel) and down-spin (right panel) states compared with the LSDA (red dotted) and LSDA+$U$ (blue dash-dot) bands.
  • Figure 2: Dual electronic nature driving double-exchange ferromagnetism.a The temperature dependence of orbital-resolved static local spin susceptibility $\chi^{\rm loc}_{\rm spin}$ obtained in the PM phase. b The imaginary part of self-energy at the lowest fermionic Matsubara frequency ($i\omega_0 = i\pi k_B T$, where $k_B$ is Boltzmann constant) in the PM phase. The inset shows an enlarged view of the low-temperature region. c Orbital-resolved $M=\mu_B(\langle n_\uparrow\rangle -\langle n_\downarrow\rangle )$ as a function of $J_H$ at $T=150~\rm{K}$. The FM phase sets in for $J_H \gtrsim 0.5$ eV.
  • Figure 3: Hallmarks of Hund metallicity.a Imaginary part of self-energy on the Matsubara frequency axis $\text{Im} \Sigma(i\omega_n)$ at $T=150~\rm{K}$ and with $J_H=0.6, 0.8,$ and 1.0 eV. b The calculated local spin susceptibility $\chi^{\rm{loc}}_{\rm{spin}}$ as a function of $J_H$ at $T=450~\rm{K}$. c Probability distribution of the Cr-$d$ orbital occupancy, $N_d$. d The temperature dependence of $k_BT\chi^{\rm{loc}}_{\rm{spin/orb}}$. The spin (solid line) and orbital (dashed line) susceptibilities $\chi$ within the $e_g$ and $t_{2g}$ manifolds are represented with blue and orange colors, respectively. Vertical arrows mark the onset temperatures for spin screening. e The valence histogram within the $t_{2g}$ manifold in terms of the electron number $N_{t_{2g}}$ and the spin-state $S^{t_{2g}}_z$.
  • Figure 4: Effect of structural deformation on monolayer magnetism.a Structural parameters of $h_{Te}$ (the Te atom height with respect to the Cr layer) and $\theta$ (the Cr--Te--Cr bond angle). The major change by the structural relaxation is the Te atom displacements (indicated by small vertical blue arrows), which increase $h_{Te}$ and reduce $\theta$ compared to the bulk case (or equivalently 1ML-b). b The calculated magnetization $M=\mu_B(\langle n_\uparrow\rangle -\langle n_\downarrow\rangle )$ as a function of temperature. The dash-dot lines are the fits to $U=5$ eV data with $M(T) = M_s(1-T/T_C)^\beta$. The fixed $J_H=0.85$ eV is used.