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Flat Topological Nodal Lines in Heavy-Fermion Compound CeCoGe$_3$

Yuting Wang, Weikang Wu, Jianzhou Zhao

Abstract

The interplay between strong electronic correlations, unconventional superconductivity, and symmetry-protected topology provides a fertile ground for discovering exotic quantum states. In this work, we investigate the correlated electronic structure and topological properties of the heavy fermion material CeCoGe$_3$ using density functional theory combined with dynamical mean-field theory calculations. Our results reveal a crossover from high temperature incoherent states to low temperature coherent heavy quasiparticles, accompanied by a mass enhancement of $m^*/m_{\text{DFT}}\sim 52.6$ at $T=25$ K. The interplay between electronic correlation, spin-orbit coupling and the noncentrosymmetric $I4mm$ crystal symmetry stabilize flat topological nodal lines within 10 meV of the Fermi level, which could contribute a significant density of states. The proximity of topological nodal lines to the Fermi surface suggests a potential role in mediating pressure induced unconventional superconductivity. Our work establishes CeCoGe$_3$ as a prototype topological nodal line Kondo semimetal. The coexistence of strong correlation, non-trivial band topology and superconductivity indicate CeCoGe$_3$ as a potential candidate for realizing topological superconductivity.

Flat Topological Nodal Lines in Heavy-Fermion Compound CeCoGe$_3$

Abstract

The interplay between strong electronic correlations, unconventional superconductivity, and symmetry-protected topology provides a fertile ground for discovering exotic quantum states. In this work, we investigate the correlated electronic structure and topological properties of the heavy fermion material CeCoGe using density functional theory combined with dynamical mean-field theory calculations. Our results reveal a crossover from high temperature incoherent states to low temperature coherent heavy quasiparticles, accompanied by a mass enhancement of at K. The interplay between electronic correlation, spin-orbit coupling and the noncentrosymmetric crystal symmetry stabilize flat topological nodal lines within 10 meV of the Fermi level, which could contribute a significant density of states. The proximity of topological nodal lines to the Fermi surface suggests a potential role in mediating pressure induced unconventional superconductivity. Our work establishes CeCoGe as a prototype topological nodal line Kondo semimetal. The coexistence of strong correlation, non-trivial band topology and superconductivity indicate CeCoGe as a potential candidate for realizing topological superconductivity.
Paper Structure (8 sections, 3 equations, 5 figures)

This paper contains 8 sections, 3 equations, 5 figures.

Table of Contents

  1. Introduction
  2. RESULTS
  3. DISCUSSION
  4. Methods
  5. Acknowledgments

Figures (5)

  • Figure 1: (a) Pressure-temperature phase diagram of CeCoGe$_3$ adapted from Ref. knebel_high_2009, illustrating six magnetic phases (in red) and the emergence of superconductivity under pressure (in blue). Inset: Body-centered tetragonal crystal structure of CeCoGe$_3$ with space group $I4mm$ and its Brillouin zone. (b) DFT-calculated band structure and DOS with orbital projected contribution: Co-3$d$ (red), Ge-4$p$ (blue), Ce-5$d$ (green) and Ce-4$f$ (orange). The crystal structure was illustrated using the VESTA software momma_vesta_2008.
  • Figure 2: Temperature evolution of correlation-driven electronic strcture. (a) Imaginary part of the self-energy $-\mathrm{Im}\Sigma(\mathrm{i}0^+)$ for Ce-$f_{5/2}$ orbital as a function of temperature. (b) 4$f_{5/2}$-projected DOS at Fermi level as a function of temperature; (c) Momentum-resolved spectral function $\mathcal{A}(k,\omega)$ at $T=500$ K; (d) $\mathcal{A}(k,\omega)$ at $T=25$ K.
  • Figure 3: The Fermi surface evolution across the Kondo temperature. (a,c) The high temperature ($T=500$ K) Fermi surface in the (001) (a) and (110) (c) planes. (b,d) The low temperature ($T=25$ K) Fermi surface in the (001) (b) and (110) (d) planes.
  • Figure 4: Effective quasiparticle band strcuture and topological nodal lines. (a) The high-temperature ($T=500$ K) band structure of the effective Hamiltonian, with spectral function $\mathcal{A}(k,\omega)$ overlaid (red). (b) The low-temperature ($T=25$ K) band structure. (c) The essential and accidental nodal lines in the BZ with red and blue colors respectively. The position of nodal lines are marked in (b) for references.
  • Figure 5: Calculated electronic structure of CeCoGe$_3$ at $P=6.5$ GPa. (a) The Ce-$4f$ projected DOS (blue line), comparing with Ce-4$f$ DOS at the ambient pressure shown by red line. (b) Momentum-resolved spectral function $\mathcal{A}(k,\omega)$.