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From Strong to Weak Correlations in Breathing-Mode Kagome van der Waals Materials : Nb3(F, Cl, Br, I)8 as a Robust and Versatile Platform for Many-Body Engineering

Aretz, Joost ; Grytsiuk, Sergii ; Liu, Xiaojing ; Feraco, Giovanna ; Knekna, Chrystalla ; Waseem, Muhammad ; Dan, Zhiying ; Bianchi, Marco ; Hofmann, Philip and Ali, Mazhar N. , et al. (2025) In Physical Review X 15(4).
Abstract

By combining ab initio downfolding with cluster dynamical mean-field theory, we study the degree of correlations in monolayer, bilayer, and bulk breathing-mode kagome van der Waals materials Nb3(F, Cl, Br, I)8. Our new material-specific many-body model library shows that in low-temperature bulk structures the Coulomb correlation strength steadily increases from I to Br, Cl, and F, allowing us to identify Nb3I8 as a weakly correlated insulator whose gap is only mildly affected by the local Coulomb interaction. Nb3Br8 and Nb3Cl8 are strongly correlated insulators, whose gaps are significantly influenced by Coulomb-induced vertex corrections.... (More)

By combining ab initio downfolding with cluster dynamical mean-field theory, we study the degree of correlations in monolayer, bilayer, and bulk breathing-mode kagome van der Waals materials Nb3(F, Cl, Br, I)8. Our new material-specific many-body model library shows that in low-temperature bulk structures the Coulomb correlation strength steadily increases from I to Br, Cl, and F, allowing us to identify Nb3I8 as a weakly correlated insulator whose gap is only mildly affected by the local Coulomb interaction. Nb3Br8 and Nb3Cl8 are strongly correlated insulators, whose gaps are significantly influenced by Coulomb-induced vertex corrections. Nb3F8 is a prototypical bulk Mott insulator whose gap is initially opened by strong correlation effects. Angle-resolved photoemission spectroscopy measurements comparing Nb3Br8 and Nb3I8 allow us to experimentally confirm these findings by revealing spectroscopic footprints of the degree of correlation. Our calculations further uncover how the thickness and the stacking affect the degree of correlations and predict that the entire material family can be tuned into correlated charge transfer or Mott-insulating phases upon electron or hole doping. Our magnetic property analysis based on our model parameter library additionally confirms that interlayer magnetic interactions likely drive the lattice phase transition to the low-temperature structures. The accompanying bilayer hybridization through interlayer dimerization yields magnetic singlet-like ground states in the Cl, Br, and I compounds. We further prove that all low-temperature compounds are dynamically stable and that electron-phonon coupling to the low-energy subspace is suppressed. Our findings establish Nb3X8 as a robust, versatile, and tunable class for van der Waals-based Coulomb and Mott engineering with a rich phase diagram and allow us to speculate on the symmetry-breaking effects necessary for the recently observed Josephson diode effect in NbSe2/Nb3Br8/NbSe2 heterostructures.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Review X
volume
15
issue
4
article number
041042
publisher
American Physical Society
external identifiers
  • scopus:105024227127
ISSN
2160-3308
DOI
10.1103/wr7w-nfhg
language
English
LU publication?
yes
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Publisher Copyright: © 2025 authors. Published by the American Physical Society.
id
d727d9fc-6cea-42e0-9423-3445ee76998d
date added to LUP
2026-01-09 18:03:55
date last changed
2026-01-12 15:21:21
@article{d727d9fc-6cea-42e0-9423-3445ee76998d,
  abstract     = {{<p>By combining ab initio downfolding with cluster dynamical mean-field theory, we study the degree of correlations in monolayer, bilayer, and bulk breathing-mode kagome van der Waals materials Nb<sub>3</sub>(F, Cl, Br, I)<sub>8</sub>. Our new material-specific many-body model library shows that in low-temperature bulk structures the Coulomb correlation strength steadily increases from I to Br, Cl, and F, allowing us to identify Nb<sub>3</sub>I<sub>8</sub> as a weakly correlated insulator whose gap is only mildly affected by the local Coulomb interaction. Nb<sub>3</sub>Br<sub>8</sub> and Nb<sub>3</sub>Cl<sub>8</sub> are strongly correlated insulators, whose gaps are significantly influenced by Coulomb-induced vertex corrections. Nb<sub>3</sub>F<sub>8</sub> is a prototypical bulk Mott insulator whose gap is initially opened by strong correlation effects. Angle-resolved photoemission spectroscopy measurements comparing Nb<sub>3</sub>Br<sub>8</sub> and Nb<sub>3</sub>I<sub>8</sub> allow us to experimentally confirm these findings by revealing spectroscopic footprints of the degree of correlation. Our calculations further uncover how the thickness and the stacking affect the degree of correlations and predict that the entire material family can be tuned into correlated charge transfer or Mott-insulating phases upon electron or hole doping. Our magnetic property analysis based on our model parameter library additionally confirms that interlayer magnetic interactions likely drive the lattice phase transition to the low-temperature structures. The accompanying bilayer hybridization through interlayer dimerization yields magnetic singlet-like ground states in the Cl, Br, and I compounds. We further prove that all low-temperature compounds are dynamically stable and that electron-phonon coupling to the low-energy subspace is suppressed. Our findings establish Nb<sub>3</sub>X<sub>8</sub> as a robust, versatile, and tunable class for van der Waals-based Coulomb and Mott engineering with a rich phase diagram and allow us to speculate on the symmetry-breaking effects necessary for the recently observed Josephson diode effect in NbSe<sub>2</sub>/Nb<sub>3</sub>Br<sub>8</sub>/NbSe<sub>2</sub> heterostructures.</p>}},
  author       = {{Aretz, Joost and Grytsiuk, Sergii and Liu, Xiaojing and Feraco, Giovanna and Knekna, Chrystalla and Waseem, Muhammad and Dan, Zhiying and Bianchi, Marco and Hofmann, Philip and Ali, Mazhar N. and Katsnelson, Mikhail I. and Grubišić-Čabo, Antonija and Strand, Hugo U.R. and Van Loon, Erik G.C.P. and Rösner, Malte}},
  issn         = {{2160-3308}},
  language     = {{eng}},
  number       = {{4}},
  publisher    = {{American Physical Society}},
  series       = {{Physical Review X}},
  title        = {{From Strong to Weak Correlations in Breathing-Mode Kagome van der Waals Materials : Nb<sub>3</sub>(F, Cl, Br, I)<sub>8</sub> as a Robust and Versatile Platform for Many-Body Engineering}},
  url          = {{http://dx.doi.org/10.1103/wr7w-nfhg}},
  doi          = {{10.1103/wr7w-nfhg}},
  volume       = {{15}},
  year         = {{2025}},
}