Zhang, Y. -S.; Yang, Z.; Xiao, C.; Isobe, M.; Minola, M.; Takagi, H.; Huang, D. Substrate tuning of the structural and electronic transition in thin flakes of the excitonic insulator candidate Ta2NiSe5 Journal Article Commun. Phys. 9, 309 (2026), datadoi: 10.5281/zenodo.22107443. @article{zhangSubstrateTuningStructural2026,
title = {Substrate tuning of the structural and electronic transition in thin flakes of the excitonic insulator candidate Ta_{2}NiSe_{5}},
author = {Y. -S. Zhang and Z. Yang and C. Xiao and M. Isobe and M. Minola and H. Takagi and D. Huang},
url = {https://doi.org/10.1038/s42005-026-02888-x},
doi = {10.1038/s42005-026-02888-x},
year = {2026},
date = {2026-09-29},
urldate = {2026-09-01},
journal = {Commun. Phys.},
volume = {9},
pages = {309},
abstract = {Ta2NiSe5 continues to draw interest for its Tc = 326 K phase transition, whose dual electronic and structural nature reflects a complex interplay of electron-hole (excitonic) and electron-lattice interactions. The majority of studies that have attempted to decipher the relative importance of these interactions, particularly through charge tuning, have been focused on bulk samples. Here, we utilize an all-dry exfoliation and transfer protocol to isolate ultrathin flakes of Ta2NiSe5 on insulating Al2O3 and conducting Au. Using polarized Raman spectroscopy, we uncover the following substrate dependence: Four layers of Ta2NiSe5 on Al2O3 show a sharp structural and electronic transition that is lowered by roughly 40 K from the bulk Tc. Meanwhile, four layers of Ta2NiSe5 on Au undergo a structural and electronic transition that is much more gradual with respect to temperature and finishes roughly 150 K below the bulk Tc. The pronounced broadening points to an atomic-scale interface effect, wherein electrostatic screening and charge transfer from Au produces a Tc gradient perpendicular to the layers of the flake. We discuss the role of excitonic physics and suggest the possibility for interface engineering to pattern nanoscale junctions in Ta2NiSe5.},
note = {datadoi: 10.5281/zenodo.22107443},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ta2NiSe5 continues to draw interest for its Tc = 326 K phase transition, whose dual electronic and structural nature reflects a complex interplay of electron-hole (excitonic) and electron-lattice interactions. The majority of studies that have attempted to decipher the relative importance of these interactions, particularly through charge tuning, have been focused on bulk samples. Here, we utilize an all-dry exfoliation and transfer protocol to isolate ultrathin flakes of Ta2NiSe5 on insulating Al2O3 and conducting Au. Using polarized Raman spectroscopy, we uncover the following substrate dependence: Four layers of Ta2NiSe5 on Al2O3 show a sharp structural and electronic transition that is lowered by roughly 40 K from the bulk Tc. Meanwhile, four layers of Ta2NiSe5 on Au undergo a structural and electronic transition that is much more gradual with respect to temperature and finishes roughly 150 K below the bulk Tc. The pronounced broadening points to an atomic-scale interface effect, wherein electrostatic screening and charge transfer from Au produces a Tc gradient perpendicular to the layers of the flake. We discuss the role of excitonic physics and suggest the possibility for interface engineering to pattern nanoscale junctions in Ta2NiSe5. |
Gimpel, T.; Büttgen, N.; Prodan, L.; Tsurkan, V.; Tsirlin, A. A.; Nakamura, H.; Kézsmárki, I. Magnetic symmetry and hyperfine fields of V_4 tetrahedral clusters in the multiferroic lacunar spinel GeV4S8 Journal Article Phys. Rev. B 114, 154418 (2026), datadoi: (10.5281/zenodo.20604906). @article{xn3r-b7g6,
title = {Magnetic symmetry and hyperfine fields of V_4 tetrahedral clusters in the multiferroic lacunar spinel GeV_{4}S_{8}},
author = {T. Gimpel and N. Büttgen and L. Prodan and V. Tsurkan and A. A. Tsirlin and H. Nakamura and I. Kézsmárki},
url = {https://link.aps.org/doi/10.1103/xn3r-b7g6},
doi = {10.1103/xn3r-b7g6},
year = {2026},
date = {2026-09-18},
urldate = {2026-09-01},
journal = {Phys. Rev. B},
volume = {114},
number = {15},
pages = {154418},
abstract = {We use 51V nuclear magnetic resonance (NMR) spectroscopy to investigate the magnetic ground state of the lacunar spinel GeV4S8, which undergoes a structural distortion at 𝑇JT≈30K followed by an antiferromagnetic (AFM) ordering at 𝑇𝑁≈15K. According to our zero- and finite-field NMR data, the four V-sites of V4 clusters become magnetically inequivalent in the AFM state: Two of them share the same internal field, while the other two sites are characterized by different internal fields. The angular dependence of the 51V NMR lines, upon rotation of an external magnetic field about the pseudocubic [110] and [100] axes, reveals that the internal fields are either parallel to the orthorhombic 𝑎 axis at all four V-sites of the V4 tetrahedra, or they form an orthogonal pattern, where two V-sites have internal field along the 𝑎 axis and the other two along the 𝑏 axis. Based on these results, further supported by the observation of distinct spin-echo modulations of the inequivalent V-sites, we conclude that the magnetic space group of the AFM state is 𝑃𝑏𝑚𝑛21 or 𝑃𝑚𝑛′2′1.},
note = {datadoi: (10.5281/zenodo.20604906)},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We use 51V nuclear magnetic resonance (NMR) spectroscopy to investigate the magnetic ground state of the lacunar spinel GeV4S8, which undergoes a structural distortion at 𝑇JT≈30K followed by an antiferromagnetic (AFM) ordering at 𝑇𝑁≈15K. According to our zero- and finite-field NMR data, the four V-sites of V4 clusters become magnetically inequivalent in the AFM state: Two of them share the same internal field, while the other two sites are characterized by different internal fields. The angular dependence of the 51V NMR lines, upon rotation of an external magnetic field about the pseudocubic [110] and [100] axes, reveals that the internal fields are either parallel to the orthorhombic 𝑎 axis at all four V-sites of the V4 tetrahedra, or they form an orthogonal pattern, where two V-sites have internal field along the 𝑎 axis and the other two along the 𝑏 axis. Based on these results, further supported by the observation of distinct spin-echo modulations of the inequivalent V-sites, we conclude that the magnetic space group of the AFM state is 𝑃𝑏𝑚𝑛21 or 𝑃𝑚𝑛′2′1. |
Que, X.; He, Q.; Zhou, L.; Prodan, L.; Tsurkan, V.; Kézsmárki, I.; Takagi, H.; Huang, D. Tunable flat band on the surface of a rhombohedral kagome ferromagnet Unpublished (2026), arXiv.2609.19857. @unpublished{que2026tunableflatbandsurface,
title = {Tunable flat band on the surface of a rhombohedral kagome ferromagnet},
author = {X. Que and Q. He and L. Zhou and L. Prodan and V. Tsurkan and I. Kézsmárki and H. Takagi and D. Huang},
url = {https://arxiv.org/abs/2609.19857},
doi = {10.48550/arXiv.2609.19857},
year = {2026},
date = {2026-09-17},
urldate = {2026-09-01},
abstract = {A central goal in the exploration of kagome-based materials is the realization of a flat band that has meV bandwidth and lies close to the Fermi energy. The prevailing assumption is that band flattening originates from destructive hopping processes on the kagome lattice. We perform scanning tunneling microscopy (STM) on the layered kagome ferromagnet Fe3Sn2 and show that it indeed hosts a flat band near the Fermi energy, which is manifested as a sharp peak in the differential tunneling conductance. First-principles slab calculations reveal, however, that this band is flattened not by the destructive interference of intralayer hopping, but by interlayer hopping between rhombohedral-stacked kagome planes in Fe3Sn2, and is confined to the surface layer. This surface band, forming in the vicinity of the Brillouin zone corners K¯ and K′¯, exhibits rich magnetic-field dependence, including fine structure due to valley-symmetry breaking by rotated Fe moments, as well as a persistent diamagnetic shift associated with orbital magnetic moments, all reproduced by our calculations. Our results, highlighting the crucial role of layer stacking on the band structure of kagome magnets, demonstrate experimentally an alternative mechanism of generating magnetically tunable flat bands in atomically thin volumes of topological magnets.},
note = {arXiv.2609.19857},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
A central goal in the exploration of kagome-based materials is the realization of a flat band that has meV bandwidth and lies close to the Fermi energy. The prevailing assumption is that band flattening originates from destructive hopping processes on the kagome lattice. We perform scanning tunneling microscopy (STM) on the layered kagome ferromagnet Fe3Sn2 and show that it indeed hosts a flat band near the Fermi energy, which is manifested as a sharp peak in the differential tunneling conductance. First-principles slab calculations reveal, however, that this band is flattened not by the destructive interference of intralayer hopping, but by interlayer hopping between rhombohedral-stacked kagome planes in Fe3Sn2, and is confined to the surface layer. This surface band, forming in the vicinity of the Brillouin zone corners K¯ and K′¯, exhibits rich magnetic-field dependence, including fine structure due to valley-symmetry breaking by rotated Fe moments, as well as a persistent diamagnetic shift associated with orbital magnetic moments, all reproduced by our calculations. Our results, highlighting the crucial role of layer stacking on the band structure of kagome magnets, demonstrate experimentally an alternative mechanism of generating magnetically tunable flat bands in atomically thin volumes of topological magnets. |
