Magnetic Frustration Enforced Electronic Reconstruction in Ni intercalated NbSe$_{2}$: Suppression of Electronic Orders

TL;DR

This work addresses how magnetic intercalation in NbSe$_{2}$ alters competing electronic orders. By combining synthesis, magnetotransport, ARPES, and DFT, the authors find a magnetically frustrated AFM ground state with $T_{order}=23.5$ K and anisotropic $\theta_{CW}$, while CDW and superconductivity are suppressed down to $0.3$ K. ARPES reveals a Ni-induced Fermi-surface reconstruction, including a $\overline{\Gamma}$-centered electron pocket and a shifted van Hove singularity, which is supported by DFT for Ni-containing configurations. These results establish a regime where magnetic frustration and electronic reconstruction cooperate to destroy conventional electronic orders, highlighting a path to engineer correlated phases in low-dimensional TMDs through partial intercalation and disorder.

Abstract

We investigate the single crystals of Ni$_{0.19}$NbSe$_2$, revealing that Ni intercalation profoundly alters the physical properties of NbSe$_2$. Magnetic measurements clearly show that the system is magnetically frustrated with antiferromagnetic ordering below 23.5\,K, with an irreversibility temperature near 10\,K, and a magnetic hysteresis with a small net magnetic moment. Overall, the system can be described as an inhomogeneous antiferromagnetic phase with magnetic disorder and magnetic frustration. We found two Curie-Weiss temperatures of -80\,K for the field in the {\it ab}-plane and -137\,K for the field out of plane, which are a consequence of anisotropic interactions in spin space and favor an orientation of the spin along the {\it c}-axis. Temperature-dependent resistivity shows a complete suppression of both charge density waves and superconducting order down to 300\,mK. Angle-resolved photoemission spectroscopy at 84\,K reveals a $\overlineΓ$-centered electron pocket in Ni$_{0.19}$NbSe$_2$, which is absent in pristine NbSe$_2$. The electronic structure results show a shift of the van Hove singularity (VHS), which is the main cause of the suppression of the electronic orders. These results align with recent theoretical predictions that Ni intercalation with cationic disorder favors frustrated antiferromagnetic stripe states, shifts the VHS and reconstructs the Fermi surface in NbSe$_2$. Our findings position Ni$_{0.19}$NbSe$_2$ within a magnetically frustrated, non-superconducting regime, highlighting how partial intercalation and disorder drive complex magnetic order and the Fermi surface reconstruction in low-dimensional quantum materials.

Figures (8)

• Figure 1: (a) Schematic of the proposed AFM2 magnetic structure in Ni$_{0.25}$NbSe$_2$, illustrating both out-of-plane ferromagnetic J$_{out}$ and in-plane antiferromagnetic J$_{in}$ coupling. The red and blue arrows represent the spin-up and spin-down of the Ni atoms. In the Ni$_{0.19}$NbSe$_2$ samples, there are Ni vacancies. (b) Core-level photoemission spectra of Ni$_{0.19}$NbSe$_2$, showing characteristic peaks from Ni, Nb, and Se orbitals. Out-of-plane (k$_{z}$) dispersion (at E$_{F}$) and corresponding waterfall plots for (c, e) pristine and (d, f) Ni-intercalated NbSe$_{2}$, revealing modifications to the electronic structure upon intercalation.
• Figure 2: Magnetic measurements on Ni$_{0.19}$NbSe$_{2}$(a) Zero-field cooled warming (ZFC) and field cooled cooling (FCC) temperature dependence of magnetization, measured with magnetic field $H$ aligned either along the c-axis (red), or lying in the ab-plane (black). (b) Hysteresis loops obtained at 5 K for two field orientations. In the inset, we present a magnified view showing an unsaturated hysteresis loop.
• Figure 3: Temperature-dependent residual resistivity ratio (RRR) of pristine NbSe$_{2}$ and Ni$_{0.19}$NbSe$_{2}$. The pristine sample exhibits less pronounced CDW transition near 30 K and a clear superconducting transition around 7 K, both of which are absent in Ni$_{0.19}$NbSe$_{2}$, indicating the suppression of collective electronic states upon Ni intercalation. The main inset shows a magnified view of the low-temperature region, and the secondary inset displays the actual crystal samples used in the transport experiments.
• Figure 4: ARPES spectra at 85 K along $\overline{K}$-$\overline{\Gamma}$-$\overline{K}$ path measured at photon energies 24, 44, 54, 64, 104 and 120 eV showing the comparison between (upper panel) pristine NbSe$_{2}$ and (lower panel) Ni$_{0.19}$NbSe$_{2}$ with extra electron pocket at the $\overline{\Gamma}$ indicated by red arrows. The colorbar reports the intensity in arbitrary units.
• Figure 5: Fermi surface maps at 84 K of pristine NbSe$_2$ and Ni-interncalated NbSe$_2$ measured using ARPES. (a, b) Comparison of the Fermi surfaces for pristine NbSe$_2$ and Ni$_{0.19}$NbSe$_2$ resp. obtained from the sum of intensities of horizontal and vertical linear polarizations. The Ni-intercalated sample shows clear Fermi surface reconstruction, indicated by red arrows. (c, d) Fermi surface maps of NbSe$_2$ and Ni$_{0.19}$NbSe$_2$ obtained from the sum of intensities of left- and right-circular polarizations, further highlighting modifications in the electronic structure due to Ni intercalation (red arrows).