Topological semimetal state and field-induced Fermi surface reconstruction in the antiferromagnetic monopnictide NdSb

We report the experimental realization of a Dirac semimetal state in NdSb, a material with antiferromagnetic ground state. The occurrence of a topological semimetal state has been well supported by our band structure calculations and the experimental observation of chiral-anomaly-induced negative magnetoresistance. A field-induced Fermi surface reconstruction is observed in response to the change of spin polarization. The observation of a topological semimetal state in a magnetic material provides an opportunity to investigate the magnetotopological phenomena.

Figure 1

(a) Magnetoresistance and (b) Hall resistivity ${\rho }_{\mathrm{xy}}$ of NdSb in the range of 0–8 T, with the magnetic field applied perpendicular to the current and sample plane. (c) SdH oscillations vs $1/{\mu }_{0}H$ in the range of 2–8 T. (d) FFT spectra of the SdH oscillations in (c).

Figure 2

(a) Magnetization vs magnetic field curves of the NdSb single crystal. (b) $M-H$ curve between 9 T and 11 T at 1.8 K. Arrows indicate the direction of sweeping field. Inset: critical fields as a function of temperature. (c) High-field MR $\mathrm{\Delta }\rho /{\rho }_0$ measured at different temperatures, with the magnetic field applied perpendicular to the current and sample plane. (d) The magnetoresistance in the range of 0–14 T at 0.39 K. Inset: $H_{\mathrm{C}}$ as a function of temperature.

Figure 3

The Fermi surfaces calculated for (a) AFM state (spin up and spin down are the same) and FM state with (b) spin up and (c) spin down. Band structures are plotted along different $k$ paths for (d, g) AFM state and (e, f, h) FM state, respectively. Dashed lines indicate the Fermi level. The Fermi surface is characteristic of Fermi pockets centered at X, K, and $\mathrm{\Gamma }$. (i) High-symmetry points in the Brillouin zone. U1 and U2 are adjacent equivalent points for crystalline symmetry.

Figure 4

(a) Low-field MR taken along different magnetic field directions at 2 K for sample A. The schematic diagram in (a) illustrates the measurement geometry. $\theta ={90}^{\circ }$ means parallel magnetic field and electrical current. Inset: lower MR part shows negative MR at $\theta ={90}^{\circ }$. (b) MR measured in different angles around $\theta ={90}^{\circ }$ (from 78° to 97.2°). (c) MR measured at various temperatures with $\theta ={90}^{\circ }$. The lines from 2 K to 200 K are shifted vertically by 0, 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6, respectively. (d) Fittings for the negative MR data at 2 K. Solid and dashed lines represent the fitted curves with chiral anomaly and WL formulas, respectively. (e) Angle-dependent and (f) temperature-dependent chiral coefficients. Solid curve represents the fitting results using the formula $C_{\mathrm{W}}\propto v_{\mathrm{F}}^3{\tau }_{\mathrm{v}}/\left(T^2+\mathrm{\Delta }{E}^2/{\pi }^2\right)$.

Figure 5

(a) MR measured at different angles around $\theta ={90}^{\circ }$ (from 82° to 98°) at 2 K for sample B. (b) MR taken between multiple pairs of contacts to rule out the current jetting effect. (c) Fitting results of the negative MR data at 2 K and $\theta ={90}^{\circ }$. Solid line represents the fitted curve with chiral anomaly formula. (d) Angle-dependent chiral coefficients.

Figure 6

(a) MR taken along different magnetic field directions at 2 K for sample C. (b) MR measured at different angles around $\theta ={90}^{\circ }$ (from 81° to 99°). (c) MR measured at various temperatures with $\theta ={90}^{\circ }$. (d) Angle-dependent chiral coefficients.

Figure 7

(a) SdH oscillations vs $1/{\mu }_{0}H$ of NdSb. Inset: oscillation at 0.39 K showing a transition at about 9.6 T. (b) FFT spectra of the SdH oscillations in (a). (c) FFT spectra of $\alpha$ branch at different temperatures. Inset: temperature dependence of the oscillation frequency of the $\alpha$ branch. (d) Comparison of FFT spectra for high field and low field in the frequency range of 0–300 T.