Magnetotransport study of Dirac fermions in ${\mathrm{YbMnBi}}_2$ antiferromagnet

We report quantum transport and Dirac fermions in ${\mathrm{YbMnBi}}_2$ single crystals. ${\mathrm{YbMnBi}}_2$ is a layered material with anisotropic conductivity and magnetic order below 290 K. Magnetotransport properties, nonzero Berry phase, and small cyclotron mass indicate the presence of Dirac fermions. Angular-dependent magnetoresistance indicates a possible quasi-two-dimensional Fermi surface, whereas the deviation from the nontrivial Berry phase expected for Dirac states suggests the contribution of parabolic bands at the Fermi level or spin-orbit coupling.

Figure 1

(a) Crystal and magnetic structure of ${\mathrm{YbMnBi}}_2$. Arrows show the ordered Mn magnetic moments, ${\mu }_{Mn}=4.3\left(1\right){\mu }_B$, refined at 4 K. The moments point along the $c$ axis; the magnetic space group describing the AFM order is $P{4}^{\prime }/n^{\prime }{m}^{\prime }m:(3/4,1/4,0|0,0,mz)(1/4,3/4,0|0,0,-mz)$. (b),(c) Neutron intensity patterns of (200) and (001) nuclear structural Bragg peaks, respectively, of a ${\mathrm{YbMnBi}}_2$ single crystal on the two-dimensional position-sensitive detector on a HB3a diffractometer, indicating perfect crystalline structure. (d),(e) Summary of the structural refinement of ${\mathrm{YbMnBi}}_2$ in the magnetically disordered phase at 310 K, and at 4 K where it is antiferromagnetically ordered. (f) High-resolution transmission electron microscopy (HRTEM) image and (g) corresponding electron diffraction pattern (EDP) viewed along the [110] direction. The inset in (g) is the FFT from the image shown in (f). (h) Structural refinement of powder-diffraction data. Ticks mark reflections, top row refers to the main phase, and bottom row refers to ${\mathrm{Bi}}_2{\mathrm{O}}_3$ due to sample preparation.

Figure 2

(a) Temperature dependence of in-plane resistivity $\left({\rho }_{ab}\right)$ for ${\mathrm{YbMnBi}}_2$ single crystals at 0 and 9 T, and out-of-plane resistivity $\left({\rho }_c\right)$ at 0 T. Inset shows the quadratic $T$ dependence at low temperature of ${\rho }_{ab}$ at 0 T. (b) Temperature dependence of the specific heat of ${\mathrm{YbMnBi}}_2$. Inset shows the fitting of the low-temperature part.

Figure 3

(a)–(c) Longitudinal and transverse in-plane resistivity vs field at different temperatures. SdH oscillatory component $\mathrm{\Delta }{\rho }_{xx}$. (b) is obtained after the background subtraction. (d) Field dependence of Hall conductivity ${\sigma }_{xy}$ at 2 K. (e) Temperature dependence of the oscillating amplitude of longitudinal oscillations at $1/B=0.33{\mathrm{T}}^{-1}$. The solid line is the fitting curve. Inset: Dingle plot for $\mathrm{\Delta }{\rho }_{xx}$. (f) LL index plots $1/B_n$ vs $n$. Inset: The Fourier transform spectrum of $\mathrm{\Delta }{\rho }_{xx}$.

Figure 4

(a) The SdH oscillatory component as a function of $1/B$ at various angles; the cartoon shows the geometry of the measurement setup. (b) FFT spectra of the SdH oscillations in (a). (a) and (b) use the same legend. (c) Angular dependence of the oscillation frequency. Sample 1 (S1) is the sample we used in this paper; sample 2 is the sample from the same batch and measured on the same probe. The cyan line is the fitting using the 2D model with $F\left(0\right)/cos\left(\theta \right)$; the dark yellow line is the ellipse model $F\left(0\right)/{({\varepsilon }^2{sin}^2\theta +{cos}^2\theta )}^{1/2}$ with an anisotropic factor $\varepsilon =-0.67$. The error bar is the peak width at half height of the FFT peaks. (d) Magnetoresistance as a function of the titled angle from the applied field. The red line is the fitting using the 2D model.

Figure 5

(a) The magnetic field dependence of the in-plane MR at different temperatures. (b) Log-log plot of MR vs magnetic field. (c) A Kohler plot for ${\mathrm{YbMnBi}}_2$. (d) Temperature dependence of the critical field $B^{*}$ (black squares); the red solid line is the fitting results using $B^{*}=(1/2e\hslash {\upsilon }_F^2)(k_{B}T+E_F){}^2$. The red circle corresponds to high-field MR linear coefficient $A_1$.