Multiple Magnetic Topological Phases in Bulk van der Waals Crystal ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$

The magnetic van der Waals crystals ${\mathrm{MnBi}}_2{\mathrm{Te}}_4/{({\mathrm{Bi}}_2{\mathrm{Te}}_3)}_n$ have drawn significant attention due to their rich topological properties and the tunability by external magnetic field. Although the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4/{({\mathrm{Bi}}_2{\mathrm{Te}}_3)}_n$ family have been intensively studied in the past few years, their close relatives, the ${\mathrm{MnSb}}_2{\mathrm{Te}}_4/{({\mathrm{Sb}}_2{\mathrm{Te}}_3)}_n$ family, remain much less explored. In this work, combining magnetotransport measurements, angle-resolved photoemission spectroscopy, and first principles calculations, we find that ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$, the $n=1$ member of the ${\mathrm{MnSb}}_2{\mathrm{Te}}_4/{({\mathrm{Sb}}_2{\mathrm{Te}}_3)}_n$ family, is a magnetic topological system with versatile topological phases that can be manipulated by both carrier doping and magnetic field. Our calculations unveil that its $A$-type antiferromagnetic (AFM) ground state stays in a ${\mathbb{Z}}_2$ AFM topological insulator phase, which can be converted to an inversion-symmetry-protected axion insulator phase when in the ferromagnetic (FM) state. Moreover, when this system in the FM phase is slightly carrier doped on either the electron or hole side, it becomes a Weyl semimetal with multiple Weyl nodes in the highest valence bands and lowest conduction bands, which are manifested by the measured notable anomalous Hall effect. Our work thus introduces a new magnetic topological material with different topological phases that are highly tunable by carrier doping or magnetic field.

Figure 1

(a) The schematic crystal structure of ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$. The blue arrows represent the ${\mathrm{Mn}}^{2+}$ spins in the $A$-type AFM structure. Green block: edge-sharing ${\mathrm{SbTe}}_6$ octahedra. Blue block: edge-sharing ${\mathrm{MnTe}}_6$ octahedra. (b) The room temperature powder x-ray diffraction peaks from the $ab$ plane of ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ crystal. Inset: Image of a typical ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ single crystal synthesized in this work. (c) The temperature dependent of transverse resistivity ${\rho }_{xx}$ at ${\mu }_{0}H=0\mathrm{T}$ measured from 2 to 100 K. The sketch for the four-probe measurements configuration is inserted. (d) The temperature dependent magnetic susceptibility $\chi$ under ${\mu }_{0}H=0.01\mathrm{T}$ for $H//c$ (green and red dotted lines) and $H//ab$ plane (blue lines). (e) The magnetic phase diagram of ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$. The solid dots and dotted line represent the critical magnetic fields as a function of temperature.

Figure 2

The band structures of (a) the $A$-type AFM state, (b) FM state with spin aligned along the $z$ direction (FMz), (c) FM state with $x$-direction spin (FMx), and (d) FM state with $y$-direction spin (FMy) of bulk ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ with considering the spin-orbital coupling effect. Here Fermi levels are set to zero and spin directions are remarked by blue arrows.

Figure 3

(a) Magnetoresistance ${\rho }_{xx}$ with $I//ab$ plane and $H//c$ at various temperatures. (b) The anomalous Hall resistivity ${\rho }_{xy}^A$. (c) The anomalous Hall conductivity ${\sigma }_{xy}^A$ at various temperatures. (d) The plot of ${\rho }_{xy}^A/(M{\rho }_{xx})$ vs ${\rho }_{xx}$, where the red dashed line denotes the linear fit when the temperature is below 8 K. (e) The calculated anomalous Hall conductivities of ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ for the three different ferromagnetic states as a function of varied Fermi energy, where the actual Femi energy is set as zero.

Figure 4

(a) ARPES intensity plot along the $\mathrm{\Gamma }-K$ direction measured at $hv=50$, 60, 70, 80, and 90 eV at 15 K. The red arrows point out the surface states. (b) Calculated band structure along the $\mathrm{\Gamma }-K$ direction of SL termination. ARPES intensity mapped along the $\mathrm{\Gamma }-K$ direction of (c) ${\mathrm{MnSb}}_4{\mathrm{Te}}_7$ and (d) $\mathrm{Mn}{({\mathrm{Bi}}_{0.15}{\mathrm{Sb}}_{0.85})}_4{\mathrm{Te}}_7$ collected at 60 eV. (e) Constant-energy surface of the Dirac cone cut for $\mathrm{Mn}{({\mathrm{Bi}}_{0.15}{\mathrm{Sb}}_{0.85})}_4{\mathrm{Te}}_7$.