Layered transition-metal pnictide SrMnBi${}_2$ with metallic blocking layer

The physical properties and the band structure of the layered pnictide SrMnBi${}_2$ were investigated. This compound has a crystal structure similar to that of the superconducting Fe pnictides, and is a bad metal with large residual resistivity. Magnetic order sets in at very high temperatures, around 290 K, as shown by magnetization, resistivity, and specific heat data. Band structure calculations using density functional theory (DFT) are consistent with the thermodynamic and transport measurements, suggesting a checkerboard antiferromagnetic (cAFM) ground state and a localized picture for the magnetism. Moreover, DFT results indicate that the Mn 3$d$ electrons are strongly correlated, and that, unlike in the known superconductors, the Sr-Bi${}_{\left(1\right)}$ layer is metallic. One more notable feature of the DFT calculation is the multiple Dirac-cone-like dispersion close to the Fermi level.

Figure 1

The measured powder X-ray diffraction pattern of SrMnBi${}_2$ (black symbols) together with the calculated positions (blue lines) for space group I4/mmm and lattice parameters $a$ $=$ 4.56 $\text{Å}$, $c$ $=$ 23.09 $\text{Å}$. Minute impurity peaks belonging to Bi are marked by asterisks [most of the marked peaks coincide with peaks for SrMnBi${}_2$ (blue vertical lines)].

Figure 2

The crystal structures of (a) SrMnBi${}_2$ (space group I4/mmm, from Ref.14), (b) hypothetical compound BaFeAs${}_2$ (space group P4/nmm, predicted in Ref. 13, and (c) BaFe${}_2$As${}_2$ (space group I4/mmm). The red atoms are alkaline earth atoms, the green atoms are transition metal atoms, and the blue atoms are pnictogen atoms. $\Delta z_T$ and $\Delta z_{\text{Pn}}$ represent the distance between adjacent $T$ layers, and the distance between Pn planes above and below the same $T$ plane, respectively.

Figure 3

Anisotropic $M\left(T\right)$ data for $H=1$ T. The two transitions at $T$${}_1$ and $T$${}_2$ are marked by vertical arrows (top inset). Bottom inset: high-temperature $M\left(T\right)$ data for $H\parallel ab$, showing the melting temperature for SrMnBi${}_2$ (vertical arrow).

Figure 4

$\rho \left(T\right)$ data for $H=0$ and current $i\parallel ab$, measured on warming (open symbols) and on cooling (full symbols). Inset is the linear fit of $\rho \sim T^2$ for cooling data, with the resistivity coefficient $A=0.125\mu \Omega \text{cm}/{\text{K}}^2$.

Figure 5

The transition temperatures could be obtained from maxima in (a) $d\left(MT\right)/dT$ (open symbols for $H\perp ab$ and full symbols for $H\parallel ab$) and (b) $d\rho /dT$ (measured on warming). (c) Specific heat $C_p\left(T\right)$ shows a broad peak at $T$${}_1$. Inset: $C_p/T$ vs $T^2$ (blue symbols), with a linear fit below $T$ $\approx$ 10 K (red line), from which the electronic specific heat coefficient $\gamma$ is determined to be $\gamma =36.5\mathrm{mJ}/\mathrm{mol}{\mathrm{K}}^2$.

Figure 6

The total and partial DOS of SrMnBi${}_2$ in PM state, with Bi${}_{\left(1\right)}$ and Bi${}_{\left(2\right)}$ defined in Fig. 2. Inset is the enlarged plot near the Fermi level.

Figure 7

Band structure of SrMnBi${}_2$ in PM state. The bands with red color are the Mn 3$d$ electrons, and the bands with green color are the 6$p$ bands from the Sr-Bi${}_{\left(1\right)}$ layer (Ref.30).

Figure 8

Band structure of SrMnBi${}_2$ in cAFM state. The color notation is the same as in Fig. 7.

Figure 9

The total and partial DOS of the AFM phase. Inset is an enlarged plot around the Fermi energy.

Figure 10

The Fermi surface of the PM phase for ${\mathrm{SrMnBi}}_2$ compound.