Surface conductivity in antiferromagnetic semiconductor ${\mathrm{CrSb}}_2$

The contribution of bulk and surface to the electrical resistance along crystallographic $b$ and $c$ axes as a function of crystal thickness gives evidence for temperature-independent surface states in an antiferromagnetic narrow-gap semiconductor ${\mathrm{CrSb}}_2$. Angle-resolved photoemission spectroscopy shows a clear electronlike pocket in the $\mathrm{\Gamma }-Z$ direction which is absent in the bulk band structure. First-principles calculations also confirm the existence of metallic surface states inside the bulk gap. Whereas combined experimental probes point to enhanced surface conduction similar to topological insulators, surface states are trivial since ${\mathrm{CrSb}}_2$ exhibits no band inversion.

Figure 1

In both directions, $R\left(T\right)$ is well described by a thermally activated semiconducting bulk contribution with a surface contribution. Size dependence of the electrical resistivity for current flow along the (a) $b$ axis and (b) $c$ axis. The resistivities along both axes have a size-dependent plateau from 50 to 80 K (red arrows). The insets show the definition of the sample dimensions. Temperature dependence of the normalized electrical resistance along the (c) $b$ axis and (d) $c$ axis. Solid lines represent fitting using a two-channel conductance model which gives the conductivity for each conducting channel. (e) and (f) show the relationship between the normalized crystal sizes and the ratio of surface contribution to conductance along the $b$ and $c$ axes at different temperatures.

Figure 2

(a) ARPES spectra at the ${\mathrm{\Gamma }}_0-Z_0$ cut in the Brillouin zone measured at 20 K show an electron pocket which is absent in the bulk band-structure calculations. (b) Hall resistivity at 20 K for different samples. Solid lines are fittings. (c) Hall effect measurements show a transition from one-band to two-band behavior with decreasing sample sizes, which confirms the increasing contribution from the surface state with decreasing sample size. Temperature dependence of the $R_H$ (S1) and high-field $R_H$ (S2 and S3).

Figure 3

(a) Conductivity vs temperature below 20 K. The sample labels are described in the text. Solid lines are two-band model fitting. (b) Conductivity of the surface (solid) and bulk state (open symbols).

Figure 4

Surface band structures. (a)–(c) Surface structures of ${\mathrm{CrSb}}_2$ for $ac, ab$, and $bc$ planes, respectively. The red dots highlight the surface states. Surface states correspond to the AFM magnetic configuration. The Fermi energy is set to zero.