Band structure of CuMnAs probed by optical and photoemission spectroscopy

The tetragonal phase of CuMnAs progressively appears as one of the key materials for antiferromagnetic spintronics due to efficient current-induced spin-torques whose existence can be directly inferred from crystal symmetry. Theoretical understanding of spintronic phenomena in this material, however, relies on the detailed knowledge of electronic structure (band structure and corresponding wave functions) which has so far been tested only to a limited extent. We show that AC permittivity (obtained from ellipsometry) and UV photoelectron spectra agree with density functional calculations. Together with the x-ray diffraction and precession electron diffraction tomography, our analysis confirms recent theoretical claim [Phys. Rev. B 96, 094406 (2017)] that copper atoms occupy lattice positions in the basal plane of the tetragonal unit cell.

Figure 1

(a) Structure of the tetragonal phase of CuMnAs. In RTP, Cu/As/Mn atoms occupy the sites $S^1/S^2/S^3$. In the inverted phase, Cu and Mn atoms are swapped. (b)–(d) Electron diffraction (PEDT) patterns: (0kl)*, (hk0)*, and (hk1)* sections of the reciprocal space reconstructed from PEDT data (PETS program [13]). The conditions $h+k=2n$ on $hk0$, $h=2n$ on $h00$ and $k=2n$ on $0k0$ are characteristic of the $n$ glide.

Figure 2

AC permittivity of CuMnAs thin film determined by ellipsometry (for comparison, Im $\epsilon /{\epsilon }_0$ for orthorhombic bulk CuMnAs grown by other method [21] is shown by the dashed line; see Supplemental Material [12], Sec. III for growth details [22]). The GGA+$U$ model uses $U=1.7$ eV and $\mathrm{\Gamma }=0.7$ eV for the interband part and $\hslash {\omega }_p=3.26$ eV and $\hslash /2\tau =120$ meV for the intraband contribution.

Figure 3

The imaginary part of relative permittivity calculated for several values of $U$. The peak shifts blue with increasing $U$, the arrows indicate the position of the maximum. Inset: density of states per spin (and Mn-partial density of states shown in red) with a Mn-dominated peak just above the Fermi level (taken as $E=0$).

Figure 4

Based on the comparison between ellipsometry and GGA+$U$ calculations [23], this band structure ($U=1.7$ eV) seems to describe well CuMnAs in tetragonal phase.

Figure 5

Experimental angle-integrated photoemission (UPS, black squares) compared to the corresponding one-step model of photoemission. Theoretical data are shown for three values of $U$; labeled features are described in the text.