Angle-resolved photoemission study of dispersive and narrow-band $5f$ states in UAsSe

Single crystals of ferromagnetic UAsSe have been investigated by angle-resolved photoemission spectroscopy (ARPES) in the photon energy range between $20\mathrm{eV}$ and $110\mathrm{eV}$. Electron kinetic energy intensities are collected as a function of angle and mapped onto the materials reciprocal space. Energy-band mapping has been carried out both for a several-eV-wide energy interval as well as for a narrow energy interval of less than $1\mathrm{eV}$ from the Fermi energy. The main features of the deduced energy bands can be explained by band-structure calculations. In the interval close to the Fermi energy, the very high energy and momentum resolution allows the observation of a narrow, yet dispersive photoemission peak mainly of $5f$ character situated within $50\mathrm{meV}$ of the Fermi energy. The Lorentzian linewidth was found to be about $35\mathrm{meV}$ with a dispersion of $30\mathrm{meV}$ along the $\Gamma$ to $Z$ direction and $40\mathrm{meV}$ dispersion along the $\Gamma$ to $X$ direction in the Brillouin zone. We have also found broader (linewidth about $70\mathrm{meV}$), hybridized $f$-character bands with a conventional dispersion of about $1\mathrm{eV}$ along the $\Gamma$ to $X$ and the $Z$ to $R$ directions in the Brillouin zone. An intriguing electronic structure emerges for UAsSe in which both relatively dispersive and narrow $5f$ bands are present. The occurrence of $5f$-band dispersions stipulates that the electronic structure of UAsSe requires lattice periodicity to be taken into account.

Figure 1

(a) Crystallographic unit cell of UAsSe in the PbFCl type of crystal structure. For crystals with $T_C=108\mathrm{K}$, $a=3.997\pm 0.001\mathrm{\AA }$, $c=8.402\pm 0.001\mathrm{\AA }$ (Ref. 12). The magnetic moments on the uranium sites are indicated by arrows. (b) Brillouin zone of UAsSe.

Figure 2

Magnetic susceptibility of the UAsSe sample under investigation. The Curie temperature was determined as $108\mathrm{K}$. Measurements of magnetization as a function of field at $T=5\mathrm{K}$ (not shown here) revealed that magnetization saturates at a value smaller than but close to $1.5{\mu }_B$.

Figure 3

The Fermi edge of platinum compared with near-$E_F$ features of UAsSe. The peak of UAsSe is located very close to the Fermi edge. The dash-dotted line shows the fitting of the PES data of UAsSe.

Figure 4

(Color online) Normal-emission ARPES of UAsSe ($\Gamma \text{−}Z$ direction in the Brillouin zone) taken at $12\mathrm{K}$ within $950\mathrm{meV}$ (a) and $150\mathrm{meV}$ (b) of the Fermi edge. Binding energy in (c) is the same as in (b), but the intensity is normalized to the maximum. Spectra marked in red show the spectra nearest to the $\Gamma$ point of the Brillouin zone whereas spectra marked in blue show the $Z$ point of the Brillouin zone.

Figure 5

(Color online) High-resolution ARPES spectra of UAsSe taken at a photon energy of $44\mathrm{eV}$ ($\Gamma \text{−}X$ direction in the Brillouin zone) within $950\mathrm{meV}$ (a) and $150\mathrm{meV}$ (b) of the Fermi edge. Binding energy in (c) is the same as in (b), but the intensity is normalized to the maximum.

Figure 6

(Color online) High-resolution ARPES spectra of UAsSe taken at a photon energy of $25\mathrm{eV}$ ($\Gamma \text{−}X$ direction in the Brillouin zone) within $950\mathrm{meV}$ (a) and $150\mathrm{meV}$ (b) of the Fermi edge. Binding energy in (c) is the same as in (b).

Figure 7

(Color online) High-resolution ARPES spectra of UAsSe taken at a photon energy of $34\mathrm{eV}$ ($Z\text{−}R$ direction in the Brillouin zone) within $950\mathrm{meV}$ (a) and $150\mathrm{meV}$ (b) of the Fermi edge. Binding energy in (c) is the same as in (b).

Figure 8

Normal-emission spectra taken at Fano resonance $(h\nu =98\mathrm{eV})$ and antiresonance $(h\nu =92\mathrm{eV})$ at $12\mathrm{K}$.

Figure 9

(Color online) Comparison of the experimental ARPES energy-band spectrum (taken at $h\nu =40\mathrm{eV}$) and the computed LSDA energy bands, assuming full spin polarization. The experimental band positions are indicated by the colors, orange color depicting a low-energy-band response, blue color a high-energy-band intensity. Note the good overall agreement between the experimental and computed energy bands, including the $5f$ bands near the Fermi level.

Figure 10

(Color online) As Fig. 9, but showing the LSDA energy bands computed assuming no spin polarization. Some parts of the bands near the Fermi edge are better captured.