P15S

HiSOR, BL-1, BL-9A / SPring-8, BL-25SUFermi surface of chiral magnet Yb(Ni1-xCux)3Al9observed by ARPES
Y. Tanimotoa, M. Sugimotoa, R. Kamimoria, Y. Nakashimab, H. Satoc,
K. Yamagamid, M. Aritac, S. Kumarc, K. Shimadac, S. Nakamurae, S. Oharae
aGraduate School of Advanced Science and Engineering, Hiroshima University,
Higashi-Hiroshima 739-8526, Japanb
Faculty of Science, Hiroshima University, Higashi-Hiroshima 739-8526, JapancHiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-0046, JapandJapan Synchrotron Radiation Research Institute, Sayo 679-5148, JapaneGraduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan
Keywords: chiral magnetic crystal, helical magnetism, angle resolved photoemission spectroscopy

Trigonal YbNi3Al9 has a chiral crystal structure belonging to space group of R32 (No. 155) and is ofinterest as the first chiral magnetic alloy discovered in 4f electron compounds [1]. The localized Yb 4f spinsare magnetically ordered below T=3.4 K, ferromagnetic in the c-plane, and exhibit left-handed or righthanded helimagnetism with propagation vector q=(0, 0, 0.8) [2]. Substitution of Ni with Cu significantly
alters the magnetic interaction and shortens the helical propagation vector to q=(0, 0, 0.4) forYb(Ni0.94Cu0.06)3Al9. Spin-polarized conduction electrons are thought to be responsible for this phenomenon.
In this study, we have performed vacuum ultraviolet and soft x-ray angle-resolved photoemission
spectroscopy (VUV-ARPES and SX-ARPES) on YbNi3Al9 and Yb(Ni0.94Cu0.06)3Al9 to observe the Fermi
surface. The experiments were carried out at BL-1 and BL-9A of Hiroshima Synchrotron Radiation Center(HSRC), Hiroshima University for VUV-ARPES and at BL-25SU of SPring-8 for SX-ARPES. Singlecrystals used for the SX-ARPES measurements were synthesized by the flux-method [3].
VUV-ARPES revealed five hole-like Fermi surfaces around the Γ̅ points and an electronic Fermi surface̅ point for YbNi3Al9 and Yb(Ni0.94Cu0.06)3Al9. The Fermi surface of Yb(Ni0.94Cu0.06)3Al9 isaround the 𝐾
shrink compared to that of YbNi3Al9, although the feature is almost unchanged with the Cu substitution.
̅ directions of the surface
Figure 1(a) shows the SX-ARPES intensity plots of YbNi3Al9 along the Γ̅-𝑀Brillouin zone measured at hv=548 eV with circular-polarized light. Figure 1(b) shows the angle integratedspectrum. Two flat bands derived from the localized Yb2+ 4f7/2 states below the Fermi level (EF) and Yb2+
4f5/2 states at EB=1.4 eV are observed. Two hole-like bands around the Γ̅ point cross EF at kx=0.31 and 0.45
Å-1. These two hole-like bands are clearly observed in the VUV-ARPES spectra measured at hv=24 eV withs-polarized geometry.
Figure 2 represents the Fermi surface of YbNi3Al9 measured at hv=450~652 eV with circular- polarized
̅ direction of the surface
geometries. The horizontal and vertical axes are the wavenumbers kx along Γ̅-𝑀Brillouin zone and kz along the Γ-Z direction of the bulk Brillouin zone, respectively. A barrel-shaped Fermi
surface the with the minimum kx at the Γ point and the maximum kx at the Z point is observed, as indicatedby a black line. Inside it, in addition, we find another barrel-shaped Fermi surface. On the other hand, theFermi surface observed around kx=0.15 Å-1(white line) appears to be a drum-shaped Fermi surface with theminimum kx at the Z point and is closed between the Γ and Z points as indicated by the arrows. These Fermi
surfaces are quantitatively consistent with the Fermi surfaces inferred from de Haas-van Alphen effect [4].

̅ direction measured at hv=548 eV withFig. 1 (a) SX-ARPES intensity plots of YbNi3Al9 measured along the Γ̅-𝑀
circular-polarized light. (b) Angle integrated spectrum of (a).

Fig. 2 Fermi surfaces of YbNi3Al9 obtained from SX-ARPES spectra measured at hv=450~652 eV with circularpolarized light.

REFERENCES
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