P04S

20AU018, 22AG005, 22BG004

BL-9A

Unexpected two-fold symmetry of the electronic structurein heavily overdoped Bi2201 observed by angle-resolved
photoemission spectroscopy
Y. Miyaia, S. Idetab, T. Kurosawac, M. Odad, K. Tanakae, M. Aritab
and K. Shimadab
aGraduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 7398526, Japanb
Hiroshima Synchrotron Radiation Center, Hiroshima University, Higashi-Hiroshima 739-8526, JapancFaculty of Science and Engineering, Muroran Institute of Technology, Muroran 050-8585, JapandDepartment of Physics, Hokkaido University, Sapporo 060-0809, Japane
UVSOR-III Synchrotron, Institute for Molecular Science, Okazaki 444-8585, Japan

Keywords: High-TC superconductor, ARPESHigh transition-temperature (TC) cuprate superconductors have attracted much interest since theirdiscovery in 1986 for their high TC as well as unusual physical properties such as a pseudogap [1] and a
Nematicity [2]. Superconductivity occurs in the CuO2 plane and the Cu 3dx2−y2 state forms the Fermi surface(FS). It has been widely believed that the CuO2 plane is four-fold symmetric so far. Recently, however,symmetry reduction of the electronic structure has been reported in Bi-based cuprate superconductors [2,3].
Note that the breaking of the four-fold rotational symmetry or nematicity has been also found in theelectronic structure of iron-based superconductors [4]. Although the nematicity in electron liquid has
attracted much interest, the rotational symmetry breaking in the electronic structure of high-TC cuprate
superconductors has not been directly clarified yet.
In this study, we examined the symmetry of the electronic structure of the cuprate superconductors
using high-resolution angle-resolved photoemission spectroscopy (ARPES). Here, as a suitable system forthis study, we have selected heavily overdoped Bi-based high-Tc cuprates, (Bi,Pb)2Sr2CuO6+δ (Pb-Bi2201)
because it has a single CuO2 plane in the unit cell and the superstructure reflections are suppressed by Pb
doping. Furthermore, the pseudogap disappears in the heavily overdoped sample and one can clearly see theentire FS in the normal state.
By mechanically rotating the sample, we found the difference of nodal distances for the two nodal
directions (#1 and #2 in the inset of Fig. 1(a)) at the Fermi level (𝐸𝐸F ). The two-fold symmetry was obvious
if we compared the observed FS with the four-fold symmetric theoretical FS given by the tight-binding
model. In addition, the ARPES spectral intensities at the 𝐸𝐸F were different for these two nodal directions.
To further examine many-body interactions, we have evaluated self-energies (Σ (#1) , Σ (#2) ) as shown in Figs.
1(a) and 1(b) along the two nodal directions #1 and #2 in the inset of Fig. 1(a). Since the experimentally
extracted real and imaginary parts of the self-energies satisfy the Kramers-Kronig relation, the two-foldanisotropy should be intrinsic, indicating that the many-body interactions such as the electron-electron andthe electron-boson (phonon) interactions are anisotropic in these two nodal directions. Note that theobserved symmetry breaking of the electronic structure is independent of temperature in the range usedin this study (20 – 260 K).
The two-fold symmetry of the electronic structures in the heavily overdoped Pb-Bi2201 may berelated to a charge order formation in heavily overdoped Pb-Bi2201 as observed by resonant inelastic X-ray
scattering [5]. Our results provide an insight for the intriguing physical properties such as the nematicity [2]and the ferromagnetic fluctuation [6] of the heavily overdoped Bi2201.

FIGURE 1. (a), (b) Experimentally obtained self-energy (Σ) along the orthogonal two nodal directions. Red and blue dots
indicate Σ(#1) and Σ(#2) extracted from #1 and #2 directions as shown in the inset of panel (a) respectively.
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M. Hashimoto et al., Nature Physics 10, 483 (2014).
S. Nakata et al., npj Quantum Materials 6, 86 (2021).
N. Auvray et al., Nature Communications 10, 5209 (2019).
H. C. Xu et al., Physical Review Letters 117, 157003 (2016).
Y. Y. Peng et al., Nature Materials 17, 697 (2018).
K. Kurashima et al., Physical Review Letters 121, 057002 (2018).