RIKEN Accel. Prog. Rep. 50 (2017)

Ⅲ-2. Atomic & Solid State Physics (Muon)ȝSSR study of ferromagnetic fluctuationsin heavily overdoped Bi-2201 cuprates
K. Kurashima,䠆1 T. Adachi,䠆2,䠆3 T. Kawamata,䠆1,䠆2 T. Noji,䠆1 I. Watanabe,䠆2 and Y. Koike䠆1,䠆2
High-temperature superconductivity in cuprates is known
to emerge by hole doping into the antiferromagnetic (AF)Mott insulators. Superconducting (SC) transition
temperature Tc indicates the maximum in the optimally
doped regime and the superconductivity disappears withheavy overdoping. Theoretical studies in this decade1,2)
have suggested that the decrease in Tc with hole doping in
the overdoped (OD) regime is related to the development offerromagnetic (FM) fluctuations. In fact, it has beenreported from zero-field (ZF) ȝSR, ab-plane electricalresistivity ȡab and magnetization measurements that the FM
fluctuations are observed in non-SC heavily overdoped(HOD) La2-xSrxCuO4.3) However, because the FM
fluctuations have been observed only in La2-xSrxCuO4 thusfar, the universality of the FM fluctuations in cuprates isstill unclear.
To investigate the universality of the FM fluctuations, weperformed ȡab, magnetization, and ȝ65 measurements onBi-2201 cuprates.4) It was found that the temperaturedependence of ȡab is proportional to T4/3 in the OD andHOD regimes in a wide temperature range between 2-310 K.
This dependence is a characteristic of metals with
two-dimensional FM fluctuations according to theself-consistent renormalization (SCR) theory.5) The
magnetization curves in the HOD regime show a tendency
to be saturated in high magnetic fields below 20 K. This is aprecursor phenomenon to the formation of a possible FMorder. Transverse-field (TF) ȝ65 measurements on HOD
Bi-2201 also show that muon spin relaxation rate Ȝincreases with decreasing temperature below 100 K and thatthe enhancement of Ȝ is more pronounced in 9.5 T than in 3T. These results suggest that the spin correlation isenhanced by the application of a magnetic field, which isconsistent with the existence of FM fluctuations. To further
investigate the temperature and doping dependences of theFM fluctuations in Bi-2201, we performed ZF-ȝSR
measurements on non-SC HOD (Tc < 2 K) and SC OD (Tc =13 K) Bi1.76Pb0.35Sr1.89CuOį single crystals (Bi-2201[A])using a MiniCryo and a 3He cryostat at RIKEN-RAL. The
hole concentration per Cu of p was estimated from thethermoelectric power at 290 K.
Figure 1 shows the temperature dependence of Ȝ in the
single crystals of non-SC HOD (p = 0.274) and SC OD (p =0.236) Bi-2201[A]. The results of HOD
Bi1.71Pb0.32Sr1.97CuOį (Bi-2201[B]) with p = 0.264 atJ-PARC, Japan, are also shown. In the HOD Bi-2201[A]and HOD Bi-2201[B], the enhancement of Ȝ is observed
below 200 K, suggesting development of the spincorrelation. For the OD Bi-2201[A], we find that Ȝ shows asmall increase with decreasing temperature. These results
suggest that the spin correlation develops with hole dopingin the HOD and OD regime, which is consistent with theexistence of FM fluctuations in the HOD regime. In light of
the resistivity results, WKHHQKDQFHPHQWRIȜEHORZ.LV
due to the development of the two-dimensional FMcorrelation.
From the temperature and doping dependences of Ȝ, weconclude that the FM fluctuations exist in HOD and OD
Bi-2201, and that the FM fluctuations are enhanced withhole doping. The existence of FM fluctuations is, therefore,a universal feature in HOD cuprates.

Bi-2201[A], p = 0.274
Bi-2201[B]p = 0.264
Bi-2201[A]p = 0.236

Fig. 1. Temperature dependence of Ȝ in HOD and OD
Bi-2201[A] and HOD Bi-2201[B].
References1) A. Kopp et al., Proc. Natl. Acad. Sci. USA 104, 6123 (2007).
2) B. Barbiellini, T. Jarlborg, Phys. Rev. Lett. 101, 157002 (2008).
3) J. E. Sonier et al., Proc. Natl. Acad. Sci. USA 107, 17131(2007).
4) K. Kurashima et al., J. Phys: Conf. Ser. 568, 022003 (2014).
5) Y. Hatatani, T. Moriya, J. Phys. Soc. Jpn. 64, 3434 (1995).

䠆1

Department of Applied Physics, Tohoku University
RIKEN Nishina Center
䠆3
Department of Engineering and Applied Sciences, Sophia University
䠆2- 232 -