Ⅲ-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 52 (2019)µSR study of the Cu-spin correlation in the electron-underdoped
Pr1.3-x La0.7 Cex CuO4+δ (x = 0.05) single crystals
T. Adachi,∗1,∗2 K. Kawabata,∗2 S. Onishi,∗2 A. Takahashi,∗3 Y. Koike,∗3 and I. Watanabe∗1

∗1

∗2
∗318

Pr1.3-xLa0.7CexCuO4+δ

16Raw Asymmetry (%)

It has widely been believed in electron-doped highT c cuprates with the so-called T’-structure that an
antiferromagnetic (AF) order is formed in a parent
compound and underdoped samples. Formerly, however, it has been reported that the superconductivity
appears even in the parent compound and underdoped
samples through the appropriate reduction of excess
oxygen from as-grown thin ﬁlms1) and polycrystals,2)
resulting in a completely diﬀerent phase diagram fromthat formerly obtained. These suggest that the superconductivity in the electron-doped cuprates cannot
be understood in terms of carrier doping into Mott
insulators as in the case of the hole-doped cuprates.
Moreover, a raising question is whether or not the Cuspin correlation is developed in superconducting (SC)samples.
Recently, through improved reduction annealing,
we have prepared SC single crystals of the underdoped Pr1.3-x La0.7 Cex CuO4+δ (PLCCO) with x =0.05 − 0.10 whose ground states had been believed to
be AF.3,4) Our recent zero-ﬁeld (ZF) µSR measurements of PLCCO with x = 0.104,5) have revealed that,through the reduction annealing, a long-range AF order changes to a short-range one coexisting with thesuperconductivity. Moreover, it has been found thatthe further reduction brings about the destruction of
the short-range AF order and the increase in the SC
transition temperature T c . However, in samples withhigh T c values, the Cu-spin correlation has been foundto be developed at low temperatures, suggesting theintimate relation between the developed Cu-spin correlation and superconductivity.
In order to investigate the doping dependence of
the Cu-spin correlation, we have performed ZF-µSR
measurements of lightly electron-doped PLCCO withx = 0.05 using a MiniCryo at RIKEN-RAL.
For the as-grown sample of x = 0.05, it has beenfound that a long-range AF order is formed below theNeel temperature TN ∼ 250 K and T N decreases downto ∼ 110 K for the moderately reduced sample. Figure 1 shows ZF-µSR time spectra of the further reduced sample of PLCCO (x = 0.05) with Tc ∼ 27 K. It
is found that the spectrum at 200 K shows slow depolarization of muon spins due to nuclear dipole ﬁelds at
the muon site. With decreasing temperature, the depolarization of muon spins becomes fast gradually andthe muon spin precession is observed below ∼ 100 K,RIKEN Nishina Center
Department of Engineering and Applied Sciences, Sophia
University
Department of Applied Physics, Tohoku University- 177 -x = 0.05

141210T = 200 K
150 K
110 K
100 K
80 K
10 K

8602468

Time (µsec)

101214Fig. 1. Zero-field µSR time spectra of the further reduced
Pr1.3-x La0.7 Cex CuO4+δ (x = 0.05) with Tc ∼ 27 K.

indicating the formation of a long-range AF order. At
the lowest temperature of 10 K, however, it is foundthat the slow depolarization is still observed in a longtime region and the amplitude of the muon-spin precession is small, suggesting that the long-range AF ordered region is not 100% in the further reduced sample
but coexists with the slowly ﬂuctuating region of Cu
spins. From the analysis of the spectra, it has been
estimated that the volume fraction of a magneticallyordered region is ∼ 25% and the slowly ﬂuctuating region exhibiting the superconductivity is ∼ 75%. These
results suggest that the long-range AF order and superconductivity with a high T c value coexist with eachother in the further reduced sample of PLCCO withx = 0.05. In the ideally reduced sample of x = 0.05,
the AF order would disappear and the superconductivity would appear homogeneously under the development of the Cu-spin correlation, which is probably thecharacteristic of the electron-doped high-T c cuprates.
References
1) O. Matsumoto et al., Physica C 469, 924 (2009).
2) T. Takamatsu et al., Appl. Phys. Express. 5, 073101(2012).
3) T. Adachi et al., J. Phys. Soc. Jpn. 82, 063713 (2013).
4) T. Adachi et al., Condens. Matter 2, 23 (2017).
5) T. Adachi et al., J. Phys. Soc. Jpn. 85, 114716 (2016).