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

RIKEN Accel. Prog. Rep. 49 (2016)µSR study of the Cu-spin correlation in heavily electron-doped
high-Tc T’-cuprates
T. Adachi,∗1,∗2 M. A. Baqiya,∗3 I. Watanabe,∗1 and Y. Koike∗1,∗3
In the history of research on high-Tc superconductivity, numerous eﬀorts have been made to the establishment of the phase diagram of both hole-doped andelectron-doped cuprates. However, Matsumoto et al.
reported that superconductivity appears even in theparent compound of x = 0 and in a wide range ofx in Nd2−x Cex CuO4 with the so-called T’ structure
through the appropriate reduction of excess oxygenfrom the as-grown ﬁlms, resulting in a completely different phase diagram from that formerly suggested.1)
The superconductivity in the parent compounds of T’cuprates has also been conﬁrmed for polycrystalline
powdered samples of La1.8 Eu0.2 CuO4 .2) These suggest that the superconductivity in electron-doped T’cuprates cannot be understood in terms of the dopingof carriers into Mott insulators as in the case of holedoped cuprates.
Recently, through improved reduction annealing,
we have succeeded in obtaining high-quality superconducting (SC) single crystals of underdoped T’Pr1.3−x La0.7 Cex CuO4+δ with x = 0.05 − 0.10 whose
ground states were believed to be antiferromagnetic(AF).3) Transport measurements have revealed thatthe strongly localized state of carriers accompanied by
the pseudogap due to AF ﬂuctuations in the as-grown
crystal changes to a Kondo state without the pseudogap in the SC crystal through reduction annealing.
Moreover, our recent µSR measurements of SC crystalsof x = 0.10 have revealed fast depolarization of muon
spins and recovery of asymmetry in a long time region at low temperatures, suggesting the coexistence ofsuperconductivity accompanied by a short-range magnetic order.4) These results as well as the superconductivity in the parent compounds can be understoodin terms of our proposed band picture based on thestrong electron correlation.3,4)
One of the next issues is investigating how superconductivity disappears through Ce doping. Our previous µSR measurements of the SC polycrystal ofT’-Pr1−x LaCex CuO4+δ (PLCCO) with x = 0.14 revealed slowing down of the Cu-spin ﬂuctuations atlow temperatures, but no short-range magnetic order
was observed.5) Therefore, we performed µSR measurements using PLCCO single crystals in the heavily
overdoped regime of x = 0.17 and 0.20 to obtain detailed information on the Cu-spin correlation. ZF andlongitudinal-ﬁeld µSR measurements were carried out
∗1
∗2
∗3

RIKEN Nishina Center
Department of Engineering and Applied Sciences, SophiaUniversity
Department of Applied Physics, Tohoku University- 211 -using a MiniCryo and a ﬂy-past-type 3 He cryostat attemperatures down to 0.3 K at RIKEN-RAL.
Figure 1 shows ZF µSR spectra of heavily overdoped
PLCCO with x = 0.20 where superconductivity disappears. At high temperatures around 200 K, the depolarization of muon spins is slow, indicating that thedevelopment of the Cu-spin correlation is weak. It isfound that, with decreasing temperature, the depolarization of muon spins becomes fast due to the growing
eﬀect of Pr3+ moments. At low temperatures, it isfound that the recovery of the asymmetry in a longtime region corresponding to the development of theCu-spin correlation5) is negligibly small. This suggeststhat the Cu-spin correlation is barely developed in thenon-SC heavily overdoped regime of PLCCO. Combined with the results in the underdoped4) and optimally doped5) regimes, it is concluded that the Cu-spincorrelation is crucial for the appearance of superconductivity in T’-cuprates.

Fig. 1. Zero-field µSR time spectra of the nonsuperconducting heavily overdoped single crystal of T’Pr1−x LaCex CuO4+δ with x = 0.20.

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., arXiv: 1512.08095.
5) Risdiana et al., Phys. Rev. B 82, 014506 (2010).