Abstract Body

Study of the Cu-spin correlation is indispensable in elucidating the mechanism of superconductivity in high-T_c cuprates. In the hole-doped cuprates, neutron-scattering [1] and muon-spin-relaxation (μSR) [2] measurements revealed that the antiferromagnetic (AF) spin correlation weakened with overdoping of holes and disappeared in the non-superconducting (SC) heavily overdoped regime, suggesting the intimate relation between the AF spin correlation and superconductivity. In the electron-doped cuprate Pr_1-xLaCe_xCuO₄, on the other hand, neutron-scattering experiments suggested the robust AF correlation in non-SC heavily overdoped regime [3], whereas μSR measurements suggested the disappearance of the development of Cu-spin correlation together with superconductivity in the heavily overdoped regime [4]. However, details remain unclear because of predominant effects of the Pr³⁺ moment on the μSR spectra.

In this study, to clarify the relationship between the Cu-spin correlation and superconductivity in the electron-doped cuprates, we performed transport and μSR measurements of La_2-xCe_xCuO₄ (LCCO) without rare-earth moments.

Overdoped LCCO (x = 0.13, 0.17) target samples were prepared by solid-state reaction [5]. Thin films were fabricated on the SrTiO₃ substrate by the pulsed-laser deposition method using a third harmonic of Nd:YAG laser (wavelength : 355 nm) as a light source, which is different from the previous report [6]. By varying the oxygen partial pressure and reduction annealing conditions, LCCO thin films with x = 0.13 and 0.17 having T_c = 20 K and 3 K were fabricated, respectively. μSR measurements using low-energy muons were performed at the MuE4 beamline at the Paul Scherrer Institut in Switzerland.

Figures show zero-field μSR spectra of optimally reduced LCCO with x = 0.13 and 0.17. Fast relaxation of muon spins is observed at low temperatures in both samples, indicating the development of the Cu-spin correlation. As the temperature dependence of the spectra is almost identical between x = 0.13 and 0.17, this suggests that the development of the Cu-spin correlation is less doping-dependent, which is different from the results of Pr_1-xLaCe_xCuO₄ [4]. The development of the Cu-spin correlation at x = 0.17, where superconductivity is almost suppressed, may be related to a recently proposed ferromagnetic order [7].

References

[1] S. Wakimoto et al., Phys. Rev. Lett. 72, 064521 (2005).

[2] Risdiana et al., Phys. Rev. B 77, 054516 (2008).

[3] M. Fujita et al., Phys. Rev. Lett. 101, 107003 (2008).

[4] M. A. Baqiya et al., Phys. Rev. B 100, 064514 (2019).

[5] T. Yamada et al., Jpn. J. Appl. Phys. 33, L168 (1994).

[6] A. Sawa et al., Phys. Rev. B 66, 014531 (2002).

[7] T. Sarkar et al., Science 368, 532 (2020).

Acknowledgment

Helpful advises on the preparation of LCCO thin films by A. Maeda, F. Nabeshima, I. Tsukada are gratefully acknowledged. A part of the resistivity and Hall measurements were performed by using the commercial apparatus (PPMS) at the CROSS-user laboratory.

Figure 1. Zero-field μSR spectra of La_2-xCe_xCuO₄ with (a) x = 0.13 and (b) x = 0.17.

Keywords: High-T_c superconducting cuprate, Thin film, Spin correlation, Muon spin relaxation