Hole trapping by Ni, Kondo effect, and electronic phase diagram in nonsuperconducting Ni-substitutedLa2−xSrxCu1−

Abstract

In order to investigate the electronic state in the normal state of high-Tc cuprates in a wide range of temperature and hole-concentration, specific-heat, electrical-resistivity, magnetization and muonspin-relaxation (µSR) measurements have been performed in non-superconducting Ni-substituted La2−xSrxCu1−yNiyO4 where the superconductivity is suppressed through the partial substitution of Ni for Cu without disturbing the Cu-spin correlation in the CuO2 plane so much. In the underdoped regime, it has been found that there exist both weakly localized holes around Ni and itinerant holes at high temperatures. With decreasing temperature, all holes tend to be localized, followed by the occurrence of variable-range hopping conduction at low temperatures. Finally, in the ground state, it has been found that each Ni 2+ ion traps a hole strongly and that a magnetically ordered state appears. In the overdoped regime, on the other hand, it has been found that a Kondo-like state is formed around each Ni 2+ spin at low temperatures. In conclusion, the ground state of non-superconducting La2−xSrxCu1−yNiyO4 changes upon hole doping from a magnetically ordered state with the strong hole-trapping by Ni 2+ to a metallic state with Kondo-like behavior due to Ni 2+ spins, and the quantum phase transition is crossover-like due to the phase separation into short-range magnetically ordered and metallic regions.

Theoretical Study of Electronic States and Excitation Spectra in Ni-Substituted Cuprates

“…The x-ray absorption fine structure (XAFS) experiment also supports the argument that holes are strongly bound at Ni impurities [3]. In addition, it has been reported that all holes tend to be localized even when hole concentration is larger than Ni concentration [4].…”

Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La2−xSrxCu<

“…These results indicate that a Fermiliquid-like ground state is realized in overdoped LSCO, as revealed from the specific-heat and electrical-resistivity measurements in the overdoped regime of Ni-substituted La 2−x Sr x Cu 1−y Ni y O 4 . [29,30] That is, the electronic state based upon the strong electron correlation in the underdoped regime might change to be Fermi-liquid-like in the overdoped regime.…”

“…[18][19][20] In underdoped YBCO, it has been suggested from nuclear-magnetic-resonance measurements that Zn tends to develop the magnetic correlation. [21,22] In the case of the substitution of magnetic Ni, recently, it has been suggested that Ni operates to pin the dynamical stripe correlations to the same degree as Zn, [23] taking into account the hole-trapping effect of Ni [24][25][26][27][28][29][30] that a hole is localized around a Ni 2+ ion leading to the formation of the so-called Zhang-Rice doublet [27]. This indicates that Ni is no longer regarded as a magnetic impurity but an electrostatic impurity [31] in HTSC.…”

μSR Studies on Magnetism in High-Tc Cuprates

“…As to the state of substituted Ni, later, it has been found that substituted Ni tends to trap a hole, forming a Zhang-Rice doublet state with the effective S ¼ 1=2 similar to that of Cu 2+ from neutron scattering, 57,58) magnetic susceptibility, 59) μSR, 60) x-ray absorption fine structure, 61) specific heat, 62,63) and a theoretical work using numerical exact diagonalization calculations. 64) This may be one reason why the effects of the Ni substitution are smaller than those of the Zn substitution.…”