arXiv subjects

Y. Tanabe

Publications and source records attributed to Y. Tanabe.

24 records · Page 2Linked to original sources

arXiv2010

Hole-trapping by Ni, Kondo effect and electronic phase diagram in non-superconducting Ni-substituted La2-xSrxCu1-yNiyO4

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 muon-spin-relaxation (muSR) 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 Ni2+ 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 Ni2+ 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 Ni2+ to a metallic state with Kondo-like behavior due to Ni2+ spins, and the quantum phase transition is crossover-like due to the phase separation into short-range magnetically ordered and metallic regions.

cond-mat.supr-con↗

arXiv2009

Magnetic-susceptibility and specific-heat studies on the inhomogeneity of superconductivity in the underdoped La_2-x_Sr_x_CuO_4_

The possible inhomogeneity of superconductivity has been investigated by means of bulk-sensitive probes, using La_2-x_Sr_x_CuO_4_ (LSCO) single crystals from the underdoped to optimally doped regime. Measurements of the magnetic susceptibility, chi, on field cooling and specific heat have revealed that both the absolute value of chi at 2 K, regarded as corresponding to the superconducting (SC) volume fraction in a sample, and the Sommerfeld constant, reflecting the density of states of quasiparticles at the Fermi level, exhibit significant dependence on x, namely, on the hole concentration. This is the first experimental work strongly suggesting that a phase separation into SC and normal-state regions takes place in the underodped regime of LSCO as well as in the overdoped regime.

cond-mat.supr-con↗

arXiv2007

Cu-spin dynamics in the overdoped regime of La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ probed by muon spin relaxation

Muon-spin-relaxation measurements have been performed for the partially Zn-substituted La_2-x_Sr_x_Cu_1-y_Zn_y_O_4_ with y=0-0.10 in the overdoped regime up to x=0.30. In the 3 % Zn-substituted samples up to x=0.27, exponential-like depolarization of muon spins has been observed at low temperatures, indicating Zn-induced slowing-down of the Cu-spin fluctuations. The depolarization rate decreases with increasing x and almost no fast depolarization of muon spins has been observed for x=0.30 where superconductivity disappears. The present results suggest that the dynamical stripe correlations exist in the whole superconducting regime of La_2-x_Sr_x_CuO_4_ and that there is no quantum critical point at x~0.19.

cond-mat.supr-con↗

arXiv2007

Weak coupling d-wave BCS superconductivity and unpaired electrons in overdoped La_{2-x}Sr_{x}CuO_{4} single crystals

The low-temperature specific heat (SH) of overdoped La_{2-x}Sr_{x}CuO_{4} single crystals (0.178=<x=<0.290) has been measured. For the superconducting samples (0.178=<x=<0.238), the derived gap values (without any adjusting parameters) approach closely onto the theoretical prediction Δ_{0}=2.14k_{B}T_{c} for the weak-coupling d-wave BCS superconductivity. In addition, the residual term γ(0) of SH at H=0 increases with x dramatically when beyond x~0.22, and finally evolves into the value of a complete normal metallic state at higher doping levels, indicating growing amount of unpaired electrons. We argue that this large γ(0) cannot be simply attributed to the pair breaking induced by the impurity scattering, instead the phase separation is possible.

cond-mat.supr-con↗

arXiv2005

Can buckling account for the features seen in graphite's Raman spectra?

Raman scattering data were collected on graphite monochromator. Spectra were interpreted in terms of the space group $P6_3mc$, a subgroup of space group $P6_3/mmc$. The latter has commonly been used for the interpretation of Raman scattering data. Space group $P6_3mc$ corresponds to the buckling of graphene sheets and is consistent with many spectral features. Both the first and second order scattering were considered. Many first order results (most notably the assignments of the band at 1350 and the peak at 1620 cm$^{-1}$) were found to agree with previous observations [Y. Kawashima and G. Katagiri, Phys. Rev. B \textbf{66}, 104109 (2002)] carried out on highly oriented pyrolytic graphite samples. To check the consistency of the model, symmetry analysis was applied to the second order spectra. Also a simple test for buckling model was done.

cond-mat.mtrl-sci↗

arXiv2005

Superconducting Volume Fraction in Overdoped Regime of La_2-x_Sr_x_CuO_4_: Implication for Phase Separation from Magnetic-Susceptibility Measurement

We have grown a single crystal of La_2-x_Sr_x_CuO_4_ in which the Sr concentration, x, continuously changes from 0.24 to 0.29 in the overdoped regime and obtained many pieces of single crystals with different x values by slicing the single crystal. From detailed measurements of the magnetic susceptibility, chi, of each piece, it has been found that the absolute value of chi at the measured lowest temperature 2 K, |chi_2K_|, on field cooling rapidly decreases with increasing x as well as the superconducting (SC) transition temperature. As the value of |chi_2K_| is regarded as corresponding to the SC volume fraction in a sample, it has been concluded that a phase separation into SC and normal-state regions occurs in a sample of La_2-x_Sr_x_CuO_4_ in the overdoped regime.

cond-mat.supr-con↗