Saturation of resistivity and Kohler's rule in Ni-dopedLa1.85Sr0.15CuO4cuprate

Abstract

We present the results of electrical transport measurements of La1.85Sr0.15Cu1−yNiyO4 thin singlecrystal films at magnetic fields up to 9 T. Adding Ni impurity with strong Coulomb scattering potential to slightly underdoped cuprate makes the signs of resistivity saturation at ρsat visible in the measurement temperature window up to 350 K. Employing the parallel-resistor formalism reveals that ρsat is consistent with classical Ioffe-Regel-Mott limit and changes with carrier concentration n as ρsat ∝ 1/ √ n. Thermopower measurements show that Ni tends to localize mobile carriers, decreasing their effective concentration as n ∼ = 0.15 − y. The classical unmodified Kohler's rule is fulfilled for magnetoresistance in the nonsuperconducting part of the phase diagram when applied to the ideal branch in the parallel-resistor model.

Pseudogap in underdoped cuprate seen in longitudinal magnetoresistance

“…In the whole investigated Ni-doping range up to y = 0.08, as we have shown previously [27], ρ(T) in the 150 K-350 K interval is extremely well described by the simple parallel-resistor formula:…”

“…The temperature behavior of resistance was monitored on the small pieces cut from the targets. The x-ray powder diffraction analysis revealed no impurity phases in all the final targets and confirmed their tetragonal K 2 NiF 4 -type structure [27,29].…”

“…For a more precise determination of the downward deviation, the exact value of ρ sat is essential. The obtained dependence of ρ sat on mobile carrier concentration n in LSCNO [27] agrees with that predicted by Boltzmann theory for the IRM limit calculated [44] for 'small' Fermi surface with n holes, ρ IRM = ( √ 2πℏ/e 2 )d/ √ n ∼ = 0.68/ √ n mΩ cm, d ∼ = 6.6 Å being the average distance between the adjacent CuO 2 planes and n ∼ = 0.15 − y [27,28]. The only reason to use fitted ρ sat and not calculated ρ IRM is sample-dependence of ρ sat for a given y, which is mainly caused by 10% uncertainty in sample thickness determination.…”

“…The magnetoresistance (MR) measurements were performed on the LSCNO samples selected on the basis of minimal residual resistivity and/or maximal T c from over 30 ones measured previously at zero field [27]. The achieved precision is much better than that in the previous study carried out on the rotator with the use of PPMS electronics (figure 1).…”

“…In our previous report regarding the electrical transport in La 1.85 Sr 0.15 Cu 1−y Ni y O 4 (LSCNO) [27], we have shown that resistivity in the system saturates at the value expected from the classical Boltzmann theory if immobilization of holes in the vicinity of Ni ions is taken into account [28]. In the current study, we focus on magnetotransport and provide a bridge between zero-field transport of underdoped cuprate analyzed in the frame of parallel-resistor model and a sharp feature found in longitudinal magnetoresistance (LMR) that indicates pseudogap opening.…”