Superconductivity effects in hopping conductivity of La2CuO4 single crystal with excess oxygen

Белевцев, Б. И.; Далакова, Н. В.; Панфилов, А. С.

doi:10.1063/1.593396

Cited by 8 publications

(14 citation statements)

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“…In Ref. [14,15] it was found that the transition from VRH to simple activation conduction [R ∝ exp(∆/kT )] occurs at temperatures below 20 K (the similar effect was described also before in Ref. [13]).…”

Section: Introductionsupporting

confidence: 70%

Non-linear effects in hopping conduction of single-crystal La2CuO4+δ

Белевцев

Далакова

Панфилов

1998

Low Temperature Physics

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The unusual non-linear effects in hopping conduction of single-crystal La 2 CuO 4+δ with excess oxygen has been observed. The resistance is measured as a function of applied voltage U (voltage controlled regime) in the temperature range 5 K < ∼ T < ∼ 300 K and voltage range 10 −3 -25 V. At relatively high voltage (approximately at U > 0.1 V) the conduction of sample investigated corresponds well to variable-range hopping (VRH). Namely, in the range 0.1 V< U < ∼ 1 V the conductivity does not depend on U (Ohmic behavior) and the temperature dependence of resistance R(T ) follows closely the Mott's law of VRH [R ∝ exp(T 0 /T ) 1/4 ]. In the range of highest applied voltage the conduction has been non-Ohmic: the resistance decreases with increasing U . This non-linear effect is quite expected in the frame of VRH mechanism, since the applied electric field increases the hopping probability. A completely different and unusual conduction behavior is found, however, in low voltage range (approximately below 0.1 V), where the influence of electric field and (or) electron heating effect on VRH ought to be neglected. Here we have observed strong increase in resistance at increasing U at T < ∼ 20 K, whereas at T > 20 K the resistance decreases with increasing U . The magnetoresistance of the sample below 20 K has been positive at low voltage and negative at high voltage. The observed unusual non-Ohmic behavior at low voltage range is attributable to inhomogeneity of the sample, and namely, to the enrichment of sample surface with oxygen during the course of the heat treatment of the sample in helium and air atmosphere before measurements. At low enough temperature (below ≈ 20 K) the surface layer with increased oxygen concentration is presumed to consist of disconnected superconducting regions in poor-conducting (dielectric) matrix. This allows to explain the observed unusual non-linear effects in the conduction of sample studied. The results obtained demonstrate that in some cases the measured transport properties of cuprate oxides can not be attributed to the intrinsic bulk properties. 72.20.Ht; 74.72Dn; 74.62Dh; Typeset using REVT E X 1

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Section: Introductionsupporting

confidence: 70%

Non-linear effects in hopping conduction of single-crystal La2CuO4+δ

Белевцев

Далакова

Панфилов

1998

Low Temperature Physics

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“…3). In previous studies, negative MR in the AF La 2 CuO 4+δ for the case of both the current and field parallel to CuO 2 was found and discussed to a certain degree [14,18]. The nature of the negative MR in rather low field H c and J a,b revealed in this work is not clear and is worthy of additional study.…”

Section: Resultsmentioning

confidence: 69%

“…In Ref. [14], a possible reason for this behavior is suggested to be determined by the presence of superconducting inclusions in insulating sample due to phase separation in La 2 CuO 4+δ .…”

Section: Resultsmentioning

confidence: 99%

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Magnetoresistive study of the antiferromagnetic–weak ferromagnetic transition in single-crystal La2CuO4+δ

Белевцев

Далакова

Savitsky

et al. 2004

Low Temperature Physics

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The resistive measurements were made to study the magnetic field-induced antiferromagnetic (AF) -weak ferromagnetic (WF) transition in La2CuO4 single-crystal. The magnetic field (DC or pulsed) was applied normally to the CuO2 layers. The transition manifested itself in a drastic decrease of the resistance in critical fields of 5-7 T. The study is the first to display the effect of the AF -WF transition on the conductivity of the La2CuO4 single-crystal in the parallel -to -CuO2 layers direction. The results provide support for the 3-dimensional nature of the hopping conduction of this layered oxide.

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