The unusual non-linear effects in hopping conduction of single-crystal La₂CuO_{4 + delta} with excess oxygen has been observed. The resistance is measured as a function of the 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). That is, 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 symbol Х exp (T₀/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 the 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.

• Белевцев Борис Йосипович (1944–2012) (фізико-математичні науки)
• Далакова Ніна Вікторівна (фізико-математичні науки)
• Панфілов Анатолій Сергійович (фізико-математичні науки)

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