∙ Goal: the study of the resistivity mechanisms for thin HTSC films in different temperature regions:

 - Low temperature region (T<Tc) – manifestation of Kosterlitz – Thouless and Jensen – Minnhagen mechanisms,

- Region of fluctuation conductivity (T~Tc),

- Region of pseudogap state (T*>T>>Tc)

∙  Objects: epitaxial thin films YBa2Cu3O7-d (subtrate SrTiO3 and YAlO3, thickness 300 nm, laser sputtering) and Bi2Sr2Ca2Cu3O10 (substrate MgO, thickness 300 nm, ion sputtering)

∙  Methods: four point dc resistance measurements, current – voltage characteristics, Jc(T, B). Temperature stabilization ±5 mK.

Current - voltage characteristics of YBCO thin films at different temperatures near Tc(R=0)=88.2 K

Thin film YBa₂Cu₃O_6.85 (SrTiO₃ substrate)
Analysis of r(T) in the region of pseudo gap state Tc<T<T*

Thin film  Bi₂Sr₂Ca₂Cu₃O₁₀ (MgO substrate)
Analysis of  r(T) in the region of pseudogap state

Temperature dependence of excess conductivity
sD = 1/r(T) – 1/rn(T)
sD = AT (1 –T/T*)exp(D*/kT) ~ ns(T/T*)/exp(-D * /kT)

•         1 - sD (1/T),    2 – ln sD (1/T)

•         3  - linear approximation ln sD (1/T) = a + b/kT

•         4  - approximation lnsD = C + ln(1 –T/T*) + D*/kT.

•         5 – the same as 4 but D*(T) = qD* (1-T/T*)1/2, q » 2.6.

Temperature dependence of excess conductivity
sD = 1/r(T) – 1/rn(T)
sD = A(1 –T/T*)exp(D*/kT) ~ ns(T/T*)/exp(-D*/kT).

 

•         1 - sD (1/T),   2 – ln sD (1/T).

•         3  - linear approximation ln sD (1/T) = a + b/kT.

•         4  - approximation lnsD = C + ln(1 –T/T*) + D*/kT.

•         5 – the same as 4 but D*(T) = qD*(1-T/T*)1/2, q » 2.6.

Results

•         Relation of Jensen – Minnhagen theory can fit current – voltage characteristics of YBCO thin films at low currents and T£Tc. Low – temperature part of R(T) can be described by Kosterlitz – Thouless relation

•         Temperature dependence of excess conductivity for YBCO (123) and BiSrCaCuO (2223) thin films and single crystals exhibits an exponential behavior over a wide range of temperature. The assumption was made and justified that the exponent in the relation can be represented in the form D*/kT, where D* is the pseudogap.

•         The value and temperature dependence of pseudogap was obtained for thin films and single crystals of underdoped HTSC materials from resistivity measurements.

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The last update was made on November 25, 2004
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