Influence of strong electron irradiation on fluctuation conductivity and pseudogap in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>YB</mml:mi><mml:msub><mml:mi mathvariant="normal">a</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:msub><mml:mi mathvariant="normal">u</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mrow><mml:mn>7</mml:mn><mml:mo>−</mml:mo><mml:mi>δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math> single crystals

Abstract

The effect of high-energy electron irradiation on the temperature dependences of the resistivity ρ(), fluctuation conductivity (FLC), and pseudogap (PG) Δ*() of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mi>YB</a:mi><a:msub><a:mi mathvariant="normal">a</a:mi><a:mn>2</a:mn></a:msub><a:mi mathvariant="normal">C</a:mi><a:msub><a:mi mathvariant="normal">u</a:mi><a:mn>3</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mrow><a:mn>7</a:mn><a:mo>−</a:mo><a:mi>δ</a:mi></a:mrow></a:msub></a:mrow></a:math> (YBCO) single crystals containing virtually no twins was studied. A linear increase in the resistivity and a linear decrease in the superconducting (SC) transition temperature <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"><f:msub><f:mi>T</f:mi><f:mi>c</f:mi></f:msub></f:math> with increasing irradiation doses φ were observed. For relatively small φ, the linear <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"><g:msub><g:mi>T</g:mi><g:mi>c</g:mi></g:msub></g:math> can be described by the Abrikosov-Gorkov (AG) pair breaking theory, and for large φ, by the Emery-Kivelson (EK) theory, which takes into account the suppression of <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"><h:msub><h:mi>T</h:mi><h:mi>c</h:mi></h:msub></h:math> by quantum phase fluctuations caused by irradiation defects. As FLC shows, at the average value of <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"><i:mrow><i:msub><i:mi>φ</i:mi><i:mn>3</i:mn></i:msub><i:mo>=</i:mo><i:mn>2.5</i:mn><i:mo>×</i:mo><i:msup><i:mrow><i:mn>10</i:mn></i:mrow><i:mn>19</i:mn></i:msup><i:mspace width="0.16em"/><i:mi mathvariant="normal">e</i:mi><i:mo>/</i:mo><i:mi mathvariant="normal">c</i:mi><i:msup><i:mrow><i:mi mathvariant="normal">m</i:mi></i:mrow><i:mn>2</i:mn></i:msup></i:mrow></i:math>, which corresponds to the AG-EK crossover, the distance between the conducting <n:math xmlns:n="http://www.w3.org/1998/Math/MathML"><n:mrow><n:mi>Cu</n:mi><n:msub><n:mi mathvariant="normal">O</n:mi><n:mn>2</n:mn></n:msub></n:mrow></n:math> planes, <p:math xmlns:p="http://www.w3.org/1998/Math/MathML"><p:msub><p:mi>d</p:mi><p:mn>01</p:mn></p:msub></p:math>, as well as the coherence lengths along the <q:math xmlns:q="http://www.w3.org/1998/Math/MathML"><q:mi>c</q:mi></q:math> axis, <r:math xmlns:r="http://www.w3.org/1998/Math/MathML"><r:msub><r:mi>ξ</r:mi><r:mi mathvariant="normal">c</r:mi></r:msub></r:math>(0), and the region of SC fluctuations, <t:math xmlns:t="http://www.w3.org/1998/Math/MathML"><t:mrow><t:mi mathvariant="normal">Δ</t:mi><t:msub><t:mi>T</t:mi><t:mi>fl</t:mi></t:msub></t:mrow></t:math>, increase sharply, and the two-dimensional contribution of the Maki-Thompson fluctuations (2D-MT) unexpectedly changes to the two-dimensional contribution of the Aslamazov-Larkin (2D-AL). Surprisingly, no features in ρ(φ) and <v:math xmlns:v="http://www.w3.org/1998/Math/MathML"><v:msub><v:mi>T</v:mi><v:mi>c</v:mi></v:msub></v:math>(φ) indicating the AG-EK crossover are observed. At the same time, at <w:math xmlns:w="http://www.w3.org/1998/Math/MathML"><w:msub><w:mi>φ</w:mi><w:mn>3</w:mn></w:msub></w:math>, a sharp increase in the opening temperature of PG, *, as well as the value of PG, Δ*, is observed, which indicates a possible decrease in DOS under the influence of defects. With a further increase in φ, all the parameters of PG and its dimensions are greatly reduced, and an unusual shape of Δ*() is found. However, quite unexpectedly, at <x:math xmlns:x="http://www.w3.org/1998/Math/MathML"><x:mrow><x:msub><x:mi>φ</x:mi><x:mn>5</x:mn></x:msub><x:mo>=</x:mo><x:mn>5.6</x:mn><x:mo>×</x:mo><x:msup><x:mrow><x:mn>10</x:mn></x:mrow><x:mn>19</x:mn></x:msup><x:mspace width="0.16em"/><x:mi mathvariant="normal">e</x:mi><x:mo>/</x:mo><x:mi mathvariant="normal">c</x:mi><x:msup><x:mrow><x:mi mathvariant="normal">m</x:mi></x:mrow><x:mn>2</x:mn></x:msup></x:mrow></x:math> the temperature dependences of both FLC and PG demonstrate curves typical for well-structured YBCO, regardless of the number of defects.

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