Predominantly Superconducting Origin of Large Energy Gaps in Underdoped<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Bi</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Sr</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">CaCu</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>8</mml:mn><mml:mo>+</mml:mo><mml:mi mathvariant="italic">δ</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>from Tunneling Spectroscopy
Annotatsiya
New tunneling data are reported in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$ which show quasiparticle excitation gaps, \ensuremath{\Delta}, reaching values as high as 60 meV for underdoped crystals with ${T}_{c}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}70\mathrm{K}$. These energy gaps are nearly 3 times larger than those of overdoped crystals with similar ${T}_{c}$. Despite the large differences in gap magnitude, the tunneling spectra display qualitatively similar characteristics over the entire doping range. Detailed examination of the spectra, including the Josephson ${I}_{c}{R}_{n}$ product measured in break junctions, indicates that these energy gaps are predominantly of superconducting origin.
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