Scanning Tunneling Spectroscopy Sensitive to Layer Structure of BSCCO |
| M. Aleszkiewicz, P. Aleszkiewicz and J. Raułuszkiewicz Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa, Poland |
| Received: August 7, 1996; revised version: December 16, 1996 |
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| Scanning tunneling microscopy images and scanning tunneling spectroscopy characteristics were measured at 4.2 K in liquid helium bath on the cleaved in air a-b surface of Bi2Sr2CaCu2O8 (BSCCO-2212). Electronic densities of states and superconductivity parameters Δ and Γ evaluated from dI/dV characteristics depend on tip-sample distance s: with shortening of the distance s superconducting gap structure becomes more distinct, i.e. Δ increases and Γ decreases. We explain this phenomenon as a non-vacuum tunneling, where for longer s tunneling electrons reach only the surface contamination layer on non-metallic BiO top-surface layer, whereas for shorter s tunneling electrons penetrate also deeper lying CuO layers reflecting their superconducting properties. The dependence of Δ on s is evaluated. This result allows to understand better the non-vacuum scanning tunneling microscopy imaging: by adjusting properly the tip-sample distance one can select suitable local density of states contributing dominantly to the scanning tunneling microscopy images taken on BSCCO. |
| DOI: 10.12693/APhysPolA.91.597 PACS numbers: 74.72.Hs, 61.16.Ch, 68.65.+g |