Analysis of the gap in high-temperature superconductors using photoemission spectroscopy

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:6464177

Wells, B O

The discovery of the cuprate superconductors had led to intensive research activity aimed at discovering the mechanism of high temperature superconductivity. A key feature in the electronic structure of a superconductor is the energy gap in the excitation spectrum. While gaps have been detected in the cuprate superconductors, traditional techniques for measuring the gap often give confusing or inconsistent results. The high transition temperatures and correspondingly large gaps of the cuprate superconductors have allowed photoemission spectroscopy to be used for the first time as a technique for studying the superconducting gap. Advantages of photoemission include that it is a direct measure of the gap, the surface studied is by necessity a clean, well defined region with variable depth, and the gap can be measured as a function of position in k-space. The largest disadvantage of photoemission as a tool for studying the gap is that the best resolution available so far is only on the order of the gap size. This makes a determination of gap size difficult. The authors have used photoemission to study the behavior of the gap near the surface of Bi2Sr2CaCu2O(8 + delta) and its variation as a function of k position. They have found that the gap does not diminish near the surface, an indication of the highly two dimensional nature of these materials. Photoemission experiments have shown no evidence of a proximity effect in a metal overlayer. They have also found that the gap is anisotropic in k space within the planes themselves. In particular, by measuring how the gap varies with k, information on the symmetry of the gap function can be obtained. Their data is consistent with a mixed s+id symmetry gap and possibly with a pure d wave gap. Determining the symmetry of the gap provides one of the most stringent experimental constraints on the theory of high T[sub c] superconductivity yet found.

• Research Organization: Stanford Univ., CA (United States)
• OSTI ID: 6464177
• Resource Relation: Other Information: Ph.D. Thesis
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HIGH-TC SUPERCONDUCTORS
ENERGY GAP
BISMUTH OXIDES
CALCIUM OXIDES
COPPER OXIDES
ELECTRONIC STRUCTURE
PHOTOELECTRON SPECTROSCOPY
STRONTIUM OXIDES
TRANSITION TEMPERATURE
ALKALINE EARTH METAL COMPOUNDS
BISMUTH COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
ELECTRON SPECTROSCOPY
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
SPECTROSCOPY
STRONTIUM COMPOUNDS
SUPERCONDUCTORS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
360207* - Ceramics
Cermets
& Refractories- Superconducting Properties- (1992-)