Josephson scanning tunneling microscopy: A local and direct probe of the superconducting order parameter

Abstract

Direct measurements of the superconducting superfluid on the surface of vacuum-cleaved Bi2Sr2CaCu2O8(BSCCO) samples are reported. These measurements are accomplished via Josephson tunneling into the sample using a scanning tunneling microscope (STM) equipped with a superconducting tip. The spatial resolution of the STM of lateral distances less than the superconducting coherence length allows it to reveal local inhomogeneities in the pair wavefunction of the BSCCO. Instrument performance is demonstrated first with Josephson measurements of Pb films followed by the layered superconductor NbSe2. The relevant measurement parameter, the Josephson ICRN product, is discussed within the context of both BCS superconductors and the high transition temperature superconductors. The local relationship between the ICRN product and the quasiparticle density of states (DOS) gap are presented within the context of phase diagrams for BSCCO. Excessive current densities can be produced with these measurements and have been found to alter the local DOS in the BSCCO. Systematic studies of this effect were performed to determine the practical measurement limits for these experiments. Alternative methods for preparation of the BSCCO surface are also discussed.

53 pages, 26 figures, editorially accepted for Physical Review B

References in corpus (12)

• Scanning tunneling spectroscopy of high-temperature superconductors
• Visualizing pair formation on the atomic scale in the high-Tc superconductor Bi2Sr2CaCu2O8+d
• Distinct Fermi-Momentum Dependent Energy Gaps in Deeply Underdoped Bi2212
• Interplay of electron-lattice interactions and superconductivity in Bi2Sr2CaCu2O8+d
• Imaging the Two Gaps of the High-TC Superconductor Pb-Bi2Sr2CuO6+x
• Electronic Origin of the Inhomogeneous Pairing Interaction in the High-Tc Superconductor Bi2Sr2CaCu2O8+d
• Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}
• Imaging nanoscale Fermi surface variations in an inhomogeneous superconductor
• A distinct bosonic mode in an electron-doped high-transition-temperature superconductor
• Role of Inelastic Tunneling through the Barrier in Scanning Tunneling Microscope Experiments on Cuprates
• Subharmonic gap structure in superconducting scanning tunneling microscope junctions
• Josephson Effect in Pb/I/NbSe2 Scanning Tunneling Microscope Junctions