RESUMO
The cuprate high-temperature superconductors exhibit many unexplained electronic phases, but the superconductivity at high doping is often believed to be governed by conventional mean-field Bardeen-Cooper-Schrieffer theory1. However, it was shown that the superfluid density vanishes when the transition temperature goes to zero2,3, in contradiction to expectations from Bardeen-Cooper-Schrieffer theory. Our scanning tunnelling spectroscopy measurements in the overdoped regime of the (Pb,Bi)2Sr2CuO6+δ high-temperature superconductor show that this is due to the emergence of nanoscale superconducting puddles in a metallic matrix4,5. Our measurements further reveal that this puddling is driven by gap filling instead of gap closing. The important implication is that it is not a diminishing pairing interaction that causes the breakdown of superconductivity. Unexpectedly, the measured gap-to-filling correlation also reveals that pair breaking by disorder does not play a dominant role and that the mechanism of superconductivity in overdoped cuprate superconductors is qualitatively different from conventional mean-field theory.
RESUMO
We report on the fabrication and performance of a new kind of tip for scanning tunneling microscopy. By fully incorporating a metallic tip on a silicon chip using modern micromachining and nanofabrication techniques, we realize so-called smart tips and show the possibility of device-based STM tips. Contrary to conventional etched metal wire tips, these can be integrated into lithographically defined electrical circuits. We describe a new fabrication method to create a defined apex on a silicon chip and experimentally demonstrate the high performance of the smart tips, both in stability and resolution. In situ tip preparation methods are possible and we verify that they can resolve the herringbone reconstruction and Friedel oscillations on Au(111) surfaces. We further present an overview of possible applications.
RESUMO
Spectroscopic-imaging scanning tunneling microscopy is a powerful technique to study quantum materials, with the ability to provide information about the local electronic structure with subatomic resolution. However, as most spectroscopic measurements are conducted without feedback to the tip, it is extremely sensitive to vibrations coming from the environment. This requires the use of laboratories with low-vibration facilities combined with a very rigid microscope construction. In this article, we report on the design and fabrication of an ultra-stable scanning tunneling microscope (STM) for spectroscopic-imaging measurements that operates in ultra-high vacuum and at low temperatures (4 K). We start from existing designs with sapphire as the main material and improve the stiffness further by performing finite element analysis calculations for the main components of the microscope to guide design choices on the geometry of the parts. With this strategy, we construct a STM head with measured lowest resonant frequencies above f 0 = 13 kHz for the coarse approach mechanism, a value three times higher than what has been previously reported and in good agreement with the calculations. This allows us to achieve an average vibration level of â¼6 fm / H z , without a dedicated low-vibration lab. We demonstrate the microscope's performance with topographic and spectroscopic measurements on the correlated metal Sr2RhO4, showing the quasiparticle interference pattern in real and reciprocal space with high signal-to-noise ratio.
