Download or read book Studies of the High T subscript c Superconductor Bi2Sr2CaCu20 subscript x Using Low Temperature Scanning Tunneling Microscopy written by Jin-Xiang Liu and published by . This book was released on 1993 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Studies of the High T subscript c Superconductor BilSrlCaCul0 subscript x Using Low Temperature Scanning Tunneling Microscopy written by Jin-Xiang Liu and published by . This book was released on 1993 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Studies of the High Tc Supercondctor Bi2Sr2CaCu20x Using Low Temperature Scanning Tunneling Microscopy written by Jinxiang Liu and published by . This book was released on 1993 with total page 200 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Studies of Superconductors Using a Low temperature Scanning Tunneling Microscope written by Roberta Kathryn Zasadzinski and published by . This book was released on 1995 with total page 266 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Variable Temperature Scanning Tunneling Microscopy Study of a High Temperature Superconductor Bi2Sr2CaCu2O8 delta written by Michael Vershinin and published by . This book was released on 2004 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Low Temperature Scanning Tunneling Microscope Study of Low dimensional Superconductivity on Metallic Nanostructures written by Jungdae Kim and published by . This book was released on 2010 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Superconductivity is a remarkable quantum phenomenon in which a macroscopic number of electrons form a condensate of Cooper pairs that can be described by a single quantum wave function. According to the celebrated Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity, there is a minimum length scale (the coherence length) below which the condensate has a rigid quantum phase. The fate of superconductivity in a system with spatial dimensions smaller than [the coherence length] has been the subject of intense interest for decades and recent studies of superconductivity in ultra-thin epitaxial metal films have revealed some surprising behaviors in light of BCS theory. Notably, it was found that superconductivity remains robust in thin lead films with thicknesses orders of magnitude smaller than the coherence length (i.e. in the extreme two dimensional limit). Such studies raise the critical question: what happens to superconductivity as all dimensions are reduced toward the zero dimensional limit? By controlling the lateral size of ultra thin 2D islands, we systematically address this fundamental question with a detailed scanning tunneling microscopy/spectroscopy study. We show that as the lateral dimension is reduced, the strength of the superconducting order parameter is also reduced, at first slowly for dimensions larger than the bulk coherence length, and then dramatically at a critical length scale of ~ 40nm. We find this length scale corresponds to the lateral decay length of the order parameter in an island containing regions of different heights and different superconducting strength. Overall, our results suggest that fluctuation corrections to the BCS theory are important in our samples and may need to be systematically addressed by theory.

Download or read book Subscript Mu SR Studies of High T Subscript C Superconductor Pb Subscript X Bi2 Subscript X Sr2 CaCu2O and Kondo Alloy Y1 Subscript X U Subscript X Pd3 written by Weidong Wu and published by . This book was released on 1995 with total page 228 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Terahertz Scanning Tunneling Microscopy of Metal and Superconductor Surfaces written by Howe Simpson and published by . This book was released on 2021 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: The advent of the terahertz scanning tunneling microscope (THz-STM) brings with it a new method of observing and characterizing the ultrafast dynamics of materials. The sub-nanometer spatial resolution of an ultra-high vacuum scanning tunneling microscope (UHV-STM) coupled with the sub-picosecond time resolution from a terahertz (THz) pulse allows for ultrafast measurements of surface dynamics across varying surface features down to the atomic scale. This thesis explores STM and THz-STM of metal and superconductor surfaces. High critical temperature superconductivity has been an area Bi2Sr2CaCu2O8 is an excellent candidate to study the superconductive process due to its high critical temperature of 95 K and ease of cleaving. STM and scanning tunneling spectroscopy measurements on the high-temperature superconductor Bi2Sr2CaCu2O8 are performed at 100 K and 55 K. STM and STS measurements were also performed on the surface of flat Au(111). Given gold's versatility as a substrate for many STM measurements, it is important to ensure that the STM system used in this study can replicate results that coincide with many other studies done on the surface of gold. The characteristics of the substrate such as flatness and cleanliness prior to deposition of other materials were investigated. The herringbone surface reconstruction of Au(111) was imaged and the topography was analysed with good agreement compared to other studies. Finally, optical-pump/THz-STM-probe measurements are performed on a silver-coated gold surface. These measurements, with tip-sample distances outside of the typical tunneling regime of the THz-STM, use photo-excited electrons from an optical pump beam to tunnel between the sample and tip. A THz pulse is then focused onto the junction between the sample and tip. The results show an interesting behaviour in the regime where the pump beam is not focused on the junction but elsewhere on the surface of the sample. These preliminary results may help gain a better understanding of the photoemission-based THz waveform measurements, as well as demonstrate a new use of the THz-STM for propagation dynamics of surface excitations.

Download or read book Variable Temperature Scanning Tunneling Microscopy Study of a High Temperature Superconductor BSCCO written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tunneling Microscopy of Superconductors and Tunneling Barriers written by Alex De Lozanne and published by . This book was released on 1988 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thin films of high temperature superconductors were made by sputtering and by co-evaporation. The former method produced thin films of YBaCuO which were completely superconducting at 82 K with 6 K transition widths. A new method was developed at the University of Texas which produced films of YBaCuO on strontium titanate that were superconducting at 84 K. This method minimizes the process temperature and produces films which are superconducting without the need for annealing. The films were also grown on silicon and sapphire substrates with zero resistance of 68 K or better. A low temperature scanning tunneling microscope was used to study the superconducting properties of these and other samples. High quality spectroscopic data was obtained which yields a value of approximately 11 for the ratio of the superconducting gap to the transition temperature. Keywords: High temperature superconductivity; Thin films; Tunneling.

Download or read book Probing the Superconducting Order Parameter of High Tc Superconductor Bi2Sr2CaCu2O8 0 by Scanning Josephson Tunneling Microscopy written by Hikari Kimura and published by . This book was released on 2009 with total page 282 pages. Available in PDF, EPUB and Kindle. Book excerpt: The technique of scanning tunneling microscopy (STM) with a normal metal tip has recently been used to study the high transition temperature (TC) superconducting cuprates and has revealed many fascinating and complex features of quasiparticle excited states of these materials. For conventional superconductors, the Bardeen-Cooper-Schrieffer theory connects the pair amplitude and the superconducting gap as measured from the quasiparticle excitation spectra, while for the high-TC materials there is still no theory to connect these quantities. We are unable to make any quantitative analysis of the superconducting ground state from the quasiparticle data. Josephson tunneling is the tunneling of the Cooper pairs between two superconductors and the Josephson current directly relates to the superconducting pair wave function amplitude. In this thesis, we have developed the superconducting STM as a local Josephson probe and carried out direct measurements of the superconducting pair amplitude of Bi2Sr2CaCu2O8+x single crystals via the c-axis Josephson tunneling between Bi2Sr2CaCu2O8+x and a conventional superconducting STM tip. Josephson measurements at different surface locations of overdoped Bi2Sr2CaCu2O8+x yield local values for the Josephson ICRN product, indicating an inhomogeneous structure of the ICRN product in overdoped Bi2Sr2CaCu2O8+x on a nanometer length scale. The corresponding energy gap was also measured at the same locations and an unexpected inverse correlation is observed between the local ICRN product and the local energy gap. Our interpretation of the ICRN vs. the energy gap relation with the phase fluctuation model for the phase diagram of high-TC superconducting cuprates will be presented. A preliminary study of the high current density effect on the density of states of Bi2Sr2CaCu2O8+x will also be reported. The effect of cleaving the Bi2Sr2CaCu2O8+x surface on its electronic structure is also discussed. This is motivated by the question that the gap inhomogeneity observed by STM is intrinsic property of this material or induced by the cleaving. Since the superconducting tunneling probes the depth of a coherence length into the sample surface and Bi2Sr2CaCu2O8+x has a very short c-axis coherence length, it's important to address this question. I will present some preliminary results of the superconducting STM studies on chemically etched Bi2Sr2CaCu2O8+x surfaces.

Download or read book High resolution Photoemission Study of Low T subscript C Superconductors written by T. Yokoya and published by . This book was released on 2001 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Tunneling Spectroscopy Studies of Superconductors written by Basu Dev Oli and published by . This book was released on 2021 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: In multiband superconductors, different bands at the Fermi surface contribute to the superconductivity with different magnitudes of superconducting gaps on different portions of the Fermi surface. Each band in a multiband superconductor has a condensate with an amplitude and phase that weakly interacts with the other bands' condensate. The coupling strength between the bands determines whether one or two superconducting transition temperatures are observed, and it is the key to many peculiar properties. In general, if there are two gaps of different magnitude, there are two different length scales associated with the suppression of these gaps in applied magnetic fields, for example. Therefore, effects of multigap superconductivity can be observed in superconducting vortices, which are twirls of supercurrents that are generated when a superconductor is placed in a magnetic field. Furthermore, the two superconducting order parameters in different bands are characterized by a magnitude and phase. In multiband superconductors, there are collective excitations corresponding to fluctuations of the relative phase of two order parameters, so-called the Leggett mode. The first material identified as multiband superconductor is Magnesium Diboride (MgB2) in 2001 with a critical temperature Tc of 39 K. MgB2 is a superconducting material with the highest transition temperature among all conventional BCS superconductors. It has two superconducting gaps \Delta_\pi ~ 2 meV and \Delta_\sigma\ ~ 7 meV and they arise from the existence of two bands \pi and \sigma bands of boron electrons. The discovery of superconductivity in MgB2 renewed interest in the field of multiband superconductivity. MgB2 has attracted many scientists' attention both for the fundamental importance of understanding the multiband superconductivity and possible applications such as magnets, power cables, bolometers, Josephson junction-based electronic devices, and radio-frequency cavities. Afterward, other materials have been identified as multiband superconductors such as NbSe2, the family of iron-based superconductors, heavy fermion superconductors, multilayer cuprates, borocarbides, etc. This dissertation uses tunneling experiments to highlight multiband superconductivity features in two systems, namely MgB2 thin films and ultrathin films of Pb. Further, we use multiple techniques to study a superconducting material, nitrogen-doped niobium, used for superconducting radio-frequency cavities. For the project on MgB2, MgB2/Native-Oxide/Ag planar junctions are fabricated and characterized down to 2.1 K and in the magnetic field parallel to the sample surface up to 6 Tesla. This work investigates how pairbreaking affects the magnitude and phase of the order parameter in a multiband superconductor. The tunneling spectra are analyzed in the framework of a two-band model developed by our theory collaborator Prof. Alex Gurevich, Old Dominion University. The model allows the extraction of the pair-breaking parameters among other quantities. The analysis shows that the order parameter in the ? band is quickly suppressed in the field, the ? band is cleaner than the ? band. The ratio of pairbreaking parameter in the ? band to the ? band rapidly increases at fields higher than ~0.1 T and then plateau at higher fields. This transition around 0.1 T magnetic field suggests a phase decoupling in the two bands of MgB2. Below the transition, the two bands are phase-locked, so mostly, the superconductivity in the ? band is affected, and after phase decoupling, both bands are affected by the applied field. These results are important for a basic understanding of multiband superconductors and the application implications of this material. This phase decoupling has a new and profound consequence on the superconducting state of a multiband superconductor that has been theoretically predicted and never observed experimentally. For the Pb project, ultrathin films of Pb in ultrahigh vacuum conditions are deposited by e-beam evaporation and characterized with low-temperature scanning tunneling microscopy and spectroscopy (STM/STS). The STM/STS allows measuring the electronic density of states with the highest spatial resolution down to atomic scale. The shape of a superconducting vortex core is determined by the superconducting gap and the Fermi velocity, and the STM allows to map anisotropies of these quantities spatially. The vortex cores of Pb film show a complex shape that evolves from triangular at short distances from the center to a six-fold symmetric star shape farther away from the center. These details are very subtle, and they can be highlighted only if one works within the clean limit (to avoid the averaging effect of the scattering) and by fabricating the heterostructure that pins the vortices spatially. The complex vortex core shape reflects the anisotropy of the two bands that contribute to superconductivity in this material. For the project on Niobium, cold and hot spots from nitrogen-doped Nb cutouts are characterized by low temperature scanning tunneling microscopy and spectroscopy (STM/STS) combined with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The radiofrequency (RF) measurements of the quality factor and temperature mapping on an N-doped Nb superconducting resonator cavity are carried out at Jefferson Laboratory before cutting out the samples. This work aims to identify possible sources of excess dissipation in hot spots and relate them to the surface chemical composition and superconducting properties. The temperature mapping revealed a strong effect of the cavity cooldown rate on the intensities of hot spots and their spatial distribution, which indicates a significant contribution of trapped vortices to the RF dissipation. SEM images acquired on the cold and hot spots using a secondary electron detector show absence of residual hydride scars and niobium nitrides on their surface. Angle-resolved XPS measurements on the native surface of these samples revealed higher oxidized Nb 3d states on the N-doped Nb cold spots, which is supported by XPS depth profiles done on the samples by Argon ion sputtering. Argon ion sputtering of oxidized Nb removes oxygen preferentially from Nb2O5 and diffuses to bulk, thickening the lower oxidation state layers. The proximity theory framework's tunneling spectra analysis suggests hot spots have stronger pairbreaking due to a weakly reduced pair potential, a thicker metallic suboxide layer, and a wide distribution of the contact resistance. STM imaging of vortex cores shows a triangular vortex lattice in both samples, and the coherence length is nearly the same in hot and cold spots. The experimental data analysis suggests weakly degraded superconducting properties at the surface of hot spot regions are not the primary sources of RF losses. Instead, they are the regions where vortices nucleate first and get trapped during cooling down. These experimental techniques and findings will be crucial in helping to qualify new recipes for SRF cavity production and to boost their performance.

Download or read book Investigation of Superconducting Transition Temperature T subscript C Anomalies in YBa2Cu3O subscript X written by Samir Abdulhamid Nasser and published by . This book was released on 1991 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scanning Tunneling Spectroscopy Studies of Multiband and Unconventional Superconductivity written by Igor Fridman and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Low temperature scanning tunneling microscopy and spectroscopy of layered superconductors written by Christophe Renner and published by . This book was released on 1993 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Il fut utilisé pour une étude topographique et spectroscopique du supraconducteur classique 2H-Nb1-xTaxSe2(x=0,0.03,0.1,0.15 et 0.2) et du supraconducteur à haute température critique Bi2Sr2CaCu2O8.

Download or read book Scanning Tunneling Microscopy and Spectroscopy Measurements of Superconductor Ferromagnet Hybrids written by Steven Alan Moore and published by . This book was released on 2015 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: The focus of this thesis work is the study of the nanoscale electronic properties of magnetically coupled superconductor/ferromagnet hybrid structures using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) under ultra-high vacuum conditions. There are a number of novel effects that can occur due to the non-homogenous magnetic field from the ferromagnet, which directly influence the global and local superconducting properties. These effects include the generation of vortices/anti-vortices by the non-uniform magnetic stray field, local modulations in the critical temperature, filamentary superconductivity close to the transition temperature, and superconducting channels that can be controlled by external magnetic fields. Prior to this dissertation the subject of superconductor/ferromagnet hybrid structures has been mainly studied using global measurements (such as transport and magnetization) or scanning probe techniques that are sensitive to the magnetic field. Scanning tunneling microscopy probes the local electronic density of states with atomic resolution, and therefore is the only technique that can study the emergence of superconductivity on the length scale of the coherence length. The novel results presented in this dissertation show that magnetically coupled superconductor/ferromagnet heterostructures offer the possibility to control and tune the strength and location of superconductivity and superconducting vortices, which has potential for promising technological breakthroughs in computing and power applications.