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 Design and Construction of a Low Temperature Scanning Tunneling Microscope for Studying High Temperature Superconductivity written by Dilushan R. Jayasundara and published by . This book was released on 2008 with total page 184 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 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 Low Temperature Scanning Tunneling Microscope Study of Metallic Thin Films and Nanostructures on the Semiconductor Substrates written by Shengyong Qin and published by . This book was released on 2008 with total page 254 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many properties of the thin films are different from the bulk value and in many cases, depend dramatically on the film thickness. In the metallic ultra-thin films epitaxially grown on the semiconductor substrate, the conduction electrons are confined by the vacuum and metal-semiconductor interface. When the film thickness is comparable to the electron Fermi wavelength, this confinement will produce discrete energy levels known as quantum well states (QWS), which dramatically modify the electronic structures of the thin film and this is called quantum size effect (QSE). QSE will have a profound effect on a lot of physical properties of the thin films. Among various systems exhibiting QSE, Pb/Si (111) is the most widely studied one and exhibits the richest phenomena in QSE. In this study, a home made low temperature Scanning Tunneling Microscopy/Spectroscopy (LT-STM/S) was used to study the superconductivities of the Pb thin films. Quantum oscillations of the superconductivity have been observed for the films down to 4 monolayer and the oscillation amplitude increases as the film gets thinner. To resolve the discrepancies between the superconductivities measured with ex-situ transport and in-situ STS. We also studied the influence of Au overlay on the Pb thin films with LT-STM/S, and found out the deposition of Au on Pb dramatically roughened the Pb films. Finally, we successfully grew large scale near perfect 2ML Pb films. There are two types of films which exhibit different Moiré patterns. LT-STS studies revealed there is big difference in the superconductivity Tc of these two films, both of which decreased dramatically from that of the 4ML film.

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 An ultra high vacuum low temperature scanning tunneling microscope and its applications to high Tc subscript c superconductors and quasi one dimensional organic conductors written by Shuheng Pan and published by . This book was released on 1991 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scanning Tunneling Microscope Studies of the High Temperature Superconductor BSCCO written by Alan Fang and published by . This book was released on 2008 with total page 140 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 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 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 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 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.

Download or read book Organic Conductors written by Jean-Pierre Farges and published by CRC Press. This book was released on 2022-09-16 with total page 874 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work examines all aspects of organic conductors, detailing recent theoretical concepts and current laboratory methods of synthesis, measurement, control and analysis. It describes advances in molecular-scale engineering, including switching and memory systems, Schottky and electroluminescent diodes, field-effect transistors, and photovoltaic devices and solar cells.

Download or read book Scanning Tunneling Microscope Studies of 2D Superconductor and 3D Intrinsic Topological Insulator written by Hyoungdo Nam and published by . This book was released on 2015 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrons show unusual and interesting behaviors both in low dimensions and on material surfaces, distinct from what they display in bulk materials. These intriguing properties have been studied in order to understand their origins. One area where this can be seen is in the case of superconductivity, where superconducting phase fluctuation in a thin superconductor is supposed to substantially suppress the superconductivity of the material as the film thickness decreases. To test this, we prepared epitaxially grown and globally flat lead (Pb) films; here, the thinnest film was 1.4 nm thick. Four different length scale measurements, ranging from the nm to the mm scale, gave consistent superconducting transition temperatures. Our results proved that the film of 1.4 nm still has strong superconducting phase stiffness; namely, the superfluid phase is rigid even in 1.4 nm thin superconductor film. Moreover, the parallel critical magnetic field is remarkably strong so that superconductivity is still observed in Zeeman fields, exceeding the Pauli limit. In addition, the surface of 3D topological insulator has a novel quantum state induced by strong spin-orbit interaction. A number of material studies were conducted to find a surface dominated conduction topological insulator that has a large energy gap and a single Dirac cone. Moreover, it is necessary for the material to be stable against aging unlike most 3D topological insulators, such as Bi2Se3. Here, Bi2Te2Se and BiSbTeSe2 were studied in terms of their structures, electronic properties, and aging effects on them. Scanning tunneling microscopy analysis attested that Bi2Te2Se is an order alloy, which has a slight randomness of 15 %, whereas BiSbTeSe2 is a random alloy. Scanning tunneling spectroscopy on BiSbTeSe2 confirmed that the Dirac point tends to stay around the Fermi level under the strong band structure change, induced by random structure. The most surprising observation was that BiSbTeSe2 showed remarkable stability despite the rich composition of selenium (Se). Even after aging for seven days, the Fermi level and the Dirac point remained at almost the same level in bulk band gap. Both observations are very important for applications to utilize the exotic topological surface state.

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 Local Probing of a Superconductor s Quasiparticles and Bosonic Excitations with a Scanning Tunnelling Microscope written by Gozlinski, Thomas and published by KIT Scientific Publishing. This book was released on 2023-03-24 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complementary to scattering techniques, scanning tunnelling microscopy provides atomic-scale real space information about a material's electronic state of matter. State-of-the-art designs of a scanning tunnelling microscope (STM) allow measurements at millikelvin temperatures with unprecedented energy resolution. Therefore, this instrument excels in probing the superconducting state at low temperatures and especially its local quasiparticle excitations as well as bosonic degrees of freedom.