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 Principles of Electron Tunneling Spectroscopy written by E. L. Wolf and published by Oxford University Press. This book was released on 2012 with total page 617 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electron tunnelling spectroscopy as a research tool has strongly advanced understanding of superconductivity. This book explains the physics and instrumentation behind the advances illustrated in beautiful images of atoms, rings of atoms and exotic states in high temperature superconductors, and summarizes the state of knowledge that has resulted.

Download or read book Scanning Tunneling Spectroscopy Studies of High temperature Cuprate Superconductors written by Ching-Tzu Chen and published by . This book was released on 2006 with total page 334 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 Inelastic Electron Tunneling Spectroscopy written by T. Wolfram and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 247 pages. Available in PDF, EPUB and Kindle. Book excerpt: Inelastic Electron Tunneling Spectroscop~ or lETS, provides a unique technique for electronically monitoring the vibrational modes of molecul (;5 adsorbed on a metal oxide surface. Since the discovery of the phenomena by JAKLEVIC and LM1BE in 1966, lETS has been developed by a number of scientists as a method for studying the surface chemistry of molecular species adsorbed on aluminum oxide. Recent applications of lETS include investigations of physical and chemical adsorption of hydrocarbons, studies of catalysis by metal particles, detection and identification of trace substances in air and water, and studies of biological molecules and electron damage to such molecules. lETS has been employed to investigate adhesive materials, and studies are currently in prog ress to investigate corrosion species and corrosion inhibitors on aluminum and its alloys. Electronic transitions of molecules have also been studied by lETS. The recent development of the "external doping" technique, whereby molecu lar species can be introduced into fabricated tunnel junctions, opens the door for a vast new array of surface chemical studies by lETS. lETS is rap idly becoming an important tool for the study of surface and interface phe nomena. In addition to its role in surface studies, inelastic tunneling has proved extremely valuable for the study of the electronic properties of thin metallic films, and the recent discovery of light emission from inelastic tunneling promises to be of some importance in the area of device physics.

Download or read book Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron Based Superconductors written by Jandke, Jasmin Maria and published by KIT Scientific Publishing. This book was released on 2019-05-02 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Schackert Michael PeterScanning Tunneling Spectroscopy on Electron Boson Interactions in Superconductors written by Schackert, Michael Peter and published by KIT Scientific Publishing. This book was released on 2015-03-23 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end.

Download or read book Elastic and Inelastic Scanning Tunneling Spectroscopy on Iron Based Superconductors written by Jasmin Maria Jandke and published by Saint Philip Street Press. This book was released on 2020-10-09 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Within this work, the pairing mechanism of conventional (Pb) and unconventional superconductors (SrFe2(As1-xPx )2, FeSe, FeSe/STO) was investigated experimentally by means of elastic and inelastic tunneling spectroscopy at temperatures down to 30 mK. The distinction between elastic and inelastic contributions to tunneling data was elaborated. The results help to identify conventional (phonon-mediated) and unconventional (e.g. spin-?uctuation mediated) superconductivity. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

Download or read book In plane Tunneling Spectroscopy of D wave Superconductors written by Puangratana Pairor and published by . This book was released on 2001 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis studies the tunneling spectroscopy of a pure d-wave BCS superconductor using a two-dimensional discrete square lattice model. The zero-temperature differential conductances of the junctions with three surface orientations: (100), (110), and (210) are calculated using the Bogoliubov-de Gennes equations and a scattering method. The idea of the surface-adapted Brillouin zone is introduced in this thesis. It provides a convenient way of obtaining which transmitted superconducting excitations that an electron from the normal metal will tunnel into. A different surface-adapted Brillouin zone must be used to describe the quasiparticle state of the superconductor for each surface orientation. In general, the surface-adapted Brillouin zone is rectangular and the Fermi surfaces are not necessarily isotropic; thus, the state can be a linear combination of more than two quasi-particle excitations of the same energy and the momenta with the same components along the surface. This thesis demonstrates that this complication has important implications for the interpretation of the tunneling spectrum. It is shown that the calculated tunneling spectra of junctions with orientations away from (100) and (110) contain gap-like peaks, whose positions are not at the maximum gap. The positions of these peaks are predicted to be related to the energy gap of the state with the momentum either parallel to the surface normal, or on the edge of the surface-adapted Brillouin zone. The magnitudes of the energy gaps of these states are found to be strongly dependent on the shape of Fermi surface. These findings open the way for the development of a new method of gaining information about the magnitude of the superconducting energy gap at different points on the Fermi surface.

Download or read book Electron Tunneling and Point Contact Andreev Reflection Studies of Superconductors written by Wenqing Dai and published by . This book was released on 2014 with total page 155 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Principles of Electron Tunneling Spectroscopy written by E. L. Wolf and published by Oxford University Press, USA. This book was released on 1985 with total page 600 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive and up-to-date treatment of solid state electron tunneling phenomena, with emphasis on their systematic application in junction devices to probe electronic and vibrational properties of superconductors, normal metals, semiconductors, and thin insulating barrier layers. The quantum-mechanical foundations of the subject are traced, and the most active areas of tunneling research are covered in a uniform and coherent manner. A thorough treatment of experimental techniques in tunneling research is provided, along with an introduction to the relevant techniques of data analysis.

Download or read book Scanning Tunneling Spectroscopy on Electron Boson Interactions in Superconductors written by Michael Peter Schackert and published by . This book was released on 2020-10-09 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work describes the experimental study of electron-boson interactions in superconductors by means of inelastic electron tunneling spectroscopy performed with a scanning tunneling microscope (STM) at temperatures below 1 K. This new approach allows the direct measurement of the Eliashberg function of conventional superconductors as demonstrated on lead (Pb) and niobium (Nb). Preparative experiments on unconventional iron-pnictides are presented in the end. This work was published by Saint Philip Street Press pursuant to a Creative Commons license permitting commercial use. All rights not granted by the work's license are retained by the author or authors.

Download or read book Advances in Theoretical and Experimental Research of High Tc Superconductivity written by Han Rushan and published by World Scientific Publishing Company. This book was released on 2019 with total page 512 pages. Available in PDF, EPUB and Kindle. Book excerpt: Researchers working at the frontier of high-Tc Superconductors have reviewed the development in this area in the past 20 years. Both experimental and theoretical aspects have been covered. New directions and possible theoretical models were suggested. The contributors of this book are from China Center of Advanced Science and Technology (CCAST); Institute of Physics Chinese Academy of Sciences (CAS); National Lab for Superconductivity, Institute of Physics, CAS; School of Physics, Peking University and Center of Advanced Study Tsinghua University. This volume will be a useful guide to those who are working in the field.

Download or read book Scanning Tunneling Spectroscopy of Bi Based High Temperature Superconductors written by Craig Martin Howald and published by . This book was released on 2002 with total page 122 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Scanning Tunneling Spectroscopy of Novel Superconductors written by Nathan Jenkins and published by . This book was released on 2009 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt:

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 Tunneling in Strongly Correlated Materials written by Marianna Maltseva and published by . This book was released on 2009 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt: Tunneling studies of strongly correlated materials provide information about the nature of electronic correlations, which is vital for investigation of emergent materials at the microscopic level. In particular, scanning tunneling spectroscopy/microscopy (STS/STM) studies have made major contributions to understanding cuprate superconductors (66), yet there is a sense that huge STM data arrays contain much more precious information to be extracted and analyzed. One of the most pressing questions in the field is how to improve the data analysis, so as to extract more information from STM data. A dominant trend in STM data analysis has been to interpret the data within a particular microscopic model, while using only basic data analysis tools. To decrease the reliance of the STM data interpretation on particular microscopic models, further advances in data analysis methods are necessary. In Chapter 2 of this Thesis, we discuss how one can extract information about the phase of the order parameter from STM data. We show that symmetrized and anti-symmetrized correlators of local density of states give rise to observable coherence factor effects. In Chapter 3, we apply this framework to analyze the recent scanning tunneling experiments on an underdoped cuprate superconductor calcium sodium oxychloride by T. Hanaguri et al. (60). In Chapter 4, we propose a model for nodal quasiparticle scattering in a disordered vortex lattice. Recently, scanning tunneling studies of a Kondo lattice material U Ru2S i2 became possible (117). If it proves possible to apply scanning tunneling spectroscopy to Kondo lattice materials, then remarkable new opportunities in the ongoing investigation may emerge. In Chapter 5, we examine the effect of co-tunneling to develop a theory of tunneling into a Kondo lattice. We find that the interference between the direct tunneling and the co-tunneling channels leads to a novel asymmetric lineshape, which has two peaks and a gap. The presence of the peaks suggests that the interference is more dramatic in the case of Kondo lattice than in the single impurity case, because of the coherence. These features should be observed in future tunneling experiments on Kondo lattice materials.