Download or read book Investigation of Scanning Tunneling Spectra on Iron based Superconductor FeSe0 5Te0 5 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: FeSe0.5Te0.5 single crystals with superconducting critical temperature of 13.5 K are investigated by scanning tunneling microscopy/spectroscopy (STM/STS) measureflents in detail. STM image on the top surface shows an atomically resolved square lattice consisted by white and dark spots with a constant of about 3.73± 0.03 Å which is consistent with the lattice constant 3.78 Å. The Se and Te atoms with a height difference of about 0.35 Å are successfully identified since the sizes of the two kinds of atoms are different. The tunneling spectra show very large zero-bias conductance value and asymmetric coherent peaks in the superconducting state. According to the positions of coherence peaks, we determine the superconducting gap 2[Delta] = 5.5 meV, and the reduced gap 2[Delta]/kBTc = 4.9 is larger than the value predicted by the weak-coupling BCS theory. The zero-bias conductance at 1.7 K only have a decrease of about 40% compared with the normal state conductance, which may originate from some scattering and broadening mechanism in the material. This broadening effect will also make the superconducting gap determined by the distance between the coherence peaks larger than the exact gap value. The asymmetric structure of the tunneling spectra near the superconducting gap is induced by the hump on the background. This hump appears at temperature more than twice the superconducting critical temperature. This kind of hump has also been observed in other iron pnictides and needs further investigation. A possible bosonic mode outside the coherence peak with a mode energy [Omega] of about 5.5 meV is observed in some tunneling spectra, and the ratio between the mode energy and superconducting transition temperature [Omega]/kBTc ≈ 4.7 is roughly consistent with the universal ratio 4.3 in iron-based superconductors. The high-energy background of the spectra beyond the superconducting gaps shows a V-shape feature. The slopes of the differential conductance spectra at high energy are very different in the areas of Te-atom cluster and Se-atom cluster, and the difference extends to the energy of more than 300 meV. The differential conductance mapping has very little information about the quasi-particle interference of the superconducting state, which may result from the other strong scattering mechanism in the sample.
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 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 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 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 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 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 The Investigation of Scanning Tunneling Microscopy and Spectroscopy on High Tc Superconductors written by Yi Yin and published by . This book was released on 2009 with total page 292 pages. Available in PDF, EPUB and Kindle. Book excerpt: Other work contributing to this thesis is focused on a cuprate superconductor, Bi 2- y Pb y Si 2 CuO 6+ [delta] . With the density of states (DOS) maps at both zero and nonzero magnetic fields, a division normalization method is applied to separate two characteristic energy scales. We extract a homogeneous hidden small gap coexisting with an apparent inhomogeneous gap. Compared with a recent experiment performed by Boyer et al. , the hidden small gap is believed to be a superconducting order and the apparent inhomogeneous gap is referred to the pseudogap phase. Under the magnetic field range in our experiment, a vortex liquid state is proposed. This technique can be extended to detect the possible superconducting information in the Nernst state above Tc .
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 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 Scanning Tunneling Microscopy Study of Metal Growth on Superconductor and Semiconductor Surfaces written by Yansheng Luo and published by . This book was released on 1993 with total page 152 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Scanning Tunneling Microspectroscopy of Solids and Surfaces Final Report written by and published by . This book was released on 2002 with total page 4 pages. Available in PDF, EPUB and Kindle. Book excerpt: Experimental and theoretical research on the bulk and surface properties of conductive solid state materials has been performed based on the techniques of scanning tunneling microscopy and scanning tunneling spectroscopy, often at cryogenic temperatures. The research has focused on the electronic properties, particularly the superconductivity, of high temperature superconductors and other layered systems. The superconducting electronic density of states N(E)=dI/dV of the high T{sub c} superconductor Bi2Sr2CaCu2O{sub 8+{delta}} was measured with spatial resolution of 5 A at 4.2K. An internal superconducting proximity effect was inferred to operate between Cu and Bi based layers of the crystal in those regions where the Bi layers are metallic in nature. This research project supported the thesis research of several young scientists, and led to a significant number of published papers, presentations and reports.
Download or read book Fundamentals of the Theory of Metals written by A. A. Abrikosov and published by Courier Dover Publications. This book was released on 2017-10-18 with total page 641 pages. Available in PDF, EPUB and Kindle. Book excerpt: This comprehensive primer by a Nobel Physicist covers the electronic spectra of metals, electrical and thermal conductivities, galvanomagnetic and thermoelectrical phenomena, the behavior of metals in high-frequency fields, sound absorption, and Fermi-liquid phenomena. Addressing in detail all aspects of the energy spectra of electrons in metals and the theory of superconductivity, it continues to be a valuable resource for the field almost thirty years after its initial publication. Targeted at undergraduate students majoring in physics as well as graduate and postgraduate students, research workers, and teachers, this is an essential reference on the topic of electromagnetism and superconductivity in metals. No special knowledge of metals beyond a course in general physics is needed, although the author does presume a knowledge of quantum mechanics and quantum statistics.
Download or read book Iron Based Superconducting Thin Films written by Silvia Haindl and published by Springer Nature. This book was released on 2021-06-27 with total page 403 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a modern introduction to the growth, characterization, and physics of iron-based superconducting thin films. Iron pnictide and iron chalcogenide compounds have become intensively studied key materials in condensed matter physics due to their potential for high temperature superconductivity. With maximum critical temperatures of around 60 K, the new superconductors rank first after the celebrated cuprates, and the latest announcements on ultrathin films promise even more. Thin film synthesis of these superconductors began in 2008 immediately after their discovery, and this growing research area has seen remarkable progress up to the present day, especially with regard to the iron chalcogenides FeSe and FeSe1-xTex, the iron pnictide BaFe2-xCoxAs2 and iron-oxyarsenides. This essential volume provides comprehensive, state-of-the-art coverage of iron-based superconducting thin films in topical chapters with detailed information on thin film synthesis and growth, analytical film characterization, interfaces, and various aspects on physics and materials properties. Current efforts towards technological applications and functional films are outlined and discussed. The development and latest results for monolayer FeSe films are also presented. This book serves as a key reference for students, lecturers, industry engineers, and academic researchers who would like to gain an overview of this complex and growing research area.
Download or read book Magneto Optical Imaging written by Tom H. Johansen and published by Springer Science & Business Media. This book was released on 2004-05-31 with total page 374 pages. Available in PDF, EPUB and Kindle. Book excerpt: Magneto-Optical Imaging has developed rapidly over the last decade to emerge as a leading technique to directly visualise the static and dynamic magnetic behaviour of materials, capable of following magnetic processes on the scale of centimeters to sub-microns and at timescales from hours to nanoseconds. The images are direct, real-time, and give space-resolved information, such as ultrafast magnetic processes and revealing the motion of individual vortices in superconductors. The book is a fully up-to-date report of the present status of the technique.
Download or read book High Tc Superconducting Technology written by Muralidhar Miryala and published by CRC Press. This book was released on 2021-11-24 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Mitigating climate change, clean environment, global peace, financial growth, and future development of the world require new materials that improve the quality of life. Superconductivity, in general, allows perfect current transmission without losses. This makes it a valuable resource for sustainability in several aspects. High-temperature superconducting (HTSC) materials will be crucial for sustainable everyday applications and more attractive for the United Nations’ SDGs. Superconducting magnets can be used as high-field magnets in magnetic resonance imaging, nuclear magnetic resonance, water purification, magnetic drug delivery, etc. Hunger can be partly avoided if there is sustainability in agriculture. In the future, DC electric energy from solar plants in Africa could be transported worldwide, especially to cold countries, using superconducting cables. Superconducting technology is an efficient way to create sustainability as well as reduce greenhouse gases. This book presents the latest global achievements in the processing and applications of high-Tc superconductors and discusses the usefulness of the SDGs. It summarizes the related advances in materials science and developments with respect to the SDGs. The book also covers large-scale applications of HTSC materials, which will be connected to the SDGs, addressed by several eminent scientists, including Prof. M. Murakami, president, Shibaura Institute of Technology, Japan; Prof. D. Cardwell, pro-vice chancellor, University of Cambridge, UK; and Prof. N. Long, director, Victoria University of Wellington, New Zealand.
Download or read book Superconductivity written by Paolo Mele and published by Springer Nature. This book was released on 2019-08-21 with total page 369 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides readers with a comprehensive overview of the science of superconducting materials. It serves as a fundamental information source on the actual techniques and methodologies involved in superconducting materials growth, characterization and processing. This book includes coverage of several categories of medium and high-temperature superconducting materials: cuprate oxides, borides, and iron-based chalcogenides and pnictides. Provides a single-source reference on superconducting materials growth, characterization and processing; Bridges the gap between materials science and applications of superconductors; Discusses several categories of superconducting materials such as cuprate oxides, borides, and iron-based chalcogenides and pnictides; Covers synthesis, characterization, and processing of superconducting materials, as well as the nanoengineering approach to tailor the properties of the used materials at the nanoscale level.
