Read Books Online and Download eBooks, EPub, PDF, Mobi, Kindle, Text Full Free.
Electronic Structures Of Novel Complex Materials Studied By Angle Resolved Photoemission Spectroscopy
Download Electronic Structures Of Novel Complex Materials Studied By Angle Resolved Photoemission Spectroscopy full books in PDF, epub, and Kindle. Read online Electronic Structures Of Novel Complex Materials Studied By Angle Resolved Photoemission Spectroscopy ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!
Book Synopsis Electronic Structures of Novel Complex Materials Studied by Angle Resolved Photoemission Spectroscopy by : Zhongkai Liu
Download or read book Electronic Structures of Novel Complex Materials Studied by Angle Resolved Photoemission Spectroscopy written by Zhongkai Liu and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electronic Structure is the key factor for identifying new material or phases and understanding the underlying physics behind emergent phenomena. In the investigation of the electronic structures of novel complex materials, the angular resolved photoemission spectroscopy (ARPES) serves as a powerful tool. The thesis summarizes two of my graduate research projects, which both involves probing electronic structures and analyzing underlying physics on novel complex materials with state-of-the-art ARPES techniques: In the first part, I would summarize our investigation on the materials with non-trivial topology. I would start from our initial work on the three-dimensional topological insulators where we identified the characteristic surface states and verified that they are robust from perturbations. Following the line of search, we discovered three-dimensional topological insulators with other interesting properties, including the strongly inversion asymmetric topological insulator BiTeCl, and the strongly correlated topological Kondo insulator SmB6. We further extended our research to Na3Bi and Cd3As2, where we found them hosting a three-dimensional Dirac point and are first examples of topological Dirac semimetals, a three-dimensional analogue of graphene. In the second part of my thesis, I would discuss the ARPES study on the electron correlation level in the iron chalcogenide family Fe(Se, Te). For the parent compound FeTe, we discovered "peak-dip-hump" spectra with heavily renormalized quasiparticles in the low temperature antiferromagnetic state, characteristic of coherent polarons seen in other correlated materials. The increase of Se ratio leads to an incoherent to coherent crossover in the electronic structure. Furthermore, the reduction of the electronic correlation in Fe(Se, Te) evolves in an orbital-dependent way, where the dxy orbital is influenced most significantly. Finally, in comparison with other members of iron chalcogenides (AxFe2-ySe2, A=K, Rb, Cs; and monolayer FeSe film on SrTiO3 substrate), we found the strong correlation behavior is universal in all iron chalcogenides. Specifically, the dxy orbital is always heavily renormalized and loses spectral weight upon raising temperature. Several physical models of the orbital dependent physics and electron correlations would be discussed.
Book Synopsis Electronic Structures of Twisted Two-dimensional Materials Studied by Angle-resolved Photoemission Spectroscopy by : Ding Pei
Download or read book Electronic Structures of Twisted Two-dimensional Materials Studied by Angle-resolved Photoemission Spectroscopy written by Ding Pei and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Exploring the Electronic Properties of Novel Spintronic Materials by Photoelectron Spectroscopy by : Alexej Herdt
Download or read book Exploring the Electronic Properties of Novel Spintronic Materials by Photoelectron Spectroscopy written by Alexej Herdt and published by Forschungszentrum Jülich. This book was released on 2012 with total page 145 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Spectroscopy of Complex Oxide Interfaces by : Claudia Cancellieri
Download or read book Spectroscopy of Complex Oxide Interfaces written by Claudia Cancellieri and published by Springer. This book was released on 2018-04-09 with total page 326 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book summarizes the most recent and compelling experimental results for complex oxide interfaces. The results of this book were obtained with the cutting-edge photoemission technique at highest energy resolution. Due to their fascinating properties for new-generation electronic devices and the challenge of investigating buried regions, the book chiefly focuses on complex oxide interfaces. The crucial feature of exploring buried interfaces is the use of soft X-ray angle-resolved photoemission spectroscopy (ARPES) operating on the energy range of a few hundred eV to increase the photoelectron mean free path, enabling the photons to penetrate through the top layers – in contrast to conventional ultraviolet (UV)-ARPES techniques. The results presented here, achieved by different research groups around the world, are summarized in a clearly structured way and discussed in comparison with other photoemission spectroscopy techniques and other oxide materials. They are complemented and supported by the most recent theoretical calculations as well as results of complementary experimental techniques including electron transport and inelastic resonant X-ray scattering.
Book Synopsis Angle-resolved Photoemission Studies of Two-dimensional Electron Systems by : Yang Liu
Download or read book Angle-resolved Photoemission Studies of Two-dimensional Electron Systems written by Yang Liu and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation examines the electronic properties of 2D electron systems, including ultrathin metallic films grown on semiconductor substrates and graphite/graphene layers. Both systems are (quasi) two-dimensional and are of particular interest due to their technological importance. The major experimental tool is angle-resolved photoemission spectroscopy, which can directly measure the spectral function of the quasiparticle. The study of ultrathin metallic films focuses on the substrate effect on the electronic structure of the film. Thin metallic films can support quantum well states, which are essentially electronic standing waves. Our work on Ag films grown on Ge(111) demonstrates that the incommensurate interface potential results in strong modifications to quantum well states. The observed electronic interference structures are attributable to the mixing of electronic standing waves by the Ag-Ge interface potential. The complex Fermi surface, as a result of this interface scattering, can affect the electronic transport properties. An even stronger modification of quantum well states can be observed when the metal films are grown on stepped substrates. More specifically, our study of corrugated Ag/Pb films grown on Si(557)-Au surface reveals multiple sets of quantum well states that are centered at the Brillouin zone boundaries corresponding to the step modulation. This indicates that the valence electrons form coherent grating cavity modes which are defined by the corrugation geometry. Graphitic materials, made of sheets of carbon atomic layers, have unusual electronic structures known as Dirac cones. Our photoemission measurements of graphite/graphene layers reveal unexpected gaps at normal emission, one at ~67 meV and another much weaker one at ~150 meV. The major gap features persist up to room temperature, and diminish with increasing emission angles. We show that these gaps arise from electronic coupling to out-of-plane and in-plane vibrational modes at the point, respectively, in accordance with conservation laws and selection rules governed by quantum mechanics. Our study suggests a new approach for characterizing phonons and electron-phonon coupling in solids.
Book Synopsis Atomic and electronic structures of two-dimensional layers on noble metals by : Jalil Shah
Download or read book Atomic and electronic structures of two-dimensional layers on noble metals written by Jalil Shah and published by Linköping University Electronic Press. This book was released on 2019-09-04 with total page 67 pages. Available in PDF, EPUB and Kindle. Book excerpt: Two-dimensional (2D) materials, in the form of a single atomic layer with a crystalline structure, are of interest for electronic applications. Such materials can be formed by a single element, e.g., by group IV or group V elements, or as a 2D surface alloy. As these materials consist of just a single atomic layer, they may have unique properties that are not present in the bulk. The (111) surfaces of the noble metals Ag and Au are important for the preparation of several 2D materials. To investigate the atomic and electronic structures, the following experimental techniques were used in this thesis: angle resolved photoelectron spectroscopy (ARPES), scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The 2D structures studied in this thesis include arsenene (an As analogue to graphene) and As/Ag(111), Sn/Au(111), and Te/Ag(111) surface alloys. Arsenene has been thoroughly investigated theoretically for many years and several interesting properties important for next generation electronic and optoelectronic devices have been described in the literature. This thesis presents the first experimental evidence of the formation of arsenene. A clean Ag(111) surface was exposed to arsenic in an ultra-high vacuum chamber at an elevated substrate temperature (250 to 350 °C ). The resulting arsenic layer was studied by LEED, STM and ARPES. Both LEED and STM data resulted in a lattice constant of the arsenic layer of 3.6 Å which is consistent with the formation of arsenene. A comparison between the experimental band structure obtained by ARPES and the theoretical band structure of arsenene based on density functional theory (DFT), further verified the formation of arsenene. The As/Ag(111) surface alloy was prepared by exposing clean Ag(111) to arsenic followed by heating to 400 °C. This resulted in an Ag2As surface alloy which formed by the replacement of every third Ag atom by an As atom in a periodic fashion. LEED showed a complex pattern of diffraction spots corresponding to a superposition of three domains of a reconstruction described by a unit cell. STM images revealed a surface with a striped atomic structure with ridges characterized by a local ?3 × ?3 structure. ARPES data showed three alloy related bands of which one can be associated with the ?3 × ?3 structure on the ridges. This band shows a split in momentum space around the point along the direction of a ?3 × ?3 surface Brillouin zone in similarity with a Ge/Ag(111) surface alloy. Sn/Au(111) surface alloys can be prepared with different periodicities. An Au2Sn phase characterized by a ?3 × ?3 periodicity and an Au3Sn phase with a 2 × 2 periodicity are formed containing 0.33 and 0.25 monolayer of Sn, respectively. The clean Au(111) surface itself, shows a complex reconstruction, the so called herringbone structure, that can be viewed as a zig-zag pattern of stripes described by a 22 × ?3 unit cell. The replacement of Au atoms by Sn results in change of the periodicity of the herringbone structure to 26 × ?3 and ? 26 × 2?3 for the Au2Sn and Au3Sn surface alloys, respectively. Furthermore, the local 1 × 1 periodicity of clean Au(111) is replaced by a ?3 × ?3 and a 2 × 2 periodicity as is clear from STM images of the respective cases. ARPES data are presented for the Au2Sn surface alloy, which reveal an electronic band structure with similarities to other striped surface alloys. In particular, the split in momentum space around the point of a ?3 × ?3 surface Brillouin zone is observed also for Au2Sn. A Te-Ag binary surface alloy can be formed by evaporating 1/3 monolayer of Te onto a clean Ag(111) surface followed by annealing. After this preparation, LEED showed sharp ?3 × ?3 diffraction spots that is evidence for a well-ordered surface layer. ARPES data revealed two distinct electronic bands that followed the ?3 × ?3 periodicity. One of these bands showed a small spin-split of the Rashba type. The experimental band structure was compared with the theoretical bands of several atomic models of Te induced structures on Ag(111). An excellent fit was obtained for a Te-Ag surface alloy with a planar honeycomb structure, with one Te and one Ag atom in the unit cell. A semiconducting electronic structure of the Te-Ag surface alloy was inferred from the ARPES data in agreement with the ?0.7 eV band gap predicted by the DFT calculations.
Book Synopsis Electronic Band Structure Engineering and Ultrafast Dynamics of Dirac Semimetals by : Changhua Bao
Download or read book Electronic Band Structure Engineering and Ultrafast Dynamics of Dirac Semimetals written by Changhua Bao and published by Springer Nature. This book was released on with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Angle-resolved Photoemission Spectroscopy of Epitaxially Strained Ruthenates by : Bulat Burganov
Download or read book Angle-resolved Photoemission Spectroscopy of Epitaxially Strained Ruthenates written by Bulat Burganov and published by . This book was released on 2017 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Complex oxides provide a platform for designing new functional material systems and manipulating the properties of the existing ones thanks to a vast array of their tunable and exotic ground states. The interactions between the internal degrees of freedom in such systems often cannot be fully accounted for by modern theory, and it is necessary to directly probe the electronic structure underlying a complex phase to reveal its nature. The emergent properties of ruthenates are particularly tunable, as evidenced by their wide variety of electronic and magnetic instabilities including unconventional superconductivity, metamagnetism and formation of electronic liquid crystalline states, ferro- and antiferromagnetism, and spin-glass behavior. Some of these phases occur in closely related compounds, or are switchable within the same compound by a small external perturbation, such as pressure, strain or magnetic field. This dissertation presents direct measurements of the electronic structure in Ba$_2$RuO$_4$ and BaRuO$_3$, close analogues of the spin-triplet superconductor Sr$_2$RuO$_4$ and ferromagnetic SrRuO$_3$, respectively, using a unique integrated oxide molecular-beam epitaxy and angle-resolved photoemission spectroscopy. This approach allows us to access compounds that have no stable bulk form and deliberately manipulate their electronic properties via epitaxial strain and dimensionality confinement. We first discuss the ARPES measurements of Ba$_2$RuO$_4$ and Sr$_2$RuO$_4$. By varying the amount of biaxial in-plane strain through epitaxial stabilization on different substrates, we reveal a systematic evolution of the Fermi surface and quasiparticle mass enhancements. We reveal a topological transition in the circular electron Fermi pocket centered at zone center as a function of strain and cation size. Near the topological Lifshitz transition, we observe clear signatures of quantum criticality. The quasiparticle mass enhancements are found to increase rapidly and monotonically with increasing Ru-O bond distance. By next studying atomically thin films of BaRuO$_3$ we are able to directly see how the dimensional confinement drives the transition from a ferromagnetic ground state to a strongly fluctuating paramagnetic state. Our results provide new insights into the physics of perovskite ruthenates and demonstrate the possibilities for using epitaxial strain and dimensional confinement as disorder-free means of manipulating emergent properties and many-body interactions in correlated quantum materials. ...
Book Synopsis Electronic Structure of Novel Materials for Next-Generation Devices by : Alex J. Shearer
Download or read book Electronic Structure of Novel Materials for Next-Generation Devices written by Alex J. Shearer and published by . This book was released on 2016 with total page 65 pages. Available in PDF, EPUB and Kindle. Book excerpt: The properties of interfacial electronic states in device-relevant materials are investigated using time- and angle-resolved two photon photoemission (TPPE) spectroscopy. Angle- and time-resolved TPPE is used to investigate electronic states in the buffer layer of 4H-SiC(0001). An image potential state (IPS) series is observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results are compared with TPPE taken on bilayer graphene, which also shows the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states are obtained from time-resolved TPPE; slightly increased lifetimes are observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons. Ultrafast response of the room temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpyr][NTf2]) to a photoinjected electron is investigated in few-monolayer films using time- and angle-resolved two-photon photoemission spectroscopy. A delocalized precursor state and a localized solvated state are resolved at early times, but after 200 fs only a single solvated state is observed. The dynamics of film response to this solvated state are shown to depend significantly on film temperature and thickness. Population lifetime measurements demonstrate that the RTIL film can significantly affect the coupling between solvated state and metal substrate, as the solvated state's average lifetime increases from 90 ± 20 fs in 1 ML films to 195 ± 83 ps in 3 ML films. Additionally, a temperature dependence of the time-dependent binding energy shift of the solvated state after c.a. 500 fs is attributed to a phase change occurring between the two temperature regimes that were investigated. Results from xenon overlayer experiments suggest that the solvation process occurs near the surface of the RTIL film. Finally, film degradation is found to be present, suggesting that the observed solvation response could involve a radical species. Valuable information about two very different interfacial materials is collected using TPPE, proving the power and versatility of the technique. The results presented here show that interfacial states can be used to monitor a variety of physical phenomena, from corrugation in graphitic materials to solvation and degradation in RTILs.
Book Synopsis The Electronic Structure of Solids Studies Using Angle Resolved Photoemission Spectroscopy by : K. E. Smith
Download or read book The Electronic Structure of Solids Studies Using Angle Resolved Photoemission Spectroscopy written by K. E. Smith and published by . This book was released on 1991 with total page 83 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Depth-resolved Electronic Structure of Spintronic Nanostructures and Complex Materials with Soft and Hard X-ray Photoemission by : Alexander Gray
Download or read book Depth-resolved Electronic Structure of Spintronic Nanostructures and Complex Materials with Soft and Hard X-ray Photoemission written by Alexander Gray and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation we describe several new directions in the field of x-ray photoelectron spectroscopy, with a particular focus on the enhancement and control of the depth sensitivity and selectivity of the measurement. Enhancement of the depth sensitivity is achieved by going to higher photon energies with hard x-ray excitation and taking advantage of the resulting larger electron inelastic mean-free paths. This novel approach provides a more accurate picture of bulk electronic structure, when compared to the traditional soft x-ray photoelectron spectroscopy (XPS) which, for some systems, may be too strongly influenced by surface effects. We present three case-studies wherein such hard x-ray photoelectron spectroscopy (HAXPES) in the multi-keV regime is used to probe the bulk properties of complex thin-film materials, which would be otherwise impossible to investigate using conventional soft x-ray XPS. Namely, (1) we directly observe the opening of a semiconducting gap in epitaxial Cr[subscript 0.08]Al[subscript 0.20] alloy thin films and confirm this with theory, (2) we study the electronic and structural properties of near-Heusler Fe[subscript x]Si[subscript 1-x] alloy thin films of various composition and degrees of crystallinity, and (3) we observe the Mott metal-to-insulator transition in the ultra-thin epitaxial LaNiO3 films via core-level and valence-band spectroscopies. By performing the experiments at the photon energy of 5.95 keV, the bulk-sensitivity of the measurements, characterized by the inelastic mean-free path of the photoemitted electrons, is enhanced by a factor of 4-7 compared to the conventional soft x-ray photoelectron spectroscopy. The experimental results are compared to calculations performed using various first-principle theoretical approaches, such as the density-functional theory and the one-step theory of photoemission. Furthermore, we present the first results of hard x-ray angle-resolved photoemission measurements (HARPES), at excitation energies of 3.24 and 5.95 keV. Compared to traditional ARPES, carried out in the UPS regime (20-100 eV), our technique enables us to probe on average 10-40 times deeper into the bulk. Single-crystal W(110) is used to demonstrate viability of the technique, with clear dispersive bands seen at 5.95 keV. As a second proof of principle for HARPES, the technologically-relevant material GaAs(001) is used to illustrate the broad applicability of the technique. In order to demonstrate the compositional sensitivity of the new method, we also compare the measurements of pure GaAs to the measurements of the ferromagnetic semiconductor Ga[subscript 0.97]Mn[0.03]As. Clear differences due to Mn-derived states are observed in the bulk band structure measured with the excitation energy of 3.24 keV. All of these experimental HARPES results are compared to free-electron final-state model calculations and more precise fully-relativistic one-step photoemission theory including matrix element effects. As noted, increasing the inelastic mean-free path, or more properly the effective attenuation length [Lambda subscript EAL] of the photoemitted electrons by going to higher photon energies increases the bulk sensitivity of the measurement, and facilitates a wider range of probing depths which can be accessed via variable take-off angle (theta subscript TOA) experiments. However, this approach does not circumvent the fact that no matter how long the photoelectron escape depth is, the photoemission signal originating closer to the surface will prevail over the signal originating from below according to I(z)=I0exp[-z /[Lambda subscript EAL]sin[theta subscript TOA]]. This constraint can be modulated in a useful way, if one were allowed to tailor the intensity profile of the electromagnetic field of the incident x-ray radiation inside the sample. In a second aspect of this dissertation, this type of depth selectivity is achieved by setting-up an x-ray standing wave field in the sample by growing it on a synthetic periodic multilayer mirror substrate, which in first-order Bragg reflection acts as the standing-wave generator. The antinodes of the standing wave function as "epicenters" for photoemission, and can be moved in the direction perpendicular to the sample surface by either scanning the incidence angle [theta subscript inc], or the photon energy through the Bragg condition. Alternatively, provided that one of the underlying layers in the structure is grown in a shape of a wedge with varying thickness, the standing wave can be scanned vertically though the sample simply by moving the sample laterally under the x-ray measurement spot. We present the first study in which the chemical and electronic-structure profiles of a magnetic tunnel junction La[subscript 0.7]Sr[subscript 0.3]MnO3/SrTiO3 (LSMO/STO) have been quantitatively determined by a combination of soft and hard x-ray standing-wave excited photoemission. By comparing experiment to x-ray optical calculations, the detailed chemical profile of the constituent layers and their interfaces is quantitatively derived with Ångstrom precision. Combined with core-hole multiplet theory incorporating Jahn-Teller distortion, these results indicate a change in the Mn bonding state near the LSMO/STO interface. Our results thus further clarify the reduced performance of LSMO/STO magnetic tunnel junction compared to ideal theoretical expectations. Finally, we demonstrate the addition of depth resolution to the usual two-dimensional images in photoelectron emission microscopy (PEEM) as a further aspect of standing-wave photoemission. We show that standing-wave excited photoelectron microscopy can be used to produce element-specific and depth-selective images of patterned samples. In conjunction with x-ray optical theoretical modeling, quantitative information about the depth-dependent chemical composition of the sample can be extracted from the photoemission data. The good agreement between our experimental results and model calculations suggests that future studies with better spatial and spectral resolution will also yield more detailed information about the interfacial regions. This addition of quantitative depth selectivity to the conventional laterally-resolved soft x-ray photoelectron emission microscopy thus should considerably enhance the capabilities of the PEEM as a research, development and metrology tool for science and industry.
Book Synopsis Electronic Structure Study of Low-dimensional Systems with Angle-resolved Photoemission Spectroscopy by : Marco Papagno
Download or read book Electronic Structure Study of Low-dimensional Systems with Angle-resolved Photoemission Spectroscopy written by Marco Papagno and published by . This book was released on 2005 with total page 75 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A New Spin on Photoemission Spectroscopy by :
Download or read book A New Spin on Photoemission Spectroscopy written by and published by . This book was released on 2008 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: The electronic spin degree of freedom is of general fundamental importance to all matter. Understanding its complex roles and behavior in the solid state, particularly in highly correlated and magnetic materials, has grown increasingly desirable as technology demands advanced devices and materials based on ever stricter comprehension and control of the electron spin. However, direct and efficient spin dependent probes of electronic structure are currently lacking. Angle Resolved Photoemission Spectroscopy (ARPES) has become one of the most successful experimental tools for elucidating solid state electronic structures, bolstered bycontinual breakthroughs in efficient instrumentation. In contrast, spin-resolved photoemission spectroscopy has lagged behind due to a lack of similar instrumental advances. The power of photoemission spectroscopy and the pertinence of electronic spin in the current research climate combine to make breakthroughs in Spin and Angle Resolved Photoemission Spectroscopy (SARPES) a high priority . This thesis details the development of a unique instrument for efficient SARPES and represents a radical departure from conventional methods. A custom designed spin polarimeter based on low energy exchange scattering is developed, with projected efficiency gains of two orders of magnitude over current state-of-the-art polarimeters. For energy analysis, the popular hemispherical analyzer is eschewed for a custom Time-of-Flight (TOF) analyzer offering an additional order of magnitude gain in efficiency. The combined instrument signifies the breakthrough needed to perform the high resolution SARPES experiments necessary for untangling the complex spin-dependent electronic structures central to today?s condensed matter physics.
Book Synopsis Electronic Structure and Collective Excitations in Correlated Materials by : Felix Tilman Schmitt
Download or read book Electronic Structure and Collective Excitations in Correlated Materials written by Felix Tilman Schmitt and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In condensed matter, electrons are not independent but are coupled to their neighbors via interactions; they are said to be correlated. This fact that electronic states are aware of their neighbors' states and changes thereof gives rise to a rich variety of properties and physics that defines the nature around us. Correlations in condensed matter can range in their effect from slight changes in the band structure to the emergence of order and symmetry breaking, which lead to novel properties and phases. These correlations exhibit themselves on different time scales. Mott-insulators, in which strong Coulomb repulsion between electrons splits a half-filled conduction band to result in an insulator, can have a band gap of several eV. On the other hand, transitions into the superconducting or charge density wave state, for example, happen on energy scales within several tens to hundreds of meV of EF. Despite the plethora of phenomena arising from these correlations, this many-body problem is hard to tackle and there is still much to be learned. This work investigates different aspects of correlated systems in and out of equilibrium with angle resolved photoemission (ARPES), and time resolved ARPES, two powerful spectroscopic techniques that are able to elucidate the dynamics and mechanics of correlations. Starting out, the experimental ARPES setup is introduced, and the ARPES system located in the Geballe Laboratory for Advanced Materials at Stanford University is described in more detail, since its maintenance and enhancement were an integral part of this work. In the following, the high energy properties of Nd2-xCexCuO4+d (NCCO) are investigated with ARPES. NCCO belongs to the electron doped side of a class of materials called high temperature superconducting Cuprates (HTSCs), so called because of their unusually high transition temperatures. The HTSCs exhibit a plethora of rich physics; including the anti-ferromagnetic insulating phase of the undoped parent compound dominated by Mott-Hubbard physics to the superconducting dome which features superconductivity with a d-wave symmetry whose origin is still a mystery. The hole doped HTSCs show a vertical band dispersion in ARPES measurements around 0.3 eV which was termed the high energy anomaly (HEA). Here, a systematic study of high energy features on NCCO revealed a similar HEA, albeit around 0.6 eV binding energy. We were able to successfully explain the HEA within the Hubbard model as being a cross-over from the quasi particle band resulting from doping and the lower or upper Hubbard band, depending on doping. The simulations also captured the difference in energy scale between hole and electron doping. Next, focusing on energies within several tens of meV of EF, a different energy scale of NCCO is explored. In the hole doped HTSCs, a discontinuity of the electronic dispersion around 50-70 meV was observed both in the region of the Brillouin zone were the d-wave superconducting gap had a node ("nodal") and where it had a maximum ("antinodal"). Conversely, in the electron doped materials this kink could only be observed in the antinodal region. If the discontinuity or "kink", which is hypothesized to originate from electron phonon coupling to certain Oxygen modes, is related to superconductivity, one would imagine it to have the same universality as the observed superconductivity. Our work demonstrates that new and improved ARPES data show a kink in the nodal region of NCCO as well, giving this discontinuity universality among the HTSCs. Superconductivity (SC) (at least conventional, electron phonon mediated superconductivity according to Bardeen-Cooper-Schrieffer) is closely related to its brethren, the spin- (SDW) or charge-density waves (CDW): all are mediated by different channels of the same type of interaction. The non-equilibrium dynamics and excitation modes of CDWs and SCs are closely related. Time resolved ARPES (tr-ARPES) is able to probe both non-equilibrium dynamics and collective excitation modes in real time. Continuing, this work explores the non-equilibrium physics of TbTe3, a model system for studying charge density waves. Our systematic study of the transient dynamics in dependence of excitation density revealed a complex picture ranging all the way from a weakly perturbed regime, in which collective modes were evident to a strongly perturbed regime, where we could observe the transient melting of the CDW state. This unprecedented insight into the dynamics of interactions will enhance our future understanding of correlated materials. Through the strengths of tr-ARPES, we were able to assign one of the collective modes we observed to the amplitude mode of the CDW. This provides a major stepping stone towards seeing a similar amplitude mode in superconductors. Especially in novel superconductors like the HTSCs or the Pnictides, where the mechanism of superconductivity is still debated, the observation of such collective modes could greatly aid towards their understanding which is needed in order to eventually exploit their huge potential for real-life applications.
Book Synopsis Modern Techniques of Surface Science by : D. P. Woodruff
Download or read book Modern Techniques of Surface Science written by D. P. Woodruff and published by Cambridge University Press. This book was released on 1994-03-03 with total page 612 pages. Available in PDF, EPUB and Kindle. Book excerpt: Revised and expanded second edition of the standard work on new techniques for studying solid surfaces.
Book Synopsis Complete Momentum and Energy Resolved TOF Electron Spectrometerfor Time-resolved Photoemission Spectroscopy by :
Download or read book Complete Momentum and Energy Resolved TOF Electron Spectrometerfor Time-resolved Photoemission Spectroscopy written by and published by . This book was released on 2007 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last decade, high-resolution Angle-Resolved Photoemission Spectroscopy (ARPES) has emerged as a tool of choice for studying the electronic structure of solids, in particular, strongly correlated complex materials such as cuprate superconductors. In this paper we present the design of a novel time-of-flight based electron analyzer with capability of 2D in momentum space (kx and ky) and all energies (calculated from time of flight) in the third dimension. This analyzer will utilize an improved version of a 2D delay linedetector capable of imaging with
Book Synopsis Photoelectron Spectroscopy by : Stefan Hüfner
Download or read book Photoelectron Spectroscopy written by Stefan Hüfner and published by Springer Science & Business Media. This book was released on 2013-11-11 with total page 525 pages. Available in PDF, EPUB and Kindle. Book excerpt: An up-to-date introduction to the field, treating in depth the electronic structures of atoms, molecules, solids and surfaces, together with brief descriptions of inverse photoemission, spin-polarized photoemission and photoelectron diffraction. Experimental aspects are considered throughout and the results carefully interpreted by theory. A wealth of measured data is presented in tabullar for easy use by experimentalists.
