715 research outputs found
Ultrafast dynamics in the presence of antiferromagnetic correlations in electron-doped cuprate La 2 − x Ce x CuO 4 ± δ
No full textWe used femtosecond optical pump-probe spectroscopy to study the photoinduced change in reflectivity of thin films of the electron-doped cuprate La[subscript 2−x]Ce[subscript x]CuO[subscript 4] (LCCO) with dopings of x=0.08 (underdoped) and x=0.11 (optimally doped). Above T[subscript c], we observe fluence-dependent relaxation rates that begin at a temperature similar to the one where transport measurements first show signatures of antiferromagnetic correlations. Upon suppressing superconductivity with a magnetic field, it is found that the fluence and temperature dependence of relaxation rates are consistent with bimolecular recombination of electrons and holes across a gap (2Δ[subscript AF]) originating from antiferromagnetic correlations which comprise the pseudogap in electron-doped cuprates. This can be used to learn about coupling between electrons and high-energy (ω>2Δ[subscript AF]) excitations in these compounds and set limits on the time scales on which antiferromagnetic correlations are static.Gordon and Betty Moore Foundation (EPiQS Initiative Grant GBMF4540)United States. Air Force. Office of Scientific Research (FA95501410332)National Science Foundation (U.S.) (DMR1410665
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Using microARPES and Machine Learning to Accelerate Experiments and Elucidate the Local Electronic and Chemical Structure of Quantum Materials
No full textPhotoemission experiments are an information rich probe into the electronic structure of materials. Angle-resolved photoemission spectroscopy (ARPES) focusing on the valence bands and X-ray photoemission spectroscopy (XPS) focusing on tightly bound core electrons give a wholistic view into the features of occupied electronic states. In this dissertation I: (1) perform the first ARPES studies of LaNiGa, (2) develop an autonomous machine learning control system to improve the speed at which ARPES data can be taken, and (3) analyze the correlation between spatially resolved XPS and ARPES studies on CoSnS. These together demonstrate the utility of ARPES and XPS for studying quantum materials as well as incorporating modern machine learning practices to extract otherwise hidden data from these rich datasets.LaNiGa is an unconventional superconductor that is reported to break time-reversal symmetry in its superconducting state, despite the absence of nearby magnetism. LaNiGa has a nonsymmorphic Cmcm space group, which enforces symmetry-protected electronic degeneracies in its band structure. ARPES measurements across the three-dimensional Brillouin zone reveal features broadly consistent with density functional theory calculations. These measurements provide direct evidence for both predicted symmetry-enforced degeneracies and accidental near-degeneracies throughout the electronic structure. These findings suggest that the interplay between these degeneracies and the Fermi surface topology may play a role in the superconducting pairing mechanism of LaNiGa. This work on LaNiGa, detailed in Chapter 3, lead to two publications [1,2].ARPES experiments often require substantial time to locate optimal sample regions for detailed study. AARDVARK, an autonomous machine learning control system, addresses this challenge by analyzing data in real time to guide measurements efficiently. The system uses uniform manifold approximation and projection (UMAP) for dimensionality reduction, followed by Gaussian process modeling to map spatial inhomogeneity. This pipeline reduces the number of measurements needed by approximately 75\% compared to traditional grid-search approaches while providing the same spatial heuristics to users. AARDVARK demonstrates the potential for integrating machine learning into photoemission spectroscopy workflows, enhancing the speed of collection of spatially resolved studies. This project is detailed in Chapter 4 and constitutes a manuscript that at the time of writing this dissertation is in preparation to be submitted for peer review.CoSnS exhibits surface heterogeneity with distinct sulfur, tin, and mixed terminations, which influence its local electronic structure. ARPES and XPS measurements were performed across a area using a micro-focused beam (), providing spatially resolved insight into the correlation between valence and core-level spectra. By combining traditional spectral integration methods with machine learning, the analysis captures termination-dependent variations in the electronic structure, forming a basis for interpreting spatial heterogeneity in hyperspectral datasets. These experiments highlight the critical role of synchrotron light sources in enabling simultaneous, high-resolution ARPES and XPS measurements, which are essential for studying spatially complex quantum materials. The study of surface heterogeneity in CoSnS in Chapter 5 is a portion of a manuscript that is still being prepared at the time of writing this dissertation
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Electronic and Chemical Photoemission signatures in correlated electron systems
No full textPhotoemission has emerged as a powerful tool capable of probing electronic structure of correlated materials. Signatures of correlated behavior is encoded into the photoemitted electron which is measured through photoemission. Photoemission, through core level analysis, also captures the chemical structure and surface composition of the material. This, combined with recent advancements in spot size reduction, improved resolution and the wider availability of synchrotrons, allows a simultaneous study of electronic and chemical structure, two key ingredients in contemporary quantum materials. Quantum materials of concern to this thesis involve the two regimes of topology and correlation. Broadly, both correlated and topological materials offer a variety of exotic electronic phases, but often require material specificity in explaining their behavior. We aim to bridge the two paradigms in an attempt to look for intersectionality by studying structurally simple members of both families using photoemission.This dissertation looks at photoemission signatures and surface characterization of the strongly correlated material HgBa2 CuO4+δ(Hg1201) and the magnetic Weyl semimetal Co3Sn2S2.Chapter 4 of the dissertation examines the correlated dispersion of the high temperature superconducting single-layer cuprate HgBa2 CuO4+δ(Hg1201). We find three dispersion anomalies at three different energy scales near the node of the brillouin zone. We find two kinks in the dispersion at ≈20 meV and ≈55 meV. We also observe a peak dip hump structure in the energy-dependent intensity profile. We examine their dependencies on doping, temperature and momentum to try to elucidate their origins.Chapter 5 of the thesis studies the relationship between topology and correlations in the magnetic Weyl semimetal Co3Sn2S2, and also identifying signatures of the different surface termination on the electronic structure. We perform spatially resolved photoemission to establish the different terminations presented by the cleaved crystal. We then observe band flattening that occurs in the paramagnetic phase and study the gradual transition as spin fluctuations increase and local moments become disordered.Given the importance of surface states in Magnetic Weyl semimetals such as Co3Sn2S2 , lastly, in Chapter 6 we make the correlation between the surface terminations and their corresponding photoemission fingerprints precise, providing a robust strategy for surface and electronic structure analysis incorporating topological machine learning. We map definitive photoemission signatures with surface defects and identify their impact on the observed band structure
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Spectroscopic Characterizations of the Topological Insulator Bi2Se3
No full textBi2Se3 is an ideal three-dimensional topological insulator in which chemical modifications such as doping and intercalation can be used to engineer surface properties or to further functionalize the topological surface state. In this work, we study the Bi2Se3 system of materials with three experimental techniques: 1) ultrafast optical pump-probe spectroscopy (OPP), 2) angle-resolved photoemission spectroscopy (ARPES), and 3) X-ray photoelectron spectroscopy (XPS). These spectroscopic techniques are utilized to study the out-of- equilibrium carrier properties, surface chemistry, and band structure of Bi2Se3, Bi2–xSbxSe3, and CuxBi2Se3.The photoexcited carrier decay in Bi2–xSbxSe3 nanoplatelets was studied with ultrafast optical pump-probe spectroscopy, demonstrating a substantial slowing of the bulk carrier relaxation time in bulk-insulating Bi2–xSbxSe3 as compared to n-type bulk-metallic Bi2Se3 at low temperatures, which approaches 3.3 ns in the zero pump fluence limit. This long-lived decay is correlated across different fluences and antimony concentrations, revealing unique decay dynamics not present in n-type Bi2Se3, namely the slow bimolecular recombination of bulk carriers.Using ambient pressure X-ray photoelectron spectroscopy, copper migration in interca- lated CuxBi2Se3 is demonstrated, occurring on a timescale of hours to days after initial surface cleaving. The increase in near-surface copper proceeds along with the oxidation of the sample surface and large changes in the selenium content, with the development of copper and selenium gradients. These complex changes are further modelled with core level spectroscopy simulations (SESSA), which suggest a composition gradient near the surface which develops with oxygen exposure. These results shed light on a phenomenon that must be considered in intercalated topological insulators and intercalated materials in general
(Motif of blood in the Inna Lisnianskaya’s poetry
No full textInna Lisnianskaya is a Russian poet who has been continuously writing since the fifties andthe author of hundreds outstanding poems. She has built her poetic universe on the basis of certainconcepts. Some of them appear more often than the others and blood is one of them. Abouta hundred of Inna Lisnianskaya’s poems that include the motif of blood was chosen for this work.Their analysis (in accordance to the studies of R. W. Langaker) is to show that the phenomenon ofsubjectification is the basis of the conceptualization process
PROSES POSTING CHARGE TO ROOM DI HOTEL GRAND INNA TUNJUNGAN SURABAYA
No full textThe goal achieved in this final preparation is to know the process of posting a
charge to room at the Grand Inna Tunjungan hotel in Surabaya. The author who
also works as a waitress for F&B Service at the Grand Inna Tunjungan Surabaya
hotel makes observations on the process of posting charge to room. The author
concludes that the process of posting a charge to room at the Grand Inna
Tunjungan hotel, Surabaya, is a process of combining costs incurred by guests
(eating and drinking,) whose payment is made when guests check out. Can be
applied to guests who are staying at the hotel who have a deposit to guarantee the
use of hotel facilities that are subject to a fee
That’s not for our kids: The strange death of philosophy and ethics in a low socioeconomic secondary school
No full textThis paper is a critical reflection on the teaching of the new Philosophy and Ethics course in a low socioeconomic context in Perth, Western Australia. It charts the successes and failures of the Philosophy and Ethics course, leading to the eventual demise of the subject at the end of 2010. We frame this reflection within Deleuzean notions of geophilosophy to advocate for a Philosophy and Ethics that is informed by nomadic thought as this offers potential for students to become innovative and creative of their selves – the critical freedom we see as potentially transformative for contemporary society. We see the strange death as being influenced by many factors, but that it is best considered as a ‘missed opportunity’ because it has so much potential to be transformative of student subjectivities in schools. We see that this critical reflection could be invaluable in a reconsideration of the scope and focus of the subject often viewed as elitist and impractical
STANDARISASI SEQUENCE OF SERVICE UNTUK MEMPERLANCAR OPERASIONAL KERJA DI PALAPA COFFEE SHOP GRAND INNA TUNJUNGAN SURABAYA
No full textThe purpose of this study was to find out how to standardize the sequence of service at Palapa Coffee Shop Grand Inna Tunjungan Surabaya. In this study, the
authors used a qualitative descriptive research type. The author can conclude that the standardization of the sequence of service at The Grand Inna Tunjungan Surabaya is greeting, guest seating, folding napkin laying, giving the menu, beverage and food taking orders, repeat orders, distribute of captain order, beverage serving, dessert suggestion, settle bill, say thank you.
Keywords: sequence of service, service, coffee shop, waiter, waitres
STANDAR OPERASIONAL PROSEDUR SANITASI PERALATAN MAKAN DAN MINUM di PALAPA COFFEE SHOP HOTEL GRAND INNA TUNJUNGAN SURABAYA
No full textThe purpose of this final project is to find out how the standard operating procedures for sanitation of eating and drinking equipment at Palapa Coffee Shop Hotel Grand Inna Tunjungan Surabaya. The author observes the operational standards of sanitation equipment for eating and drinking equipment at the palapa coffee shop, Grand Inna Tunjungan Hotel, Surabaya. The author draws the conclusion that with the SOP cleaning the eating and drinking equipment greatly helps employees to carry out the work of washing food and drink equipment in the restaurant Palapa Coffee Shop in accordance with the standards set by the hotel.
Keywords: Standard Operating Procedures, sanitation, cutlery and drinks, restaurants
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ARPES Studies of Cuprate Fermiology: Superconductivity, Pseudogap and Quasiparticle Dynamics
No full textWe present angle-resolved photoemission spectroscopy (ARPES) studies of the cuprate high-temperature superconductors which elucidate the relation between superconductivity and the pseudogap and highlight low-energy quasiparticle dynamics in the superconducting state. Our experiments suggest that the pseudogap and superconducting gap represent distinct states, which coexist below T{sub c}. Studies on Bi-2212 demonstrate that the near-nodal and near-antinodal regions behave differently as a function of temperature and doping, implying that different orders dominate in different momentum-space regions. However, the ubiquity of sharp quasiparticles all around the Fermi surface in Bi-2212 indicates that superconductivity extends into the momentum-space region dominated by the pseudogap, revealing subtlety in this dichotomy. In Bi-2201, the temperature dependence of antinodal spectra reveals particle-hole asymmetry and anomalous spectral broadening, which may constrain the explanation for the pseudogap. Recognizing that electron-boson coupling is an important aspect of cuprate physics, we close with a discussion of the multiple 'kinks' in the nodal dispersion. Understanding these may be important to establishing which excitations are important to superconductivity
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