{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/125511"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/125511","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Long-wavelength density fluctuations and momentum scrambling In the strange metal Bi2Sr2CaCu2O8+x","abstract":"Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_html":"Submission original under an indefinite embargo labeled &#x27;Open Access&#x27;. The submission was exported from vireo on 2025-02-04 without embargo terms","abstract_has_math":false,"creators":["Chen, Jin"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Abbamonte, Peter","Chiang, Tai-Chang","Phillips, Philip W.","Uchoa, Bruno"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-05-23","date_published":"2024-05-23","updated_at":"2026-07-22T22:25:02Z","subjects":["Electron Energy Loss Spectrum","Strange Metal","Plasmon","Unconventional Superconductor"],"languages":["en","eng"],"rights":["Copyright 2024 Jin Chen"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://hdl.handle.net/2142/125511","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Abbamonte, Peter","Chiang, Tai-Chang","Phillips, Philip W.","Uchoa, Bruno"]},{"key":"dc:creator","label":"Author","values":["Chen, Jin"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2024-05-23","2024-08"]},{"key":"dc:type","label":"Dc Type","values":["text","Thesis"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Electron Energy Loss Spectrum","Strange Metal","Plasmon","Unconventional Superconductor"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en","eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2024 Jin Chen"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://hdl.handle.net/2142/125511"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, Jin Chen, accepted the attached license on 2024-05-22 at 20:36.","The student, Jin Chen, submitted this Dissertation for approval on 2024-05-22 at 21:19.","This Dissertation was approved for publication on 2024-05-23 at 16:35.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20809 on 2025-02-04 at 21:03:24","There is currently a major controversy about plasmons in strange metals, which can be resolved by studying the momentum-dependent density fluctuation spectrum. Recently published papers, based on momentum-resolved energy-loss spectroscopy (M-EELS) at large q, show a frequency-independent continuum in the strange metal Bi2Sr2CaCu2O8+x [Mitrano, PNAS 115, 5392 (2018); Husain, PRX 9, 041062 (2019)], reminiscent of the marginal Fermi liquid (MFL) hypothesis of the late 1980s [Varma, PRL 63, 1996 (1989)]. However, our observations, which were done at large q, have been difficult to reconcile with infrared (IR) optics, done at q = 0, which see a well-defined plasmon excitation. In this thesis, we present M-EELS data taken with ∼4× better momentum resolution, allowing us to reach the optical limit, q ∼ 0, where direct comparison with IR optics can be made. We see a clear plasmon feature for q < 0.04 r.l.u. that, when analyzed with an old theoretical framework of Jain & Allen [Jain, PRB 32, 997 (1985)], shows quantitative consistency between M-EELS and IR experiments. For q > 0.04 r.l.u., the spectra become incoherent. Instead of a conventional dispersive plasmon, the spectra show a constant-in-frequency continuum. Our results resolve the controversy and show how the density response of strange metals evolves from the Brillouin zone boundary down to the optical limit, q ∼ 0. We speculate that electrons in such a planckian metal undergo momentum scrambling at finite frequency, ω, and nonzero q. Black phosphorus, as a layered semiconductor, is well-known for its tunable narrow energy gap and large in-plane optical anisotropy, holding great potential for diverse applications such as optical sensors. However, few studies of the dynamic charge response at finite momentum transfer have been reported. Using M-EELS, we measured the interband transitions of black phosphorus as a function of temperature and momentum transfer. We observe a temperature dependent, non-dispersive, isotropic gap in M-EELS spectrum in bulk black phosphorus. Beyond M-EELS, we propose a new technique called two-electron M-EELS, where there are two electrons coming in and two electrons going out, undergoing momentum and energy transfer. We calculated the cross section in the case of reflection geometry, similar to M-EELS. With such a technique, we are able to measure electron interaction inside the materials, such as the coulomb interaction or phonon-mediated interaction, among others. In this thesis, we take a coulomb interaction as an example and calculate the corresponding cross section."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Long-wavelength density fluctuations and momentum scrambling In the strange metal Bi2Sr2CaCu2O8+x"]}]}],"canonical_facts":{"dc:contributor":["Abbamonte, Peter","Chiang, Tai-Chang","Phillips, Philip W.","Uchoa, Bruno"],"dc:creator":["Chen, Jin"],"dc:date":["2024-05-23","2024-08"],"dc:description":["Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2025-02-04 without embargo terms","The student, Jin Chen, accepted the attached license on 2024-05-22 at 20:36.","The student, Jin Chen, submitted this Dissertation for approval on 2024-05-22 at 21:19.","This Dissertation was approved for publication on 2024-05-23 at 16:35.","DSpace SAF Submission Ingestion Package generated from Vireo submission #20809 on 2025-02-04 at 21:03:24","There is currently a major controversy about plasmons in strange metals, which can be resolved by studying the momentum-dependent density fluctuation spectrum. Recently published papers, based on momentum-resolved energy-loss spectroscopy (M-EELS) at large q, show a frequency-independent continuum in the strange metal Bi2Sr2CaCu2O8+x [Mitrano, PNAS 115, 5392 (2018); Husain, PRX 9, 041062 (2019)], reminiscent of the marginal Fermi liquid (MFL) hypothesis of the late 1980s [Varma, PRL 63, 1996 (1989)]. However, our observations, which were done at large q, have been difficult to reconcile with infrared (IR) optics, done at q = 0, which see a well-defined plasmon excitation. In this thesis, we present M-EELS data taken with ∼4× better momentum resolution, allowing us to reach the optical limit, q ∼ 0, where direct comparison with IR optics can be made. We see a clear plasmon feature for q < 0.04 r.l.u. that, when analyzed with an old theoretical framework of Jain & Allen [Jain, PRB 32, 997 (1985)], shows quantitative consistency between M-EELS and IR experiments. For q > 0.04 r.l.u., the spectra become incoherent. Instead of a conventional dispersive plasmon, the spectra show a constant-in-frequency continuum. Our results resolve the controversy and show how the density response of strange metals evolves from the Brillouin zone boundary down to the optical limit, q ∼ 0. We speculate that electrons in such a planckian metal undergo momentum scrambling at finite frequency, ω, and nonzero q. Black phosphorus, as a layered semiconductor, is well-known for its tunable narrow energy gap and large in-plane optical anisotropy, holding great potential for diverse applications such as optical sensors. However, few studies of the dynamic charge response at finite momentum transfer have been reported. Using M-EELS, we measured the interband transitions of black phosphorus as a function of temperature and momentum transfer. We observe a temperature dependent, non-dispersive, isotropic gap in M-EELS spectrum in bulk black phosphorus. Beyond M-EELS, we propose a new technique called two-electron M-EELS, where there are two electrons coming in and two electrons going out, undergoing momentum and energy transfer. We calculated the cross section in the case of reflection geometry, similar to M-EELS. With such a technique, we are able to measure electron interaction inside the materials, such as the coulomb interaction or phonon-mediated interaction, among others. In this thesis, we take a coulomb interaction as an example and calculate the corresponding cross section."],"dc:format":["application/pdf"],"dc:identifier":["https://hdl.handle.net/2142/125511"],"dc:language":["en","eng"],"dc:rights":["Copyright 2024 Jin Chen"],"dc:subject":["Electron Energy Loss Spectrum","Strange Metal","Plasmon","Unconventional Superconductor"],"dc:title":["Long-wavelength density fluctuations and momentum scrambling In the strange metal Bi2Sr2CaCu2O8+x"],"dc:type":["text","Thesis"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:02Z"}