{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/45598"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/45598","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"NMR studies of slow motion in the organic superconductors k-(BEDT-TTF)2Cu[N(CN)2]X, X= Br, Cl","abstract":"Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2013-05-10T21:50:06Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Lui_TakKei.pdf: 11830561 bytes, checksum: 5477b7fed52668dabb3a0d337cc0bf19 (MD5)","abstract_html":"Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2013-05-10T21:50:06Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Lui_TakKei.pdf: 11830561 bytes, checksum: 5477b7fed52668dabb3a0d337cc0bf19 (MD5)","abstract_has_math":false,"creators":["Lui, Tak Kei"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Giannetta, Russell W.","Phillips, Philip W.","Slichter, C.P.","Stack, John D."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2013,"date_issued":"2013-08-22T16:49:07Z","date_published":"2013-08-22T16:49:07Z","updated_at":"2026-07-22T22:25:36Z","subjects":["Nuclear magnetic resonance (NMR)","Organic superconductor","Bis(ethylenedithio)tetrathiafulvalene(BEDT-TTF)","Motion"],"languages":["en"],"rights":["Copyright 2013 Tak Kei Lui"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/45598","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Giannetta, Russell W.","Phillips, Philip W.","Slichter, C.P.","Stack, John D."]},{"key":"dc:creator","label":"Author","values":["Lui, Tak Kei"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2013-08-22T16:49:07Z","2015-08-22T10:00:52Z","2013-08"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"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":["Nuclear magnetic resonance (NMR)","Organic superconductor","Bis(ethylenedithio)tetrathiafulvalene(BEDT-TTF)","Motion"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 2013 Tak Kei Lui"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/45598"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2013-05-10T21:50:06Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Lui_TakKei.pdf: 11830561 bytes, checksum: 5477b7fed52668dabb3a0d337cc0bf19 (MD5)","Made available in DSpace on 2013-08-22T16:49:07Z (GMT). No. of bitstreams: 2 Tak Kei_Lui.pdf: 11832199 bytes, checksum: c2808356c2f2604c451c877d0506286c (MD5) license.txt: 4057 bytes, checksum: 72976bc6bdfe5028205ab30017321e8d (MD5)","Restriction data tranferred 2014-07-01T11:34:39-05:00 Original Data Group with Access UIUC Users [automated] Release Date: 2015-08-22 11:49:27 UTC Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Seth Robbins (srobbins@illinois.edu) on 2013-08-22T16:49:45Z Item is restricted until 2015-08-22T16:49:27Z","U of I Only Restriction Lifted for Item 45580 on 2015-08-22T10:00:52Z.","The $^{13}$C NMR absorption lines in the organic superconductors $\\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]X, X~=~Br ($T_C=11.6$~K), Cl ($T_C=12.8$~K at 0.3~kbar) show an abrupt increase in the linewidth at 170~K at 9.4~T. This line broadening transition is believed to be caused by the abrupt slowing down of some ``motion'' as suggested by a sharp peak in the exponential component of the transverse relaxation rate ($1/T_{2E}$) at a slightly lower temperature at 9.4~T. To investigate the characteristics of this motion, we applied the multi-pulse ``S-shape'' sequence. Two preparation pulses label the spins according to their precession frequencies and modulate the NMR spectrum. We then allow the spins to evolve for a time $T_{ev}$, after which inspection pulses are applied to observe changes in the spectrum. The modulation in the NMR spectrum shows a decay as $T_{ev}$ increases. The decay is described by 2 time constants, $R_\\mathrm{fast}(T)$ and $R_\\mathrm{slow}(T)$. Each rate shows a sharp peak at some temperature near to, but not at, the linewidth transition. Outside the transition region, $R_\\mathrm{fast}$ is independent of $T$ and is close to the Gaussian component of the transverse relaxation rate $1/T_{2G}$. $R_\\mathrm{fast}$ represents the relaxation of the spectrum modulations by dipolar coupling. $R_\\mathrm{slow}$ is also largely $T$ independent outside the transition region. Unlike $R_\\mathrm{fast}$, $R_\\mathrm{slow}$ shows a strong $T_p$ dependence, namely, $R_\\mathrm{slow}$ varies as $T_p^2$. $T_p$ is the delay between the 2 preparation pulses, and $\\pi/T_p$ is equal to the separation between the adjacent peaks and troughs in the spectrum modulations. The $T_p^2$ dependence of $R_\\mathrm{slow}$ reflects the diffusive nature of the motion relaxing the modulations. It has been proposed that the motion causing the linewidth transition is the rotation of the ethylene end groups. But a second moment calculation reveals that the ethylene end groups contribute only a small fraction of the total measured $^{13}$C linewidth below the linewidth transition. An anisotropic Knight shift calculation suggests that the (ET)$_2$ dimers only need to deviate from its equilibrium position by $2.5^\\circ$ to produce a large enough spread in Knight shifts to account for the total measured linewidth below the linewidth transition. We believe a diffusive rotational motion of the (ET)$_2$ dimers together with a BPP style relaxation model is the cause of the peak of $R_\\mathrm{slow}$, the $T_p^2$ dependence of $R_\\mathrm{slow}$, the linewidth transition, as well as the peak in $1/T_{2E}$."]},{"key":"dc:title","label":"Title","values":["NMR studies of slow motion in the organic superconductors k-(BEDT-TTF)2Cu[N(CN)2]X, X= Br, Cl"]}]}],"canonical_facts":{"dc:contributor":["Giannetta, Russell W.","Phillips, Philip W.","Slichter, C.P.","Stack, John D."],"dc:creator":["Lui, Tak Kei"],"dc:date":["2013-08-22T16:49:07Z","2015-08-22T10:00:52Z","2013-08"],"dc:description":["Item withdrawn by Mark Zulauf (zulauf@illinois.edu) on 2013-05-10T21:50:06Z Item was in collections: University of Illinois Theses & Dissertations (ID: 1) No. of bitstreams: 1 Lui_TakKei.pdf: 11830561 bytes, checksum: 5477b7fed52668dabb3a0d337cc0bf19 (MD5)","Made available in DSpace on 2013-08-22T16:49:07Z (GMT). No. of bitstreams: 2 Tak Kei_Lui.pdf: 11832199 bytes, checksum: c2808356c2f2604c451c877d0506286c (MD5) license.txt: 4057 bytes, checksum: 72976bc6bdfe5028205ab30017321e8d (MD5)","Restriction data tranferred 2014-07-01T11:34:39-05:00 Original Data Group with Access UIUC Users [automated] Release Date: 2015-08-22 11:49:27 UTC Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Seth Robbins (srobbins@illinois.edu) on 2013-08-22T16:49:45Z Item is restricted until 2015-08-22T16:49:27Z","U of I Only Restriction Lifted for Item 45580 on 2015-08-22T10:00:52Z.","The $^{13}$C NMR absorption lines in the organic superconductors $\\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]X, X~=~Br ($T_C=11.6$~K), Cl ($T_C=12.8$~K at 0.3~kbar) show an abrupt increase in the linewidth at 170~K at 9.4~T. This line broadening transition is believed to be caused by the abrupt slowing down of some ``motion'' as suggested by a sharp peak in the exponential component of the transverse relaxation rate ($1/T_{2E}$) at a slightly lower temperature at 9.4~T. To investigate the characteristics of this motion, we applied the multi-pulse ``S-shape'' sequence. Two preparation pulses label the spins according to their precession frequencies and modulate the NMR spectrum. We then allow the spins to evolve for a time $T_{ev}$, after which inspection pulses are applied to observe changes in the spectrum. The modulation in the NMR spectrum shows a decay as $T_{ev}$ increases. The decay is described by 2 time constants, $R_\\mathrm{fast}(T)$ and $R_\\mathrm{slow}(T)$. Each rate shows a sharp peak at some temperature near to, but not at, the linewidth transition. Outside the transition region, $R_\\mathrm{fast}$ is independent of $T$ and is close to the Gaussian component of the transverse relaxation rate $1/T_{2G}$. $R_\\mathrm{fast}$ represents the relaxation of the spectrum modulations by dipolar coupling. $R_\\mathrm{slow}$ is also largely $T$ independent outside the transition region. Unlike $R_\\mathrm{fast}$, $R_\\mathrm{slow}$ shows a strong $T_p$ dependence, namely, $R_\\mathrm{slow}$ varies as $T_p^2$. $T_p$ is the delay between the 2 preparation pulses, and $\\pi/T_p$ is equal to the separation between the adjacent peaks and troughs in the spectrum modulations. The $T_p^2$ dependence of $R_\\mathrm{slow}$ reflects the diffusive nature of the motion relaxing the modulations. It has been proposed that the motion causing the linewidth transition is the rotation of the ethylene end groups. But a second moment calculation reveals that the ethylene end groups contribute only a small fraction of the total measured $^{13}$C linewidth below the linewidth transition. An anisotropic Knight shift calculation suggests that the (ET)$_2$ dimers only need to deviate from its equilibrium position by $2.5^\\circ$ to produce a large enough spread in Knight shifts to account for the total measured linewidth below the linewidth transition. We believe a diffusive rotational motion of the (ET)$_2$ dimers together with a BPP style relaxation model is the cause of the peak of $R_\\mathrm{slow}$, the $T_p^2$ dependence of $R_\\mathrm{slow}$, the linewidth transition, as well as the peak in $1/T_{2E}$."],"dc:identifier":["http://hdl.handle.net/2142/45598"],"dc:language":["en"],"dc:rights":["Copyright 2013 Tak Kei Lui"],"dc:subject":["Nuclear magnetic resonance (NMR)","Organic superconductor","Bis(ethylenedithio)tetrathiafulvalene(BEDT-TTF)","Motion"],"dc:title":["NMR studies of slow motion in the organic superconductors k-(BEDT-TTF)2Cu[N(CN)2]X, X= Br, Cl"],"dc:type":["text"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:36Z"}