Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu13377136222021-08-03T06:05:02Z Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements Yong, Jie Physics superfluid density penetration depth superconductivity strongly underdoped cuprate films iron-based superconducting films pairing symmetry Beresinskii-Kosterlitz-Thouless transition quantum critical scaling thermal phase fluctuations <p>Superfluid density n<sub>s</sub>(T) [∝ λ<sup>-2</sup>(T) and λ is the penetration depth] is a fundamental parameter in superconductivity. In my Ph. D. work, by measuring the complex sheet conductivity of thin superconducting films in a two-coil mutual inductance apparatus, both the amplitude and the temperature dependence of superfluid density are determined in various superconducting systems. This is then used to understand various physics like pairing symmetry, and thermal and quantum critical fluctuations in low dimensions, in the following materials:</p> <p>(1)Bi<sub>2</sub>Sr<sub>2</sub>CaCu<sub>2</sub>O<sub>8+x</sub> (Bi-2212) films: A wide range of doping is achieved by pulsed laser deposition (PLD) and sputtering with transition temperatures (T<sub>c</sub>) ranging from 80K near optimal doping to 6K for severely underdoped ones. In moderately underdoped Bi-2212 films with T<sub>c</sub> > 50K, Beresinskii-Kosterlitz-Thouless (BKT) transition, an evidence of 2-D thermal critical behavior, is observed by a sharp downturn of superfluid density near T<sub>c</sub>. This is consistent with the extremely anisotropic nature of Bi-2212. However, this thermal critical behavior disappears for severely underdoped Bi-2212 with T<sub>c</sub> < 45K. At this regime, T<sub>c</sub> scales linearly with the superfluid density λ<sup>-2</sup>(0). These two results are the evidence of the 2-D quantum critical behavior in deeply underdoped Bi-2212 near a quantum critical point (QCP).</p> <p>(2) Iron-based Ba(Co<sub>x</sub>Fe<sub>1-x</sub>)<sub>2</sub>As<sub>2</sub> films near optimal doping: At low temperatures, superfluid density varies like λ<sup>-2</sup>(T) ∝ T<sup>2.55</sup>, consistent with a novel s± pairing symmetry with significant interband scattering between two different Fermi surfaces. Overall, λ<sup>-2</sup>(T) can be fit by a dominant small BCS-like superconducting gap 2Δ/k<sub>B</sub>T<sub>c</sub> ~2.1. The possible bigger gap vanishes and this may due to its strong intraband scattering.</p> <p>(3) Ultrathin NbN and Pb films: sharp downturns, which clearly deviate λ<sup>-2</sup>(T) from its standard BCS theory predictions, are observed in these ultrathin films near T<sub>c</sub>. They are associated with two dimensional thermal critical fluctuations and are clear evidences of Beresinskii-Kosterlitz-Thouless (BKT) transitions. However, it seems that downturns always occur earlier than what XY model predicts. This means that the vortices are energetically easier to create, and the reason behind this finding is still unclear. </p> 2012-06-22 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1337713622 http://rave.ohiolink.edu/etdc/view?acc_num=osu1337713622 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
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English |
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NDLTD |
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Physics superfluid density penetration depth superconductivity strongly underdoped cuprate films iron-based superconducting films pairing symmetry Beresinskii-Kosterlitz-Thouless transition quantum critical scaling thermal phase fluctuations |
| spellingShingle |
Physics superfluid density penetration depth superconductivity strongly underdoped cuprate films iron-based superconducting films pairing symmetry Beresinskii-Kosterlitz-Thouless transition quantum critical scaling thermal phase fluctuations Yong, Jie Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| author |
Yong, Jie |
| author_facet |
Yong, Jie |
| author_sort |
Yong, Jie |
| title |
Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| title_short |
Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| title_full |
Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| title_fullStr |
Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| title_full_unstemmed |
Quantum Critical Behavior in Deeply Underdoped Cuprate Films and Pairing Symmetry in Iron Pnictide Superconductors Probed by Penetration Depth Measurements |
| title_sort |
quantum critical behavior in deeply underdoped cuprate films and pairing symmetry in iron pnictide superconductors probed by penetration depth measurements |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2012 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1337713622 |
| work_keys_str_mv |
AT yongjie quantumcriticalbehaviorindeeplyunderdopedcupratefilmsandpairingsymmetryinironpnictidesuperconductorsprobedbypenetrationdepthmeasurements |
| _version_ |
1719430621488480256 |