Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session A2: Invited Session: Novel Superconductivity in FE Selenide Superconductors |
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Sponsoring Units: DCMP Chair: Douglas Scalapino, University of California at Santa Barbara Room: Ballroom II |
Monday, March 18, 2013 8:00AM - 8:36AM |
A2.00001: Ab initio calculations and crystal symmetry considerations for novel FeSe-based superconductors Invited Speaker: Igor Mazin Density functional calculations disagree with the ARPES measurements on both K$_{0.3}$Fe$_2$Se$_2$ superconducting phase and FeSe/SrTiO$_3$ monolayers. Yet they can still be dramatically useful for the reason that they respect full crystallographic symmetry and take good account of electron-ion interaction. Using just symmetry analysis, it is shown that nodeless d-wave superconductivity is not an option in these systems, and a microscopic framework is derived that leads to a novel s-wave sign-reversal state, qualitatively different from the already familiar s$_\pm$ state in pnictides and bulk binary selenides. Regarding the FeSe monolayer, bonding and charge transfer between the film and the substrate is analyzed and it is shown that the former is weak and the latter negligible, which sets important restrictions on possible mechanisms of doping and superconductivity in these monolayers. In particular, the role of the so-called ``Se etching,'' necessary for superconductivity in FeSe monolayers, is analyzed in terms of electronic structure and bonding with the substrate. [Preview Abstract] |
Monday, March 18, 2013 8:36AM - 9:12AM |
A2.00002: Scanning tunneling microscopy study on superconductivity of FeSe thin films Invited Speaker: Xucun Ma Searching for superconducting materials with high transition temperature (T$_{C})$ is one of the most exciting and challenging fields in physics and materials science. By using MBE technique, we are able to prepare stoichiometric and superconducting FeSe single crystalline films on various substrates, which enables us investigate superconductivity mechanism of FeSe thin films in well-controlled way [1-3]. Most importantly, by using low temperature scanning tunneling spectroscopy, a superconductive gap as large as 20 meV and the vortex state under high magnetic field are revealed in the single unit-cell thick FeSe films on SrTiO$_{3}$(001) substrate [4]. Such a high Tc superconductor is further confirmed by recent transport measurement. The study not only demonstrates a powerful way for finding new superconductors and for raising T$_{C}$, but also provides a well-defined platform for systematic study of the mechanism of unconventional superconductivity by using different superconducting materials and substrates. The study is collaborated with Professor Qi-Kun Xue, Department of Physics, Tsinghua University, China.\\[4pt] References:\\[0pt] [1] C. L. Song, Y. L.Wang, P. Cheng, Y. P. Jiang, W. Li, T. Zhang, Z. Li, K. He, L. L. Wang, J. F. Jia, H. H, Hung, C. J. Wu, X. C. Ma, X. Chen, and Q. K. Xue, \textbf{Science 332}, 1410 (2011).\\[0pt] [2] C. L. Song, Y. L. Wang, Y. P. Jiang, Z. Li, L. L. Wang, K. He, X. Chen, X. C. Ma, and Q. K. Xue, \textbf{Phys. Rev. B} \textbf{84}, 020503 (2011).\\[0pt] [3] C. L. Song, Y. L. Wang, Y. P. Jiang, L. L. Wang, Ke He, Xi Chen, J. E. Hoffman, X. C. Ma, and Q. K. Xue, \textbf{Phys. Rev. Lett. 109}, 137004 (2012).\\[0pt] [4] Wang Qingyan, Li Zhi, Zhang Wenhao, Zhang Zuocheng, Zhang Jinsong, Li Wei, Ding Hao, Ou Yunbo, Deng Peng, Chang Kai, Wen Jing, Song Canli, He Ke, Ji Shuaihua, Jia Jinfeng, Wang Yayu, Wang Lili, Chen Xi, Ma Xucun, and Xue Qikun, \textbf{Chin. Phys. Lett. 29}, 037402 (2012). [Preview Abstract] |
Monday, March 18, 2013 9:12AM - 9:48AM |
A2.00003: Phase Diagram and High Temperature Superconductivity at 65K in the Single-Layer FeSe Films Revealed by ARPES Invited Speaker: Shaolong He The discovery of the iron-based superconductors in 2008 not only provides another venue to understand the origin of high-Tc superconductivity but also a new playground to explore novel superconductors with higher superconducting transition temperature. The latest report of possible high temperature superconductivity in the single-layer FeSe films grown on SrTiO3 substrate is both surprising and interesting [1]. In this talk, we report the electronic structure and phase diagram of the single-layer FeSe films by angle-resolved photoemission spectroscopy (ARPES) [2,3]. Our high-resolution ARPES results show that it has a simple Fermi surface topology consisting only of electron pockets near the zone corner without indication of any Fermi surface around the zone center. In addition, our observation of large and nearly isotropic superconducting gap in this strictly two-dimensional system rules out existence of node in the superconducting gap. We also established a phase diagram in this single-layer FeSe films by an annealing procedure to tune the charge carrier concentration over a wide range. By optimizing the annealing process, we observed evidence of a record high Tc of $\sim$ 65K in the single-layer FeSe films. The wide tunability of the system across different phases, and its high-Tc, make the single-layer FeSe film ideal not only to investigate the superconductivity physics and mechanism, but also to study novel quantum phenomena and for potential applications.\\[4pt] [1] Q.Y. Wang et al., Chin. Phys. Lett. 29, 037402 (2012)\\[0pt] [2] D. F. Liu et al., Nature Communications. 3, 931 (2012)\\[0pt] [3] S. L. He et al., arXiv:1207.6823v1, (2012) [Preview Abstract] |
Monday, March 18, 2013 9:48AM - 10:24AM |
A2.00004: Pairing and Fermiology in iron-chalcogenide superconductors Invited Speaker: Dung-Hai Lee ``Stripe''-type magnetic fluctuations has been postulated as the trigger of Cooper pairing in iron-based superconductors. In iron pnictides the matching of the peak magnetic fluctuations wavevector and the Fermiology lands support to the above idea. However recent ARPES results on high T$_{\mathrm{c}}$ A$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_{\mathrm{2}}$ and FeSe/SrTiO$_{\mathrm{3}}$ and neutron results on A$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_{\mathrm{2}}$ pose challenges to the above picture. In this talk we will take a fresh new look at the purported pairing mechanism of iron-based superconductors. [Preview Abstract] |
Monday, March 18, 2013 10:24AM - 11:00AM |
A2.00005: S$_{4}$ Symmetric Microscopic Model for Iron Based Superconductors Invited Speaker: Jiangping Hu How are cuprates and iron-based high temperature superconductors correlated? What is the common mechanism behind two different families of iron-based superconductors, iron-pnicitides and iron-chalcogenides? These two questions are two major challenges in the today's field of high temperature superconductors. In this talk, we will show when the lattice symmetry, the \textbf{S}$_{\mathbf{4}}$ symmetry, of the building block, the tri-layer structure of FeAs or FeSe, is properly considered, the low energy physics of iron-based superconductors is governed by a two-orbital Hamiltonian near half filling that can be divided two weakly coupled one-orbital model. We will discuss the microscopic origin and some unique properties of the model, including magnetism and pairing symmetry. The model provides a unified understanding of iron pnictides and iron chalcogenides, and suggests that cuprates and iron-based superconductors share an identical high-T$_{c}$~superconducting mechanism. The model leads to a natural classification of pairing symmetry according to \textbf{S}$_{\mathbf{4}}$ symmetry. When the pairing is driven by antiferromagnetic exchange couplings, there are two different s-wave states. One s-wave is the well-studied s$\pm$ pairing which is in the A phase of \textbf{S}$_{\mathbf{4}}$ symmetry ( even under \textbf{S}$_{\mathbf{4}}$ symmetry operation), and the other is a new type of extended s-wave pairing which is in the B phase of \textbf{S}$_{\mathbf{4}}$ symmetry ( odd under\textbf{S}$_{\mathbf{4}}$ symmetry operation). The superconductivity order in the B phase are characterized by opposite signs between up and bottom As(Se) layers in the trilayer Fe-As(Se) structure. The 122 Iron-chalcogenides and the single layer FeSe are most likely in the B-phase. We believe that the model establishes a new foundation for exploring novel properties of iron based superconductors. \\[4pt] References: J.P. Hu and Ningning Hao, Phys. Rev. X, 021009 (2012); T. X. Ma, H.Q. Lin and J.P. Hu, Arxiv:1206.6277 (2012); N.N. Hao, Y.P. Wang and J.P. Hu, Arxiv: 1207.6798 (2012); J.P. Hu, and NingNing Hao, unpublished; J.P. Hu, Arxiv: 1208.6201 (2012) [Preview Abstract] |
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