Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session J13: Focus Session: ARPES in Fe-Based Superconductors |
Hide Abstracts |
Sponsoring Units: DMP Chair: Alessandra Lanzara, University of California, Berkeley Room: 207 |
Tuesday, March 4, 2014 2:30PM - 3:06PM |
J13.00001: ARPES study on FeSe films Invited Speaker: Donglai Feng The record of superconducting transition temperature (Tc) has long been 56 K for the iron-based high temperature superconductors (Fe-HTS's). Recently, in single layer FeSe films grown on SrTiO$_3$ substrate, signs for a new 65 K Tc record are reported. Combining molecular beam epitaxy and in situ angle resolved photoemission spectroscopy (ARPES), we study the ultra thin FeSe films on various substrates. We substantiate the presence of collinear antiferromagnetic order (CAF) in FeSe films, a key ingredient of Fe-HTS that was missed in FeSe before, which weakens with increased thickness or reduced strain. We demonstrate that the superconductivity occurs when the electrons transferred from the oxygen-vacant substrate suppress the otherwise most pronounced CAF in single layer FeSe. We establish the phase diagram of FeSe vs. lattice constant that contains all the essential physics of Fe-HTS's [1]. With first principle calculations, we show that the superexchange interactions across Fe-As-Fe is enhanced with increased lattice constant [2]. Therefore, with heavy electron doping, the FeSe would have been an overdoped non-superconductor likely due to the weakened spin fluctuation; however by expanding its lattice in thin films, the magnetism is enhanced and superconductivity is restored. By fabricating FeSe/STO/KTO heterostructure, we further enhanced the lattice constant of FeSe, and increased the gap-closing temperature to 70K. Two un-hybridized electron Fermi surfaces are resolved, and the superconducting gap exhibits strong anisotropy around the individual Fermi surface. This observation contradicts many existing theories on the pairing symmetry of Fe-HTS's with only electron pockets [3].\\[4pt] [1] S. Tan et al., Nature Materials 12, 634--640 (2013)\\[0pt] [2] Hai-Yuan Cao et al., arXiv:1310.4024\\[0pt] [3] R. Peng et al., arXiv:1310.3060 [Preview Abstract] |
Tuesday, March 4, 2014 3:06PM - 3:18PM |
J13.00002: Spin resonance in A$_x$Fe$_{2-y}$Se$_2$ with s-wave pairing symmetry Sudhakar Pandey, Andrey Chubukov, Maxim Khodas We study spin resonance in the superconducting state of recently discovered alkali-intercalated iron selenide materials A$_x$Fe$_{2-y}$Se$_2$ (A=K,Rb,Cs) with an aim to address the basic issue of pairing symmetry and gap structure in these materials. As the Fermi surface of these materials has only electron pockets, the widely believed $s^{+-}$ symmetry for several iron based superconductors, which implies a sign changing gap between the hole and electron pockets, becomes questionable in case of these materials. While the earlier proposed d-wave symmetry is ruled out in ARPES studies, the observations of a spin-resonance like feature in the inelastic neutron scattering experiments indicate for a sign changing gap in these materials. In this study we demonstrate that the hybridization-induced sign-changing unconventional $s^{+-}$-wave symmetry, where the SC gap changes its sign between the hybridized electron pockets, supports spin resonance, and the dynamical structure factor is consistent with the results of inelastic neutron scattering. This ``other'' s-wave symmetry is also consistent with the recent ARPES studies. [Preview Abstract] |
Tuesday, March 4, 2014 3:18PM - 3:30PM |
J13.00003: Small and nearly isotropic hole-like Fermi surfaces in LiFeAs detected through de Haas--van Alphen effect Bin Zeng, Daiki Watanabe, Qiu Zhang, Gang Li, Tiglet Besara, Theo Siegrist, Lingyi Xing, Xiancheng Wang, Changqing Jin, Pallab Goswami, Michelle Johannes, Luis Balicas We show a detailed dHvA study unveiling small and nearly isotropic Fermi surface sheets in LiFeAs single crystals, which is not observed by previous dHvA results, as well as the cylindrical electron-like Fermi surfaces. Our results are in partial agreement with the ARPES results, and the small, nearly isotropic Fermi surface should correspond to the hole-like pocket, suggesting a prominent role for the electronic correlations in LiFeAs. The absence of gap nodes, in combination with the coexistence of quasi-two-dimensional and three-dimensional Fermi surfaces, favor an s-wave pairing symmetry for LiFeAs. [Preview Abstract] |
Tuesday, March 4, 2014 3:30PM - 3:42PM |
J13.00004: Interplay between the nematic and SDW states in iron-pnictides and iron-chalcogenides Yan Zhang, Ming Yi, Donghui Lu, Zhongkai Liu, Wei Li, James Lee, Robert Moore, Felix Schmitt, Masamichi Nakajima, Hiroshi Eisaki, Makoto Hashimoto, Zhi-Xun Shen Utilizing the angle-resolved photoemission spectroscopy (ARPES) and detwinning method, we have studied the electronic structure reconstruction in the nematic and SDW states of iron-based superconductors. The key features associated with the symmetry breaking process across the structure and magnetic transitions have been resolved. In the nematic state, we found that the energy splitting of the $d_{xz}$ and $d_{yz}$ bands is strongly momentum dependent. It is negligible in the zone center and reaches maximum at the zone corner, which is inconsistent with the ferro-orbital ordering scenario. In the SDW state, the reconstruction of the electronic structure is dominated by the SDW gap opening, whose orbital dependence and momentum dependence could be well described by the theoretical calculations. More intriguingly, we found that the coupling between the nematic and SDW states is strong in iron-pnictides, but very weak in iron-chalcogenides. Our findings resolve controversies on the electronic structure reconstruction in the nematic and SDW states of iron-based superconductors, and have strong implications on theory. [Preview Abstract] |
Tuesday, March 4, 2014 3:42PM - 4:18PM |
J13.00005: Electronic Structure and High Temperature Superconductivity of the FeSe /SrTiO3 Films Invited Speaker: Xingjiang Zhou High resolution angle-resolved photoemission measurements have been carried out to study the electronic structure and high temperature superconductivity of the single-layer FeSe films grown on SrTiO3 substrate [1]. Distinct Fermi surface topology and nearly isotropic superconducting gap without nodes are observed in the system [2]. Phase diagram is established and electronic indication of high temperature superconductivity at $\sim$65K is observed in tuning the carrier concentration of the single-layer FeSe film [3]. With a variation of the charge carriers, an insulator-superconductor transition in the single-layer FeSe/SrTiO3 is observed. A dichotomy of electronic structure and superconductivity is revealed between the single-layer and double-layer FeSe/SrTiO3 films. Implications of these results on the superconductivity mechanism of the iron-based superconductors will be discussed. \\[4pt] References:\\[0pt] [1]. Qing-Yan WANG, Zhi LI, Wen-Hao ZHANG, Zuo-Cheng ZHANG, Jin-Song ZHANG, Wei LI, Hao DING, Yun-Bo OU, Peng DENG, Kai CHANG, Jing WEN, CanLi SONG, Ke HE, Jin-Feng JIA, Shuai-Hua JI, Ya-Yu WANG, Li-L WANG i, Xi CHEN, Xu-Cun MA, Qi-Kun XUE, Chinese Physics Letters 29 (2012) 037402.\\[0pt] [2]. Defa Liu*, Wenhao Zhang*, Daixiang Mou*, Junfeng He*, Yun-Bo Ou, Qing-Yan Wang, Zhi Li, Lili Wang, Lin Zhao, Shaolong He, Yingying Peng, Xu Liu, Chaoyu Chen, Li Yu, Guodong Liu, Xiaoli Dong, Jun Zhang, Chuangtian Chen, Zuyan Xu, Jiangping Hu, Xi Chen, Xucun Ma, Qikun Xue, and X. J. Zhou, Nature Communications 3 (2012) 931.\\[0pt] [3]. Shaolong He*, Junfeng He*, Wenhao Zhang*, Lin Zhao*, Defa Liu, Xu Liu, Daixiang Mou, Yun-Bo Ou, Qing-Yan Wang, Zhi Li, Lili Wang, Yingying Peng, Yan Liu, Chaoyu Chen, Li Yu, Guodong Liu, Xiaoli Dong, Jun Zhang, Chuangtian Chen, Zuyan Xu, Xi Chen, Xucun Ma, Qikun Xue, and X. J. Zhou, Nature Materials 12 (2013) 605. [Preview Abstract] |
Tuesday, March 4, 2014 4:18PM - 4:30PM |
J13.00006: ARPES observation of strong Mn-pnictide hybridization and small electronic correlations in BaMn$_2$Pn$_2$ (Pn = As, Sb) Pierre Richard, W.-L. Zhang, N. Xu, P. Zhang, H. Miao, S.-F. Wu, T. Qian, S.-M. Nie, Z.-J. Wang, A. van Roekeghem, Z. Fang, Hong Ding, Athena S. Sefat ARPES experiments on Fe-based superconductors indicate non-negligible band renormalization due to electronic correlations. The key role attributed to a significant Hund's rule coupling in these materials and in their related isostructural nonferropnictide counterparts in tuning the electronic correlations depends strongly on the filling of the 3$d$ electronic shell and are expected to reach a maximum at half-filling (Mn 3$d^5$). Here we report an ARPES study of BaMn$_2$As$_2$ and BaMn$_2$Sb$_2$, which are isostructural to BaFe$_2$As$_2$. We show the existence of a strongly $k_z$-dependent band gap with a small minimum at the Brillouin zone center, in agreement with the semiconducting properties of these compounds. In contrast to the common expectation, we show that the electronic correlations in these materials are small. Our photon energy dependent study provides evidence for strong Mn-pnictide hybridization, which might play a role in reducing the electronic correlations in these compounds. [Preview Abstract] |
Tuesday, March 4, 2014 4:30PM - 4:42PM |
J13.00007: Role of bonding angle on superconductivity in iron pnictide: Comparative electronic structure study on LiFeAs and Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$ Y.K. Kim, S.-K. Mo, Y.Y. Koh, W.S. Kyung, G.R. Han, C. Kim, B.-S. Lee, K.-H. Kim, J.M. Ok, J.S. Kim The special relation between As-Fe-As bonding angle and superconductivity is the most remarkable universal feature in iron-based supercondutor. The maximum Tc can be achieved only with the certain bonding angle, the optimal angle that makes FeAs$_{4}$ tetrahedron regular. Despite its importance, a hinge behind the relationship between bonding angle and Tc is unclear and less considered so far. In this presentation, we present the comparative electronic structure study on two representative systems, LiFeAs and Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$. LiFeAs has small bonding angle with relatively lower Tc at 18 K and Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$ shows higher Tc at 37 K and its bonding angle is close to the optimal value. Using ARPES, the band dispersion including kz dependence and its orbital characters are explored. Detailed analysis reveals only Sr$_{4}$V$_{2}$O$_{6}$Fe$_{2}$As$_{2}$ electronic structure has orbital mixed nature and relatively strong Fermi surface nesting instability. Both feature indicate strong inter-orbital coupling and its possible role to the superconductivity, which can be the hinge between bonding angle and Tc. [Preview Abstract] |
Tuesday, March 4, 2014 4:42PM - 4:54PM |
J13.00008: Insulator to Superconductor Transitions and Strong Electronic Correlations in Single-Layer FeSe/SrTiO$_3$ Films Lin Zhao, Junfeng He, Xu Liu, Wenhao Zhang, Defa Liu, Shaolong He, Daixiang Mou, Fansen Li, Chenjia Tang, Zhi Li, Lili Wang, Yingying Peng, Yan Liu, Chaoyu Chen, Li Yu, Guodong Liu, Xiaoli Dong, Jun Zhang, Chuangtian Chen, Zuyan Xu, Xi Chen, Xucun Ma, Qikun Xue, Xingjiang Zhou There has been a debate on whether an appropriate starting point in describing these compounds should go from an itinerant picture or a localized picture. The single-layer FeSe/SrTiO$_3$ films have recently generated great interest for its simplicity of crystal structure and electronic structure, as well as possible high superconducting transition temperature. In this talk, by performing detailed doping-dependent measurements with ARPES, we report an insulator-metal-superconductor transition in the S phase of the single-layer FeSe/SrTiO$_3$ films. The results indicate that strong electronic correlations should be considered in the single-layer FeSe/SrTiO$_3$ films that might be on the verge of Mott physics. [Preview Abstract] |
Tuesday, March 4, 2014 4:54PM - 5:06PM |
J13.00009: Electronic anisotropy and orbital ordering in Ru doped BaFe2As2 revealed by ARPES and XLD Yoonyoung Koh, Yeongkwan Kim, Jungjin Seo, Manjin Eom, Junsung Kim, Hangu Lee, Byeonggyu Park, Jaeyoung Kim, Changyoung Kim A central issue in iron pnictides is the origin of electronic anisotropy. It is considered that its role in iron pnictides is important to the nature of magnetism and superconductivity. It was proposed that orbital ordering may play a key role. Since XLD can observe different occupation numbers for dyz and dzx orbitals, it is regarded to provide an experimental signature for the existence of orbital ordering. The work was motivated by the goal of exploring whether the orbital ordering and its fluctuation would explain the underlying mechanism on magnetism and superconductivity. We performed temperature dependent measurements both ARPES and XLD on Ba(Fe1$-$xRux)2As2 to experimentally verify existence of electronic anisotropy and orbital ordering. [Preview Abstract] |
Tuesday, March 4, 2014 5:06PM - 5:18PM |
J13.00010: ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ Xiaoping Wang, N. Xu, P. Richard, X. Shi, A. Van Roekeghem, T. Qian, H. Ding, K. Nakayama, T. Sato, E. Ieki, T. Takahashi, J. Xing, H.-H. Wen, M. Shi, E. Rienks, S. Thirupathaiah We used high-energy resolution angle-resolved photoemission spectroscopy to extract the momentum dependence of the superconducting gap of Ru-substituted Ba(Fe$_{0.75}$Ru$_{0.25}$)$_2$As$_2$ ($T_c = 15$ K). Despite a strong out-of-plane warping of the Fermi surface, the magnitude of the superconducting gap observed experimentally is nearly isotropic and independent of the out-of-plane momentum. More precisely, we respectively observed 5.7 meV and 4.5 meV superconducting gaps on the inner and outer $\Gamma$-centered hole Fermi surface pockets, whereas a 4.8 meV gap is recorded on the M-centered electron Fermi surface pockets. Our results are consistent with the $J_1-J_2$ model with a dominant antiferromagnetic exchange interaction between the next-nearest Fe neighbors. [Preview Abstract] |
Tuesday, March 4, 2014 5:18PM - 5:30PM |
J13.00011: Remarkable doping effects beyond altering Fermi surface on the superconductivity of iron-based superconductors Z.R. Ye, Y. Zhang, F. Chen, M. Xu, J. Jiang, X.H. Niu, C.H.P. Wen, B.P. Xie, D.L. Feng, L.Y. Xing, X.C. Wang, C.Q. Jin The superconductivity in Fe-based superconductors could be achieved by doping the parent compounds. Previous researches were focusing on the charge carrier density or Fermi surface alteration by doping only. However, the dominating factors based on Fermiology have many inconsistencies, which indicates that some other effects induced by doping are neglected. Using ARPES, we have established the microscopic and more comprehensive picture of doping on the electronic structure beyond altering Fermi surface. We have figured out other two critical effects of doping, scattering and changing correlation. With doping, the dxy-related band around the zone center is found to be much more sensitive than the dxz/dyz-related bands and the strength of the impurity scattering strongly depends on the position of dopants, which resembles the case in cuprates. On the other hand, we observed that the electron correlation decreases with doping, which is universal in various systems of Fe-based superconductors. Moderate electron correlation is critical for the high Tc. The two effects we observed here both are very important for the superconductivity, and explain a lot of previous mysteries and unresolved issues. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700