Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Z5: Focus Session: Competing Order and ARPES in Fe-Based Superconductors |
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Sponsoring Units: DMP DCOMP Chair: Andrey Chubukov, University of Minnesota Room: Juan Gorman Room 005 |
Friday, March 6, 2015 11:15AM - 11:51AM |
Z5.00001: Competing phases in iron-based superconductors Invited Speaker: Donghui Lu A common aspect of high temperature superconductivity in both cuprates and iron-based superconductors is that it always appears in the vicinity of other competing phases, whose suppression brings the full emergence of superconductivity. In iron-based superconductors, the competing phases take the form of collinear spin-density-wave phase and nematic phase. Characterization of these competing phases and associated phase transitions is essential to establishing a comprehensive understanding of the phase diagram of high temperature superconductors and ultimately the mechanism of unconventional superconductivity. In this talk, I will present our angle-resolved photoemission study of different family of iron-based superconductors. Our early data on detwinned Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{\mathrm{2}}$As$_{\mathrm{2}}$ and NaFeAs not only revealed a symmetry breaking orbital anisotropy in the nematic phase, but also identified the spectroscopic signatures associated with each phase transition in our ARPES spectra [1,2]. More recent results from underdoped Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$, on the other hand, provided the direct spectroscopic evidence for the coexistence and competition between SDW phase, nematic phase, and superconducting phase [3]. Finally, our latest data on multilayer FeSe film demonstrate the presence of a nematic state without long range magnetic order, suggesting the importance of orbital degree of freedom in driving the nematicity. [1] M. Yi, D. H. Lu, J.-H. Chu, J. G. Analytis, A. P. Sorini, A. F. Kemper, B. Moritz, S.-K Mo, R. G. Moore, M. Hashimoto, W.-S. Lee, Z. Hussain, T. P. Devereaux, I. R. Fisher, and Z.-X. Shen, Proc. Natl. Acad. Sci. 108, 6878 (2011). [2] M. Yi, D. H. Lu, R. G. Moore, K. Kihou, C.-H. Lee, A. Iyo, H. Eisaki, T. Yoshida, A. Fujimori and Z.-X. Shen; New Journal of Physics 14, 073019 (2012). [3] M. Yi, Y. Zhang, Z.-K. Liu, X. Ding, J.-H. Chu, A. F. Kemper, N. Plonka, B. Moritz, M. Hashimoto, S.-K. Mo, Z. Hussain, T. P. Devereaux, I. R. Fisher, H. H. Wen, Z.-X. Shen, and D. H. Lu; Nature Communications 5, 3711 (2014). [Preview Abstract] |
Friday, March 6, 2015 11:51AM - 12:03PM |
Z5.00002: Electron correlation tuned superconductivity in iron chalcogenide superconductors Ming Yi, Meng Wang, Donghui Lu, Alexander Kemper, Sung-Kwan Mo, Zhi-Xun Shen, Robert Birgeneau The iron chalcogenide superconductors, A$_{\mathrm{x}}$Fe$_{\mathrm{2-y}}$Se$_{\mathrm{2}}$ (A$=$K, Rb, Cs), is an interesting system where superconductivity occurs without the existence of hole Fermi pockets, hence lacking the nesting conditions needed under a spin fluctuation mediated pairing scenario. It is then important to understand the ingredients needed for superconductivity in these materials. It has been shown that sulfur substitution for selenium in this system can continually reduce the T$_{\mathrm{C}}$ from 30K to zero, providing an opportunity for understanding the occurrence of superconductivity in these materials. In this talk, I will present angle-resolved photoemission spectroscopy data on the Rb$_{\mathrm{x}}$Fe$_{\mathrm{2}}$(Se$_{\mathrm{1-y}}$S$_{\mathrm{y}})_{\mathrm{2}}$ series, where we show that electron correlation strength is the crucial parameter that tunes superconductivity in this family. [Preview Abstract] |
Friday, March 6, 2015 12:03PM - 12:15PM |
Z5.00003: ARPES of K-doped iron selenide superconductor Takayoshi Yokoya, Masanori Sunagawa, Kensei Terashima, Takahiro Hamada, Hirokazu Fujiwara, Masashi Tanaka, Hiroyuki Takeya, Yoshihiko Takano, Masashi Arita, Kenya Shimada, Hirofumi Namatame, Masaki Taniguchi, Katsuhiro Suzuki, Hidetomo Usui, Kazuhiko Kuroki, Takanori Wakita, Yuji Muraoka In iron pnictide superconductors, the characteristic Fermi surface(FS) topology, namely nesting of hole-like FS at the zone center and electron-like FS at the zone corner, is considered to induce spin/orbital fluctuation leading to high-Tc superconductivity [1,2]. In K-doped iron selenide superconductors, however, ARPES studies reported absence of hole-like FS at the zone center, which is different from that observed in iron pnictides [3]. So far, proposed models for the superconductivity based on the FS topology appear to fail to explain available experimental results. In this talk, we present our recent ARPES studies on a K-doped iron selenide superconductor performed with careful tuning of experimental conditions, which show a hole-like FS around the zone center. [1] I. I. Mazin et al., Phys. Rev. Lett. 101, 057003 (2008); K. Kuroki et al., Phys. Rev. Lett. 101, 087004 (2008). [2] H. Kontani et al., Phys. Rev. Lett. 104, 157011 (2010). [3] Y. Zhang et al., Nat. Mater. 10, 273 (2011); T. Qian et al., Phys. Rev. Lett. 106, 187001 (2011). [Preview Abstract] |
Friday, March 6, 2015 12:15PM - 12:27PM |
Z5.00004: What do we actually see in ARPES? Generalized unfolding method and application to Fe-based superconductors Milan Tomic, Harald O. Jeschke, Roser Valenti Interpretation of angle resolved photoemission (ARPES) measurements relies heavily on comparison with ab-initio (DFT) band structures. However, ARPES-observed band structures and DFT band structures often disagree on the unit cell periodicities as well as position of band structure features relative to the Brillouin zone. We present a novel, symmetry-based approach to band structure unfolding which utilizes irreducible representations of space groups. Within the unified framework we can treat both the translational and point group symmetries and explain how ARPES measurements sometimes reflect crystal structure features with a reduced unit cell. We will present some examples in the context of Fe-based superconductors. [Preview Abstract] |
Friday, March 6, 2015 12:27PM - 12:39PM |
Z5.00005: ARPES investigations of parent compounds of 122 Fe-based superconductors and their 3d transition metal cousins Pierre Richard, W.-L. Zhang, S.-F. Wu, A. van Roekeghem, P. Zhang, H. Miao, T. Qian, S.-M. Nie, G.-F. Chen, H. Ding, N. Xu, S. Biermann, C. Capan, Z. Fisk, B.I. Saparov, A.S. Sefat It is widely believed that the key ingredients for high-temperature superconductivity are already present in the non-superconducting parent compounds. With its ability to probe the single-particle electronic structure directly in the momentum space, ARPES is a very powerful tool to determine which parameters of the electronic structure are possibly relevant for promoting superconductivity. Here we report ARPES studies on the parent compounds of the 122 family of Fe-based superconductors and their $3d$ transition metal pnictide cousins. In particular, we show that the Fe-compound exhibits the largest electronic correlations, possibly a determining factor for unconventional superconductivity. [Preview Abstract] |
Friday, March 6, 2015 12:39PM - 12:51PM |
Z5.00006: Observation of strong electron pairing on band without Fermi surfaces in LiFe1-xCoxAs Hu Miao, Tian Qian, Xun Shi, Pierre Richard, T. Kim, M. Hoesch, Lingyi Xing, Xiangcheng Wang, Changqing Jin, JInagping Hu, Hong Ding In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe1-xCoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi energy upon Co substitution. The observed Fermi surface free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the superconducting order parameter is not tied to the Fermi surface as a result of a Fermi surface instability. [Preview Abstract] |
Friday, March 6, 2015 12:51PM - 1:03PM |
Z5.00007: Dynamic coexistence of competing orders in multi-component superconductors Maxim Dzero, Alex Levchenko We study the nonequilibrium dynamics of an electronic model with competing spin-density wave and unconventional superconductivity in the context of iron-pnictides. Focusing on the collisionless regime we find that magnetic and superconducting order parameters may coexist dynamically after the quench even though the equilibrium state has only one order parameter. We consider different initial conditions concomitant with the phase diagram and in a certain regime identify new oscillatory amplitude modes with incommensurate frequencies for magnetic and superconducting responses. At the technical level we solve equations of motion for the electronic Green's functions and self-consistency conditions by reducing the problem to a closed set of Bloch equations in the pseudospin representation. [Preview Abstract] |
Friday, March 6, 2015 1:03PM - 1:15PM |
Z5.00008: Correlation-induced self-doping in iron-pnictide superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O Tian Qian, Junzhang Ma, A. van Roekeghem, Pierre Richard, Guanghan Cao, Silke Biermann, Hong Ding The electronic structure of the iron-based superconductor Ba$_{2}$Ti$_{2}$Fe$_{2}$As$_{4}$O ($T_{\mathrm{c}}^{\mathrm{onset}} = $ 23.5 K) has been investigated by using angle-resolved photoemission spectroscopy and combined local density approximation and dynamical mean field theory calculations. The electronic states near the Fermi level are dominated by both the Fe 3$d$ and Ti 3$d$ orbitals, indicating that the spacer layers separating different FeAs layers are also metallic. By counting the enclosed volumes of the Fermi surface sheets, we observe a large self-doping effect, $i$.$e$. 0.25 electrons per unit cell are transferred from the FeAs layer to the Ti$_{2}$As$_{2}$O layer, leaving the FeAs layer in a hole-doped state. This exotic behavior is successfully reproduced by our dynamical mean field calculations, in which the self-doping effect is attributed to the electronic correlations in the 3$d$ shells. Our work provides an alternative route of effective doping without element substitution for iron-based superconductors. [Preview Abstract] |
Friday, March 6, 2015 1:15PM - 1:27PM |
Z5.00009: Extraordinary Doping Effects on Quasiparticle Scattering and Bandwidth in Iron-Based Superconductors Donglai Feng Iron-based superconductors exhibit very rich phenomena with doping. We systematically investigate the behavior of dopants in a variety of iron-based superconductors with angle-resolved photoemission spectroscopy (ARPES), we find that dopants modify the carrier density, introduce quasiparticle scattering, and vary the bandwidth in extraordinary ways [1]. Particularly, we find that instead of Fermi surface topology or carrier density, the bandwidth, which is closely related to electronic correlations, is likely the most universal electronic parameter to dominate superconductivity in various iron-pnictides and 11 and 122* types of iron-chalcogenides --- superconductivity disappears when the bandwidth is tuned beyond a common range by either heterovalent or isovalent doping. This microscopic picture of doping facilitates a comprehensive and generic understanding of the rich phase diagram of various iron-based superconductors. Furthermore, our results highlight future directions to search for new iron-based superconductors with higher superconducting transition temperatures. \\[4pt] [1] X. R. Ye, et al, Phys. Rev. X 4, 031041 (2014). [Preview Abstract] |
Friday, March 6, 2015 1:27PM - 1:39PM |
Z5.00010: Electronic structure of LiFe1-xMnxAs (x$=$0, 0.04) Jeongjin Seo, Bumsung Lee, Kee Hoon Kim, Changyoung Kim ~We studied the Mn substitution effect in LiFeAs with Angle Resolved Photoemission Spectroscopy. We found that the slopes of the middle and inner hole bands near the Fermi energy decrease upon Mn doping, resulting in downward shift of the band tops. Meanwhile, band positions away from the Fermi energy remain more or less the same. We attribute such change to the change in the coupling strength between electron and a bosonic mode. In addition, the size of the band splitting between the middle and inner hole bands at the Gamma point which was suggested to represent the size of Ferro-orbital fluctuation does not change, in a sharp contrast to the case of Co doped LiFeAs. This result suggests that the band splitting is not related to the T$_{c}$ suppression in LiFe1-xMnxAs system. [Preview Abstract] |
Friday, March 6, 2015 1:39PM - 1:51PM |
Z5.00011: Nematic order and Fermi surface reconstruction of chalcogen Fe-based superconductors Jiunn-Yuan Lin We utilized the transport property measurements and polarized Fe L-edge XAS to explore nematic order and Fermi surface reconstruction in FeSe. Temperature-dependent magnetoresistance and the Hall coefficient, together with XAS and XLD, on single crystals with state-of-art quality will be carried out through both the nematic and the pseudogap temperatures. This work is to elucidate the existence of Fermi surface reconstruction in FeSe in which no SDW was observed. Moreover, whether this electronic structure change has a nematic or magnetic origin will be answered. [Preview Abstract] |
Friday, March 6, 2015 1:51PM - 2:03PM |
Z5.00012: On the Phase Diagram of FeSe$_{1-x}$As$_{x}$ Khalil Ziq, T. Owolabi Structural, magnetic and transport measurements have been performed on FeSe$_{1-x}$As$_{x}$ samples in the normal and superconducting state in an effort to obtain the phase diagram. It is found that As-substitution drastically suppress the superconducting state while it has little effect of structural transformation as the temperature decreases. Moreover, low As-concentration ($\sim$ 1{\%}As) has been found very effective in stabilizing the $\beta $-FeSe phase. [Preview Abstract] |
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