Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session Y41: Fe-based Superconductivity. C_4 and other SubjectsFocus
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Sponsoring Units: DMP DCMP Chair: Anna Boehmer, Iowa State Room: 388 |
Friday, March 17, 2017 11:15AM - 11:51AM |
Y41.00001: Universal Properties of the C$_{4}$ Magnetic Phase in Hole Doped Ternary Superconducting Pnictides Invited Speaker: Omar Chmaissem $A$Fe$_{2}$As$_{2}$ (A$=$Alkali Earth) superconductors exhibit phase diagrams that are remarkably similar when substitutions are made at any of the available crystallographic sites. In recent work, we demonstrated that some hole-doped compositions with low temperature orthorhombic structures exhibit universal phase reentrance back to the tetragonal symmetry with the formation of a previously unknown magnetic C$_{4}$ phase facilitated by the recovery of magnetic degeneracy coupled with spin reorientation from the in-plane to the out-of-plane $c$-axis direction. Using neutron diffraction and Mossbauer spectroscopy, we unraveled the nature of this new phase as being a rare double-Q magnetic structure in which two orthogonal spin density waves combine to produce the tetragonal magnetic symmetry with a checkerboard --like Fe sublattice in which half the sites are magnetic (magnetic moment nearly doubled) while the other half are not. Our results give strong evidence for the electronic itineracy of the system and provide a definite proof that the structural and magnetic transitions are driven by magnetic fluctuations rather than other mechanisms. The exact location and shape of the C$_{4}$ phase space have somewhat remained until recently a mystery as the phase shifted together with the superconducting dome to different doping levels in various phase diagrams but with no any clear trends. Noting the complete absence of this phase in any known electron or isovalent-substituted analog, it has become clear that detailed mapping of the phase properties requires hole-doped systems that go beyond the customary binary diagrams. In this talk, I will present and discuss the properties of a two dimensional map in a broad range of compositions that extend between binary end-members of elaborate ternary phase diagrams. This work establishes the universality of the C$_{4}$ phase, its robustness and provides a quantitative relationship between the magnetic properties and the $A$-site ionic size and internal structural parameters. [Preview Abstract] |
Friday, March 17, 2017 11:51AM - 12:03PM |
Y41.00002: Mapping the Superconducting Anti-ferromagnetic C$_{\mathrm{4}}$ Phase in Iron-Pnictides Ryan Stadel, Keith Taddei, Dan Bugaris, Saul Lapidus, Helmut Claus, Daniel Phelan, Duck Young Chung, Mercouri Kanatzidis, Raymond Osborn, Stephan Rosenkranz, Omar Chmaissem Following the discovery of the microscopic coexistence of antifermagnetic spin density waves and superconductivity in Ba$_{\mathrm{1-x}}$K$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2\thinspace }}$and the low temperature re-entrance to the novel magnetic C$_{\mathrm{4}}$~tetragonal phase in Ba$_{\mathrm{1-x}}$Na$_{\mathrm{x}}$Fe$_{\mathrm{2}}$As$_{\mathrm{2}}$, there has been significant interest in developing an understanding of the properties and formation of these phases and analyzing their dependence on temperature and composition in hole-doped 122 alkaline earth metal/iron-pnictides. We describe the mapping of various Ba, Sr, and Ca 122 phase diagrams with systematically controlled levels of hole-doping of alkaline metal onto the alkaline earth metal site, which was investigated via x-ray and neutron diffraction. Our elaborate synthesis, diffraction work, and analysis maps and firmly establishes the C$_{\mathrm{4}}$ phase space in these ternary diagrams as well as the boundary lines that separate the individual phases, and provides natural clues as well as a framework to investigate the stability and formation of the C$_{\mathrm{4\thinspace }}$domes that shift location with doping contents in the phase diagrams. [Preview Abstract] |
Friday, March 17, 2017 12:03PM - 12:15PM |
Y41.00003: Electronic structure of the C4 magnetic phase in iron-based superconductors Ming Yi, Meng Wang, Liran Wang, Frederic Hardy, Peter Schweiss, Peter Adelmann, Thomas Wolf, Donghui Lu, Christoph Meingast, Robert Birgeneau Superconductivity arises in the iron-based materials amongst a host of competing phases. Typically, these competing phases appear as a combination of structural distortion and magnetic ordering in the iron pnictides. However, it has recently been found that in hole-doped Ba122 materials, there exists a magnetically ordered phase that preserves C$_{\mathrm{4}}$ rotational symmetry. In this talk, I will discuss the electronic structure of this C4 magnetic phase as measured by angle-resolved photoemission spectroscopy. In particular, we will examine the orbital anisotropy and nesting conditions of this phase, compare and contrast them with those from the neighboring nematic magnetic phase in order to understand the origin of this phase in the iron-based superconductors. [Preview Abstract] |
Friday, March 17, 2017 12:15PM - 12:27PM |
Y41.00004: Atomic scale observation of C$_{\mathrm{4}}$-plaquette antiferromagnetic order coexisting with superconductivity in iron-based superconductor Sr$_{\mathrm{2}}$VO$_{\mathrm{3}}$FeAs Seokhwan Choi, Won-Jun Jang, Jong Mok Ok, Hyun-Jung Lee, Se-Jong Kahng, Young Kuk, Ja-Yong Koo, SungBin Lee, Sang-Wook Cheong, Yunkyu Bang, Jun Sung Kim, Jhinhwan Lee The symmetry requirement and the origin of magnetic orders coexisting with superconductivity have been strongly debated issues of iron-based superconductors (FeSCs): it has been argued that the $C_{2}$-symmetric magnetism is a pre-requisite for the superconductivity in FeSCs. $C_{4}$-symmetric antiferromagnetism in superconducting ground state indeed has never been observed in real-space yet, likely due to the onset of $C_{2}$ structural orthorhombicity. The superconducting material Sr$_{\mathrm{2}}$VO$_{\mathrm{3}}$FeAs with its magnetism ($T_{N}$ \textasciitilde 50 K) and superconductivity ($T_{c}$ \textasciitilde 37 K) coexisting at parent state, has no reported structural orthorhombic distortion and thus makes a perfect system to look for some of the theoretically expected $C_{4}$ magnetisms. In this work, we studied the magnetic ground state and its phase transition using spin-polarized scanning tunneling microscopy. We observed $C_{4}$-symmetric plaquette antiferromagnetic order coexisting with superconductivity in tetragonal Fe spin lattice, and confirmed that the plaquette order can only be explained by Fe local moments picture. Furthermore, the inconsistency of its modulation $Q$ vectors from the nesting condition implies that the nesting-based $C_{2}$-symmetric magnetism is not a unique pre-requisite of high-$T_{c}$ FeSC. [Preview Abstract] |
Friday, March 17, 2017 12:27PM - 12:39PM |
Y41.00005: Unravelling incommensurate magnetism and the path to topological phases in iron-based superconductors Morten Holm Christensen, Brian Andersen, Panagiotis Kotetes Motivated by recent experiments on iron-based superconductors hinting at incommensurate magnetic order, we investigate generic itinerant systems exhibiting a tendency towards incommensurate magnetism with ordering wavevectors $\mathbf{Q}_{1,2}=(Q,0)/(0,Q)$ and retrieve the complete phase diagram and leading instabilities near the paramagnetic-magnetic transition via a Landau approach. The aspect of incommensurability introduces a plethora of new exotic phases that can either preserve or violate C$_4$-symmetry. We additionally aim at unveiling prominent candidates for the recently observed, and yet unresolved, C$_2$ magnetic phase in Ba-doped iron-based superconductors (FeSCs). Within a representative five-orbital model we show that these nonstandard incommensurate magnetic phases become indeed favored in FeSCs. In fact, a C$_4$-preserving non-coplanar texture becomes stabilized and can be rendered skyrmionic by applying an infinitesimaly small external magnetic field. We illustrate how the microscopic coexistence of the latter with superconductivity, a feasible scenario for FeSCs, opens new perspectives for realizing intrinsic topological superconductivity. [Preview Abstract] |
Friday, March 17, 2017 12:39PM - 12:51PM |
Y41.00006: Pressure dependence of the Fermi surface of the nematic superconductor FeSe$_{1-x}$S$_x$ Pascal Reiss, David Graf, Amir A. Haghighirad, Amalia I. Coldea Upon application of hydrostatic pressure the phase diagram of bulk FeSe evolves from a nematic phase with low T$_c \approx $ 11K towards a magnetic phase which harbours a high-T$_c$ superconductor with T$_c \approx$ 40K [1, 2]. This complex interplay between different competing orders suggests that superconductivity may be dominated by both nematic and spin-fluctuations that are tuned by applied pressure. Similar to hydrostatic pressure, chemical pressure by sulphur doping suppresses the nematic phase but no magnetic order has been detected yet [3]. Here, we will present quantum oscillation studies of FeSe$_{1-x}$S$_x$ up to 45T under applied hydrostatic pressure and we will follow the evolution of the Fermi surface from the nematic phase towards the high pressure high T$_c$ state. The temperature dependence of the quantum oscillations allows us to determine the quasiparticle masses and to follow the effect of electronic correlations as a function of applied pressure. \\ \, [1] Terashima \textit{et al.}, Phys. Rev. B \textbf{93}, 094505 (2016) \\ \, [2] Medvedev \textit{et al.}, Nat. Mater. \textbf{8}, 630 - 633 (2009) \\ \, [3] Watson \textit{et al.}, Phys. Rev. B \textbf{91}, 155106 (2015) [Preview Abstract] |
Friday, March 17, 2017 12:51PM - 1:03PM |
Y41.00007: High-pressure electronic phase diagrams in FeSe$_{1-x}$S$_x$ superconductors Kohei Matsuura, Yuki Arai, Suguru Hosoi, Kousuke Ishida, Yuta Mizukami, Tatsuya Watashige, Shigeru Kasahara, Yuji Matsuda, Naoyuki Maejima, Akihiko Machida, Tetsu Watanuki, Tatsuo Fukuda, Yoshiya Uwatoko, Takasada Shibauchi The spin fluctuations are believed to be related to the mechanism of the unconventional superconductors. On the other hand, many recent studies suggest that the nematic order that spontaneously breaks rotational symmetry of the system exists in the Fe-based superconductors and its quantum fluctuations may play an essential role for the superconductivity. However, this remains unclear because the nematic order usually coexists with the magnetic order. To solve this issue, FeSe exhibiting a nonmagnetic nematic order is a key system. Under pressure, this order is suppressed and concurrently magnetic order appears, which competes with high-${\it T}_c$ superconducting phase. In isovalent substitution system FeSe$_{1-x}$S$_x$, we found a nonmagnetic nematic quantum critical point. Here we report our recent high-pressure studies in high-quality single-crystalline FeSe$_{1-x}$S$_x$ up to 8 GPa. We find a systematic change of the pressure phase diagram in FeSe by the S-substitution. Our results imply that the respective role of nematic and magnetic fluctuations can be elucidated from the precise control of pressure and substitution in this system. [Preview Abstract] |
Friday, March 17, 2017 1:03PM - 1:15PM |
Y41.00008: Pressure-temperature phase diagrams of FeSe$_{1-x}$S$_{x}$ superconductor Li Xiang, Udhara Kaluarachchi, Anna Böhmer, Valentin Taufour, Makariy Tanatar, Ruslan Prozorov, Sergey Bud'ko, Paul Canfield The pressure dependence of the superconducting, magnetic and structural transition temperatures and of the upper critical field were studied on sulfur-doped single crystalline FeSe. Both interplane and inplane resistance were measured under hydrostatic pressures up to 1.8 GPa with magnetic fields parallel to tetragonal $c$-axis. We will present the pressure-temperature phase diagrams of FeSe$_{1-x}$S$_{x}$. Different doping will be compared and discussed, specifically in the context of potential chemical pressure effects. [Preview Abstract] |
Friday, March 17, 2017 1:15PM - 1:27PM |
Y41.00009: Pressure induced magnetic order in high-temperature superconductor FeSe: Unusual enhancement of quantum fluctuation with larger local moments Wei Ku, Yu-Ting Tam, Tianyu Zhang, T. Zou, A. M. dos Santos, Dao-Xin Yao, Xianglin Ke We investigate the microscopic mechanisms of pressure induced magnetic order recently observed in high-temperature superconductor FeSe, via experimental high-pressure X-ray structural refinement and a theoretical ordered-state stability anaalysis withing the realistic spin-fermion model that incorporates both the itinernat carriers and the large local moments. Opposite to the common lore on insulating magnetism, the larger local moment in FeSe (in comparison with other Fe-pnictides) turns out to suffer even stronger long-range quantum fluctuation that deminishes its ordering at ambient pressure. Upon applying pressure, the itinerancy-induced quantum fluctuation reduces systematically and eventually allows long-range order to emerge. We further illustrate the role of ferro-orbital order and address the current debate on its interplay with the magnetism concerning the origin of the strong nematicity. Our work clarifies the nature of magnetic order/disorder and its interplay with nematicity in FeSe with a consistant framework that unifies all Fe-based superconductors, and establishes the strongly correlated building blocks for high-temperature superconductivity in these systems. [Preview Abstract] |
Friday, March 17, 2017 1:27PM - 1:39PM |
Y41.00010: Tuning superconductivity in BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ thin films by tetrahedral geometry design Jong-Hoon Kang, P. J. Ryan, J. W. Lee, J. W. Kim, Y. Choi, J. Jiang, E. E. Hellstrom, D. C. Larbalestier, C.B. Eom Significant progress has been made in fabricating high-quality epitaxial thin films of iron-based superconductors. Strain engineering offers the possibility of tailoring the structural distortions at the atomic scale and enhancing superconducting properties. Here, we report that tetrahedral geometry driven by thin film strain leads to a significant enhancement of the superconducting transition temperature (T$_{\mathrm{c}})$ of optimal Co-doped epitaxial BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ thin films above the value of the bulk single crystals. We have found that the As-Fe-As bond angles were strongly modified by both epitaxial and thermal strains caused by the temperature-dependent lattice mismatch between BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ thin films and the substrates. Synchrotron x-ray diffraction and resonant scattering demonstrate that the As-Fe-As bond angle and T$_{\mathrm{c}}$ are systematically tuned by in-plane strain and reach maximum T$_{\mathrm{c}}$ at the optimum bond angle of 109.5$^{\mathrm{o}}$. Strain engineering can provide a path toward tailoring superconducting properties and understanding superconductivity in other Fe-based superconducting thin films such as monolayer FeSe. [Preview Abstract] |
Friday, March 17, 2017 1:39PM - 1:51PM |
Y41.00011: Superconducting Enhancement in Nickel-Pnictide Superconductors Chris Eckberg, Daniel Campbell, Tyler Drye, Hyunsoo Kim, Peter Zavalij, Phil Piccoli, Jeff Lynn, Johnpierre Paglione While the relationship between phase criticality and superconductivity is understood in several conventional systems, open questions remain in many families of high Tc superconductors, wherein structure and magnetic order are closely linked. Utilizing superconducting BaNi2As2 we are able to explore the behavior of superconductivity near a structural instability decoupled from magnetic ordering. Here we present the details and results of both Sr and Co substitutional studies in (Ba,Sr)Ni2As2 and Ba(Ni,Co)2As2, respectively, comparing the evolution of structural and superconducting phases in each case. The resulting phase diagrams as well as the possible mechanism for superconducting enhancement in these systems will be discussed. [Preview Abstract] |
Friday, March 17, 2017 1:51PM - 2:03PM |
Y41.00012: Band-selective quantum criticality in iron-pnictide metal Ba(Fe,Ni,Co)$_2$As$_2$ Johnpierre Paglione, Yasuyuki Nakajima, Tristin Metz, Christopher Eckberg, Kevin Kirshenbaum, Alex Hughes, Renxiong Wang, Shanta Saha Quantum-mechanical fluctuations between competing phases in the vicinity of a quantum critical point induce the breakdown of Landau's Fermi liquid theory. The non Fermi liquid behavior has been believed to be involved in exotic superconductivity observed in the strongly correlated electron systems, such as cuprate and iron pnictide superconductors [1]. Utilizing very low temperature thermodynamic and transport measurements, we reveal non-Fermi liquid behavior in non-superconducting iron-pnictide Ba(Fe,Ni,Co)$_2$As$_2$ associated with quantum critical instabilities, showing quantum critical scaling between temperature and applied field in the charge transport and thermodynamics. Together with the unusual scaling, we will discuss the emergence of hole-like carrier tuned by both magnetic field and temperature, highlighting the presence of band-selective quantum criticality in the iron pnictide system. [1] T. Shibauchi et al., Annu. Rev. Condens. Matter Phys. 5, 113 (2014). [Preview Abstract] |
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