Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session E39: Fe-based Superconductivity - 122 Structure Materials |
Hide Abstracts |
Sponsoring Units: DMP DCMP Chair: Jannis Maiwald, University of Augsburg Room: 386 |
Tuesday, March 14, 2017 8:00AM - 8:12AM |
E39.00001: Coexistence of antiferromagnetic and ferromagnetic spin correlations in Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ studied by$^{\, 75}$As NMR Yuji Furukawa, Jinfang Cui, Paul Wiecki, Sheng Ran, Sergey L. Bud'ko, Paul C. Canfield Recent nuclear magnetic resonance (NMR) measurements revealed the coexistence of stripe-type antiferromagnetic (AFM) and ferromagnetic (FM) spin correlations in both the hole- and electron-doped BaFe$_{2}$As$_{2}$ families of iron-pnictide superconductors by a Korringa ratio analysis.[1] Motivated by the NMR work, we have carried out $^{75}$As NMR measurements in another iron pnictide superconducting family, Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2\, }$[2] in order to investigate magnetic fluctuations, especially focusing on possible existence of FM fluctuations. By analyzing $^{75}$As NMR data, we found clear evidence for the coexistence of stripe-type AFM and FM spin correlations in the Ca(Fe$_{1-x}$Co$_{x})_{2}$As$_{2\, }$system. In this talk, we discuss the characteristic magnetic fluctuations in the system. [1] P. Wiecki, et al., Phys. Rev. Lett. \textbf{115}, 137001 (2015). [2] J. Cui, et al., Phys. Rev. B \textbf{92}, 184504 (2015); J. Cui, et al., Phys. Rev. B (in print). [Preview Abstract] |
Tuesday, March 14, 2017 8:12AM - 8:24AM |
E39.00002: Low Temperature X-Ray Diffraction Study on CaFe$_{2}$As$_{2}$ Shuyuan Huyan, Liangzi Deng, Zheng Wu, Kui Zhao, Bing Lv, Yiyu Xue, Ching-wu Chu For undoped CaFe$_{2}$As$_{2}$ single crystals, we observed that utilizing thermal treatments could stabilize two pure tetragonal phases PI and PII. Both phases are non-superconducting, while the superconductivity with a T$_{c}$ up to 25 K can be induced through proper thermal treatment. Room temperature X-ray studies suggest that the origin of superconductivity arises from the interface of the mesoscopically stacked layers of PI and PII. To further investigate, a systematic low temperature X-ray study was conducted over a series of thermal treated CaFe$_{2}$As$_{2}$ single crystals. From which, we observed the phase aggregation of PI and PII upon cooling, more importantly, an ordered stacking structure exists at low temperature, which closely related to superconducting volume fraction and the ratio of PI and PII. These results further support the proposal of interface-enhanced superconductivity in undoped CaFe$_{2}$As$_{2}$. References L. Z. Deng, B. Lv, K. Zhao, F. Y. Wei, Y. Y. Xue, Z. Wu, and C. W. Chu, Phys. Rev. B 93, 054513(2016) K. Zhao, B. Lv, L. Z. Deng, S. Y. Huyan, Y. Y. Xue, and C. W. Chu, Proc. Natl. Acad. Sci. doi: 10.1073/pnas.1616264113 [Preview Abstract] |
Tuesday, March 14, 2017 8:24AM - 8:36AM |
E39.00003: Robust fully - gapped $s_\pm$ superconductivity in CaKFe$_4$As$_4$ single crystals from penetration depth and STM spectroscopy Ruslan Prozorov, K. Cho, S. Teknowijoyo, M. A. Tanatar, K. R. Joshi, N. M. Nusran, T. Kong, W. Meier, U. Kaluarachchi, S. L. Bud'ko, P. C. Canfield, A. Fente, I. Guillam\'{o}n, H. Suderow, M. Ko\'{n}czykowski Low - temperature variation of the London penetration depth, $\Delta \lambda (T)$, and tunneling conductance in single crystals of stoichiometric iron - based superconductor CaKFe$_4$As$_4$ (CaK1144) show nodeless superconductivity with two effective gaps in the range of 6 - 10 meV and 1-4 meV. Substantial rate of $T_c$ suppression and robust exponential low-temperature behavior of $\Delta \lambda (T)$ upon electron irradiation provide a strong argument for a sign-changing $s_{\pm}$ pairing in this compound. Overall, the observed behavior and extracted parameters are quite similar to a slightly overdoped (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ (BaK122), e.g. $x=$0.54, $T_c \approx$ 34 K. Considering the results obtained on BaK122 across the superconducting ``dome" and varying disorder [1], we conclude that $s_{\pm}$ superconductivity is a robust pairing state in iron - based superconductors, independent of the degree of substitutional or lattice damage disorder. [1] K. Cho {\it et.~al}, Sci. Adv. {\bf 2}, 1600807 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 8:36AM - 8:48AM |
E39.00004: Optimizing the solution growth of the superconductor CaKFe$_{4}$As$_{4}$ William R. Meier, T. Kong, G. Drachuck, S. M. Saunders, A. Sapkota, A. Kreyssig, A. I. Goldman, S. L. Bud'ko, P. C. Canfield High-quality single crystals of the new iron-based superconductor CaKFe$_{4}$As$_{4}$ were grown from a high-temperature, quaternary, iron-arsenic rich solution[1]. The characteristics of this four-element system lead to a modified optimization routine of the growth protocol exploiting measurements of physical properties (resistance and magnetization) in addition to more routine x-ray phase analysis. We will emphasize how events informed our adjustments of the protocol and present a schematic phase diagram established by the process. \linebreak $[1]$ W. R. Meier {\it et al.}, Phys. Rev. B 94, 064501 (2016). [Preview Abstract] |
Tuesday, March 14, 2017 8:48AM - 9:00AM |
E39.00005: Evolution of Spin fluctuations in CaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ with Co-doping. A. Sapkota, P. Das, A. E. B\"{o}hmer, D. L. Abernathy, P. C. Canfield, A. Kreyssig, R. J. McQueeney, A. I. Goldman Spin fluctuations are an essential ingredient for superconductivity in Fe-based supercondcutors. In Co-doped BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$, the system goes from the antiferromagnetic (AFM) state to the superconducting (SC) state with Co doping, and the spin fluctuations also evolve from well-defined spin waves with spin gap in the AFM regime to gapless overdamped or diffused fluctuations in the SC regime. CaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ has a stronger magneto-elastic coupling than BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ and no co-existence of SC and AFM region as observed in BaFe$_{\mathrm{2}}$As$_{\mathrm{2\thinspace }}$with Co doping. Here, we will discuss the evolution of spin fluctuations in CaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ with Co doping. [Preview Abstract] |
Tuesday, March 14, 2017 9:00AM - 9:12AM |
E39.00006: Possible Interface Superconductivity in Rare-earth Doped CaFe2As2 and Undoped CaFe2As2 L. Z. Deng, B. Lv, K. Zhao, S. Y. Huyan, Z. Wu, M. Gooch, B. Lorenz, F. Y. Wei, Y. Y. Xue, C. W. Chu Interface superconductivity has been proposed as a mechanism that provides continual inspiration and hope as a route to reach HTS/RTS. Difficulties do exist, as most of these proposed materials are artificially designed heterostructure materials and are by nature delicate and easily disturbed by strain and change in the stoichiometry at the interface. The discovery of superconductivity in rare-earth doped CaFe2As2 (Ca122) with Tc up to 49 K [1], brought renewed hope and detailed material studies were systematically carried out on rare-earth (R) doped Ca122 single crystals with R $=$ La, Ce, Pr, and Nd [2,3]. The experimental observations lead us to the conjecture that the Tc enhancement may be related to naturally occurring chemical interfaces associated with defects and thereby provide a new paradigm to find superconductors with higher Tc. Most recently, we discovered interface-induced superconductivity in the undoped Ca122 with a Tc up to \textasciitilde 25 K [4], which provides the most direct evidence to date for possible interfacial superconductivity in single crystals and also sheds light on the understanding of the superconductivity in rare-earth doped Ca122. References: [1] B. Lv et al, PNAS (2011). [2] F. Y. Wei et al., Philos. Mag. (2014); [3] L. Z. Deng et al., Phys. Rev. B (2016); [4] K. Zhao et al., PNAS (2016). [Preview Abstract] |
Tuesday, March 14, 2017 9:12AM - 9:24AM |
E39.00007: Interface-induced superconductivity at $\sim $25 K at ambient pressure in undoped CaFe2As2 single crystals C. W. Chu, K. Zhao, L. Z. Deng, B. Lv, S. Y. Huyan, Z. Wu, Y. Y. Xue, M. Gooch, B. Lorenz Superconductivity has been reversibly induced/suppressed in undoped CaFe2As2 (Ca122) single crystals with Tc at $\sim $25 K at ambient pressure and up to 30 K at 1.7 GPa. We found that Ca122 can be stabilized in two distinct tetragonal (T) phases: PI with a nonmagnetic collapsed tetragonal (cT) phase at low temperature and PII with an antiferromagnetic orthorhombic (O) phase at low temperature. Neither phase at ambient pressure is superconducting down to 2 K. However, systematic annealing for different time periods at 350 $^{\circ}$ C on the as-synthesized crystals reveals the emergence of superconductivity over a narrow time window. Detailed X-ray diffraction profile analyses further reveal mesoscopically stacked layers of the PI and the PII phases. The deduced interface density correlates well with the superconducting volume measured. The transport anomalies of the T--cT transition and the T--O transition are gradually suppressed over the superconductive region, presumably due to the interface interactions between the nonmagnetic metallic cT phase and the antiferromagnetic O phase. The results provide the most direct evidence to date for interface-enhanced superconductivity in undoped Ca122, consistent with the recent theoretical prediction. Reference: K. Zhao et al., doi: 10.1073/pnas.1616264113, PNAS (2016). [Preview Abstract] |
Tuesday, March 14, 2017 9:24AM - 9:36AM |
E39.00008: Discovery of a bi-critical point between antiferromagnetic and superconducting phases in pressurized single crystal Ca$_{\mathrm{0.73}}$La$_{\mathrm{0.27}}$FeAs$_{\mathrm{2}}$ Liling Sun, Yazhou Zhou, Qi Wu, Jing Guo, Wei Yi, Zhongxian Zhao, Vladimir Sidorov, Guangming Zhang, Shan Jiang, Ni Ni, Ke Yang, Sheng Jinag, Aiguo Li One of the most strikingly universal features of the high-temperature superconductors is that the superconducting phase emerges in the close proximity of the antiferromagnetic phase, and the interplay between these two phases poses a long-standing challenge. It is commonly believed that, as the antiferromagnetic transition temperature is continuously suppressed to zero, there appears a quantum critical point, around which the existence of antiferromagnetic fluctuation is responsible for the development of the superconductivity. In contrast to this scenario, we report the discovery of a bi-critical point identified at 2.88 GPa and 26.02 K in the pressurized high-quality single crystal Ca$_{\mathrm{0.73}}$La$_{\mathrm{0.27}}$FeAs$_{\mathrm{2}}$ by complementary \textit{in-situ} high pressure measurements. At the critical pressure, we find that the antiferromagnetism suddenly disappears and superconductivity simultaneously emerges at almost the same temperature, and that the external magnetic field suppresses the superconducting transition temperature but hardly affects the antiferromagnetic transition temperature. [Preview Abstract] |
Tuesday, March 14, 2017 9:36AM - 9:48AM |
E39.00009: Collective excitations of dynamic Fermi surface deformations in BaFe$_2$(As$_{0.5}$P$_{0.5}$)$_2$ Shangfei Wu, Girsh Blumberg, Hsiang-Hsi Kung, Alexander Lee, Weilu Zhang, Ding Hu, Huican Mao, Pierre Richard, Hong Ding, Pengcheng Dai Recent transport studies of the overdoped BaFe$_2$(As$_{0.5}$P$_{0.5}$)$_2$ superconductor reported a crossover from non-Fermi liquid(NFL) to Fermi liquid(FL) behavior at around 100 K\footnote{J. Analytis et al. Nat.Phys.10,194(2014)}. Here we elucidate the spectroscopic signatures in this crossover regimes using polarization resolved Raman spectroscopy. In the FL regime below 100 K, we detect long-lived collective quadrupole symmetry excitations at about 32 meV in the B$_{1g}$ and B$_{2g}$ channels. We assign them to Pomeranchuk oscillations related to dynamical Fermi surface (FS) deformations. The Pomeranchuk oscillations show a similarity for the B$_{1g}$ and B$_{2g}$ quadrupole channels, which we explain by the large As/P disorder. We explain that the small Fermi energy is an essential condition for Pomeranchuk oscillations to be underdamped at low temperature\footnote{S.Wu et al. arXiv:1607.06575}. [Preview Abstract] |
Tuesday, March 14, 2017 9:48AM - 10:00AM |
E39.00010: Multi-Method Specific Heat Investigation of the Overdoped High-Tc Superconductor, BaFe$_{\mathrm{2}}$(As$_{\mathrm{1-x}}$P$_{\mathrm{x}})_{\mathrm{2}}$ Camilla M. Moir, Scott C. Riggs, Jose A. Galvis, Xiujun Lian, Jiun-Haw Chu, Philip Walmsley, Ian R. Fisher, Arkady Shekhter, Greg S. Boebinger We examine the specific heat of the iron-based high-temperature superconductor, BaFe$_{\mathrm{2}}$(As$_{\mathrm{1-x}}$P$_{\mathrm{x}})_{\mathrm{2}}$ for 0.44$\le $x$\le $0.60 using three distinct methods: zero-magnetic-field analysis of the jump in specific heat at T$_{\mathrm{c}}$, zero-magnetic-field determination of the electronic specific heat in the T$=$0 limit, and, most importantly, high-magnetic-field measurement of the electronic specific heat in which we suppress superconductivity to reveal the normal state specific heat [1]. We report the coupling strength parameter $\alpha_{\mathrm{c}}=\Delta $C/($\gamma _{\mathrm{n}}$T$_{\mathrm{c}})$ as a function of doping. We also observe a finite, zero-temperature specific heat, which has also been reported in Ba(Fe$_{\mathrm{1-x}}$Co$_{\mathrm{x}})_{\mathrm{2}}$As$_{\mathrm{2}}$ [2] and the cuprates [3]. By comparing the three methods, we are able to deduce a consistent treatment of specific heat measurements in this iron-based high-temperature superconductor. The data establish that mass enhancement occurs in multiple bands as optimal doping is approached and, furthermore, $\alpha_{\mathrm{c}}$ deviates from the expected BCS value. [1] Moir, C.M. et. al. arXiv:1608.07510 (2016) [2] Gang, MU, et. al. Chinese Phys. Lett. 27 037402 (2010) [3] Brooks, J.S. and J. R. Schieffer, editors. Handbook of High-Temperature Superconductivity, (2007). [Preview Abstract] |
Tuesday, March 14, 2017 10:00AM - 10:12AM |
E39.00011: High Field Hall Effect and Critical Physics in BaFe2(As1-xPx)2 Ian Hayes, Brad Ramshaw, Gilbert Lopez, James Analytis Thirty years after the discovery of the cuprates, the precise nature of the electronic state that leads to very high superconducting transition temperatures is still a mystery. A significant clue has come from the charge transport properties of these systems, which are similar to those seen in quantum critical metals. These properties include a T-linear resistivity and a cotangent of the Hall angle that grows as T-squared. However, it is difficult to say whether these properties are accidental or essential to the physics of High-Tc superconductivity. The iron-based high-Tc superconductors provide an important point of comparison on this question. I will report on high-field magnetoresistance measurements, including Hall effect data up to 65 Tesla, on the iron-pnictide compound BaFe2(As1-xPx)2. Although the presence of multiple bands in these materials may lead us to expect otherwise, the charge transport in these materials reflects many of the universal properties of quantum critical metals that also appear in the cuprates, suggesting that these properties are intimately connected to the physics of High-Tc superconductivity. [Preview Abstract] |
Tuesday, March 14, 2017 10:12AM - 10:24AM |
E39.00012: Substitution and doping in iron pnictides M. Merz, P. Schweiss, P. Nagel, M.-J. Huang, A. Plog, R. Eder, Th. Wolf, H. v. Löhneysen, S. Schuppler The composition-dependent electronic structure of iron pnictides, in particular the question if and how charge carriers are introduced to the system upon substitution -- by Sr or alkali metals (\textit{AM}) for Ba; by transition metals (\textit{TM}) for Fe; and/or by P for As -- continues to provide surprises. Our systematic study of spatial structure and electronic states by x-ray diffraction and x-ray absorption, performed on a large number of compositions in the (Ba,Sr,\textit{AM})(Fe,\textit{TM})$_{2}$(As,P)$_{2}$ family of compounds, shows, for instance, that valences are often different from expectations, that doping can be ``effective'' or not, depending on substituent, and that many doping effects are ``site decoupled'', meaning that they occur \textit{either} on the Fe site \textit{or} on the As site but not on both simultaneously. Furthermore, the energy-level schemes derived from electronic and spatial structure differ from the present ``standard'' assumptions. In all, it appears that indirect, structural effects of substitution may in many cases be more important for magnetism and superconductivity in iron pnictides than direct, charge-carrier doping effects. [Preview Abstract] |
Tuesday, March 14, 2017 10:24AM - 10:36AM |
E39.00013: Multi-probe mapping of optimally doped BaFe$_2$(As$_{1-x}$P$_x$)$_2$ Eric Thewalt, James Hinton, Ian Hayes, Arielle Little, Shreyas Patankar, Liang Wu, Toni Helm, Nobumichi Tamura, Dung-Hai Lee, James Analytis, Joseph Orenstein The superconductor BaFe$_2$(As$_{1-x}$P$_x$)$_2$ has a rich phase diagram. Much like in the cuprates, the parent compound has an antiferromagnetic phase that yields to superconductivity with doping. Evidence for a variety of nematic phenomena, including a nematic phase transition extending above the superconducting dome and a nematic quantum critical point at optimal doping, has emerged. We have studied an optimally doped sample using scanning X-ray microdiffraction and pump-probe birefringence microscopy. Combining these techniques allows us to image built-in strain and its dynamical effects locally, and we report correlations between local strain and ultrafast dynamics. [Preview Abstract] |
Tuesday, March 14, 2017 10:36AM - 10:48AM |
E39.00014: Tuning structure and properties of BaCr$_2$As$_2$ and BaFe$_2$As$_2$ by doping in transition-metal sites G. Wang, L. Wang, N. Liu, Z. P. Lin, S. J. Shen, X. L. Chen, W. R. Meier, P. C. Canfield ThCr$_2$Si$_2$-type structure is common for over 800 compounds and many of them exhibit interesting physical properties, such as superconductivity, quantum critical transition and so on. The typical layered structural feature makes them easier to be tuned in structure and physical properties by structural manipulation, carrier injection, or application of pressure. Here I will present the tuning of structure and physical properties of two ThCr$_2$Si$_2$-type materials by doping in transition-metal sites. Corresponding single crystals have been grown using flux method in order to access their intrinsic physical properties to a higher extent. For transition-metal doped BaCr$_2$As$_2$, a clear change of electronic transport behavior has been observed under pressure. While the spin-density-wave anomaly in BaFe$_2$As$_2$ is effectively suppressed by non-transition-metal doping. The underlying mechanisms for these phenomenons are still under investigation now. [Preview Abstract] |
Tuesday, March 14, 2017 10:48AM - 11:00AM |
E39.00015: Magnetic penetration depth in KFe$_2$As$_2$ Joe Wilcox, Liam Malone, Frederic Hardy, Carsten Putzke, Thomas Wolf, Peter Adelmann, Christoph Meingast, Antony Carrington KFe$_2$As$_2$ is the end member of the (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ series of iron-pnictide superconductors. Previous measurements have suggested that the gap structure of KFe$_2$As$_2$ is nodal, either accidentally or due to the symmetry of the pairing state, in contrast to the rest of the series. Our measurements of the magnetic penetration depth, $\lambda(T)$ of (Ba$_{1-x}$K$_x$)Fe$_2$As$_2$ for $x=0.85,0.91,1.0$ all show $\lambda(T)$ saturates at low temperature, which is indicative of either a small energy gap or a small amount of residual disorder. To differentiate between these possibilities we studied both the effect of non-linear, field dependent, corrections, as well as the effect of disorder, on $\lambda(T)$. [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