Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session L31: Organic Superconductors |
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Sponsoring Units: DCMP Chair: Arthur Hebard, University of Florida Room: LACC 407 |
Wednesday, March 7, 2018 11:15AM - 11:27AM |
L31.00001: Probing Low Energy Excitation by 13C NMR in the Field-Driven Inhomogeneous Superconducting State of β” Compound Hsin-Hua Wang, Sebastian Molatta, Georgios Koutroulakis, John Schlueter, Joachim Wosnitza, Hannes Kühne, Stuart Brown Non-zero momentum Cooper pairs, such as has been proposed in underdoped cuprates (pair density wave state) or the field-induced version (FFLO) pertaining to specific organic superconductors, has attracted extensive research interest recently. Towards quantifying the low-lying magnetic excitations of field-induced inhomogeneous superconductivity (FFLO), 13C (T1T)-1 is studied in the layered superconductor β”-(BEDT-TTF)2SF5CH2CF2SO3 over a wide range of fields and temperatures. Enhancement of (T1T)-1 over the normal state case is most pronounced in the vicinity of the phase boundaries, uniform-SC/FFLO and FFLO/normal. Modeling the NMR relaxation rate based on both the isolated and dense domain wall picture results in relaxation rates too small to account for the observations. The discrepancy calls for considering other contributions, for example the possibility for significant relaxation associated with extended state quasiparticles near to the phase boundary. Specific heat results lend support to this interpretation. A large enhancement of (T1T)-1 at tilted fields is suggested to be associated with interlayer decoupling. |
Wednesday, March 7, 2018 11:27AM - 11:39AM |
L31.00002: Deviations from half-filling and charge ordering tendencies in β''-type purely organic charge transfer salts Harald Jeschke The β''-(BEDT-TTF)2X class of charge-transfer salts with sulfonate anions X- forms a purely organic family with metallic and superconducting members. The X-=SF5CH2CF2SO3 anion is an especially interesting compound which superconducts and for which the spatially modulated Fulde Ferrell Ovchinnikov Larkin (FFLO) superconducting order parameter has been reported. The X-=SF5CHFCF2SO3 compound is known for a metal insulator transition which occurs as function of temperature. Other members of this family of materials have X-=SF5CHFSO3, X-=SF5CH2SO3 and X-=CF3CH2SO3 anions. |
Wednesday, March 7, 2018 11:39AM - 11:51AM |
L31.00003: Superconductivity in correlated organic materials: gap symmetry and critical temperatures Karim Zantout, Michaela Altmeyer, Roser Valenti Despite considerable efforts, no consensus about the superconducting gap symmetry in κ-(ET)2X was found to date. Several theoretical studies proposed gap symmetries that range from s- to d-wave. A recent RPA spin fluctuation theory study proposed an exotic eight-node gap (extended s+dx2-y2) for a large family of κ-(ET)2X superconductors. In addition, it was found that those materials lie close to the phase boundary to dxy symmetry and might therefore allow to switch symmetries by tuning the hopping. |
Wednesday, March 7, 2018 11:51AM - 12:03PM |
L31.00004: Magnetic transitions in K-doped biphenyl and p-terphenyl Guo-Hua Zhong, Chao Zhang, Xiao-Jia Chen, Hai-Qing Lin Recently, the superconductivity in K-doped p-terphenyl was reported with the transition temperatures range from 7 to 123 Kelvin, which attracts much attention. In this work, to investigated the possible magnetism and the transition between magnetism and superconductivity, we have studied the magnetism of K-doped biphenyl and p-terphenyl by combining the first-principles calculations with magnetization measurements. We found that the tilting between two successive benzene rings drives the antiferromagnetic spin ordering of electrons transferred to C atoms from K atoms at the low doping concentration. With the increase of charge transferring, the spin ordering disappears in systems while the superconductivity occurs. Namely, the transition from antiferromagnetic to superconducting behavior occurs with the increase of K doping contents. In fabricated K-doped biphenyl sample, the magnetic susceptibility measurement confirmed the existence of AFM characteristics, which is in good agreement with theoretical predictions. For K-doped p-terphenyl, more experimental observations is needed. Our results is helpful for understanding the superconducting transition in this kind of materials. |
Wednesday, March 7, 2018 12:03PM - 12:15PM |
L31.00005: Structural and electronic properties of K-doped p-terphenyl superconductor Jia-Xing Han, Guo-Hua Zhong, Xiaohui Wang, Chao Zhang, Xiao-Jia Chen, Hai-Qing Lin Recently, there is a series of reports by Wang et al. on the superconductivity in K-doped p-terphenyl with the transition temperatures range from 7 to 123 Kelvin. Identifying the structural and electronic character is the key to understand the superconducting phases and the related properties. Therefore we carried out an extensive study on the crystal structures with different doping levels and investigate the thermodynamic stability, structural, electronic, and magnetic properties by the first-principles calculations. Our calculated structures capture most features of the experimentally observed x-ray diffraction patterns for the sample with Tc~7 Kelvin. The K doping concentration is constrained to within the range of 2 and 3. The obtained formation energy indicates that the system at x ~ 2.5 is more stable. The charge transfer accounts for the metallic feature of the doped materials. For a small amount of charge transferred, the tilting force between the two successive benzenes drives the system to stabilize at the antiferromagnetic ground state, while the system exhibits non-magnetic behavior with increasing charge transfer. The multiformity of band structures near the Fermi level indicates that the driving force for superconductivity is complicated. |
Wednesday, March 7, 2018 12:15PM - 12:27PM |
L31.00006: Electron-Phonon Coupling in Doped p-Terphenyl Jia Chen, Andrew Millis, David Reichman Potassium-doped para-terphenyl has been reported to be a high critical temperature superconductor. {1,2,3} As a necessary step towards understanding this novel superconductivity, we study electronic structure and electron-phonon coupling in electron doped p-terphenyl using density functional (pertubation) theory calculations for both isolated molecules and extended crystals. Migdal-Elaishberg and dynamical mean field methods are then used to analyse quasiparticle properties and superconducting instabilities. The relevance of polaron physics to this superconductor will also be discussed. |
Wednesday, March 7, 2018 12:27PM - 12:39PM |
L31.00007: Superconductivity in K-doped triphenylamine Di Peng, Renshu Wang, Jiafeng Yan, Kai Zhang, Huang Ge, Xiao-Jia Chen, Qin Anjun, Hai-Qing Lin, Guo-Hua Zhong Organic compounds especially which with π-electron are promising candidates to exhibit high temperature or even room temperature superconductivity. Triphenylamine is a fundamental materials in Organic Light Emitting Diode (OLED) which with special electronic transport in the molecules. We successfully synthesized potassium-doped triphenylamin. Superconductivity was found in this material at a critical temperature of 7 K. We obtained the superconductive parameters such as the critical fields, penetration depth and Ginzburg-Landau coherence length for this superconductor. This finding open an encouraging window for the search of superconductors in aniline compounds. |
Wednesday, March 7, 2018 12:39PM - 12:51PM |
L31.00008: Superconductivity in Potassium Doped P-Terphenyl Muhammad Nadeem, Tae-Ho Park, Han-Yong Choi Aromatic hydrocarbon p-terphenyl (C18H14) has exhibited a diamagnetic signal when doped with potassium1, which seems to indicate superconductivity with the critical temperature (Tc) up to 123 K. In order to explore the possible high Tc superconductivity in this material, we have performed the density functional theory calculations for the structural, electronic and phononic properties of the pristine and K3 p-terphenyl. The crystal structure was optimized for the K3 p-terphenyl and then the phonon spectra were calculated using the density functional perturbation theory. Contributions of phonon eigen-modes related to K-atoms and p-terphenyl inter and intra-molecular vibrations in the electron-phonon coupling and spectral function have been analyzed using EPW2 in Quantum-Espresso suite. Tc was estimated from the Allen-Dynes formula with empirical values of Coulomb pseudopotential parameter. These results are presented in comparison with the structurally related and better studied K3 picene3 (K3C22H14) superconductor of Tc = 18 K. (References) 1. Ren-Shu Wang, Yun Gao, Zhong-Bing Huang, and Xiao-Jia Chen, arXive:1703.06641 (2017) 2. S. Poncé et al, Comput. Phys. Comm (2016). 3. M. Casuala, M.Clandra, G. Profeta and F. Mauri, PRL 107, 137006 (2011) |
Wednesday, March 7, 2018 12:51PM - 1:03PM |
L31.00009: Superconductivity above 120 kelvin in potassium-doped p-terphenyl Renshu Wang, Yun Gao, Zhong-Bing Huang, Xiao-Jia Chen Exploring high temperature superconductors is the main direction of the superconducting field for more than 100 years. Recently, we observed superconductivity at 123 K at ambient pressure in potassium-doped p-terphenyl, a chain link organic molecule. Through a large number of experiments, we find that there are four superconducting phases with the critical temperatures of 4.3 K, 7.2 K, 43 K and 123 K in different samples, respectively. Interestingly, there is an aging effect for these superconducting phases. Raman spectra show the formation of the bipolarons during doping. The doping effects are examined by comparing with early X-ray diffraction and Raman spectra. Undoubtedly, all of these results open up a new visual field to discover more high temperature superconductors in organic molecules. |
Wednesday, March 7, 2018 1:03PM - 1:15PM |
L31.00010: Spectroscopic Evidence of Low Energy Gaps Persisting Towards 120 Kelvin in Surface-Doped p-Terphenyl Crystals Haoxiang Li, Xiaoqing Zhou, Stephen Parham, Tom Nummy, Justin Griffith, Kyle Gordon, Eric Chronister, Daniel Dessau The possibility of high temperature superconductivity in organic compounds has been discussed since the pioneering work of Little in 1964 [i], with unsatisfactory progress until the recent report of a weak Meissner shielding effect at 120 Kelvin in potassium-doped para-terphenyl samples [ii]. To date however, no other signals of the superconductivity have been shown, including the zero resistance state or evidence for the formation of the Cooper pairs that are inherent to the superconducting state. Here, using high-resolution photoemission spectroscopy on potassium surface-doped para-terphenyl crystals, we uncover low energy gaps that persist to approximately 120 K. Among a few potential origins for these gaps, we argue that the onset of electron pairing within molecules is most likely. And while pairing gaps are a prerequisite for high temperature superconductivity they do not guarantee it. Rather, the development of long-range phase coherence between the paired states on the molecules is necessary, requiring good wavefunction overlap between molecular states– something that is in general difficult for such weakly overlapping molecules. |
Wednesday, March 7, 2018 1:15PM - 1:27PM |
L31.00011: Evolution of superconductivity in K-doped tris(4-methylphenyl)bismuthine L. C. Chen, Xiao-Lin Wu, Renshu Wang, Yun Gao, Zhong-Bing Huang, Xiao-Jia Chen We report the finding of superconductivity in K-doped tris(4-methylphenyl)bismuthine through both magnetization and resistivity measurements. The evolution of superconductivity and phases with pressure for this new superconductor was examined by the resistivity and Raman scattering measurements. At low pressures below 1.6 GPa, the obtained superconducting transition temperature Tc of 3.6 K remains unchanged. With further increasing pressure, a second superconducting phase with Tc of 7.2 K occurs. The phase transformation is detected by Raman scattering spectra accompanying the Tc enhancement. |
Wednesday, March 7, 2018 1:27PM - 1:39PM |
L31.00012: Superconductivity in K-doped p-sexiphenyl G. Huang, Di Peng, Renshu Wang, Xiao-Jia Chen, Hai-Qing Lin, Guo-Hua Zhong Organic compounds with π-electron network present great potential to be high temperature superconductors. Here we report the finding of superconductivity at a critical temperature of 7.4 K in para-sexiphenyl with the intercalation of potassium. By removing strong ferromagnetic background, the Messiner effect can be clrealy observed from the M-H plots. The obvious bipolaronic character is detected from Raman scattering measurements. Amorphous phase is found in the sample from X-ray diffraction patterns. |
Wednesday, March 7, 2018 1:39PM - 1:51PM |
L31.00013: Superconductivity in K-doped p-quinquephenyl Ge Huang, Renshu Wang, Xiao-Jia Chen, Guo-Hua Zhong, Hai-Qing Lin The chain-like organic compounds with conjugated structure have the potential to become high temperature superconductors. P-Quinquephenyl with five benzene rings connected in para positions is found to exhibit superconductivity at a critical transition temperature of 7.3 K. The dc and ac magnetic measurements reveal the Messiner effect and the realization of superconducting state. The occurrence of bipolarons discovered by Raman spectra guarantees potassium metal intercalated into p-quinquephenyl. X-ray diffraction patterns indicate the doped samples are poorly crystallized. |
Wednesday, March 7, 2018 1:51PM - 2:03PM |
L31.00014: Exploration of superconductivity in polyparaphenylene oligomers Xiao-Jia Chen, Renshu Wang, Kai Zhang, G. Huang, Liu-Cheng Chen, Jia-Feng Yan, Di Peng, Zhong-Bing Huang, Yun Gao, Guo-Hua Zhong, Hai-Qing Lin The appearance of superconductivity accompanied by some charge or spin order is the common feature for many unconventional superconductors. Suppressing such an order can bring about superconductivity in the systems such as cuprates, transition-metal dichalcogenides, and electron-transferred salts. We examine the case in polyparaphenylene oligomers. The birth of superconductivity in these molecules is indeed accompanied by the suppression of the charge order together with the formation of bipolarons. The latter can even exist at temperatures as high as 500 K. These findings open an encouraging window for the search of high temperature superconductors in chain link organic molecules. |
Wednesday, March 7, 2018 2:03PM - 2:15PM |
L31.00015: Superconductivity in potassium-doped p-quaterphenyl JiaFeng Yan, Renshu Wang, Kai Zhang, G. Huang, Di Peng, Xiao-Jia Chen, Guo-Hua Zhong, Hai-Qing Lin Exploring new materials with high temperature superconductivity has attracted great interests. By doping potassium into p-quaterphenyl with four phenyl rings connected by single C-C bond in para position, we find that this material can have two superconducting phases with the critical temperature of 4.3 K and 7.2 K, respectively. Their superconducting parameters and phase diagram are obtained and compared with other members of polyparaphenylene oligomers. The formation of bipolarons and the effect of dopant are determined by Raman scattering measurements. |
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