Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C30: Superconductivity: Less Common Materials |
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Sponsoring Units: DCMP Chair: Robert Cava, Princeton University Room: LACC 406B |
Monday, March 5, 2018 2:30PM - 2:42PM |
C30.00001: Effect of chemical and physical pressure on the superconducting properties of LaZn2-xSn2 Alessia Provino, Arjun Pathak, Vitalij Pecharsky, Marina Putti, Carlo Ferdeghini, Volodymyr Smetana, Anja Mudring, Pietro Manfrinetti The new series of rare earth intermetallic compounds with composition RZn2-xSn2 has been recently discovered for the light lanthanides (R=La,Ce,Pr,Nd,Sm). Their crystal structure is a derivative of the CaBe2Ge2-type (tP10, P4/nmm). Single crystal structural refinements revealed defects and disorder in the structure of these compounds, with Zn-site vacancies and mixed Zn/Sn atomic occupations leading to a stoichiometry of ≈ RZn1.5Sn2. Physical property measurements have shown appearance of superconductivity for the La homologue, with Tc ≈ 5.5 K. This observation is unexpected in heavily disordered phases. In present work we have investigated the effect of chemical pressure brought about by atomic substitution of Zn and Sn with other properly chosen elements (Mg, Cu and Cd for Zn and In, Ge and Pb for Sn). The results will be discussed and compared with the effects of physical pressure on the superconducting properties of this material. LaZn1.5Sn2 represents a pristine compound for a new series of superconducting materials. |
Monday, March 5, 2018 2:42PM - 2:54PM |
C30.00002: Absence of Polar Kerr Signal in the Superconducting Phase of Bi3Ni Single Crystal Jingyuan Wang, Peng-Chao Xu, Xiangde Zhu, Xiaofeng Jin, Jing Xia Superconductivity and ferromagnetism are two competing ground states in condensed matter systems. So far, the coexistence of superconductivity and ferromagnetism has only been discovered in a few systems. Bi3Ni is an intermetallic superconductor with critical temperature around 4.06K, coexistence of superconductivity and ferromagnetism has been reported in Bi3Ni nanostructures and polycrystals. Using ultrasensitive loop-less fiber-optic Sagnac interferometer, we studied Polar Kerr effect on Bi3Ni single crystal. Crystal was cooled down to 3.5K in zero field and then warmed up to 5.7K, measurement showed no significant change in Kerr signal around critical temperature during the warm up. To find an upper boundary of Kerr rotation of Bi3Ni, we used pure silicon as reference, the difference in Kerr rotation between Bi3Ni and pure silicon was smaller than 50 nanoradians during the warm up process, suggesting the Kerr rotation caused by Bi3Ni was smaller than 50 nanoradians. Sample cooled in magnetic field of 100 Oe showed similar result, indicating there is no ferromagnetic order and time reversal symmetry breaking in Bi3Ni single crystal in its superconducting phase. |
Monday, March 5, 2018 2:54PM - 3:06PM |
C30.00003: Superconductivity in Doped Black Phosphorus? Hanming Yuan, Liangzi Deng, Bing Lv, Zheng Wu, Shuyuan Huyan, Sheng Li, Ze Yang, Yizhou Ni, Jingying Sun, Shuo Chen, Hui Wang, Dezhi Wang, Fei Tian, Zhifeng Ren, Paul Chu Superconductivity has been predicted theoretically in Li-doped black phosphorus (BP) [1, 2]. To experimentally verify the prediction, BP crystals were synthesized from red phosphorus by two different methods: 1) the chemical vapor transport technique, and 2) the high-pressure technique. The BP crystals were then intercalated by two different methods: 1) n-Butyllithium treatment for Li-intercalant, and 2) electrochemical treatment for Li- and Na-intercalants. The pristine and the intercalated BPs were characterized by XRD, EDS, transport and magnetic measurement. Superconductivity with Tc of 3.8 K was detected in some of the intercalated BP crystals, but not in all. Detailed studies are still in progress. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C30.00004: Magnetism and Superconductivity in the Filled Skutterudite Pr1-xEuxPt4Ge12 System Ram Adhikari, Dom Kunwar, Inho Jeon, Shen Ran, M Brian Maple, Carmen Almasan We present results of heat capacity (HC) measurements on filled skutterudite Pr1-xEuxPt4Ge12 (0 ≤ x ≤ 1) system to investigate the effect of Eu substitution on superconductivity (SC) and magnetism in this system. Increasing Eu content leads to the suppression of the SC transition temperature (Tc), with no evidence of SC for samples with x > 0.5 both from resistivity and HC measurements down to 0.5 K. The x > 0.7 samples display antifferomagnetism (AFM) with the Neel temperature increasing with increasing Eu content. The HC data reveal the presence of HC anomaly for the whole Eu doping range (0.05 ≤ x ≤ 1). The HC peak for the samples with x > 0.5 reflects the AFM of Eu moments since it is suppressed to lower T with increasing magnetic field. The HC peak for the samples with x ≤ 0.5 is a result of a net moment present at T < Tc since the position of the peak shifts to higher T with increasing magnetic field. In addition, the magnetic entropy increases linearly with increasing Eu content and it reveals an octet ground state, i.e., S = xRln8. The net internal field lifts this degeneracy and gives rise to the Schottky anomaly in HC. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C30.00005: Investigating the unconventional superconductivity in single crystals of the noncentrosymmetric superconductor La7Ir3 Daniel Mayoh, Toshiro Takabatake, Don Paul, Geetha Balakrishnan, Martin Lees In superconductors, the inversion symmetry of the crystal structure plays a central role in the formation of the Cooper pairs. Systems lacking a center of inversion exhibit a nonuniform lattice potential, giving rise to a Rashba-type antisymmetric spin-orbit coupling. This can lead to exotic physics, such as time-reversal symmetry (TRS) breaking, below the superconducting transition temperature Tc. Until recently, only two NCS compounds, Re6Zr and LaNiC2, have been shown to break TRS below Tc [1,2]. The nature of the pairing states in these superconductors continues to be a puzzling and challenging question. Now we have discovered a third NCS material, polycrystalline La7Ir3, that shows broken TRS below Tc [3]. Here, we report the first growth of single crystals of La7Ir3. We present experimental data on these single crystals that shed light on to the unconventional superconducting state of La7Ir3. We compare our results with other members of the La7T3 (T = transition metal) family of superconductors and discuss the unconventional superconductivity in this exciting new family of materials. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C30.00006: Electron-phonon coupling and polaronic effects in the high-Tc superconductor Ba1-xKxBiO3 Muntaser Naamneh, Dariusz Gawryluk, Tian Shang, Daniel McNally, Marcus Dantz, Jonathan Pelliciari, Joel Mesot, Ming Shi, milan radovic, Thorsten Schmitt, Steven Johnston, Nicholas Plumb Ba1-xKxBiO3 (BKBO) is a phonon-mediated superconductor (max Tc ~ 32 K) exhibiting many hallmarks of “unconventional” superconductivity. It is therefore an ideal system for exploring how electron-phonon interactions may give rise to unexpectedly high Tc’s and other anomalous behaviors. In order to probe collective excitations in BKBO, we have performed resonant inelastic x-ray scattering (RIXS) at the O-K edge on thin films of BKBO in the doping range from x = 0 (insulator) to x = 0.4 (superconductor near optimal doping). The data have been analyzed by a cluster exact diagonalization approach, adapting a model successfully employed on 3d transition metal oxides to the s-p orbital system of BKBO. For all dopings, the extracted coupling constant exceeds a critical strength, beyond which bipolarons tend to become stabilized. The results help to quantify the polaronic nature of BKBO and imply that these compounds are susceptible to intrinsic disorder due to polaronic distortions across the entire investigated doping range. Implications for superconductivity will be discussed. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C30.00007: Possible high-Tc superconductivity in Ruddlesden-Popper compounds: Incipient narrow bands originating from “hidden ladders” Daisuke Ogura, Hideo Aoki, Kazuhiko Kuroki It has been suggested[1] that superconductivity should be strongly enhanced in systems with coexisting wide and narrow bands, as in the two-leg Hubbard ladder with the second-neighbor hopping when the Fermi level EF is put near the narrow band edge. As a way to realize this situation in actual materials, we introduce a concept of a “hidden ladder” electronic structure in the bilayer Ruddlesden-Popper compounds. When EF crosses the bands with t2g orbital character, an electron in the dxz/yz orbital selectively hops in the x/y direction as well as in the z direction normal to the bilayer. This means that the dxz/yz orbital form a ladder with x/y and z directions being the leg and rung directions, respectively. We propose that Sr3Mo2O7 and Sr3Cr2O7 are candidates for the hidden ladder materials where EF sits right in the vicinity of the narrow-band edge. Based on this electronic structure, we discuss possible occurrence of high-Tc superconductivity in these materials originating from the large number of interband pair-scattering channels between the wide and the “incipient” narrow bands[2]. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C30.00008: Contribution of hydrogen vibration to superconducting pairing at ambient pressure: A first principles study on hole-doped perovskite oxyhydrides Minjae Ghim, Nobuya Sato, Ryosuke Akashi, Seung-Hoon Jhi, Shinji Tsuneyuki The recent technique of chemical substitution of oxide (O2-) to hydride (H-) ions in the perovskite oxides ABO3 has paved a way to explore new physics involving special features of hydrogen. Along this line, we have recently proposed an unsynthesized group of compounds ATiO2H (A: Alkaline metal), where H-1s orbitals comprise an appreciable fraction of the highest valence band [J. Chem. Phys. 147,034507 (2017)]. The hole doping into this band could realize the superconductivity boosted by the Cooper pairing via the hydrogen vibration, which has been thought to occur only at megabar pressure. To examine this possibility, we investigate the superconducting properties of hole-doped ATiO2H by density functional theory for superconductors. Both the uniform doping and direct substitution (Ti-->Sc) schemes yield superconducting state with Tc~1K. In the latter case Tc is lowered by subtle modification of the electronic states such as deformation of the Fermi surface and charge density wave; nevertheless, by fine-tuning of the doping ratio, superconducting phase contributed by hydrogen 1s orbital can be realized. Our results draw a new prospective path to the metallic and superconducting hydrogen at accessibly low pressures. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C30.00009: Time-reversal symmetry breaking superconductivity in (Pr,La)Pt4Ge12 Jian Zhang, Z. F. Ding, Kevin Huang, Adrian Hillier, Pabitra Biswas, Cheng Tan, Lei Shu Zero-field muon spin relaxation (µSR) measurements were carried out on the PrxLa1-xPt4Ge12 alloys, revealing a second-order like suppression of broken time reversal symmetry (TRS) on approaching x = 0. For x > 0.3 compounds, the onset temperatures of time-reversal violating phase is lower than the superconductivity (SC) transition temperatures. Both temperature dependence of upper critical field Hc2(T) and lower critical field Hc1(T) in x > 0.3 alloys have two different quadratic temperature regions. The SC order parameter of PrPt4Ge12 is then discussed in the context of TRS phase determined by µSR measurements, Hc2(T) and Hc1(T) results, and gap point nodes illustrated by our specific heat data (down to 0.1 K). |
Monday, March 5, 2018 4:18PM - 4:30PM |
C30.00010: Fulde-Ferrell-Larkin-Ovchinnikov State in Spin-Orbit-Coupled Superconductor: Application to Li2Pd3B Fei Yang, Ming-Wei Wu We show that in the presence of magnetic field, two superconducting phases with the center-of-mass momentum of Cooper pair parallel to the magnetic field are induced in spin-orbit-coupled superconductor Li2Pd3B. Specifically, at small magnetic field, the center-of-mass momentum is induced due to the energy-spectrum distortion and no unpairing region with vanishing singlet correlation appears. We refer to this superconducting state as the drift-BCS state. By further increasing the magnetic field, the superconducting state falls into the Fulde-Ferrell-Larkin-Ovchinnikov state with the emergence of the unpairing regions. The observed abrupt enhancement of the center-of-mass momenta and suppression on the order parameters during the crossover indicate the first-order phase transition. Enhanced Pauli limit and hence enlarged magnetic-field regime of the Fulde-Ferrell-Larkin-Ovchinnikov state are revealed. We also address the triplet correlations induced by the spin-orbit coupling, and show that the Cooper-pair spin polarizations, generated by the magnetic field and center-of-mass momentum with the triplet correlations, exhibit totally different magnetic-field dependences between the drift-BCS and Fulde-Ferrell-Larkin-Ovchinnikov states. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C30.00011: Scanning tunneling microscopy studies of atomic impurities on the non-centrosymmetric superconductor BiPd Hao Ding, Mallika Randeria, Benjamin Feldman, Yuwen Hu, Satya Kushwaha, Robert Cava, Ali Yazdani In the non-centrosymmetric superconductor BiPd, electrons are exposed to strong Rashba spin-orbit coupling in the bulk, which can allow for both spin-singlet and spin-triplet pairing channels. Introducing impurities to such a superconductor can generate various types of in-gap states. Bound states around non-magnetic impurities are expected in the presence of triplet pairing, and magnetic impurities give rise to Yu-Shiba-Rusinov states. Moreover, the combination of magnetism, spin-orbit coupling and superconductivity provides the essential ingredients for topological superconductivity. Here we use a dilution refrigerator scanning tunneling microscope to study the nature of the superconductivity in BiPd, whose bulk Tc is 3.8 K. We further explore the in-gap bound states of individual atomic impurities on its surface, and discuss the potential of this system as a new platform for Majorana fermions. |
Monday, March 5, 2018 4:42PM - 4:54PM |
C30.00012: Single-band superconductivity in low density SrTiO3 Terence Bretz-Sullivan, J Jiang, Alexey Suslov, John Pearson, Alex Martinson, Anand Bhattacharya Bulk strontium titanate is a well-known low density multi-band superconductor. Recently, it was found that superconductivity persists to an order of magnitude lower doping (≤1018 cm-3). Superconductivity in the low density single-band regime is interesting because the nominal Debye energy is comparable to or greater than the Fermi energy, also known as the non-adiabatic limit. We present a study that combines standard magneto-transport, measurements of Shubnikov de Haas oscillations and superconducting properties to better understand superconductivity in the very low density limit in high mobility reduced single crystals of SrTiO3. |
Monday, March 5, 2018 4:54PM - 5:06PM |
C30.00013: Investigating Superconductivity in Barium Bismuthate Yau Chuen Yam, Mi Jiang, Mona Berciu, George Sawatzky Hole-doped BaBiO3 has a rather high critical superconducting temperature Tc at ~30-40K. Density functional calculations suggest a rather modest electron phonon coupling. This strongly suggests looking for either other mechanisms or for mechanism by which the electron phonon coupling might be strongly enhanced. A strong enhancement could also lead to rather small polaron behaviour leaning more towards a Bose Einstein Condensation theory. Recent interpretation of the density functional calculations of BaBiO3 strongly suggests that there is a condensation of two mainly O holes connected to the short bond length Bi suggesting bipolaron behaviour in the hole doped materials. We study the possibility of superconductivity in BaBiO3 based on the idea of pre-formed pairs, using an effective model obtained from Density Functional Theory. |
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