Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session F11: Odd-Parity Superconductivity |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Daoxin Yao, Sun Yat-sen University Room: 007B |
Tuesday, March 3, 2015 8:00AM - 8:12AM |
F11.00001: Influence of Fermi Surface Geometry and Geometric Phases on Spin-Triplet correlations in Superconductor-Ferromagnet Hybrid Structures Matthias Eschrig During the past 15 years a new field has emerged, which combines superconductivity and spintronics, with the goal to pave a way for new types of devices for applications combining the virtues of both, namely quantum coherence and interference on one side, and spin-selectivity and spin magnetism on the other. The building block of this new ``superspintronics'' are spin-triplet Cooper pairs, which are generated at the interface between a conventional superconducting and a ferromagnetic material. Non-collinear magnetic inhomogeneity mixes triplet pairs among each other, thus creating long-ranged equal-spin Cooper pairs in the ferromagnet, and non-coplanar inhomogeneity introduces geometric phases giving rise to unusual current phase relations. Considerable Fermi surface mismatch is unavoidable for hybrid structures involving strongly spin-polarized ferromagnets. We perform calculations showing that Fermi surface geometry has important implications for the sign and magnitude of induced triplet correlations in the superconductor, as well as for the generation of spin currents. We discuss under which conditions spin currents are generated, and how the triplet correlations can be maximized for applications. [Preview Abstract] |
Tuesday, March 3, 2015 8:12AM - 8:24AM |
F11.00002: Proximity-induced triplet superconductivity in Rashba materials Christopher Reeg, Saurabh Maiti, Dmitrii Maslov We study a proximity junction between a conventional $s$-wave superconductor and a conductor with Rashba spin-orbit coupling. Our specific focus is on the spin structure of the induced pairing in the Rashba conductor, where the mixing of spin-up and spin-down states converts the purely spin-singlet Cooper pairs of the superconductor into a mixture of spin-singlet and spin-triplet pairs. Because the induced triplet component of the pairing is generated entirely by a singlet order parameter and a single-particle spin-orbit term that preserves time-reversal symmetry, the triplet component is expected to persist even in the presence of disorder. We also propose an experimental setup to verify the triplet nature of the induced pairing. [Preview Abstract] |
Tuesday, March 3, 2015 8:24AM - 8:36AM |
F11.00003: Possible correlation-driven odd-parity superconductivity in LaNi$_{7/8}$Co$_{1/8}$O$_3$ (111) bilayers Bing Ye, Andrej Mesaros, Ying Ran Using the functional renormalization group technique we demonstrate a route for potentially high temperature odd-parity superconductivity in ferromagnetic materials caused by repulsive electron interactions, where the superconducting pairing is driven by charge-density wave fluctuations. Our model is directly applicable to a lightly cobalt-doped LaNiO$_3$ bilayer grown in the (111) direction. As the on-site repulsive interaction grows, a charge-density wave state with a charge pattern that respects all point-group symmetries of the bilayer is replaced by a superconducting state with an f-wave pairing. [Preview Abstract] |
Tuesday, March 3, 2015 8:36AM - 8:48AM |
F11.00004: Spin-Triplet Superconductivity in Sr$_2$RuO$_4$ due to Orbital and Spin Fluctuations: 2D fRG Analysis Masahisa Tsuchiizu, Youichi Yamakawa, Seiichiro Onari, Hiroshi Kontani We study the mechanism of the triplet superconductivity in Sr$_2$RuO$_4$, by applying the functional renormalization group (fRG) method to the multi-orbital Hubbard model [1]. Thanks to the vertex correction, we observe the strong spin and orbital fluctuations at $Q \approx (2\pi/3, 2\pi/3)$ in the quasi-one-dimensional Fermi surfaces (which are composed of $d_{xz}$ and $d_{yz}$ orbitals). Moreover, due to the cooperation of spin and orbital fluctuations, the triplet superconductivity emerges where the superconducting gap is given by the linear combination of $(\Delta_x (k), \Delta_y (k)) \approx (\sin 3k_x, \sin 3k_y)$ [2]. These results can also be confirmed by a diagrammatic calculation of the vertex correction. \\ \noindent [1] M. Tsuchiizu, Y. Ohno, S. Onari, and H. Kontani, PRL \textbf{111}, 057003 (2013). \\ \noindent [2] M. Tsuchiizu, Y. Yamakawa, Y. Ohno, S. Onari, and H. Kontani, arXiv:1405.2028. [Preview Abstract] |
Tuesday, March 3, 2015 8:48AM - 9:00AM |
F11.00005: ABSTRACT WITHDRAWN |
Tuesday, March 3, 2015 9:00AM - 9:12AM |
F11.00006: Search for half-flux-quantum Little-Parks oscillations in mesoscopic rings of Sr$_2$RuO$_4$ Xinxin Cai, Brian Zakrzewski, Yiqun Ying, David Fobes, Tijiang Liu, Zhiqiang Mao, Ying Liu Recent cantilever magnetometry measurements on micron-sized, doubly-connected crystals of Sr$_2$RuO$_4$ have indicated that a half-flux-quantum state may be present in this material. To provide independent evidence for the presence of this new topological object by electrical transport measurements and examine its stability, we carried out Little-Parks (L-P) oscillation measurements, which trace out the phase boundary of a system, on mesoscopic rings of Sr$_2$RuO$_4$. Sr$_2$RuO$_4$ rings were fabricated using a combination of mechanical exfoliation of Sr$_2$RuO$_4$ single crystals, photolithography, and focused ion beam techniques. Without an in-plane magnetic field, large-amplitude resistance oscillations of a full-flux quantum were found as ramping the out-of-plane field. When the in-plane field and the measurement current were sufficiently large, a pronounced second set of resistance peaks was observed in one sample, supporting the existence of half-flux-quantum states. Preparation and measurements on more samples have been carried out and the most recent measurements suggest that the half-flux-quantum states, if indeed present, are likely to be metastable. [Preview Abstract] |
Tuesday, March 3, 2015 9:12AM - 9:24AM |
F11.00007: Large Chern Number and Edge Currents in Sr2RuO4 Thomas Scaffidi, Steven Simon Using the results of a previously reported microscopic calculation, we show that the most favored chiral superconducting order parameter in Sr$_2$RuO$_4$ has Chern number $|C|=7$ in the weak coupling limit. This order parameter has a momentum dependence of the type $\sin(k_x) \cos(k_y) + i \sin(k_y) \cos(k_x)$ and lies in the same irreducible representation $E_u$ of the tetragonal point group as the usually assumed gap function $\sin(k_x) + i \sin(k_y)$. While the latter gap function leads to $C=1$, the former leads to $C =-7$, which is also allowed for an $E_u$ gap function since the tetragonal symmetry only fixes $C$ modulo 4. Since it was shown that the edge currents of a $|C|>1$ superconductor vanish exactly in the continuum limit, and can be strongly reduced on the lattice, this form of order parameter could help resolve the conflict between experimental observation of time-reversal symmetry breaking and yet the absence of observed edge currents in Sr$_2$RuO$_4$. [Preview Abstract] |
Tuesday, March 3, 2015 9:24AM - 9:36AM |
F11.00008: Is the anisotropy of the upper critical field of Sr$_2$RuO$_4$ consistent with a helical $p$-wave state? Richard Klemm, Jingchuan Zhang, Qiang Gu, Christopher Loerscher We calculate the angular and temperature $T$ dependencies of the upper critical field $H_{c2}(\theta,\phi,T)$ for the $C_{4v}$ point group helical $p$-wave states, assuming a single uniaxial ellipsoidal Fermi surface, Pauli limiting, and strong spin-orbit coupling that locks the spin-triplet $\vec{\bf d}$-vectors onto the layers. Good fits to the Sr$_2$RuO$_4$ $H_{c2,a}(\theta,T)$ data of Kittaka et al. [2009 Phys. Rev. B 80, 174514] are obtained. Helical states with $\vec{\bf d}({\bf k})=\hat{\bf k}_x\hat{\bf x}-\hat{\bf k}_y\hat{\bf y}$ and $\hat{\bf k}_y\hat{\bf x}+\hat{\bf k}_x\hat{\bf y}$ (or $\hat{\bf k}_x\hat{\bf x}+\hat{\bf k}_y\hat{\bf y}$ and $\hat{\bf k}_y\hat{\bf x}-\hat{\bf k}_x\hat{\bf y}$) produce $H_{c2}(90^{\circ},\phi,T)$ that greatly exceed (or do not exhibit) the four-fold azimuthal anisotropy magnitudes observed in Sr$_2$RuO$_4$ by Kittaka et al. and by Mao et al. [2000 Phys. Rev. Lett. 84, 991], respectively. [Preview Abstract] |
Tuesday, March 3, 2015 9:36AM - 9:48AM |
F11.00009: Possible $f$-wave pairing in the low-doping regime of monolayer MoS$_2$ Carsten Honerkamp, Jie Yuan We investigate the possible superconducting pairing state in a theoretical model for monolayer-MoS$_2$ by using the temperature-flow functional renormalization group (fRG). In the low doping regime, the dominant instability lies in the odd-parity pairing channel. It has a $f$-wave pairing structure within the $D_{3h}$ point-group symmetry. We also compute the fRG phase diagram below the van-Hove filling. In the superconducting regime, the critical temperature grows with increasing doping, comparable to the experiments. We demonstrate that the pairing is driven by ferromagnetic fluctuations. When the band filling is close to the van-Hove filling, the system favors a ferromagnetic state. [Preview Abstract] |
Tuesday, March 3, 2015 9:48AM - 10:00AM |
F11.00010: Possible restoration of superconductivity in the quasi-one-dimensional conductor Li$_{0.9}$Mo$_6$O$_{17}$ in pulsed high magnetic field $H\approx 100$ T Otar Sepper, Andrei Lebed We present a theoretical study of restoration of superconductivity in the form of the triplet reentrant superconducting phase in the quasi-one-dimensional (Q1D) conductor. Substitution of known band and superconducting parameters of the presumably triplet Q1D superconductor Li$_{0.9}$Mo$_6$O$_{17}$ into our theoretical equations shows that such restoration can happen in non-destructive pulsed magnetic fields of the order of $H\approx 100$ T. We investigate in detail how small inclinations of a direction of magnetic field from its optimal experimental geometry decrease the superconducting transition temperature of the reentrant phase, which is important for its experimental discovery. If confirmed experimentally, the reentrant superconducting phase in Li$_{0.9}$Mo$_6$O$_{17}$ would be the first example of the survival of superconductivity in ultra high magnetic fields and would, in addition, unequivocally confirm the spin-triplet pairing nature in this compound. [Preview Abstract] |
Tuesday, March 3, 2015 10:00AM - 10:12AM |
F11.00011: Fluctuation effects in a two-component $p$-wave superconductor Mark H. Fischer, Erez Berg For a tetragonal material, order parameters of $p_x$ and $p_y$ symmetry are related by rotation and hence have the same $T_c$. This degeneracy can be lifted by a symmetry-breaking field, like (uniaxial) in-plane strain, such that at $T_c$, the order parameter is only of $p_x$ or $p_y$ symmetry. Only at a lower temperature also the respective other order parameter condenses. We analyze consequences of (thermal) fluctuations on these transition temperatures within a Ginzburg-Landau approach to obtain a comprehensive strain-temperature phase diagram. We find that the fluctuations can both enhance or suppress the effect of the symmetry breaking field, and even drive the system into a preemptive chiral phase. Possible consequences for the spin-triplet superconductor Sr$_2$RuO$_4$ will be discussed. [Preview Abstract] |
Tuesday, March 3, 2015 10:12AM - 10:24AM |
F11.00012: Long range p-wave proximity effect into a disordered metal Aydin Cem Keser, Valentin Stanev, Victor Galitski We use quasiclassical methods of superconductivity to study the superconducting proximity effect from a topological $p$-wave superconductor into a disordered one-dimensional metallic wire. We demonstrate that the corresponding Eilenberger equations with disorder reduce to a closed non-linear equation for the superconducting component of the matrix Green's function. Remarkably, this equation is formally equivalent to a classical mechanical system (i.e., Newton's equations), with the Green function corresponding to a coordinate of a fictitious particle and the coordinate along the wire corresponding to time. This mapping allows to obtain exact solutions in the disordered nanowire in terms of elliptic functions. A surprising result that comes out of this solution is that the $p$-wave superconductivity proximity-induced into the disordered metal remains long-range, decaying as slowly as the conventional $s$-wave superconductivity. It is also shown that impurity scattering leads to the appearance of a zero-energy peak. [Preview Abstract] |
Tuesday, March 3, 2015 10:24AM - 10:36AM |
F11.00013: Colossal proximity effect in a superconducting triplet spin valve based on the half-metallic ferromagnet CrO2 Amrita Singh, Stefano Voltan, Kaveh Lahabi, Jan Aarts Combining superconductors (S) and ferromagnets (F) offers the opportunity to create a new class of superconducting spintronic devices. In particular, the S/F interface can be specifically engineered to convert singlet Cooper pairs to spin-polarized triplet Cooper pairs. The efficiency of this process can be studied using a so called triplet spin valve (TSV), which is composed of two F-layers and an S-layer. When the magnetization in the two F-layers are not collinear, singlet pairs are drained from the S-layer, and injected as triplet generation is therefore signalled by a decrease of the critical temperature $T_c$. Here, we build highly efficient TSVs using a 100\% spin polarized half-metallic ferromagnet, CrO$_{2}$. The application of large out of plane magnetic fields results in an extremely strong suppression of $T_c$, by almost a Kelvin. The observed effect is nearly an order of magnitude larger than previous studies on TSVs with standard ferromagnets. Furthermore, we clearly demonstrate that this triplet proximity effect is strongly dependent on the transparency and spin activity of the interface. Our results are particularly important in view of the growing interest in generating long range triplet supercurrents for dissipationless spintronics. [Preview Abstract] |
Tuesday, March 3, 2015 10:36AM - 10:48AM |
F11.00014: Quantum Limit in a Magnetic Field for Triplet Superconductivity in a Quasi-One-Dimensional Conductor Andrei Lebed, Otar Sepper We theoretically consider the upper critical magnetic field, perpendicular to a conducting axis in a triplet quasi-one-dimensional superconductor [1]. In particular, we demonstrate that, at high magnetic fields, the orbital effects against superconductivity in a magnetic field are reversible and, therefore, superconductivity can restore. It is important that the above mentioned quantum limit can be achieved in presumably triplet quasi-one-dimensional superconductor Li$_{0.9}$Mo$_6$O$_{17}$ [J.-F. Mercure et al., Phys. Rev. Lett. ${\bf 108}$, 187003 (2012)] at laboratory available pulsed magnetic fields of the order of $H = 500-700 \ T$. [1] A.G. Lebed and O. Sepper, Phys. Rev. B ${\bf 90}$, 024510 (2014). [Preview Abstract] |
Tuesday, March 3, 2015 10:48AM - 11:00AM |
F11.00015: Universal spin-triplet superconducting correlation of Majorana Fermions Xin Liu, Jay Deep Sau In this work, we show that Majorana fermions (MFs) on the boundary of topological superconductors (TSCs) only have spin-triplet superconducting correlation no matter the bulk superconducting gap is spin singlet or triplet. This is universal for all TSCs as long as they have, on the boundary, odd number of MFs for BDI or D class and odd number pairs of MFs for DIII class. As a result, the Andreev reflection induced by the Majorana fermions always introduces spin-triplet Cooper pairs in the leads. This spin-triplet condensate results in the the spin-orbit coupling (SOC) controlled oscillatory critical current without $0-\pi$ transition in the TSC/SOC-semiconductor/TSC Josephson junction. The observation of this unique current-phase relation can serve as a signal of Majorana fermions. Moreover our study open a new way to manipulate Majorana fermions based on their spin-triplet superconducting correlation. [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