Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session X08: Superconductivity: Odd-Frequency, Non-Centrosymmetric and Other Exotic States |
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Sponsoring Units: DCMP Chair: Stuart Brown, Univ of California - Los Angeles Room: BCEC 150 |
Friday, March 8, 2019 8:00AM - 8:12AM |
X08.00001: The Effect of Antisymmetric Spin-Orbit Coupling on the Superconducting Order Parameter in Noncentrosymmetrical Superconducting PbTaSe2 Single Crystal Cong Ren In superconducting material without an inversion center of symmetry the spin degeneracy of the conducting band is lifted by an antisymmetric spin orbit coupling (ASOC). As a consequence, spin and parity cannot be seperately used to classify the Cooper pairing states. The superconducting order parameter is generally a mixture of spin singlet and triplet pairing states. However, such spin mixture state has rarely been revealed in weakly correlated noncentrosymmetrical superconductors. In this talk, we report a pressure-dependent point contact Andreev reflection measurement on high quality single crystals of the noncentrosymmetrical superconductor PbTaSe2. The experimental result reveals the effects of ASOC on the superconducting order parameter of PbTaSe2. |
Friday, March 8, 2019 8:12AM - 8:24AM |
X08.00002: Magnetization and spin current in non-centrosymmetric superconductors with Rashba spin-orbit interaction Kanta Hiroki, James Jun He, Keita Hamamoto, Naoto Nagaosa Spintronics is attracting intensive attention as a candidate for the next generation devices. In spintronics, spin current play an important role and there are several methods to make spin current, for example, spin Hall effect and spin pumping. As for the electrical spin generation, the Edelstein-effect with Rashba spin-orbit interaction (RSOI) is a representative one. |
Friday, March 8, 2019 8:24AM - 8:36AM |
X08.00003: Occurrence of Non-Centrosymmetric Superconductivity by Tuning the Antisymmetric Spin-orbital Coupling in La(PtxSi1-x)2 Thin Films Yunbo Ou, Jian Liao, Cigdem Ozsoy-Keskinbora, Stephan Kraemer, David Bell, Xiaoyan Shi, Jagadeesh Moodera The physical properties of solid compounds are governed by the symmetry of their crystal structure. In superconductors, an unconventional mixed-parity pairing which is neither spin singlet nor triplet state can emerge due to Fermi surface splitting caused by the absence of inversion symmetry. The complicated spin structure originating from mixed-parity pairing can cause topologically nontrivial surface or edge states in non-centrosymmetric superconductors. In this work, La(PtxSi1-x)2 thin films have been grown by systematically varying x from 0 to 0.68 by MBE technique. The superconductivity has been observed up to 2.60 K by transport measurement. The increasing concentration of Pt tends to suppress the transition temperature. Furthermore, incorporating Pt without changing the crystal structure can continuously tune the strength of the asymmetric spin-orbital coupling (ASOC) in La(PtxSi1-x)2 thin films, which thereby results in a non-centrosymmetric superconductor with multiple unconventional phases. Our work could facilitate the search for topologically nontrivial surface or edge states in non-centrosymmetric superconductors. |
Friday, March 8, 2019 8:36AM - 8:48AM |
X08.00004: Fermi surface instabilities of spin-orbit-coupled metals Tilman Schwemmer, Domenico di Sante, mario Fink, Xianxin Wu, Werner R Hanke, Ronny Thomale The pursuit of novel phases in correlated electron systems, such as possibly topological instances of unconventional superconductivity, must consider multiple energy scales including interaction strength, electronic band width, and, in particular, spin-orbit coupling (SOC). While density functional theory and related ab initio techniques can provide a detailed description of a materials electronic structure that can carefully account for the effects of SOC, it is necessary to additionally refine quantum many body techniques to study Fermi surface instabilities in the presence of SOC. Starting from a picture of itinerant electrons, we study the effect of electronic correlations on the Fermi surface via renormalization group techniques. Combining ab initio electronic structures with perturbative and functional renormalization group calculations, we develop the toolbox to analyse a plethora of symmetry breaking phases arising from the interplay of SOC, fermi surface topology, and electronic correlations. |
Friday, March 8, 2019 8:48AM - 9:00AM |
X08.00005: Superconducting pairing transition tuned by structural distortions in strong spin-orbit coupled systems Austin Lindquist, Hae-Young Kee Strong spin-orbit coupled systems have been gaining increased attention, as they may host exotic phases such as spin liquids and topological superconductors. In particular, Sr2IrO4 has been suggested as a potential candidate for a high temperature d-wave superconductor. However, these materials have strong spin-orbit couplings, and the electronic band structures are sensitive to the structural distortions such as the rotation and tilting of the octahedral cages. Here, we study the effects of these structural distortions on pairing instabilities, and present the transitions between spin-singlet and spin-triplet pairings tuned by structural distortions. Testing our proposals using a series of superlattices is also discussed. |
Friday, March 8, 2019 9:00AM - 9:12AM |
X08.00006: Singlet-Quintet Mixing in Superconductors with j=3/2 Fermions Jiabin Yu, Chao-Xing Liu Recently, a new pairing state with the mixing between s-wave singlet channel and isotropic d-wave quintet channel induced by centrosymmetric spin-orbit coupling has been theoretically proposed in the superconducting materials with j = 3/2 electrons. It is the first realistic proposal of the mixing between different spin channels that preserves the inversion symmetry in solid state systems. As physical consequences, the singlet-quintet pairing mixing can give rise to topological nodal-line superconductivity and surface Majorana flat bands. In this talk, the singlet-quintet-mixed state will be reviewed. Moreover, its experimental signatures, inlcuding spin susceptibility, upper critical field, disorder effect and surface local density of states, will be discussed. |
Friday, March 8, 2019 9:12AM - 9:24AM |
X08.00007: Odd-frequency pairing in a superconductor coupled to two parallel nanowires Christopher Triola, Annica M Black-Schaffer We study the behavior of Cooper pair amplitudes that emerge when a two-dimensional superconductor is coupled to two parallel nanowires, focusing on the conditions for realizing odd-frequency pair amplitudes in the absence of spin-orbit coupling or magnetism. In general, any finite tunneling between the superconductor and the two nanowires induces odd-frequency spin-singlet pair amplitudes in the substrate as well as a substantial odd-frequency interwire pairing. Since these amplitudes are odd in spatial parity, they do not directly impact the local observables. However, in the regime of strong superconductor-nanowire tunneling, we find that the presence of two nanowires allows for the conversion of non-local odd-frequency pairing to local even-frequency pairing. By studying this higher-order symmetry conversion process, we are able to characterize the effect of the odd-frequency pairing in the superconductor on local quantities accessible by experiments. Specifically, we find that odd-frequency pairing has a direct impact on the local density of states of the superconductor and on the maximum Josephson current, measurable using Josephson scanning tunneling microscopy. |
Friday, March 8, 2019 9:24AM - 9:36AM |
X08.00008: Odd-frequency spin-triplet superconductivity in two dimensional disordered electron liquid. Vladimir Zyuzin, Alexander Finkelstein In this work we theoretically study the odd-frequency spin-triplet superconductivity in disordered two dimensional electron liquid. We propose a pairing mechanism based on the interplay of screened Coulomb interaction and the interference of electrons due to the impurity scattering. The mechanism suppresses possible attraction in the singlet part of the Cooper channel, and depending on the ratio of repulsive interaction in the charge and spin channels, it results in attraction between electrons in the odd-frequency spin triplet part of the Cooper channel. Being derived for the metallic phase of the system, it can be relevant for the metal to insulator transition point. |
Friday, March 8, 2019 9:36AM - 9:48AM |
X08.00009: Odd frequency Berezinski pairing and cross junction coherence in Josephson effect. Alexander Balatsky, Sergey Pershoguba, Christopher Triola Odd frequency or Berezinski pairing state is now claimed to be present in multiple heterjunctions. We now demonstrate the emergence of odd-frequency pair amplitudes as a cross junction Berezinski coherence in conventional Josephson junctions. We considerate both in the absence of a voltage (DC effect) and in the presence of a finite voltage (AC effect). In both cases, we find that Berezinski interlead pairing emerges whenever a Josephson current is expected to flow. Additionally, we show that the interlead spin-susceptibility is directly influenced by the presence of the odd-frequency pair amplitudes. Specifically, we find that the spin-susceptibility is suppressed when the odd-frequency component is the largest. By establishing a novel link between the physics of Josephson junctions and Berezinski pairing, we extend the notion of Berezinski pairing to cross junction coherences and to conventional Josephson effect. |
Friday, March 8, 2019 9:48AM - 10:00AM |
X08.00010: Study of chiral d-wave superconductor candidate URu2Si2 by using scanning SQUID microscopy Yusuke Iguchi, Irene Zhang, Eric Bauer, Filip Ronning, Kathryn Ann Moler The heavy electron superconductor URu2Si2 has been extensively studied since the transitions of its hidden order and superconducting state were reported by the specific heat measurement in 1985[1]. Recent studies of thermal conductivity[2] and optical Kerr measurement[3] on URu2Si2 have shown evidence of chiral d-wave superconductivity. The chiral d-wave order superconductivity has also been suggested by a theoretical calculation of the magnetic excitation spectrum[4]. A chiral superconductor is expected to show chiral edge current modes analogous to a topological insulator. In order to search for evidence of chiral superconductivity in URu2Si2, we will report a study of the local superconducting and local charge current states of URu2Si2 single crystals using a scanning SQUID microscope. |
Friday, March 8, 2019 10:00AM - 10:12AM |
X08.00011: Ir d-band derived superconductivity in the lanthanum-iridium system LaIr3 system Neel Haldolaarachchige, Leslie Schoop, Mojammel Alam Khan, Wenxuan Huang, Huiwen Ji, Kalani Hettiarachchilage, David P Young Here, we have reported the synthesis and characterization of LaIr3, which displays superconductivity below Tc = 3.3 K. |
Friday, March 8, 2019 10:12AM - 10:24AM |
X08.00012: Low-Energy Quasiparticle Excitations in Half-Heusler Superconductors with j = 3/2 Fermions Kota Ishihara, Takaaki Takenaka, Yijie Miao, Yuta Mizukami, Orest Pavlosiuk, Piotr Wisniewski, Dariusz Kaczorowski, Takasada Shibauchi In noncentrosymmetric half-Heusler compounds where the strong spin-orbit coupling causes a band inversion, fermions with total angular momentum j = 3/2 contribute mainly to the transport phenomena, including the superconductivity. Interestingly, Cooper pairs formed by the j = 3/2 fermions can form not only usual singlet and triplet states but also even-parity quintet and odd-parity septet states. Recently, it has been reported that the temperature dependence of magnetic penetration depth shows a power-law behavior in YPtBi, which suggests an unconventional nodal gap structure. Several theories with the quintet or septet pairings have been proposed to explain this result, whereas it is still experimentally unclear whether the reported nodal structure is universal or not in the non-magnetic half-Heusler superconductors with j = 3/2 fermions. To study the gap structure in several half-Heusler superconductors, we have measured the magnetic penetration depth on YPtBi, LuPtBi, and LuPdBi with different spin-orbit coupling strength. Our data suggest the existence of gap minima rather than nodes in all the materials, which strongly indicates that the nodal structure is not protected by symmetries. Based on these results, we discuss the pairing symmetry of these half-Heusler compounds. |
Friday, March 8, 2019 10:24AM - 10:36AM |
X08.00013: Nonlinear susceptibility of unconventional superconductors Damjan Pelc, Zachary Anderson, Biqiong Yu, Sajna Hameed, Martin Greven Nonlinear magnetic response can be used to investigate several important features of superconductors: the pre-pairing regime above Tc, the superconducting gap features through the low-temperature nonlinear Meissner effect, and time-reversal symmetry. Based on our work on the superconducting precursor in oxides [1,2], we present complementary experiments on a wide range of conventional and unconventional superconductors. Several characteristic types of behavior are observed, including mean-field Ginzburg-Landau nonlinear response, an inhomogeneity-dominated precursor, and strong fluctuations not described by mean-field theory. |
Friday, March 8, 2019 10:36AM - 10:48AM |
X08.00014: Suppression of odd-frequency superconducting pairing by phase-disorder in a nanowire coupled to Majorana zero modes Dushko Kuzmanovski, Annica M Black-Schaffer, Jorge Cayao Majorana zero modes (MZMs) exhibit pure odd-frequency superconducting pairing correlations. Recently, it was reported that a robust odd-frequency superconducting pairing can be induced in a spin-polarized wire due to an array of MZMs, where their coupling to the wire was considered real. |
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