Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L48: Superconductivity: Theories and Models |
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Sponsoring Units: DCMP Chair: Peter Hirschfeld, University of Florida Room: Mile High Ballroom 1A |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L48.00001: Spin-orbit-coupled ferroelectric superconductivity and multiorbital effects in SrTiO3 Shota Kanasugi, Youichi Yanase Motivated by recent discoveries of the coexistent phenomena of superconductivity and ferroelectricity in doped SrTiO3 [1,2], we investigated the feasibility of ferroelectric (FE) superconductivity in which superconductivity coexists with a FE-like order. By analyzing an electron-lattice coupled model for a two-dimensional superconductor, we show that the FE superconductivity is realized through two different mechanisms that rely on the intrinsic spin-orbit coupling [3]. First, the FE superconducting state is stabilized by the ferroelectricity-induced Lifshitz transition in low carrier density regimes. Second, the FE superconducting state is stabilized under a Zeeman magnetic field owing to the suppression of the Pauli depairing effect in the FE phase. Furthermore, we show that the FE superconductivity in SrTiO3 is strongly affected by the multiorbital effect of t2g electrons [4]. Then, we predict a topological Weyl superconducting state in the FE superconducting phase of bulk SrTiO3. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L48.00002: Capillary waves on ferroelastic domain walls as a pairing mechanism in strontium titanate David Pekker, C Stephen Hellberg, Anthony Tylan-Tyler, Jeremy Levy While it has long been known that strontium titanate is a superconductor, with a transition temperature of ~300 mK, the pairing mechanism that leads to superconductivity remains a mystery. We gather insight from recent experiments on superconductivity in the two-dimensional gas formed in lanthanum aluminate/strontium titanate heterostructures. These experiments provide evidence that superconductivity is localized to the edge of the electron gas, which is also associated with a ferroelastic domain wall between an out-of-plane deformation associated with the high electron density region and an in-plane deformation associated with the electron poor region. While the energy scales associated with bulk ferroelastic domains are quite large, on the order of 100 K, we show that capillary waves on domain walls can have much lower energy scales. Further, we argue that these capillary waves are strongly coupled to charge, making them a compelling candidate for an intermediate boson that mediates pairing interaction. We put these notions together in a model of ferroelastic domain walls that supports electron pairing. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L48.00003: Unconventional High Temperature Superconductivity in Cubic Zinc-blende Transition Metal Compounds Qiang Zhang, Kun Jiang, Yuhao Gu, Jiangping Hu Recently, we have identified a key character, called high temperature superconductivity "gene", which separates the cuprates and iron-based superconductors from other transitional metal compounds, and proposed some candidates for unconventional superconductivity. All of them are quasi-two dimensional. Here we propose a three dimensional candiate, transition metal compounds in a cubic zinc-blende lattice with electronic filling d^7. We argue that upon doping, this electronic environment can be one of ``genes" to host unconventional high temperature superconductivity with a time reversal symmetry broken d+id pairing symmetry. With gappless nodal points along the diagonal directions, this state is a direct three dimensional analogue to the two dimensional B1g d-wave state in cuprates. We suggest that such a case may be realized in electron doped zinc-blende CoN. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L48.00004: Superconducting pairing in non-pseudospin electron bands Kirill Samokhin We develop the symmetry classification of superconducting gap functions in electron bands that do not transform like the pure spin-1/2 states under the crystal point group operations. Generalizing the commony used Ueda-Rice prescription, we define the Bloch bases in twofold degenerate bands with spin-orbit coupling in a way which satisfies all symmetry and continuity requirements. These bases are used to construct general multiband pairing Hamiltonians in centrosymmetric crystals. Focusing on single band pairing, several exceptional cases are identified in which the triplet superconducting gap function does not transform under the point-group operations as a pseudovector, with a significant impact on the nodal structure. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L48.00005: A microscopic picture of pseudogap phase related to charge fluxes Xin Li Pseudogap phase in unconventional superconductors is mysterious. Previously, our work disclosed a new relation that the strength of apical charge flux in different families of cuprate superconductors obtained from our computation is correlated with the superconducting transition temperatures reported in previous experiments [1]. A microscopic picture about how such flux can further modulate the in-plane hopping of individual charge carrier was also proposed [1]. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L48.00006: Multiband Superconductivity: Anisotropy, Scattering and Bound States Tom Saunderson, Gabor Csire, James F Annett, Balazs Ujfalussy, Martin Gradhand First principles modeling of phonon mediated s-wave superconductors has been largely successful for bulk crystals [1], however, the incorporation of impurities in such theories will be much harder. This problem becomes particularly relevant as impurities affect the superconducting state and magnetic impurities are pair breaking and lead to bound states [2]. Such states are a possible source of Majorana Fermions [3]. Here we present the implementation of the Bogoliubov-de Gennes (BdG) equation into a Green’s function (KKR) first principles method [4]. This method is ideal to model impurities and interfaces without the need of artificial supercells. We parameterize the pairing potential but solve the BdG equation self-consistently incorporating microscopic electronic properties of real materials. Our method allows us to investigate the rich complexity of gap anisotropy on the Fermi surface and also how real magnetic and non-magnetic impurities interfere with the superconducting state. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L48.00007: Using unsupervised machine learning to predict critical temperatures of superconductors Benjamin Roter, Sasa Dordevic We use the superconductors from the SuperCon database to |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L48.00008: Superconducting Neural Networks for Faster Machine Learning Alexandra Day, Alexander Wynn, Evan Golden Next-generation neural networks have the potential to deliver advanced performance and higher processing speeds for applications in machine learning and artificial intelligence. MIT Lincoln Laboratory is investigating the feasibility of a superconducting neural network to support faster and lower-energy computing. We will present a conceptual framework for a superconducting neural network and its related benchmarks, along with simulation results for simple circuits. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L48.00009: Novel Magnetoelectric Effects in Gyrotropic Superconductors and a Case Study of Transition Metal Dichalcodenides Wenyu He, Kam Tuen Law In this work, we classify superconductors according to their magnetoelectric response. Among all the noncentrosymmetric superconductors, only superconductors with gyrotropic point groups have non-zero magnetoelectric response such that a supercurrent can induce a nite spin magnetization. We call these superconductors gyrotropic superconductors. Importantly, the general form of the magnetoelectric response is dictated by the point group symmetry and lead to novel magnetoelectric effects. Novel magnetoelectric effects of several noncentrosymmetric superconductors, including superconductors with chiral lattice symmetry and atomically thin superconducting transition metal dichalcogenides are discussed. Using a newly discovered monolayer 2H-structure NbSe2 as an example, we further show that how an unconventional magnetoelectric response can be induced by strain in superconductors with non-gyrotropic point groups. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L48.00010: Resonant study of the vortex state in LSCO cuprates up to 35 T. Arkady Shekhter, Ali Bangura, Andreas Rydh, Kimberly Modic, Gregory Scott Boebinger, Brad J Ramshaw, Ross McDonald We used a newly developed resonant probe of elastic moduli to explore the phase diagram of the vortex state in LSCO cuprates near critical doping x=0.20, up to 35 T. The elastic anomaly at the vortex melting transition---jump down upon entry into the vortex solid---is consistent with a second order phase boundary. The magnitude of the jump, ~0.1 GPa at 20 T is consistent with expected magnitude ~H2/8π of elastic moduli of the vortex lattice. We also observe a second thermodynamic anomaly at around 5T in the vortex-solid state that is weakly dependent on temperature and field orientation that appears to have dynamic origin. Finally, we will discuss magnetotropic coefficient measurements in the same system. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L48.00011: Four-fold anisotropy of the parallel upper critical magnetic field in a layered d-wave superconductor at T = 0 Andrei Lebed It is well known that a four-fold symmetry of the parallel upper |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L48.00012: Three Corollaries to the
Three Laws of Electronic Thermal Conductivity
of High Temperature Superconductors (HTSCs)
via Dipolon Theory Ram Sharma
|
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L48.00013: Detecting superconductivity out-of-equilibrium Sebastian Paeckel, Benedikt Fauseweh, Alexander Osterkorn, Thomas Koehler, Dirk Manske, Salvatore Manmana Recent pump-probe experiments on underdoped cuprates and similar systems suggest the existence of a transient superconducting state above Tc . This poses the question how to reliably identify the emergence of long-range order, in particular superconductivity, out-of-equilibrium. We investigate this point by studying a quantum quench in an extended Hubbard model and by computing various observables, which are used to identify (quasi-)long-range order in equilibrium. Our findings imply that, in contrast to current experimental studies, it does not suffice to study the time evolution of the optical conductivity to identify superconductivity. In turn, we suggest to utilize time-resolved ARPES experiments to probe for the formation of a condensate in the single- and two-particle channel. |
Wednesday, March 4, 2020 10:36AM - 10:48AM |
L48.00014: Computational Simulations of the Cooling of Type II Superconductors Using a Material Specific Formulation of the Ginzburg Landau Equations Aiden Harbick, Alden Pack, Braedon Jones, Mark Transtrum Superconducting Radio Frequency (SRF) cavities play a fundamental role in particle accelerators. Efficient operation depends on expelling magnetic flux from the cavity, and any residual flux that remains trapped after cooling below the critical temperature can have a significant impact on performance. Experimental evidence suggests that cooling protocols can have a strong impact on subsequent performance. To better understand this phenomenon, we use time-dependent Ginzburg-Landau theory implemented as finite-element simulations. We adapt the theory to allow spatial variation of material-specific parameters along with realistic temperature dependencies. We report on numerical experiments for different configurations of pinning sites and cooling protocols and discuss implications for SRF cavity design and operation. |
Wednesday, March 4, 2020 10:48AM - 11:00AM |
L48.00015: Hall anomalies and vortex charge in layered superconductors Daniel Arovas, Assa Auerbach The Hall anomalies in the flux flow regime are associated with moving vortex charge (MVC) in the superconducting layers, which are screened by immobile charges in neighbouring dopant layers. The MVC depends on the logarithm of the magnetic field, and proportional to the doping dependent superfluid stiffness and interlayer dielectric constant. The MVC is shown to add to the Hall conductivity by reformulating Flux Flow transport theory as a current response to applied electric and magnetic field, without the use of vortex forces or complex relaxation rates. MVC curves are extracted from experimental resistivities of hole and electron doped cuprates. These are fit to theory using measured London penetration depths, and a reasonable value of interlayer dielectric constant. |
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