Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session R08: Non-uniform states in Superconductors |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Anton Vorontsov, Montana State University, Bozeman Room: BCEC 150 |
Thursday, March 7, 2019 8:00AM - 8:12AM |
R08.00001: Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) State in a Strongly Correlated d-wave Superconductor Anushree Datta, Kun Yang, Amit Ghosal TThe FFLO state is an unconventional superconducting (SC) state found under the influence of the Zeeman field. This is identified by finite center-of-mass momenta in the Cooper pairs which causes the pairing amplitude to modulate in real space. On the other hand, strong repulsion smears out spatial variations in the order parameters. We investigate the effects of strong correlation on the FFLO state in a d-wave superconductor within an integrated framework of Hartree-Fock-Bogoliubov theory and Gutzwiller approximation. Zeeman field causes a superconductor to undergo from BCS to FFLO and finally to a normal state with itinerant magnetism. We find that strong interaction enhances the phase space for the FFLO phase by shifting its boundaries significantly. With strong interaction, the density of states features a significantly sharper mid-gap peak in the FFLO phase creating strongly localized Andreev bound states. We discuss the fate of the FFLO phase in a competing ordered ground state (GS) by considering a GS with d-wave SC and antiferromagnetic (AFM) orders. Upon exposing such a GS to Zeeman field, we find that the FFLO modulation survives along with the AFM order with contrasting spatial features in the presence of strong correlation. |
Thursday, March 7, 2019 8:12AM - 8:24AM |
R08.00002: Surface pair-density-wave state and generalisation of Fulde-Ferrell-Larkin-Ovchinnikov state to chiral and nematic superconductors Mats Barkman, Alexander Zyuzin, Egor Babaev The paramagnetic interaction between the applied magnetic field and the spin of the electrons in a superconductor may lead to the formation of Cooper pairs with non-zero momentum. This results in inhomogeneous superconducting states, breaking translational symmetry, which characterizes the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state. We find that the transition from the FFLO to normal state is not direct. As temperature or applied magnetic field is increased, superconductivity vanishes first in the bulk while the pair-density-waves (PDW) exist on the boundaries. The surface PDW state can exist for significantly larger field and temperature than the FFLO state. I will also discuss generalisation of FFLO states to systems with unconventional pairing. One of the found states is a nematic superconductor where the nematicity vector breaks rotational and translational symmetries due to spontaneous spatial modulation. Another state is a chiral superconductor with spontaneously broken time reversal and translational symmetries, resulting in spatially alternating chirality. |
Thursday, March 7, 2019 8:24AM - 8:36AM |
R08.00003: Broken translational symmetry at edges of unconventional superconductors Patric Holmvall, Anton Vorontsov, Mikael Fogelstrom, Tomas Lofwander Flat bands of zero-energy states at edges of d-wave superconductors have a topological origin. However, a mechanism that can shift the band to finite energies would lower the free energy, break the initial topological protection, and thereby enable a phase transition. We present results [1] for a second-order phase transition at T≈0.2Tc, where Tc is the superconducting transition temperature, where time-reversal and continuous translational symmetry along the surface are spontaneously broken. The order parameter, the superfluid momentum ps, forms a non-trivial planar vector field with sources and sinks, that satisfies a generalized Poincaré-Hopf theorem, relating the sum of Poincaré indices to the Euler characteristics of the system. We discuss the robustness of this phase against an external magnetic field, mesoscopic surface roughness, and system size. We also present signatures for experimental verification by calorimetry and magnetometry. |
Thursday, March 7, 2019 8:36AM - 8:48AM |
R08.00004: Phase crystallization near surfaces of unconventional superconductors Anton Vorontsov, Patric Holmvall, Tomas Lofwander, Mikael Fogelstrom We demonstrate that a pairbreaking surface leads to an instability in the phase of the superconducting order parameter. Initially uniform U(1) phase acquires spatial variation, and thus breaks the time-reversal symmetry, below a transition temperature T* that is only a few times smaller than the bulk Tc. The phase modulation appears through a second-order phase transition from the trivial superconducting phase. The most favorable phase distortion occurs at a finite wave vector, thus spontaneously breaking continuous translational symmetry along the surface, and generating periodic superflow and current patterns localized near the surface, which have been previously seen in numerical simulations. We analytically derive the non-local Ginzburg-Landau coefficient that is responsible for this transition, and clarify conditions under which this instability occurs, the reason for the periodic modulation, and the geometry of emerging superflow and current patterns. |
Thursday, March 7, 2019 8:48AM - 9:00AM |
R08.00005: Fine structure in the thermal conductivity of unconventional superconductor CeCoIn5 in rotating magnetic field Roman Movshovich, Shizeng Lin, Duk Young Kim, Eric Bauer, Filip Ronning Thermal-conductivity measurements are a powerful method of studying superconductivity. Cooper pairs of the condensate do not carry heat, and only unpaired electrons participate in a heat transport. We have measured the thermal conductivity of unconventional superconductor CeCoIn5 in a rotating magnetic field. At a sufficiently low temperature below 100 mK, multiple features, including sharp resonances, are observed in the thermal conductivity as a function of the direction of the magnetic field. This fine structure of thermal conductivity may come from the interaction between the magnetic field and normal electrons in this multiband superconductor. Our measurements represent a new way of studying the superconducting state of a material. |
Thursday, March 7, 2019 9:00AM - 9:12AM |
R08.00006: Time-reversal symmetry breaking in superconductors through loop pair-current order Sudeep Ghosh, Jorge Quintanilla, James Annett We propose a superconducting instability where microscopic loop pair-currents form spontaneously within a unit cell at the critical temperature, Tc . Such currents break time-reversal symmetry (TRS) without needing an unconventional pairing mechanism. Using Ginzburg-Landau theory |
Thursday, March 7, 2019 9:12AM - 9:24AM |
R08.00007: Study of inhomogenous superconducting gap in titanium nitride (TiN) films measured by low-temperature STM Wan-Ting Liao, Kevin Daniel Osborn, Robert E Butera, Christopher J Lobb, Frederick C Wellstood, Michael Dreyer Titanium nitride films with low loss and high kinetic inductance show great promise for use in superconducting qubits and resonators. Here we report STM measurements performed at 500 mK on 25 nm and 50 nm thick films of TiN that have been prepared with oxygen. After gentle Ar-ion sputter cleaning of the surface, we observe a topographically rough surface with tip-sample current-voltage (I-V) characteristics that show a superconducting gap. We use both the Dynes model and the Blonder-Tinkham-Klapwijk (BTK) model to fit the I-V data. The Dynes model fits depend upon the superconducting gap and a quasiparticle lifetime (broadening) parameters, while the BTK model depends upon the gap, the temperature and the barrier transparency. Surprisingly, the two models yield strikingly different results and we present evidence that in these samples the BTK model yields the correct physical interpretation. |
Thursday, March 7, 2019 9:24AM - 9:36AM |
R08.00008: Spatially modulated superconductivity in CeIrIn5 microstructures George Ferguson, Maja Bachmann, Florian Theuss, Tobias Meng, Carsten Putzke, Toni Helm, Kent Shirer, YOU-SHENG LI, Kimberly Modic, Michael Nicklas, Markus Koenig, David Low, Sayak Ghosh, Andrew Mackenzie, Frank Arnold, Elena Hassinger, Ross McDonald, Laurel Winter, Eric Bauer, Filip Ronning, Brad Ramshaw, Philip Moll, Katja Nowack We present scanning SQUID microscopy of CeIrIn5 Focused Ion Beam (FIB) defined microstructures. By imaging the diamagnetic response of the microstructure, we identify micrometer scale modulation in the superconducting transition temperature. We find that the rich spatial structure of the superconducting and metallic regions in the device is determined by a strain field generated by the thermal contraction mismatch between CeIrIn5 and the sapphire substrate. By imaging microstructures with different FIB defined features, we demonstrate that the both the strain field and the geometry of the superconducting regions can be controlled with the FIB. Given that strain can serve as a clean tuning parameter for strongly correlated matter, our experimental approach illustrates a general approach to modulating the electronic properties of these materials on micrometer length scales. |
Thursday, March 7, 2019 9:36AM - 9:48AM |
R08.00009: Topological Behavior of Pair Density Waves on a Kondo-Heisenberg Ladder Ryan Levy, Julian May-Mann, Bryan Clark, Eduardo Hector Fradkin The pair density wave (PDW) phase, characterized by an oscillating superconductor order parameter, was proposed as part of the rich phase diagram of certain high temperature superconductors such as LBCO. One model exhibiting this phase in 1D is the Kondo-Heisenberg model (KHM). Past work has predicted that the PDW phase is topological, hosting protected edge modes. Using the density matrix renormalization group (DMRG), we explicitly illustrate the topological properties of the PDW phase of the KHM on finite systems. In particular, we show the emergence spin ½ edge states within the PDW phase. |
Thursday, March 7, 2019 9:48AM - 10:00AM |
R08.00010: Suppression of superfluid stiffness near Lifshitz-point instability to finite momentum superconductivity Jonatan Wardh, Brian Andersen, Mats Granath We derive the effective Ginzburg-Landau theory for finite momentum (FFLO/PDW) superconductivity without spin population imbalance from a model with local attraction and a repulsive pair-hopping. We find that the GL free energy must include up to sixth order derivatives of the order parameter, providing a unified description of the interdependency of zero and finite momentum superconductivity. For weak pair-hopping, there is of a line of Lifshitz points with a continuous change from zero to finite momentum which for larger pair-hopping is replaced by a bicritical region where pair momentum changes discontinuously. Proximity to a Lifshitz point provides a mechanism for reduced superfluid stiffness and we discuss implications of the model for the cuprate superconductors. |
Thursday, March 7, 2019 10:00AM - 10:12AM |
R08.00011: Orbitally limited pair-density wave phase of multilayer superconductors David Möckli, Youichi Yanase, Manfred W Sigrist We investigate the magnetic field dependence of an ideal superconducting vortex lattice in the parity-mixed pair-density wave phase of multilayer superconductors. In multilayer systems, due to local inversion symmetry breaking, a Rashba spin-orbit coupling is induced at the outer layers. This combined with a perpendicular paramagnetic limiting magnetic field stabilizes a layer dependent pair-density wave phase in the superconducting singlet channel. The high-field pair-density wave phase is separated from the low-field BCS phase by a first-order phase transition. The motivating guiding question in this paper is: what is the minimal necessary Maki value for the appearance of the pair-density wave phase of a superconducting trilayer system? To address this problem we generalize the circular cell method for the regular flux-line lattice of a type-II superconductor to include paramagnetic depairing effects. Then, we apply the model to the trilayer system, where each of the layers are characterized by Ginzburg-Landau parameter, and a Maki value. We find that when the spin-orbit Rashba interaction compares to the superconducting condensation energy, the orbitally limited pair-density wave phase stabilizes for Maki values above 10. |
Thursday, March 7, 2019 10:12AM - 10:24AM |
R08.00012: Mass hierarchy in collective modes of pair-density-wave superconductors Shaokai Jian, Michael M Scherer, Hong Yao We study collective modes near the quantum critical point of a pair-density-wave (PDW) superconductor in 2+1 dimensions. The fate of gaps of various collective modes is investigated by functional renormalization. For incommensurate PDW superconductors, we show that the gapless Leggett mode, protected by the emergent U(1) symmetry, can induce an exponentially small Higgs mass compared to the superconducting gap. Further, for commensurate PDW superconductors, we find an emergent mass hierarchy in the collective modes, i.e., the masses of Leggett boson, Higgs boson, and the superconducting gap can differ by several magnitudes in the infrared. This may shed light to a mechanism underlying the hierarchy problem in the Standard Model of particle physics. |
Thursday, March 7, 2019 10:24AM - 10:36AM |
R08.00013: Study of over-doped thin film LSCO with scanning squid microscopy Ruby Shi, Carolina Adamo, John Robert Kirtley, J. Steven Dodge, Kathryn Ann Moler The high-temperature superconductor cuprates, with their complex phase diagram, offer an intriguing playground for testing new theories. It has recently been proposed that homogeneous, intermediate-strength disorder is responsible for several previously unexplained features of the superfluid density in the overdoped cuprates [1]. To test the validity of this picture, we have characterized the spatial homogeneity of zero-frequency superfluid density using scanning-SQUID microscopy. We performed simultaneous magnetometry and susceptometry scans of various-doped LSCO epitaxially grown on LSAO by MBE. We observed higher than expected critical temperature (45K for x=0.23) and spatial inhomogeneity of superfluid density (variation by a factor of 10 across 3mm). Therefore, local variation of superfluid density in these LSCO thin film samples has to be taken into account for future experiments. |
Thursday, March 7, 2019 10:36AM - 10:48AM |
R08.00014: Inhomogeneous superconductivity in PdTe2 Goutam Sheet, Anshu Sirohi, Shekhar Das, Amit Vashist, Priyo Adhikary, Sirshendu Gayen, Rajeswari Roy Chowdhury, Yogesh Singh, Tanmoy Das PdTe2 is a type II Dirac semimetal which also shows superconductivity below 1.7 K. We have performed scanning tunneling microscopy and spectroscopy on single crystals of PdTe2 and have shown that despite such unique co-existence of Dirac physics and superconductivity, the superconducting phase of PdTe2 is conventional in nature. As revealed by our magnetic field dependent STM experiments, the single crystals of PdTe2 display a type I-like behavior at certain points and type-II like behavior at certain other points. We will discuss the details of this inhomogeneous superconducting phase and comment on its relationship with the intrinsic electronic inhomogeneity that was also detected in the normal state of PdTe2. |
Thursday, March 7, 2019 10:48AM - 11:00AM |
R08.00015: Local versus Global Superconductivity in Atomic Layer Indium on Si(111) Mengke Liu, Hyoungdo Nam, Jungdae Kim, Chih-Kang Shih Superconductivity at the two dimensional limit has attracted intense interest, and monolayer Indium on Si(111) provides a perfect platform for investigating this fascinating phenomenon. To better understand the role of defects in superconductivity, we studied superconducting monolayer Indium films by tailoring the step density of the substrate. We probed the superconductivity microscopically using scanning tunneling microscopy and spectroscopy. The macroscopic superconducting properties of the same sample were also probed using in-situ double coil mutual inductance measurements to determine the superfluid density and the transition temperature (Tc). By establishing local and global Tc correspondence, we uncover the intriguing nature of 2D superconductivity in indium atomic layer superconductors. |
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