Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z57: Superconductivity: Spin Properties & Response to FieldsRecordings Available
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Sponsoring Units: DCMP Chair: Richard Klemm, University of Central Florida Room: Hyatt Regency Hotel -Clark |
Friday, March 18, 2022 11:30AM - 11:42AM |
Z57.00001: Magnetic Resonance for Arbitrary Spins for Arbitrary B Field Directions ZHICHEN LIU, Sunghyun Kim, Richard A Klemm In 1952, Schwinger published On Angular Momentum, which indicates arbitrary angular momentums can be reduced to harmonic oscillators. In 1966, Gottfried solved the Schroedinger equation for magnetic resonance for arbitrary spins by transforming the system to a rotating frame. At last year's APS meeting, we presented a simple way to calculate the magnetic resonance of arbitrary spins by the rotation wave approximation. The situations above always have a B field along the z-direction and an oscillatory B field in the x-y plane. However, we don’t have a theory to calculate the B field's case in arbitrary directions. In here, we provide a way to calculate magnetic resonance for arbitrary directions and arbitrary B fields precisely. First, we refresh the rotating wave approximation method we used at last year's APS March meeting. Then, we will use the effective Hamiltonian we calculated to compare with the Hamiltonian without using the rotating wave approximation to find the (Liu-Klemm) symmetric and skew-symmetric relations for matrices. Then, we will use the relationship we found to solve for the magnetic resonance for arbitrary spins with fields in arbitrary directions. |
Friday, March 18, 2022 11:42AM - 11:54AM |
Z57.00002: Rotation and Reverse-Rotation Methods for Magnetic Resonance Quantization Sunghyun Kim, ZHICHEN LIU, Richard A Klemm Eigenvalues of a spin Hamiltonian operator, H=ω0Sz+ω1[Sxcos(f)+Sysin(f)], are not directly estimable because the operator is not generally diagonal; the field continuously oscillates in the xy plane with the washboard frequency as a function of time f=f(t)= ωt + g(t), g(t+2π/ω)=g(t). |
Friday, March 18, 2022 11:54AM - 12:06PM |
Z57.00003: Negative Spin Cross-Correlation in a Cooper Pair Splitter Arunav Bordoloi, Valentina Zannier, Lucia Sorba, Christian Schönenberger, Andreas Baumgartner The control and measurement of the spin degree of freedom of solid-state electrons has a wide range of prospective applications, be it in spintronics logic devices or in fundamental research, for example to demonstrate spin correlations in quantum mechanical systems. To this end, we have introduced ferromagnetic split-gates (FSGs) to individually polarize the electron spins in semiconductor quantum dots (QDs) [1]. We first demonstrate the working principle of such electronic spin filters in a double QD spin valve [2], consisting of two individually polarized, weakly coupled QDs in series, showing spin polarization up to 80%. We then implement such spin filters in a Cooper pair splitting (CPS) device [3] with two FSG/QD elements coupled in parallel to a superconducting reservoir to demonstrate a negative correlation between the spin currents emitted from the splitting of spin-singlet Cooper pairs. We measure a strong negative spin correlation of -1/3, which deviates from the ideal value of -1 mainly due to the finite spin polarization of the QD states [4]. Such QD spin filters are suitable for various applications, for example in spin projection experiments investigating spin structures in Rashba nanowires [5], or, in equal spin Andreev reflection [6] at Majorana type bound states. |
Friday, March 18, 2022 12:06PM - 12:18PM |
Z57.00004: Normal state field induced modulated magnetism in superconducting CeCo0.5Rh0.5In5 Chris Stock, Johnpierre Paglione We apply neutron diffraction as a function of magnetic field to access a critical point separating superconducting and incommensurate magnetic orders in CeCo0.5Rh0.5In5. At zero applied field, CeCo0.5Rh0.5In5 displays both superconductivity (Tc=1.3 K) and spatially long-ranged commensurate antiferromagnetism (TN=3.5 K) with a propagation vector of Q=(1/2, 1/2, 1/2). On applying a magnetic field that suppresses the superconducting order parameter, the magnetic intensity scales linearly in the vortex state. In the low temperature field induced normal phase, an incommensurate magnetic order with propagation vector of Q=(1/2, 1/2, 1/2+δ) (δ=0.0055 $\pm$ 0.0007 r.l.u.) replaces the commensurate response present in the superconducting and vortex phases. Metallic incommensurate order competes with intertwined unconventional superconductivity and commensurate magnetism in the ``115" superconductor series. |
Friday, March 18, 2022 12:18PM - 12:30PM Withdrawn |
Z57.00005: Investigation of Nematic Electronic Phases With In-Situ Strain Variation Using Nuclear Magnetic Resonance Techniques Silverio G Johnson, Erick Garcia, Rong Cong, Johanna Palmstrom, Ian R Fisher, Vesna F Mitrovic We present our study of the effect of in-situ applied strain on the nature of nematic phases in the high temperature superconductivity of iron-based pnictides using high-sensitivity NMR measurements. Nuclear magnetic resonance (NMR) is the ideal probe to explore such properties because it is sensitive to spin and charge degrees of freedom while allowing the measurement of nematic properties in the superconducting state. It has been shown that strain can be fully transmitted to samples up to approximately 100 μm thick using piezoelectric stacks [J.H. Chu et al. Science 2012], but there are practical limitations in the application of such techniques in NMR. The nontrivial issue of probing such small samples can be overcome by the novel use of surface coils that enhance the signal to noise ratio [W. Liu et al. Rev. Sci. Instrum. 2017] and allow for in-situ sample rotations and controllable application of strain. In this talk, we demonstrate how to simultaneously implement such techniques in NMR experiments. |
Friday, March 18, 2022 12:30PM - 12:42PM Withdrawn |
Z57.00006: NMR measurements in LaNiGa2 Phurba Sherpa, Igor Vinograd, Jackson R Badger, Michihiro Hirata, Valentin Taufour, Nicholas J Curro LaNiGa2 is a layered centrosymmetric superconductor with an orthorhombic crystal structure. ??SR experiments have observed spontaneous magnetic fields at the onset of superconducting state, implying time-reversal symmetry breaking and suggesting the possibility of triplet pairing. We previously reported on the observation of the enhancement of the NMR relaxation rate just below TC, suggesting the presence of a Hebel-Slichter coherence peak, but were limited by the base temperature of our cryostat. These data have now been extended down to 100 mK. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z57.00007: Signatures of electronic correlations and spin-susceptibility anisotropy in nuclear magnetic resonance Stephen T Carr, Charles A Snider, Dmitri E Feldman, Chandrasekhar Ramanathan, Brad B Marston, Vesna F Mitrovic We present a methodology for probing the details of electronic susceptibility through minimally-invasive nuclear magnetic resonance techniques. Specifically, we classify electron-mediated long-range interactions in an ensemble of nuclear spins by revealing their effect on simple spin echo experiments. We find that pulse strength and applied field orientation dependence of these spin echo measurements resolves the spatial extent and anisotropy of electronic spin susceptibility. These nuclear-nuclear interactions provide an alternate explanation to unusual NMR results in superconducting and magnetically-ordered systems, commonly attributed to heating effects. The methodology has direct applications for sensing and characterizing spin structure in correlated electronic phases. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z57.00008: Cavity-Mediated Superconductor–Ferromagnet Interaction Andreas Janssønn, Henning G Hugdal, Arne Brataas, Sol H Jacobsen We present a microscopic, perturbative theoretical analysis of interactions between a ferromagnetic (FM) and a superconducting (SC) monolayer mediated by photons in a cavity. This facilitates interactions over macroscopic distances, in contrast with extensively researched FM–SC proximity systems, and ensures there is no interfacial suppression of their respective order parameters. Specifically, we deduce the anisotropy field induced across the FM due to the presence of the SC when the system is subjected to a symmetry-breaking external field. Other quantities such as renormalized dispersion relations can also be deduced. The model is a modification and quantum mechanical extension of the principle presented in PRB 102, 180506(R), 2020. Their separation means the FM and SC may be held at different temperatures, suggesting a potential application as a bridge in spintronic–superconducting circuitry. |
Friday, March 18, 2022 1:06PM - 1:18PM |
Z57.00009: Photo-induced superconductivity at integer filling = activated discrete time crystal? Zhehao Dai, Vibhu Ravindran, Norman Y Yao, Michael P Zaletel Parametric resonance has been widely discussed as a mechanism of both photo-induced superconductivity and discrete time crystal. we reveal a possible connection between the two seemingly different phenomena. We show that a parametrically driven system with global U(1) symmetry has an intrinsically nonequilibrium steady state, which spontaneously breaks both the discrete time translation symmetry and the U(1) symmetry. The U(1)-breaking order parameter oscillates at half of the drive frequency, resembling a parametrically-driven oscillator. When coupling to electromagnetic field, this nonequilibrium phase exhibits perfect conductivity and Meissner effect, even though the time average of the order parameter is zero. |
Friday, March 18, 2022 1:18PM - 1:30PM |
Z57.00010: Optical conductivity of superconductors with supercurrent Michal Papaj, Joel E Moore In this work we show how the presence of a supercurrent can lead to non-zero optical conductivity in the clean limit, even in single band superconductors. Such interband transitions are forbidden in usual circumstances due to particle-hole and inversion symmetries, therefore requiring strong disorder as described by Mattis and Bardeen. Our approach circumvents this limitation and in conjunction with using the screening supercurrent arising from the external magnetic field enables a detailed investigation of the superconducting state. In particular, we focus on the cases of parabolic bands and Dirac fermions with s-wave order parameter, and parabolic bands with d-wave order parameter. We demonstrate how optical conductivity can be used both to distinguish the nature of the underlying normal state, as well as the type of the superconducting order parameter. |
Friday, March 18, 2022 1:30PM - 1:42PM |
Z57.00011: In-phase and out-of-phase Bardasis–Schrieffer modes from the electronic Raman response of multiband superconductors Igor Benek-Lins, Saurabh Maiti It is known that non-resonant electronic Raman spectroscopy can be used to probe collective modes of a superconductor in different angular momentum symmetry channels by tracking the location of spectral resonances in distinct scattering geometries. What is less appreciated is the information contained in the details of spectral line profiles themselves. To demonstrate this point, we discuss the Raman spectrum for a two-band 2D superconductor. Due to the multiband nature of the system, sub-leading interactions could lead to multiband Bardasis–Schrieffer collective modes resulting from in-phase and out-of-phase fluctuations, analogous to the Nambu–Goldstone and Leggett modes in the leading channel. We show that the Raman probe couples to these modes in a characteristically distinguishable manner and that these differences manifest themselves through the suppression or enhancement of 2Δ features relative to the collective mode features in the spectrum. Since the formation of collective modes can be directly related to the sign of the components of the pairing interaction in the sub-leading channel, one is able to deduce phase-sensitive information about the pairing interaction from the Raman responsez |
Friday, March 18, 2022 1:42PM - 1:54PM |
Z57.00012: Gapped plasmon excitations and interlayer hopping in cuprate superconductors Matthias Hepting, Matías Bejas, Abhishek Nag, Hiroyuki Yamase, Nunzia Coppola, Davide Betto, Mirian Garcia-Fernandez, Stefano Agrestini, Ke-Jin Zhou, Matteo Minola, Luigi Maritato, Pasquale Orgiani, Haofei Wei, Kyle M Shen, Darrell G Schlom, Alice Galdi, Andrés Greco, Bernhard Keimer Acoustic plasmons emerge in layered systems with conducting planes and poorly screened interlayer Coulomb interaction. Here, we use resonant inelastic x-ray scattering (RIXS) to probe the dispersion of plasmons in the electron-doped cuprate superconductor Sr0.9La0.1CuO2 (SLCO). We detect a plasmon gap of ∼120 meV at the two-dimensional Brillouin zone center, indicating that low-energy plasmons in SLCO are not strictly acoustic. Our t-J-V model calculations accurately capture the plasmon gap and establish that its size is directly related to the magnitude of the interlayer hopping tz—a parameter that is of key importance for realistic theories, yet notoriously difficult to assess with other techniques. Our work signifies the three-dimensionality of the charge dynamics in layered cuprates and provides a new method to determine tz. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z57.00013: Hofstadter Superconductivity Daniel Shaffer, Luiz H Santos, Jian Wang While the conventional wisdom is that the orbital effect is detrimental to superconductivity, it has long been predicted theoretically that re-entrant superconductivity should be possible at very high magnetic fields when only a few Landau levels are occupied. The orbital effect can be significant already at lower fields in systems with large unit cells, with the flux per unit cell Φ is on the order of the flux quantum Φ0, resulting in the Hofstadter butterfly. Motivated by this, we investigate the problem of pairing within Hofstadter bands for a rational flux Φ=p/q Φ0 by studying the symmetry properties of the order parameter under magnetic translation symmetries. Surprisingly, the irreducible representations realized by the superconducting order parameter are distinct from the well-known representations realized by the single-particle Bloch states. We show that as a result, Hofstadter superconductors necessarily break at least some magnetic translation symmetries, resulting in degenerate ground states that may preserve an order q symmetry, with implications for the topology of the states. With the recent advance of superconducting moiré systems in which the Hofstadter butterfly has already been seen, it may soon be possible to examine Hofstadter superconductors in experiment. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z57.00014: Microwave-Based Optomagnetics in Superconductors Hamed Majedi The optomagnetic effect is mainly known as a nonlinear optical phenomenon in light of the inverse Faraday effect (IFE), i.e. the generation of static magnetization by circularly polarized |
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