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 zdirection and an oscillatory B field in the xy 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 (LiuKlemm) symmetric and skewsymmetric 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 ReverseRotation Methods for Magnetic Resonance Quantization Sunghyun Kim, ZHICHEN LIU, Richard A Klemm Eigenvalues of a spin Hamiltonian operator, H=ω_{0}S_{z}+ω_{1}[S_{x}cos(f)+S_{y}sin(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 CrossCorrelation 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 solidstate 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 splitgates (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 spinsinglet 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 CeCo_{0.5}Rh_{0.5}In_{5} 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 CeCo_{0.5}Rh_{0.5}In_{5}. At zero applied field, CeCo_{0.5}Rh_{0.5}In_{5} displays both superconductivity (T_{c}=1.3 K) and spatially longranged commensurate antiferromagnetism (T_{N}=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 InSitu 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 insitu applied strain on the nature of nematic phases in the high temperature superconductivity of ironbased pnictides using highsensitivity 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 insitu 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 LaNiGa_{2} 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 timereversal 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 HebelSlichter 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 spinsusceptibility 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 minimallyinvasive nuclear magnetic resonance techniques. Specifically, we classify electronmediated longrange 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 nuclearnuclear interactions provide an alternate explanation to unusual NMR results in superconducting and magneticallyordered 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: CavityMediated 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 symmetrybreaking 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: Photoinduced 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 photoinduced 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 parametricallydriven 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 nonzero optical conductivity in the clean limit, even in single band superconductors. Such interband transitions are forbidden in usual circumstances due to particlehole 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 swave order parameter, and parabolic bands with dwave 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: Inphase and outofphase Bardasis–Schrieffer modes from the electronic Raman response of multiband superconductors Igor BenekLins, Saurabh Maiti It is known that nonresonant 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 twoband 2D superconductor. Due to the multiband nature of the system, subleading interactions could lead to multiband Bardasis–Schrieffer collective modes resulting from inphase and outofphase 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 subleading channel, one is able to deduce phasesensitive 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 GarciaFernandez, Stefano Agrestini, KeJin 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 xray scattering (RIXS) to probe the dispersion of plasmons in the electrondoped cuprate superconductor Sr_{0.9}La_{0.1}CuO_{2} (SLCO). We detect a plasmon gap of ∼120 meV at the twodimensional Brillouin zone center, indicating that lowenergy plasmons in SLCO are not strictly acoustic. Our tJV model calculations accurately capture the plasmon gap and establish that its size is directly related to the magnitude of the interlayer hopping t_{z}—a parameter that is of key importance for realistic theories, yet notoriously difficult to assess with other techniques. Our work signifies the threedimensionality of the charge dynamics in layered cuprates and provides a new method to determine t_{z}. 
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 reentrant 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 Φ_{0}, resulting in the Hofstadter butterfly. Motivated by this, we investigate the problem of pairing within Hofstadter bands for a rational flux Φ=p/q Φ_{0} 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 wellknown representations realized by the singleparticle 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: MicrowaveBased 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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