Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session A27: Superconductivity: General I |
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Sponsoring Units: DCMP Chair: Danfeng Li, City University of Hong Kong Room: Room 219 |
Monday, March 6, 2023 8:00AM - 8:12AM |
A27.00001: Angle Resolved Photoemission Spectroscopy Studies of hole overdoped Ba1-xKxFe2As2 Elena Corbae, Zhi-Xun Shen, Donghui Lu, Makoto Hashimoto, Cong Li, Oscar Tjernberg, Egor Babaev, Vadim Grinenko, Kunihiro Kihou, Chul-Ho Lee While the superconducting transition temperature of hole doped BaFe2As2 decreases from the optimally doped region, superconductivity does not completely disappear even for the fully doped KFe2As2 compound. This presents a stark difference compared to the overdoped region of the cuprates and thus offers an opportunity to gain insight into the universality and diversity of these novel superconductors. Additionally, electronic structure calculations lack consistent results across all doping levels. Angle Resolved Photoemission Spectroscopy (ARPES) is a natural technique to investigate these anomalies. Thus far, most ARPES superconducting gap measurements of Ba1-xKxFe2As2 have focused in the vicinity of optimal doping (x=0.4). This is mainly due to limitations of energy resolution and sample temperature of the ARPES instrument compared to the superconducting gap magnitude and transition temperature away from the optimal doping. We use ARPES to study three doping levels (x=0.53, 0.78, 0.89) of Ba1-xKxFe2As2 above optimal doping at low temperatures and high energy resolution to attempt to understand the electronic structure and its relation to the displayed physical phenomena. |
Monday, March 6, 2023 8:12AM - 8:24AM |
A27.00002: Probing continuous electronic phase transitions with in-situ temperature gradient Jinming Yang, Siqi Wang, Wenzheng Wei, Tyler L Werner, zhibo kang, Makoto Hashimoto, Donghui Lu, Frederick J Walker, Charles H Ahn, Yu He Angle-resolved photoemission spectroscopy (ARPES) is a powerful tool to probe electronic structure in quantum materials. In recent years, noval sample tuning methods, such as strain control and electrostatic gating, advanced rapidly, making ARPES a valuable tool to investigate both quantum and classical critical phenomena. However, uncontrolled outgassing and sample drift during temperature ramping deteriorates sample surface and severely limits the efficiency and reliability of temperature tuning in conventional ARPES measurements. Here, we circumvent this difficulty by creating a real-space temperature gradient on the sample surface with a home-made heating puck. In combination with micro-spot ARPES, we demonstrate at least 10x efficiency and high repeatability in temperature tuning. Our method opens up the possibility for in-situ phase diagram mapping and studies of critical phenomena in correlated systems. It also creates a new arena to study the electronic behavior in steady state phenomena such as the thermal Hall effect. |
Monday, March 6, 2023 8:24AM - 8:36AM |
A27.00003: Limiting magnetic fields of superconductors with arbitrary potential and pair-breaking scattering Ruslan Prozorov, Vladimir G Kogan The upper critical magnetic field, Hc2(T), the nucleation field of surface superconductivity, Hc3(T), and the thermodynamic critical magnetic field, Hc(T), were evaluated within the weak-coupling Eilenberger formalism with arbitrary TRANSPORT and pair-breaking scatterings. We find that the maximum of Hc3(T)/Hc2(T) is surprisingly robust and is confined to the interval between 1.5 and 2.4, even in the gapless state. Similar calculations of the nucleation field were conducted for ultra-thin films in a parallel magnetic field. There we find a substantial enhancement of the transition temperature Tc by the field. We also find regimes of field-induced re-entrant superconductivity. Finally, we discuss a singularity in the free energy third derivative corresponding to a type-2½ topological quantum phase transition from a gapped to a gapless superconducting state. |
Monday, March 6, 2023 8:36AM - 8:48AM |
A27.00004: Nonlinear Meissner Effect in Disordered Superconductors James A Sauls Theoretical results for the nonlinear Meissner screening current and field-dependence of the London penetration depth are reported as a function of temperature, external field, Fermi-surface anisotropy and disorder, the latter represented by the transport scattering rate 1/τ. The breaking of time-reversal symmetry by an imposed current leads to pair breaking by nonmagnetic impurities, and to suppression of the screening current that can be supported as the superconductor becomes increasingly disordered. Furthermore, the screening current is generally a nonlinear function of the condensate momentum. In the absence of vortices the Meissner current can be related to the gauge field in the region of the superconducting-vacuum interface js ∝ A (1 − θ |A|2/Ac2), where A is the vector potential. The mean pairing self energy, Δ, and Fermi velocity, vf, determine the scale for the gauge field, Ac ∝ Δ/vf. The dimensionless parameter, θ, determines the magnitude of the nonlinear current response and field dependence of the London penetration depth. For fully gapped BCS superconductors in the clean limit θ vanishes exponentially at low temperatures. Disorder decreases the superfluid fraction monotonically; however, θ remains finite at zero temperature and is a non-monotonic function of the pair-breaking parameter, α ∝ 1/τTc, with a maximum near the cross-over to the dirty limit. We discuss new experimental signatures of the nonlinear current response for superconducting resonators and related devices. |
Monday, March 6, 2023 8:48AM - 9:00AM |
A27.00005: Nonlinear Meissner Interferometry Alexander V Gurevich, James A Sauls We propose a nonlinear Meissner interferometer in which a high-Q superconducting resonator is excited by the third harmonic generated by the nonlinear Meissner response in a superconducting film. This effect can be used to greatly increase the field amplitude of the nonlinear electromagnetic response and generate a giant third harmonic at GHz frequencies. We calculated the resonance line of the third harmonics B3ω(T) and showed how the measurements of the temperature dependence of B3ω(T) can reveal the fundamental mechanisms of the nonlinear Meissner effect and superconducting gap symmetry in conventional and unconventional superconductors. |
Monday, March 6, 2023 9:00AM - 9:12AM |
A27.00006: Collective modes in multiband superconductors Nico A Hackner, Philip Brydon We theoretically investigate collective modes in a minimal model of a multiband superconductor. Specifically, we consider a two-band model which results from an additional sublattice degree of freedom and includes all symmetry-allowed spin-orbit coupling and inter-sublattice hopping terms. Starting from a uniform BCS ground state, we derive a Gaussian effective action for the condensate, including fluctuations into competing odd-parity channels. We find that the spin-orbit coupling is essential for the existence of these fluctuations, and evaluate the possibility for the experimental detection of the associated collective modes. |
Monday, March 6, 2023 9:12AM - 9:24AM |
A27.00007: A model of superconducting rf dissipation from Bogoliubov quasiparticles in a modified two-fluid framework Michelle Kelley, Sean Deyo, Nathan S Sitaraman, Thomas Oseroff, Danilo B Liarte, Matthias U Liepe, James P Sethna, Tomas A Arias Investigating Nb surface treatments to optimize superconducting rf (SRF) applications revealed a peculiar trend in certain Nb SRF cavities: a quality factor that increases as a function of field, referred to as an "anti-Q slope". Specifically referring to the temperature-dependent component of the surface resistance decreasing with field strength, this curious behavior is not captured in long-established theories quantifying SRF dissipation. We present a simple yet effective theoretical framework that is successful in not only producing an anti-Q slope, we also include a proposed mechanism on how to turn the anti-Q slope on and off. By numerically solving the Bogoliubov-de Gennes self-consistent field equations for a superconducting surface in a parallel AC magnetic field, we compute density profiles using a two-fluid framework to characterize the underlying single-particle excitations and condensed pairs responding to an oscillating field. Surface resistances are calculated from Ohmic dissipation in a semi-classical theory of conductivity, and this analysis is combined with complementary density-functional theory (DFT) calculations to quantify realistic elastic scattering times of electrons interacting with impurities in Nb. Finally, we show the temperature and frequency dependencies of this new model agree well with established theories of SRF dissipation. |
Monday, March 6, 2023 9:24AM - 9:36AM |
A27.00008: Nonlinear photoconductivity distortion in pump-probe spectroscopy Leya Lopez Lovely, J. Steven Dodge, Derek G Sahota Optical pump-probe spectroscopy typically involves a procedure to derive the photoexcited conductivity from the measured changes in the reflection amplitude. Although the photoconductivity depth profile is typically not measured directly, it is commonly assumed that it decays exponentially with depth, over the length scale of the pump penetration depth. Recently we showed that nonlinearity can distort this depth profile at high pump fluence, and that this can introduce large systematic errors in the optical response functions derived from it. I will describe the general features of this systematic error and show how to correct for it. |
Monday, March 6, 2023 9:36AM - 9:48AM |
A27.00009: Interplay between Cavity Quantum Electrodynamics and Superconductivity Hongjing Xu, Fuyang Tay, Andrey Baydin, Jaime M Moya, Manukumara Manjappa, Motoaki Bamba, Emilia Morosan, Junichiro Kono There is currently much interest in studying solids placed in optical cavities to uncover new phases and phenomena in the complete absence of any external fields other than the fluctuating vacuum, or zero-point, electromagnetic fields. Judicious engineering of the quantum vacuum surrounding the matter inside the cavity can lead to nonintuitive modifications of electronic states and novel properties. Here we study superconducting films inside terahertz cavities in search of some of the recently predicted phenomena due to a redistribution of Bogoliubov quasiparticles as well as the formation of novel superconductor-cavity-polaritons. We measured the transition temperatures of both Bardeen-Cooper-Schrieffer (BCS) and non-BCS superconducting thin films of various thicknesses inside a cavity by temperature-dependent electrical resistivity measurements. We also performed terahertz time-domain spectroscopy measurements to study the influence of cavity fields on the optical conductivity spectra of the films. The obtained results will be analyzed using existing theoretical models, and future steps for uncovering new phenomena in the superconductor cavity light–matter coupled system will be discussed. |
Monday, March 6, 2023 9:48AM - 10:00AM |
A27.00010: Quasiparticle interference as a direct experimental probe of bulk odd-frequency superconducting pairing Debmalya Chakraborty, Annica M Black-Schaffer We show that quasiparticle interference (QPI) due to omnipresent weak impurities and probed by Fourier transform scanning tunneling microscopy and spectroscopy acts as a direct experimental probe of bulk odd-frequency superconducting pairing. Taking the example of a conventional $s$-wave superconductor under applied magnetic field, we show that the nature of the QPI peaks can only be characterized by including the odd-frequency pairing correlations generated in this system. In particular, we identify that the defining feature of odd-frequency pairing gives rise to a bias asymmetry in the QPI, present generically in materials with odd-frequency pairing irrespective of its origin. |
Monday, March 6, 2023 10:00AM - 10:12AM |
A27.00011: Inelastic dephasing rate for fluctuations of the local density of states in a 2D multifractal superconductor Pavel Nosov, Igor Burmistrov, Srinivas Raghu Strong mesoscopic correlations of the local density of states (LDOS) are one of the main signatures of a multifractal superconductor, emerging due to the interplay between Anderson localization and short-ranged interactions. Analytical and numerical calculations of the moments of LDOS within the mean-field approximation typically lead to expressions that are logarithmically divergent with the system size, similarly to weak localization corrections to conductivity. One of the mechanisms that can regularize these divergencies is the dephasing of quasiparticles caused by inelastic electron-electron scattering. In this work, we calculate the dephasing rate in a multifractal superconductor, assuming that Coulomb repulsion is sufficiently screened. We find that the superconducting fluctuations provide the dominant contribution to the dephasing rate near the transition, while at low temperatures and close to the coherence peaks, dephasing is primarily due to collective modes. |
Monday, March 6, 2023 10:12AM - 10:24AM |
A27.00012: Long-time dynamics of optically pumped metals from projected purification John Sous, Mattia Moroder, Sebastian Paeckel The non-equilibrium dynamics of matter whose vibrations are excited by light fields may produce electronic phases, such as laser-induced high-transition-temperature superconductivity, that do not exist in equilibrium. Simulation of these systems presents a theoretical challenge because of the absence of separation of energy scales, and is further impeded by the large local Hilbert space dimension associated with vibrational modes. Here we employ a recently introduced approach known as projected purification [SciPost Phys. 10, 058 (2021)] in order to overcome this challenge and use the time-dependent variational principle (TDVP) in matrix-product-state (MPS) manifolds to simulate the dynamics of a metal driven at initial time by a spatially uniform pump that excites dipole-active vibrational modes which couple nonlinearly to electrons. We compare our results to those of [Nat. Commun. 12, 5803 (2021)], finding excellent agreement, and show that access to significantly longer times perhaps extending to the long-time limit is now within reach. |
Monday, March 6, 2023 10:24AM - 10:36AM |
A27.00013: The pathway to light-induced superconductivity Marios H Michael Over the past decade, the condensed matter community has been consumed by the possibility of intense light creating superconductivity at room temperature. The excitement has been mainly driven by advances in pump and probe experiments, where pumping materials such as K3C60 and kappa-salts of the family κ-(ET)2-X by strong Mid-IR laser light has shown optical signatures consistent with a long-lived and a short-lived superconductivng state respectively. In this talk, I will present a microscopic mechanism based on light coupled to electronic band transitions as the most natural way to achieve photo-induced superconductivity. I will comment how such a microscopic model can be used to derive other mechanisms proposed in the literature. The success of the multi-band photo-induced superconductivity mechanism lies in explaining resonant features in current experiments not present in previous models. Finally, we take advantage of the resonances inherent in the microscopic model, to propose new photo-induced superconductors made up of 2D materials placed on substrates that can support surface plasma modes as a new avenue to deliberately engineer high-temperature photo-induced superconductivity. |
Monday, March 6, 2023 10:36AM - 10:48AM |
A27.00014: Appearance of Odd-Frequency Superconductivity in a Relativistic Scenario Patrick J Wong, Alexander V Balatsky Odd-frequency superconductivity is an exotic pairing mode in superconducting systems in which the symmetry of the gap function is odd in energy. Here we show that an inherent odd-frequency mode emerges dynamically under application of a Lorentz transformation of the anomalous Green function with an anisotropic gap function. To see this, we consider a Dirac model with quartic potential and perform a mean-field analysis to obtain a relativistic Bogoliubov-de Gennes system. Solving the resulting Gor'kov equations yields expressions for relativistic normal and anomalous Green functions. The form of the relativistically invariant pairing term is chosen such that it reduces to BCS form in the non-relativistic limit. We choose an ansatz for the gap function in a particular frame which is even-frequency and analyze the effects on the anomalous Green function under a boost into a relativistic frame. In the boosted frame the order parameter contains terms which are both even and odd in frequency: Δ(ω,k) ~ ω2 → γ2ω2 + β2γ2k2 + 2βγ2kω. The relativistic correction to the anomalous Green function to first order in the boost parameter is completely odd in frequency. The odd-frequency pairing emerges dynamically as a result of the boost. This work provides evidence that odd-frequency pairing may form intrinsically within superconductors. |
Monday, March 6, 2023 10:48AM - 11:00AM |
A27.00015: Self Organized Nano-Structures in SrTiO3 Induced by Plastic Deformation Liam Thompson, Issam Khayr, Chiou Yang Tan, Sajna Hameed, Damjan Pelc, Hayden Binger, Devon Uram, Martin Greven, Alexander S McLeod
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