Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R31: Superconductivity: Nonequilibrium 
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Sponsoring Units: DCMP Chair: Larry Carr, NSLSII, Brookhaven Room: LACC 407 
Thursday, March 8, 2018 8:00AM  8:12AM 
R31.00001: Correlationinduced superconductivity dynamically stabilized and enhanced by laser irradiation Kota Ido , Takahiro Ohgoe , Masatoshi Imada Studies on outofequilibrium dynamics have paved a way to realize a new state of matter. Recently, superconductorlike properties above critical temperatures in equilibrium were observed in correlated electron materials whose phonon modes were selectively excited by strong laser irradiation. These observations have inspired studies on an alternative and general strategy to be pursued for hightemperature superconductivity. 
Thursday, March 8, 2018 8:12AM  8:24AM 
R31.00002: Transient superconducting fluctuations in the fermionic Hubbard model after a quantum quench Valentin Kasper , Eugene Demler We study the evolution of superconducting correlations in the fermionic Hubbard model following a quantum quench of the attractive interaction. Using a phase space approach, we investigate the dynamics of single and twoparticle correlations. Our study explores the connection of the singleparticle relaxation dynamics and the growth of superconducting correlations. We demonstrate that the quantum quench from a noninteracting to an interacting Hamiltonian leads to a transient, shortrange ordered state characterized by pairing correlations. Moreover, during the evolution, the single particle quantities shows properties of a zerotemperature Fermiliquid. 
Thursday, March 8, 2018 8:24AM  8:36AM 
R31.00003: Quench dynamics and gap oscillations of nonequilibrium multiband superconductors Tianbai Cui , Michael Schütt , Peter Orth , Rafael Fernandes Superconductors driven to nonequilibrium steady states display the remarkable phenomenon of coherent gap oscillations. With the rapid advances in THz pumpandprobe techniques, this concept has been widely explored both theoretically and experimentally. In several superconductors of general interest, such as SrTiO_{3}, iron pnictides, Sr_{2}RuO_{4}, and heavy fermions, multiple bands cross the Fermi level, giving rise to multiband superconductivity. Here, we combine analytical and numerical methods to solve the timedependent multiband BCS equations and investigate the gap oscillations in quenched multiband superconductors. We find the existence of multiple oscillation frequencies, which can promote beating of the gap oscillations. Interestingly, we find that the oscillations decay faster than in the one band case, with a powerlaw of 1/t^{3/2} instead of 1/t^{1/2}. We explore a variety of different parameter regimes and discuss the relevance of our results to experiments. 
Thursday, March 8, 2018 8:36AM  8:48AM 
R31.00004: Theory of nonequilibrium pump/probe electronic Raman scattering in strongly correlated materials James Freericks , Oleh Matveyev , Andrij Shvaika , Thomas Devereaux We employ nonequilibrium dynamical meanfield theory to solve for the nonresonant B_{1g} response of a strongly correlated material after a large electric field pump. This electronic Raman scattering channel has no vertex corrections even in nonequilibrium. The problem can be exactly solved for the FalicovKimball model at halffilling, which exhibits a Mott metalinsulator transition. We describe what the response looks like for these nonequilibrium systems and show what features emerge due to the nonequilibrium nature of the experiment. Similar calculations can also be done for the A_{1g} response, but they require vertex corrections. 
Thursday, March 8, 2018 8:48AM  9:00AM 
R31.00005: Higgs spectroscopy of nonequilibrium superconductors Benedikt Fauseweh , Lukas Schwarz , Naoto Tsuji , Nathan Cheng , Nikolaj Bittner , Holger Krull , Mona Berciu , Goetz Uhrig , Andreas Schnyder , Stefan Kaiser , Dirk Manske In addition to the superconducting gap symmetry, when a superconductor is excited, the collective excitations of the condensate can exhibit an additional symmetry, which also mirrors the underlying lattice symmetry. Therefore the aggregate of these symmetries can result in one or more amplitudeHiggs modes depending on the geometry of the excitation. We study swave and dwave superconducting symmetries on a lattice with D_{4h} space group symmetry, which is the lattice symmetry of cuprate highT_{c} superconductors. We report analytic results on the specific geometries of a quench needed for producing oscillation modes along different geometries. Remarkably, we find that, in addition to the wellstudied 2△_{∞ }mode, a second low energy mode can also be excited, depending on the symmetry of the quench. Lastly, we also predict results for timeresolved Higgs spectroscopy with a realistic experimental pulse. 
Thursday, March 8, 2018 9:00AM  9:12AM 
R31.00006: Transport Signatures of Nonequilibrium Criticality in Quenched Superfluids Yonah Lemonik , Aditi Mitra We suggest employing recent advances in ultrafast measurement to study 
Thursday, March 8, 2018 9:12AM  9:24AM 
R31.00007: Terahertz LightInduced Formation of Metastable Quantum State in a Nb_{3}Sn Superconductor Martin Mootz , Ilias Perakis , Jigang Wang Exploration and characterization of metastable quantum phases hidden by superconductivity is one of the fundamental issues in hightemperature superconductivity research. We demonstrate the existence of a metastable quantum phase of prethermalized, gapless electron fluid in a Nb_{3}Sn superconducter, not accessible by equilibrium thermodynamics. The quantum state forms after ultrafast quenching of the superconduncting gap using an intense monocycle terahertz pulse and is absent for nearinfrared optical excitation. Above a critical fluence threshold, the formed metastable state exhibits coherent transport with vanishing scattering towards low frequency together with longlived prethermalization plateau and quantum memory that exceed the quasiparticle energy relaxation times by one order of magnitude. We present theoretical results that attribute the observations to a dynamic coexistence and interference of superconductivity with martensitic order parameter. 
Thursday, March 8, 2018 9:24AM  9:36AM 
R31.00008: Locating the missing superconducting electrons in overdoped cuprates Fahad Mahmood , Xi He , Ivan Bozovic , Peter Armitage Overdoped hightemperature cuprate superconductors have been widely believed to be described by the physics of dwave BCSlike superconductivity. However, recent measurements indicate that the superconducting transition temperature (T_{c}) is correlated with the superfluid density rather than being independent of it as predicted by BCS theory. Here, we combine timedomain THz spectroscopy with kHz range mutual inductance measurements to determine both the superfluid and the uncondensed carrier density as a function of doping for overdoped La_{2x}Sr_{x}CuO_{4} films. A significant fraction of the carriers remain uncondensed in a Drudelike peak even as T → 0 with a conductivity and scattering rate that rules out disorder as the determining factor in suppressing the superfluid density. Analysis of the low frequency spectral weight distribution in terms of a quantum Debye Waller factor suggests the prominent role of quantum phase fluctuations as the critical doping is approached. 
(Author Not Attending)

R31.00009: Nonequilibrium Andreev bound states population in short superconducting junctions coupled to a resonator Wolfgang Belzig , Raffael Klees , Gianluca Rastelli Inspired by recent experiments, we study a superconducting junction shorter than the coherence length inserted in a dcSQUID containing an ancillary Josephson tunnel junction. We evaluate the nonequilibrium occupation of the Andreev bound states (ABS) for the case of a conventional junction and a topological junction, with the latter case of ABS corresponding to a Majorana mode. We take into account small phase fluctuations of the Josephson tunnel junction, acting as a damped LC resonator, and analyze the role of the distribution of the quasiparticles of the continuum assuming that these quasiparticles are in thermal distribution with an effective temperature different from the environmental temperature. We also discuss the effect of strong photon irradiation in the junction leading to a nonequilibrium occupation of the ABS. We systematically compare the occupations of the bound states and the supercurrents carried by these states for conventional and topological junctions. 
Thursday, March 8, 2018 9:48AM  10:00AM 
R31.00010: LightEnhanced Spin Fluctuations and dWave Superconductivity at a Phase Boundary Yao Wang , ChengChien Chen , Brian Moritz , Thomas Devereaux Timedomain techniques have shown the potential of photomanipulating existing orders and inducing new states of matter in strongly correlated materials. Using timeresolved exact diagonalization, we perform numerical studies of pump dynamics in a MottPeierls system with competing charge and spin density waves. A lightenhanced dwave superconductivity is observed when the system resides near a quantum phase boundary. By examining the evolution of spin, charge and superconducting susceptibilities, we show that a subdominant state in equilibrium can be stabilized by photomanipulating charge order to allow superconductivity to appear and dominate. This work provides an interpretation of lightinduced superconductivity from the perspective of order competition, and offers a promising approach for designing novel emergent states out of equilibrium. 
Thursday, March 8, 2018 10:00AM  10:12AM 
R31.00011: Collapse of highT_{c} superconductivity via ultrafast quenching of the phase coherence Fabio Boschini , Eduardo Da Silva Neto , Elia Razzoli , Marta Zonno , Simone Peli , Ryan Day , Matteo Michiardi , Michael Schneider , Berend Zwartsenberg , Pascal Nigge , Ruidan Zhong , John Schneeloch , Genda Gu , Sergey Zhdanovich , Arthur K. Mills , Giorgio Levy , David J. Jones , Claudio Giannetti , Andrea Damascelli One of the most tantalizing properties of lowdensity condensates is the emergence of phase transitions driven solely by the fragility of the phase coherence. This intriguing physics has triggered an intense search for tools to control the rigidity of superconducting phases and investigate the collapse of superconductivity induced by phase fluctuations. Here, we exploit the capabilities of timeresolved photoemission spectroscopy to probe and drive the phase fragility of the Bi_{2}Sr_{2}CaCu_{2}O_{8+δ} cuprate superconductor, up to the point of completely quenching the phase coherence without affecting the electron pairing. In particular, we thoroughly track and disentangle the dynamics of phase fluctuations and charge excitations [1]. We demonstrate the dominant role of phase coherence in the emergence of hightemperature superconductivity. Moreover, we offer a new benchmark for nonequilibrium investigations of the phase diagram in the normal state at low electronic temperatures. 
Thursday, March 8, 2018 10:12AM  10:24AM 
R31.00012: Evidence for Dissipative Glauber Dynamics in the Charge Ordered Phase of La_{1.875}Ba_{0.125}CuO_{4} studied with an Xray FreeElectron Laser Matteo Mitrano , Sangjun Lee , Ali Husain , Gilberto De La Pena , Young Joe , Alexander Reid , Tim van Driel , Scott Wandel , Giacomo Coslovich , John Schneeloch , Genda Gu , Peter Abbamonte Charge order (CO) is a ubiquitous feature of the phase diagrams of all the cuprate superconductor families that usually anticorrelates with superconductivity (SC). Despite recent studies of the structure of chargeorder in the cuprates, little is known about its collective modes. Here, we investigate the collective dynamics of CO in La_{1.875}Ba_{0.125}CuO_{4}. By suddenly quenching the CO peak with an optical pulse and probing it with ultrafast Xrays at the LCLS freeelectron laser, we find no evident signatures of coherent collective modes, at variance with other CO systems. Instead, we observe a surprising momentumdependent relaxation time that implies a purely dissipative Glauber dynamics of CO. Our work suggests that the CO phase is strongly coupled to an incoherent continuum of states implying highly unconventional fluctuation dynamics of CO in cuprate superconductors. 
Thursday, March 8, 2018 10:24AM  10:36AM 
R31.00013: Superconducting tunnel junction lasers: photon emission at twicethegap energy Armen Gulian Contemporary laser physics spans from black holes to nanoneedles. Solidstate lasers cover wide range of photonic spectrum. However, superconducting materials are not yet quite serving this task. Despite remarkable recent progress in the field of coherent photon emission from Josephson junctionbased lasers, these devices are not emitting in terahertz range. That is not a positive factor for applications, because existing terahertz lasers are bulky and cannot be used in cryogenic environment, especially when the heatload on the cold platform is an issue. Thus, having compact and high efficiency lasers can make difference for some demanding applications. Achieving superconducting lasers requires population inversion, or the so called “negative temperature” state. Injection of electron excitations in tunnel junctions can be a solution. However, a great accuracy in applying correct values of pairbreaking voltages in these junctions, as well as choosing right parameters, both material and geometric, are required. We discuss these topics, as well as address competing physical processes at the “negative temperature” state in superconductors. 
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