Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B57: Superconductivity: Response to E&M FieldsRecordings Available
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Sponsoring Units: DCMP Chair: Hikaru Ueki, Northwestern University Room: Hyatt Regency Hotel -Clark |
Monday, March 14, 2022 11:30AM - 11:42AM |
B57.00001: Anomalously small superconducting gap in the strong spin-orbit coupled superconductor: β - Tungsten Prashant K Chauhan, Peter N Armitage, Ramesh C Budhani Thin films of β-tungsten host superconductivity in the presence of strong spin-orbit coupling. This non-equilibrium crystalline phase of tungsten has attracted considerable attention in recent years due to its giant spin Hall effect and the potential promise of exotic superconductivity. However, more than 60 years after its discovery, superconductivity in this material is still not well understood. Using time-domain THz spectroscopy, we measure the frequency response of the complex optical conductivity of β-tungsten thin film with a Tc of 3.7 K in its superconducting state. At temperatures down to 1.6 K, we find that both the superconducting gap and the superfluid spectral weight are much smaller than that expected for a weakly coupled superconductor given the Tc. The conclusion of a small gap holds up even when accounting for possible inhomogeneities in the system, which could come from other crystalline forms of tungsten (that are not superconducting at these temperatures) or surface states on β-tungsten grains. Using detailed X-ray diffraction measurements, we preclude the possibility of a significant amount of other tungsten allotropes, strongly suggesting the topological surface states of β-tungsten play the role of inhomogeneity in these films. Our observations pose a challenge and opportunity for a theory of strongly anisotropic normal metals with strong spin-orbit coupling to describe. |
Monday, March 14, 2022 11:42AM - 11:54AM |
B57.00002: Sub-gap quasi-particle scattering and dissipation in superconducting Nb thin films Samuel J Haeuser, Di Cheng, Richard Kim, Joongmok Park, Liang Luo, Jigang Wang Niobium (Nb) thin films are used extensively in superconducting quantum circuits for quantum information science applications. We report on the terahertz time-domain spectroscopy (THz-TDS) experiments in which we measure the electrodynamics of superconducting (SC) Nb films at low temperatures in the GHz and THz spectral range. Above critical temperature (Tc), the thin film exhibits Drude-like response for both real and imaginary conductivity at normal state. Below Tc, the imaginary conductivity exhibits a diverging 1/ω response arising from SC condensate, whose conductivity can be derived from London equation. The real part of conductivity shows a quasi-particle peak at frequencies below, where the photon energy is insufficient to break a cooper pair. This sub-gap peak originates from impurity scattering different from thermally excited quasiparticles. Extended Drude model is performed to extract optical self-energy of quasiparticles, which provides information about impurity scattering, electron-phonon renormalization. Simulation of THz conductivity and quasi-particle scattering will be discussed and compared with our experiment data. |
Monday, March 14, 2022 11:54AM - 12:06PM |
B57.00003: Microwave investigation of Higgs Mode in a superconducting wire Laurine M Marian, Edouard Pinsolle, Samuel Houle, Christian Lupien, Bertrand Reulet Higgs mode in superconductors is an analogous of the Higgs boson in high energy physics that has been predicted by Anderson in the late 50s [1]. Its detection is usually difficult because of its weak coupling with electromagnetic fields. However, a recent theory predicted a huge increase of this coupling in the presence of a DC current, which translates into an anomaly in the complex conductivity at frequencies of the order of 2Δ [2]. |
Monday, March 14, 2022 12:06PM - 12:18PM |
B57.00004: Microwave response of strongly demagnetized anisotropic samples Timothy Branch, Graham Baker, James Day, David Broun, Douglas A Bonn Understanding the electromagnetic response of conducting samples in magnetic fields is necessary to interpret the results of radio- and microwave- frequency experiments. A common geometry used is that of a platelet sample aligned perpendicularly to the applied field, but this induces strong demagnetizing effects that are still the subject of ongoing study because of the difficulty of modelling fields near sharp edges and corners. Furthermore, in materials exhibiting non-local electrodynamics, the surface impedance associated with each face may be different, meaning the weighted contributions from different sample faces to the apparent surface impedance become harder to disentangle. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B57.00005: Electrodynamics of spin waves in triplet superconductors Nicholas R Poniatowski, Jonathan B Curtis, Charlotte Boettcher, Victor M Galitski, Amir Yacoby, Prineha Narang, Eugene Demler Spin triplet superconductors are among the most exotic of quantum materials, featuring a rich phenomenology including topological surface states, fractional vortices, and re-entrant superconducting phases. Fundamentally, spin triplet condensates are distinguished from their conventional spin singlet counterparts by the fact that they carry non-trivial spin quantum numbers, and are in a sense "magnetically ordered." In this talk, we discuss the dynamics of spin triplet condensates, and their ability to support collective modes corresponding to the long-wavelength precession of the superconducting vector order parameter which we show are analogous to spin waves in conventional magnetically ordered systems. We will discuss the interaction of these modes with classical electromagnetic fields, and show how they can readily be excited and detected using well-established microwave spin wave resonance techniques. In light of this, we propose that the detection of these modes offers a novel and direct means for the identification of spin triplet superconductivity, as well as possible applications in a new field of superconducting magnonics. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B57.00006: Light-Induced Switching between Singlet and Triplet Superconducting States Steven Gassner, Martin Claassen While the search for triplet superconductors has garnered much attention as a fertile ground for topological superconductivity, most known superconducting compounds prefer spin-singlet pairing. Here, we devise a theory of competing superconducting orders that permits ultrafast optical switching to an opposite-parity metastable superconducting state in centrosymmetric crystals with strong spin-orbit coupling. Remarkably, since inversion and spin-exchange symmetries are linked for a Cooper pair, dynamical inversion symmetry breaking due to a tailored light pulse can induce odd-parity (spin triplet) order in a conventional even-parity (spin singlet) superconductor, trapping the system in a long-lived metastable state after the pulse. We analyze this effect both with a microscopic description of quasiparticle dynamics under irradiation with a laser, and with a phenomenological time-dependent Ginzburg-Landau theory of multiple competing order parameters, revealing a protocol to efficiently switch to an odd-parity instability. Our results suggest a new avenue for manipulating metastable electronic states of matter, which among other applications may allow an out-of-equilibrium realization of topological superconductivity. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B57.00007: Controlling Cavity-Mediated Superconductivity and Criticality by Engineering Quantum States of Light AHANA CHAKRABORTY, Francesco Piazza Recent success in coupling electrons in two-dimensional materials to the quantum electromagnetic field of optical cavities has opened up many exciting but yet unexplored avenues of quantum electrodynamics, among which one promising idea is to use the photons in the cavity to mediate pairing between electrons, inducing superconducting states with novel properties. An exciting prospect, that makes photons the more interesting mediator with respect to the phonons of the standard BCS paradigm, is to exploit state-of-the-art engineering of the quantum states of light to control superconductivity. A naturally emerging question, which remains still open, is whether one can enhance superconductivity by feeding the cavity with certain quantum states of the photons. This new playground for quantum manybody physics is at the same time exciting and theoretically challenging to describe, requiring us to develop new approaches merging quantum optics, condensed matter, and quantum-field-theory. We recently developed a non-equilibrium field-theory approach that allows to tackle this question. I will describe our current understanding of the problem focusing on how critical properties of the superconducting transitions can be manipulated by initializing the photons in non-thermal initial density matrices. |
Monday, March 14, 2022 12:54PM - 1:06PM |
B57.00008: Electromagnetic Response of Nb Superconducting RF Cavities Hikaru Ueki, Mehdi Zarea, James A Sauls Niobium superconducting radio-frequency (SRF) cavities have been improved in terms of the quality factor Q by infusing N into the Nb surface [1]. These high-Q cavities provide a new technology platform for both quantum processors and quantum sensors for dark matter (DM) candidates. The sensitivity to axion DM signals depends on the quality factors of both the emitter and receiver cavity [2]. To understand the fundamental limitations on Q we have developed nonequilibrium theory of superconducting Nb with impurity disorder, including numerical methods to compute the quality factor and frequency shift of N-doped Nb cavities. For strong disorder, h/2π τTc » 2π, pair breaking limits the Q, but for intermediate disorder, Q has a peak of upper convexity as a function of the quasiparticle-impurity scattering rate, suggesting that with ``impurity engineering'' Q ∼ 1012 are possible. We present new theoretical results for the effects of inhomogeneous disorder on the transition temperature and frequency shift of SRF cavities. Our results are excellent agreement with experimental results reported in Ref.[3], and provide a new tool for characterization of high-Q SRF cavities. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B57.00009: Superheating Field of Inhomogeneous Surface Layers in Ginzburg-Landau Theory Benjamin L Francis, Mark K Transtrum, Yundi Quan, Ajinkya C Hire, Richard G Hennig, Michelle Kelley, Nathan S Sitaraman, Tomas A Arias SRF cavities are used in particle accelerators to obtain high accelerating gradients with very high efficiency. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B57.00010: Nontrivial behavior of hydrides in the superconducting state of high-purity niobium used for high-Q resonant cavities Kamal R Joshi, Sunil Ghimire, Makariy A Tanatar, Ruslan Prozorov, Alexander Romanenko, Anna Grassellino The formation of niobium hydrides is a known issue for superconducting applications of high purity niobium, for example, in high-quality factor resonant cavities. The hydrides precipitation occurs roughly below 150 K upon the first cooldown, and the final structure of the precipitates depends on the material's thermal cycling history, making it challenging to study. A wide array of experimental probes was employed over the years for their studies, yet the microscopic behavior of the hydrides in the superconducting state is not established. It has always been assumed that these non-superconducting precipitates are detrimental to applications. Here we report direct visualization of hydrides-rich phase that forms well-outlined "boomerang" shape regions tens of micrometers in scale. Surprisingly, these regions show a much higher critical current density compared to the surrounding areas. We suggest that in this case, nanoscale hydride precipitates act as strong pinning centers and stabilize type-II behavior of low-kappa high-purity niobium. A more systematic investigation is planned to fully understand this physics and, perhaps, find regimes where hydrides would be not detrimental to superconducting applications that benefit from enhanced pinning. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B57.00011: Microscopic Investigation of Nb Film Impurities by Nonlinear Microwave Response Chung-Yang Wang, Steven M Anlage The microscopic origins of Superconducting Radio Frequency (SRF) cavity breakdown by surface defects are not completely understood. In particular, a clear indication of which defects are harmful for SRF operation, and which are not, is important to establish. One approach is to compare cavities/samples made by various fabrication methods. Here we examine several Nb films on Cu substrates fabricated by different methods. To locally study the electrodynamics of superconductors, a near-field magnetic microwave microscope was built. We study the 3rd harmonic response as a function of rf field amplitude and temperature. By studying 3rd harmonic response of these Nb films, we find that some of them show evidence for superconducting transitions with transition temperatures between 6 K and 7 K. One possible explanation of such impurities is that they come from surface oxides of Nb. Time-dependent Ginzburg-Landau modeling of the probe/sample interaction is used to better understand the origins of the measured nonlinear signals. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B57.00012: Feasibility study for axion searches: non-linearity investigation in Nb SRF cavities Bianca Giaccone, Asher Berlin, Anna Grassellino, Roni Harnik, Yonatan Kahn, Oleksandr Melnychuk, Alexandr Netepenko, Roman Pilipenko, Sam Posen, Alexander Romanenko The SQMS Physics and Sensing thrust is working toward the implementation of multiple axion search schemes to improve upon the current state-of-the-art sensitivity. The search schemes under consideration utilize either single or multiple SRF cavities in several distinct manners. This work presents the first results of multi-mode and single mode non-linearity measurements carried out on 1.3 GHz Nb SRF cavities that give insights on the fundamental behavior of these resonators as well as the feasibility of the proposed axion search schemes. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B57.00013: The Anomalous Resonant Frequency Variation of Microwave Superconducting Niobium Cavities Near Tc Daniel Bafia, Anna Grassellino, Mattia Checchin, John F Zasadzinski, Alexander Romanenko Superconducting radio-frequency (SRF) niobium cavities are the modern means of particle acceleration and an enabling technology for record coherence superconducting quantum systems and ultra-sensitive searches for new physics. Here, we report a systematic effect in Nb cavities indicative of improved superconducting properties - an anomalous decrease (dip) in the resonant frequency at temperatures just below the critical temperature Tc. The frequency dip magnitude correlates with cavity quality factor, near-surface impurity distribution, and Tc. It is also a precursor of the peculiar decrease in the BCS surface impedance with increasing RF current. A first demonstration of the coherence peak in the AC conductivity in Nb SRF cavities is also presented and found to correlate with a large frequency dip. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B57.00014: Transient excitation of Higgs and high-harmonic generation in superconductors with quench-drive spectroscopy Matteo Puviani, Rafael Haenel, Dirk Manske Time-resolved terahertz spectroscopies are powerful techniques to excite and probe non-equilibrium states of superconductors, directly addressing collective modes. Over the last decade, most of the debate was focused on the contribution of the amplitude collective mode (Higgs) and the quasiparticles to the superconducting response, both having the same excitation energy of twice the superconducting gap. In pump-probe spectroscopies, THz pulses are used to either quench or drive the system, which is subsequently probed by either a THz or optical pulse. In this work, we analyze and discuss a new spectroscopy setup where we both quench and drive the superconductor, changing the time delay between the two pulses, and we calculate the time evolution of the current generated by the superconductor. We calculate the superconducting response in Fourier space with respect to both the real time and the quench-drive delay time. In particular, we notice the presence of a transient modulation of higher harmonics, induced by a difference-frequency generation (DFG) process of the quench pulse, which excites the quasiparticles and the Higgs mode at the same time. |
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