Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session B48: Proximity Effect and Andreev ReflectionLive
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Sponsoring Units: DCMP Chair: Marcio de Andrade, Naval Information Warfare Center Pacific |
Monday, March 15, 2021 11:30AM - 11:42AM Live |
B48.00001: Proximity effects in the charge density wave order and superconductivity in single-layer NbSe2 Wen Wan, Paul Dreher, Alla Chikina, Haojie Guo, Rishav Harsh, Marco Bianchi, Marco Gobbi, Jose-Maria Gomez-Rodriguez, Antonio Javier Martinez-Galera, Philip Hofmann, Jill A. Miwa, Miguel Ugeda Collective electronic states such as the charge density wave (CDW) order and superconductivity respond dramatically to external perturbations. In two-dimensional materials hosting such states, the closeness to unavoidable supporting substrates may lead to significant changes in their properties. Here we explore the impact of proximity effects on the CDW and superconducting states in single-layer NbSe2. We performed the electronic characterization of single-layer NbSe2 on several substrates of opposite metallicity by means of STM/STS at 350 mK, ARPES and 4-point probe transport measurements. In particular, we have epitaxially grown single-layer NbSe2 by MBE on two different metals, Au(111) and BLG/SiC(0001), and two insulators, bulk WSe2 and monolayer h-BN/Ir(111). While both phases disappear on Au(111), they persist on BLG/SiC. The fate of the CDW and superconducting phases is more intricate on insulating substrates, which are largely affected, however, despite of the electronic decoupling of the 2D superconductor with the substrate states. |
Monday, March 15, 2021 11:42AM - 11:54AM Live |
B48.00002: Effects of SU(4) symmetry breaking on Andreev reflection in a graphene-superconductor junction in the quantum Hall regime Joseph Cuozzo, Enrico Rossi A quantum Hall (QH) edge state in proximity to a superconductor becomes a mixture of electron-like and hole-like states due Andreev processes. Such a state is called an Andreev edge state. In graphene valley and spin degeneracy lead to an approximate SU(4) symmetry that is reflected in the approximate 4-fold degeneracy of graphene's Landau levels (LLs). Interactions and the Zeeman effect break such approximate symmetry and the corresponding degeneracy of the LLs. In this talk, I will discuss the effects of SU(4) symmetry breaking terms on the transport properties of a graphene-superconductor junction when the graphene is in the QH regime. I will focus on the "n=1" and "n=0" LLs. For the n=0 LL I will show how the competition between interactions and Zeeman effect that lead to the canted antiferromagnetic phase affect the transport of the Andreev edge states. |
Monday, March 15, 2021 11:54AM - 12:06PM Live |
B48.00003: Phase-dependent dissipation and supercurrent of a graphene-superconductor ring under microwave irradiation Ziwei Dou, Taro Wakamura, Pauli Virtanen, Nian-Jheng Wu, Richard Deblock, Sandrine Autier-Laurent, Kenji Watanabe, Takashi Taniguchi, Sophie Gueron, Helene Bouchiat, Meydi Ferrier A junction with two superconductors coupled by a normal metal hosts Andreev bound states whose energy spectrum is phase-dependent and exhibits a minigap, resulting in a periodic supercurrent. Phase-dependent dissipation also appears due to finite-time relaxation in Andreev levels. While current phase relation and dissipation have previously been measured near thermal equilibrium, their behavior in nonequilibrium is still elusive. By measuring the ac susceptibility of a graphene-superconductor junction under irradiation, we observe the nonequilibrium dissipation and supercurrent simultaneously for the first time. We find the supercurrent dependence on frequency and power deviates from adiabatic ac Josephson effect due to finite relaxation rate. Notably, with irradiation frequency larger than the minigap, the dissipation shows an enhancement at phase 0 where the minigap is largest and dissipation is minimum in equilibrium. We argue that this is evidence of the nonequilibrium distribution function which allows additional transitions between levels on the same side of the minigap. Our results demonstrate the ultra-sensitivity of the dissipation measurement for other proximitised superconducting systems where novel physics can be revealed by nonequilibrium-induced level transitions. |
Monday, March 15, 2021 12:06PM - 12:18PM Live |
B48.00004: Magneto-transport in Planar Graphene/d-wave Superconductor Junctions Kevin Seurre, Vincent Humbert, David Perconte, Christian Ulysse, Anke Sander, Juan Trastoy, Bruno Dlubak, Pierre Seneor, Javier E Villegas We have recently shown experimental evidence for proximity-induced d-wave superconductivity in graphene using planar graphene/d-wave YBaCuO7-x (YBCO) junctions, as evidenced by the conductance dependence on bias and gate voltages [1,2]. Here, we investigate the magnetic field effects on the junctions’ conductance. We find two striking effects. On the one hand, the superconducting-gap related features are progressively suppressed upon increasing the applied magnetic field, and vanish above a characteristic field in the range of 0.5-1 T. On the other hand, we find field-induced periodic oscillations of the conductance, which are only observed at energies below the superconducting gap. These oscillations are the most visible for YBCO/graphene interfaces of relatively low transparence. These findings will be discussed by considering the creation of superconducting vortices in the proximitized graphene, based on which we performed numerical simulations that can account for some of the observed behaviors. |
Monday, March 15, 2021 12:18PM - 12:30PM Live |
B48.00005: Superconducting proximity effect in ultra-scaled pure Ge quantum dots. Jovian Delaforce, Masiar Sistani, Roman B. G. Kramer, Martien den Hertog, Nicolas Roch, Cécile Naud, Alois Lugstein, Olivier Buisson The diverse applications and rich physics of hybrid superconducting-semiconducting systems has attracted significant research interest in improving the quality of these devices. Significant focus has been made on hybrid systems using a combination of Ge and Si to form a high mobility hole gas. However, there has been little research on pure Ge systems. |
Monday, March 15, 2021 12:30PM - 12:42PM Live |
B48.00006: Superconducting Proximity Effect on a Magnetically Doped Topological Insulator Controlled by Magnetization Rikizo Yano, Masahiro Yamamoto, Kohei Tsumura, Hishiro T. Hirose, Vasily S. Stolyarov, Yukio Tanaka, Hiromi Kashiwaya, Yasuhiro Asano, Takao Sasagawa, Satoshi Kashiwaya Proximity effect (PE) on magnetized topological insulators (TIs) has the potential to induce unconventional Cooper pairs, some of which can host Majorana fermions whose antiparticles are themselves. Theory predicts that the magnetized TI systems can tune its PE from a topological to a non-topological state by magnetization and chemical potential. |
Monday, March 15, 2021 12:42PM - 12:54PM Live |
B48.00007: Scanning Tunneling Spectroscopy Study of the Superconducting Proximity Effect in (110)-oriented Manganite/Cuprate and Nickelate/Cuprate Thin Films Rainni K. Chen, Chao Zhang, Chris Granstrom, John Y.T. Wei An anomalously long-ranged (~ 30 nm) superconducting proximity effect was previously reported in thin-film heterostructures of ferromagnetic La2/3Ca1/3MnO3 (LCMO) and superconducting YBa2Cu3O7−δ (YBCO), and attributed to the induction of spin-triplet pairing [1,2]. However, there remains debate over the existence of this long-ranged proximity effect, since scanning tunneling spectroscopy (STS) on c-axis LCMO/YBCO bilayers has failed to observe any direct and microscopic evidence of this effect [3]. In this work, we extend prior STS studies to (110)-oriented films, the orientation most likely to produce d-wave Andreev resonances that show up as zero-bias conductance peaks (ZBCP). We observe these ZBCPs ubiquitously on our unilayer YBCO films, but do not observe them on our bilayer LCMO/YBCO films down to an LCMO overlayer thickness of ~ 5 nm. The ZBCPs also do not appear on (110)-oriented LaNiO3/YBCO bilayers, measured as a non-magnetic control. Our results are inconsistent with proximity-induced spin-triplet superconductivity in LCMO/YBCO structures. |
Monday, March 15, 2021 12:54PM - 1:06PM Live |
B48.00008: Interplay of proximity effects in Nb/FePd heterostructures: domain-superconductivity, spin-triplet Cooper pair generation, and the impact on the ferromagnet Annika Stellhorn, Anirban Sarkar, Emmanuel Kentzinger, Patrick Schöffmann, Tanvi Bhatnagar-Schöffmann, Vitaliy Pipich, Kathryn Lynn Krycka, Thomas Brückel Proximity effects in superconductor/ferromagnet thin film heterostructures are highly topical issues due to their potential application in superconducting spin valves [1]. Physical properties can be controlled by an applied magnetic field and emerge for example as stray-field generated domain-superconductivity or spin-triplet correlations. Our goal is to investigate their interplay and tunability by an external magnetic field. We use a heterostructure system of Nb/FePd with varying strength of magnetic anisotropy and a lateral domain structure, grown by molecular beam epitaxy. |
Monday, March 15, 2021 1:06PM - 1:18PM Live |
B48.00009: Superconducting proximity effect and order parameter fluctuations in disordered and quasiperiodic systems Gautam Rai, Stephan Wolfgang Haas, Anuradha Jagannathan We study the superconducting proximity effect in a hybrid system, where the superconducting part is homogeneous and the non-superconducting part is either disordered, modelled by the off-diagonal Anderson Hamiltonian, or quasicrystalline, modeled by a Fibonacci tight-binding Hamiltonian. We find that when the wave functions are extended, as in the case of weak disorder, or critical, as in the quasicrystal, the pair amplitude at zero temperature spatially decays as a power law away from the interface. In the case of strong disorder, where wave functions are localized, the pair amplitude decays exponentially. In this respect, the quasicrystal has more in common with homogeneous systems than with disordered systems. However, if we consider fluctuations in the induced order parameter by studying the form of its distribution, the quasicrystal behaves more like a strongly disordered system. Furthermore, we demonstrate that the real space profile of the pair correlations in the quasicrystal exhibits two typical features seen in quasi-periodic systems: self-similarity, and enhancement or suppression around sites with high local symmetry depending on the Fermi level. |
Monday, March 15, 2021 1:18PM - 1:30PM Live |
B48.00010: Electrodynamic Response of a Solitary Andreev Level – Theoretical Model Pavel Kurilovich, Vladislav Kurilovich, Valla Fatemi, Michel Devoret, Leonid Glazman Andreev levels provide mesoscopic superconductivity systems that are both rich and tractable. While their underlying physics may be revealed through their electrodynamic responses, investigations have so far been limited. Here, we present results on the dynamical response of an intuitive basic system – the Josephson resonant level: a quantum dot with a single weakly-interacting fermionic level tunnel-coupled to two superconducting leads. |
Monday, March 15, 2021 1:30PM - 1:42PM Not Participating |
B48.00011: Time-resolved measurement of quaiparticle tunneling between two Andreev levels in quantum dots Filip Malinowski, Damaz De Jong, Lin Han, Christian Prosko, Yu Liu, Peter Krogstrup, Leo Kouwenhoven, Jonne Koski We investigate a triple-quantum-dot InAs nanowire device. The central dot is proximitized by a superconducting aluminum shell. The superconducting proximity effect indirectly leads to a formation of Andreev levels in the two normal end dots, located 2 μm apart. By means of radio-frequency dispersive sensing we measure individual quasiparticle jumps between those two Andreev levels separated by a hard-gapped superconducting island. We discuss whether the quasiparticle jumps originate from coherent tunneling or from quasiparticle poisoning, and the implications for the qubits based on hybrid super-semiconducting nanowires. |
Monday, March 15, 2021 1:42PM - 1:54PM Live |
B48.00012: Electrodynamic Response of a Solitary Andreev Level – Experimental Measurements Valla Fatemi, Pavel Kurilovich, Max Hays, Nicholas Frattini, Daniel Bouman, Vladislav Kurilovich, Thomas Connolly, Spencer Diamond, Peter Krogstrup, Jesper Nygard, Attila Geresdi, Leonid Glazman, Michel Devoret Andreev levels provide mesoscopic superconductivity systems that are both rich and tractable. While their underlying physics may be revealed through their electrodynamic responses, investigations have so far been limited. Here, we present results on the dynamical response of an intuitive basic system – the Josephson resonant level: a quantum dot with a single weakly-interacting fermionic level tunnel-coupled to two superconducting leads. |
Monday, March 15, 2021 1:54PM - 2:06PM On Demand |
B48.00013: Engineering Crossed Andreev Reflection in Double-Bilayer Graphene Geon-Hyoung Park, Kenji Watanabe, Takashi Taniguchi, Gil-Ho Lee, Hu-Jong Lee Crossed Andreev reflection (CAR) is a nonlocal process that converts an incoming electron (hole) from one normal electrode to an out-going hole (electron) in another normal electrode through a superconductor (SC). CAR corresponds to the inverse process of Cooper pair splitting, which generates a quantum-entangled electron pair with spatial separation. Here, we fabricated vertically stacked double bilayer graphene (BLG) connected via a superconducting electrode and achieved a spacing between BLG sheets of ∼14 nm, which is far shorter than the superconducting coherence length. We confirm the highly efficient CAR effect by observing strong negative differential resistance in a nonlocal configuration and demonstrate that the competing processes against the CAR can be effectively suppressed by separately tuning the chemical potential of each BLG. The dependence of nonlocal signals on bias voltage, temperature, and chemical potential is consistent with the predicted CAR process. Our results provide a new pathway to a novel SC-based quantum entangler with the in situ tunability of the correlated-pair-splitting efficiency. |
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