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 YY04: V: Superconductivity III |
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Sponsoring Units: DCMP Chair: Thais Victa Trevisan, Lawrence Berkeley National Laboratory Room: Virtual Room 4 |
Wednesday, March 22, 2023 10:00AM - 10:12AM |
YY04.00001: Generalized plasma waves in layered systems: general properties and relevance for THz spectroscopy Francesco Gabriele In a layered and strongly anisotropic superconducting (SC) system the hybrid modes provided by the propagation of electromagnetic waves in the matter identify two well separate energy scales connected to the large in-plane plasma frequency and to the soft out-of-plane Josephson plasmon. Due to such a large spectrum of excitations, there is a wide interest in the detection and manipulation of plasmons, by means of different experimental protocols, in layered systems. Indeed, the anisotropy of the superfluid response leads to two intertwined hybrid light-matter modes with mixed longitudinal and transverse character, also known as generalized plasmons. Such modes are intimately related to phase coherence, i.e. the key feature of the SC phase: as such, a deep insight on the nature of such modes can also shed light on the pairing mechanism occurring in the SC phase of layered cuprates, for which an unanimously accepted theory is still lacking. |
Wednesday, March 22, 2023 10:12AM - 10:24AM |
YY04.00002: Two distinct superconducting states controlled by orientations of local wrinkles in LiFeAs Lu Cao, Wenyao Liu, Geng Li, Guangyang Dai, Qi Zheng, Yuxin Wang, Kun Jiang, Shiyu Zhu, Li Huang, Lingyuan Kong, Fazhi Yang, Xiancheng Wang, Wu Zhou, Xiao Lin, Jiangping Hu, Changqing Jin, Hong Ding, Hongjun Gao For iron-based superconductors, the phase diagrams under pressure or strain exhibit emergent phenomena between unconventional superconductivity and other electronic orders, varying in different systems. As a stoichiometric superconductor, LiFeAs has no structure phase transitions or entangled electronic states, which manifests an ideal platform to explore the pressure or strain effect on unconventional superconductivity. Here, we observe two types of superconducting states controlled by orientations of local wrinkles on the surface of LiFeAs. Using scanning tunneling microscopy/spectroscopy, we find type-I wrinkles enlarge the superconducting gaps and enhance the transition temperature, whereas type-II wrinkles significantly suppress the superconducting gaps. The vortices on wrinkles show a C2 symmetry, indicating the strain effects on the wrinkles. By statistics, we find that the two types of wrinkles are categorized by their orientations. Our results demonstrate that the local strain effect with different directions can tune the superconducting order parameter of LiFeAs very differently, suggesting that the band shifting induced by directional pressure may play an important role in iron-based superconductivity. |
Wednesday, March 22, 2023 10:24AM - 10:36AM |
YY04.00003: Characterizing the order parameter of high-temperature cuprate superconductivity in the a-b plane Jay C LeFebvre, Ethan Cho, Shane A Cybart Understanding superconductivity at high temperatures has been an evasive scientific hurdle. This talk outlines efforts taken to exploit recent advances in nanofabrication through helium focused ion beam microscopy for the advancement of scientific and technical understanding of high-transition temperature superconductivity. Ion irradiation incident on cuprate materials undergoes a metal to insulator transition and may be directed to create a Josephson junction with clean interfaces and a barrier on the dimensional scale of the coherence length. These Josephson junctions are directly written and offer a novel way to characterize cuprate superconductors in their a-b plane regarded to be the site of superconductivity in these materials. Differential conductance measurements are taken across these junctions to characterize the density of states within the a-b plane. A practical order parameter of cuprate superconductivity is defined. Measurements of the order parameter are taken at variable angles to help determine the practical pairing symmetry. Measurements indicate a significant s-wave component mixed with no more than 30% of the prominent d-wave symmetry. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY04.00004: Peculiar near-contact regime of Andreev reflection at the breakdown of a tunnel junction Petro Maksymovych, Jose Lado, Sang Yong Song, Wonhee Ko Recently we introduced non-contact Andreev reflection (NCAR) - a new experimental approach to quantify Andreev reflection in a tunable tunnel junction [1]. NCAR detects Andreev current in STM geometry through renormalized tunnneling decay rate. This technique therefore enables atomic-scale imaging of Andreev current and quantitative detection of the superconducting state, while avoiding invasive and mesoscale mechanical contacts of the well-established PCAR methodology. One peculiar observation enabled by NCAR is that Andreev reflection does not have a monotonous dependence on tip-sample separation. Here we will explore this effect using both classical and unconventional superconductors as model systems. We will describe the fundamental connection between the tunneling barrier dependence of Andreev reflection and the order in perturbation theory responsible for the tunneling current. The combination of non-contact and near-contact regimes of Andreev reflection then enables a definitive probe of unconventional superconductivity, which we will demonstrate using the canonical FeSe. Moreover, the quantitative comparison to tight-binding modeling enabled by this technique provides even deeper insight, including possible inference of the order parameter symmetry. 1. W. Ko, J. Lado, P. Maksymovych, Nano Lett. 22 (2022) 4042. |
Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY04.00005: Symmetry breaking effects in SNS junctions with a proxitimized planar germanium hole gas Kushagra Aggarwal, Marco Valentini, Andrea Hofmann, Andrea Ballabio, Daniel Chrastina, Giovanni Isella, Jeroen Danon, Georgios Katsaros Planar Ge offers an attractive platform for developing and integrating quantum devices due to inherently strong spin-orbit coupling and large perpendicular g-factor. However, most studies characterize these physical properties in zero and one-dimensional systems [1,2]. In two-dimensional systems, heavy hole-light hole mixing can result in marked corrections to these properties. Here we explore the evolution of Fraunhofer diffraction patterns in a proximitized Ge junction, a direct probe of supercurrent density, in presence of an in-plane magnetic field. We observe significant changes in Fraunhofer pattern depending on the direction of in-plane magnetic field and relate them to the symmetries of the Hamiltonian of this hybrid system. We investigate the evolution of supercurrent density with in-plane magnetic field to elucidate the interplay of spin-orbit interaction, Zeeman splitting and disorder in planar Ge. |
Wednesday, March 22, 2023 11:00AM - 11:12AM |
YY04.00006: Interference, diffraction, and diode effects in superconducting array based on Bi0.8Sb1.2Te3 topological insulator* Alexander N Romanov, Xiangyu Song, Soorya Suresh, Yang Bai, Dmitry Gobulev, Irina Burkova, Eduard Ilin, James N Eckstein, Alexey Bezryadin It is a well-known phenomenon in optics that spectroscopic resolution of a diffraction grating is much better compared to an interference device having just two slits, as in the Young's famous double-slit experiment. On the other hand, it is well known that a classical superconducting quantum interference device (SQUID) is analogous to the optical double-slit experiment. Here we report experiments and present a model describing a superconducting analogue to the diffraction grating, namely an array of superconducting islands positioned on a topological insulator (TI) film Bi0.8Sb1.2Te3. In the limit of extremely weak field, of the order of one vortex per the entire array, such devices exhibit a critical current peak that is much sharper than the analogous peak of an ordinary SQUID. Because of this, such arrays can be used as sensitive absolute magnetic field sensors. An important finding is that, due to the inherent asymmetry of such arrays, the device also acts as a superconducting diode. |
Wednesday, March 22, 2023 11:12AM - 11:24AM |
YY04.00007: Superconducting diode effect in graphene-based multi-terminal Josephson junctions Fan Zhang, Nitin Samarth, Asmaul Smitha Rashid, Morteza Kayyalha, Mostafa Tanhayi Ahari, George J De Coster, Matthew J Gilbert, Takashi Taniguchi, Kenji Watanabe Reciprocal superconducting devices show a symmetric critical current for opposite current directions. By simultaneously breaking time-reversal and inversion symmetry, one can engineer a non-reciprocal superconducting diode effect (SDE). This effect has been experimentally demonstrated in two dimensional van der Waals heterostructures and systems with magneto-chiral anisotropy. In this work, we report a tunable magnetic-field-free SDE arising from circuit network effects in graphene-based multi-terminal Josephson junctions (MTJJs). We observe the SDE between two of the terminals when a non-zero current is applied to a third terminal. We further demonstrate voltage rectification with a pulsed current realizing a superconducting diode efficiency up to 100%. |
Wednesday, March 22, 2023 11:24AM - 11:36AM |
YY04.00008: Proximity-induced superconductivity and finite energy pairing in the Rashba surface state of gold Philipp Ruessmann, Masoud Bahari, Björn Trauzettel The interplay of superconductivity and strong spin-orbit coupling has gained a lot of attention in recent year. For instance, it was realized that Cooper pairing can occur intrinsically away from the Fermi surface in j=3/2 superconductors with strong spin-orbit coupling [Phys. Rev. Research 4, L012017 (2022)]. In this work, we present a theoretical study of the proximity-induced superconducting coupling in a Rashba surface state due to its contact to an s-wave superconductor. |
Wednesday, March 22, 2023 11:36AM - 11:48AM |
YY04.00009: Two-dimensional cuprate high-temperature superconductivity Hengsheng Luo, Yijun Yu, Liguo Ma, Dongjoon Song, Ruidan Zhong, Peng Cai, Jian Shen, Genda Gu, Hiroshi Eisaki, Xianhui Chen, Ruan Wei, Yuanbo Zhang Dimensionality is of fundamental importance in cuprate high-temperature superconductivity: all cuprate superconductors adopt layered structure, and most high-temperature superconductivity theories are based on two-dimensional (2D) models. A monolayer Bi2201 contains only a single layer of CuO2 plane, and therefore represents a cuprate superconductor in the ultimate 2D limit. Here, we probe the high-temperature superconductivity in La doped Bi2201 (Bi2Sr2-xLaxCuO6+δ) single crystals down to monolayer (i.e. half unit cell). We show that monolayer Bi2201 has a transition temperature Tc approximately 3 K lower than the bulk Tc, and the transport in the vortex liquid regime is also distinctively different from that in the bulk. The extreme thickness brings unprecedented tunability. We succeed in covering the entire phase diagram of Bi2201 with controlled oxygenation in a single monolayer sample. Taking advantages of such tunability, we discover an anomalous metal phase in the superconductor-insulator transition. Our results establish monolayer Bi2201 as a new two-dimensional material with highly tunable high-temperature superconductivity. |
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