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 F47: One and Two Dimensional Superconductivity 2Live
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Sponsoring Units: DCMP Chair: Shanti Deemyad, University of Utah |
Tuesday, March 16, 2021 11:30AM - 11:42AM Live |
F47.00001: Microwave spectroscopy of two-dimensional superconductivity at LaAlO3/SrTiO3(111) interfaces Edouard Lesne, Yildiz Gozde Saglam, Marios Kounalakis, Marc Gabay, Gary Steele, Andrea Caviglia The emergent two-dimensional electron system (2DES) formed at the interface between LaAlO3 (LAO) and SrTiO3 (STO) insulating oxides has been a subject of great attention in condensed matter physics during the last decade. Recently, (111)-oriented LAO/STO interfaces have been shown to exhibit an electronic correlation driven reconstruction of its band structure and a 2D superconducting (SC) ground state, both tunable by electrostatic field-effect. |
Tuesday, March 16, 2021 11:42AM - 11:54AM Live |
F47.00002: Discovery of two-dimensional anisotropic superconductivity at KTaO3 (111) interfaces Changjiang Liu, Xi Yan, Dafei Jin, Yang Ma, Haw-Wen Hsiao, Yulin Lin, Terence Bretz-Sullivan, Xianjing Zhou, John Pearson, Brandon Fisher, J Samuel Jiang, Wei Han, Jian-Min Zuo, Jianguo Wen, Dillon D Fong, Jirong Sun, Hua Zhou, Anand Bhattacharya The unique electronic structure found at interfaces between materials can allow unconventional quantum states to emerge. One prominent example is the emergence of a superconducting electron gas at the interface of LaAlO3/SrTiO3. Here we observe superconductivity in electron gases formed at interfaces between (111) oriented KTaO3 and insulating overlayers of either EuO or LaAlO3. The superconducting transition temperature, approaching 2.2 K, is about one order of magnitude higher than that of the LaAlO3/SrTiO3 system. Strikingly, similar electron gases at (001) KTaO3 interfaces remain normal down to 25 mK. The critical field and IV measurements indicate that the superconductivity is two dimensional. Low carrier density EuO/KTaO3(111) samples, with higher mobilities, show spontaneous in-plane transport anisotropy at temperatues prior to the onset of global superconductivity, suggesting the emergence of a 'stripe' phase where the superconductivity is nearly homogeneous in one direction, but modulated in the other. |
Tuesday, March 16, 2021 11:54AM - 12:06PM Live |
F47.00003: Unexpected two-fold symmetric superconductivity in few-layer NbSe2 Alex Hamill, Brett Heischmidt, Egon Sohn, Daniel Shaffer, Kan-Ting Tsai, Xi Zhang, Xiaoxiang Xi, Alexey Suslov, Helmuth Berger, Laszlo Forro, Fiona Burnell, Jie Shan, Kin Fai Mak, Rafael Fernandes, Ke Wang, Vlad Pribiag Transition metal dichalcogenides (TMDs) have attracted significant interest due to properties such as layer-dependent inversion symmetry, valley-contrasted Berry curvatures, and strong spin-orbit coupling (SOC). Few-layer niobium diselenide (NbSe2) exhibits Ising SOC, which helps stabilize the superconducting state and could lead to exotic properties such as topological superconductivity. Here, we report transport measurements of few-layer NbSe2 under in-plane external magnetic fields. In contrast to the three-fold symmetry of the lattice, we observe the magnetoresistance, critical field, and differential conductance measurements all exhibit a two-fold oscillation confined to the superconducting phase. We attribute the behavior to the mixing between two closely competing pairing instabilities. Our results demonstrate the unconventional character of the pairing interaction in a few-layer TMD, opening a new avenue to search for exotic superconductivity in this family of 2D materials. |
Tuesday, March 16, 2021 12:06PM - 12:18PM Live |
F47.00004: The effects of charge carriers, organic solvents and magnetic ions on the superconductivity of doped 1T-SnSe2 Hanlin Wu, Sheng Li, Daniel Peirano Petit, Bing Lv We reported bulk superconductivity up to 7.6 K through careful manipulation of the charge carrier density and basal spacing d in the chemically intercalated two dimensional CdI2-type 1T-SnSe2 phase. We found out the very unusual scaling behaviour of Tc with the basal spacing distance caused by different organic co-intercalation, meanwhile the Tc appears to be almost independent with the alkali metal concentration. In this presentation, we focus on more chemical doping studies that close to the insulator-superconducting transition regime, more precisely-controlled doping level and various organic molecules have been tested through soft chemical methods. In addition, intercalation of the magnetic molecules are also carried out to study the interplay of superconductivity, magnetism, and possible charge density wave transition in these intercalated system. The details of the results will be presented with their physics origins being further elaborated. |
Tuesday, March 16, 2021 12:18PM - 12:30PM Live |
F47.00005: Co-appearance of high-Tc superconductivity and ferromagnetism in a Ca2RuO4 nanocrystal Hiroyoshi Nobukane, Kosei Yanagihara, Yuji Kunisada, Yunito Ogasawara, Kakeru Isono, Kazushige Nomura, Keita Tanahashi, Takahiro Nomura, Tomohiro Akiyama, Satoshi Tanda We report the realization of high-temperature superconductivity in Ca2RuO4 nanofilm single crystals. Ca2RuO4 thin film with the highest transition temperature Tc (midpoint) of 64 K exhibits zero resistance in electric transport measurements. The superconducting critical current exhibited a logarithmic dependence on temperature and was enhanced by an external |
Tuesday, March 16, 2021 12:30PM - 12:42PM Live |
F47.00006: Yu-Shiba-Rusinov states in Van Hove superconductors Mateo Uldemolins, Andrej Mesaros, Pascal Simon A magnetic impurity in a conventional superconductor gives rise to Yu-Shiba-Rusinov (YSR) bound states inside the superconducting energy gap. |
Tuesday, March 16, 2021 12:42PM - 12:54PM Live |
F47.00007: Quantum Geometric Contributions to the BKT Transition: Beyond Mean Field Theory Zhiqiang Wang, Gaurav Chaudhary, Qijin Chen, Kathryn Levin We study quantum geometric contributions to the Berezinskii-Kosterlitz-Thouless (BKT) transition temperature, $T_{\mathrm{BKT}}$, in the presence of fluctuations beyond BCS theory. Because quantum geometric effects become progressively more important with stronger pairing attraction, a full understanding of 2D multi-orbital superconductivity requires the incorporation of preformed pairs. We find it is through the effective mass of these pairs that quantum geometry enters the theory and this suggests that the quantum geometric effects are present in the non-superconducting pseudogap phase as well. Increasing these geometric contributions tends to raise $T_{\mathrm{BKT}}$ which then competes with fluctuation effects that generally depress it. We argue that a way to physically quantify the magnitude of these geometric terms is in terms of the ratio of the pairing onset temperature $T^*$ to $T_{\mathrm{BKT}}$. They can be extracted from the same voltage-current measurements which are generally used to establish BKT physics. We use these observations to provide rough preliminary estimates of the magnitude of the geometric contributions in, for example, magic angle twisted bilayer graphene. |
Tuesday, March 16, 2021 12:54PM - 1:06PM Live |
F47.00008: Antiferromagnetic and superconducting order parameters and critical temperatures in the two-dimensional Hubbard model Demetrio Vilardi, Pietro Bonetti, Walter Metzner We analyse the competition of antiferromagnetism and superconductivity |
Tuesday, March 16, 2021 1:06PM - 1:18PM Live |
F47.00009: The crossover between the orbital and paramagnetic limits in angle dependence of Hc2 of 2D NbSe2 Hideki Matsuoka, Masaki Nakano, Takashi Shitaokoshi, Takumi Ouchi, Yue Wang, Yuta Kashiwabara, Satoshi Yoshida, Kyoko Ishizaka, Masashi Kawasaki, Yoshimitsu Kohama, Tsutomu Nojima, Yoshihiro Iwasa Two-dimensional (2D) NbSe2 is a recently-developed non-centrosymmetric superconductor with the giant upper critical field Hc2 for the parallel magnetic fields (Hc2||) originating from the unique Ising paring. Here we report the angle dependence of Hc2 in 2D NbSe2, which turned out to exhibit the cusp-like behavior around the parallel fields even far below the superconducting critical temperature despite that Hc2|| is dominated purely by the paramagnetic effect[1]. This behavior is well understood within the Ginzburg-Landau framework by considering different origins of Hc2 for the parallel and perpendicular fields. The proposed model is widely applicable to all the superconductors, offering a powerful approach for a comprehensive understanding of the origin of Hc2. |
Tuesday, March 16, 2021 1:18PM - 1:30PM Live |
F47.00010: Capping layer influence and isotropic in-plane upper critical field of the superconductivity at the FeSe/SrTiO3 interface Yanan Li, Ziqiao Wang, Run Xiao, Qi Li, Ke Wang, Anthony R. Richardella, Jian Wang, Nitin Samarth Understanding the superconductivity at the interface of FeSe/SrTiO3 is a problem of great contemporary interest due to the significant increase in critical temperature (Tc) compared to that of bulk FeSe. We report a study of the influence of a capping layer on superconductivity in thin films of FeSe grown on SrTiO3 using molecular beam epitaxy. Our results show that FeTe provides an optimal cap that barely influences the inherent Tc found in pristine FeSe/SrTiO3. In addition, ex situ magnetoresistance measurements are done in FeTe-capped FeSe films to extract the angular dependence of the in-plane upper critical magnetic field. Our observations reveal an almost isotropic in-plane upper critical field, providing insight into the symmetry and pairing mechanism of high temperature superconductivity in FeSe. |
Tuesday, March 16, 2021 1:30PM - 1:42PM Live |
F47.00011: Local magnetic measurements of a few-layer van der Waals superconductor Alexander Jarjour, George Ferguson, Brian T. Schaefer, Menyoung Lee, Debanjan Chowdhury, Katja Nowack Measurements of thermodynamic properties of few-layer van der Waals superconductors are scarce due to the inherently small volume of mechanically exfoliated samples. Here we measure the magnetic susceptibility of a van der Waals superconductor by using local magnetic measurements enabled by scanning SQUID microscopy. Specifically, we study transition metal dichalcogenide MoS2 which exhibits a superconducting dome with a maximum critical temperature of nearly 10 K in ionic-gated few-layer devices. We combine the magnetic measurements with simultaneous electrical transport and map out changes in superfluid stiffness as a function of temperature and carrier density across the dome. We observe magnetic signatures consistent with a Kosterlitz-Thouless transition, and report our progress towards extracting absolute values of the superfluid stiffness and density from these measurements. |
Tuesday, March 16, 2021 1:42PM - 1:54PM Live |
F47.00012: Raman response modelling in multiband superconductors with competing order parameter symmetries Igor Benek-Lins, Saurabh Maiti Recent experimental studies in the hole-doped iron pnictide BaFe2As2 observed features in its Raman response that are consistent with the existence of particle-particle excitons, also known as Bardasis–Schrieffer (BaSh) modes. The presence of such collective modes indicates the existence of a strong d-wave subleading channel in an otherwise s-wave superconductor. In light of such results, a spin-fluctuation based pairing mechanism seems the most promising and some studies argue that the ground-state symmetry could become a pure d-wave state in some cases. To facilitate the connection between experiments and theory of the pairing mechanism in these systems with symmetry competition, we formulate a self-consistent framework to calculate the Raman response in multiband 2D superconductors using any pairing interaction of electronic origin, which is applicable to models with any Fermi surface geometry. Our unified framework not only reproduces all the known collective modes, like BaSh modes and Leggett modes in the appropriate symmetry channels, but also allows one to study the Raman response of models with an arbitrary number of bands. We will present our results for two-band models and discuss the implications for the five-band system Ba1−xKxFe2As2. |
Tuesday, March 16, 2021 1:54PM - 2:06PM Live |
F47.00013: Uniaxial strain effects on Superconducting nano-wires at LaAlO3/SrTiO3 interface Xinyi Wu, Jianan Li, Megan K Briggeman, Joseph A Albro, Jungwoo Lee, Hyungwoo Lee, Chang-Beom Eom, Patrick R Irvin, Jeremy Levy Oxide interfaces offer new ways to probe superconductivity in reduced spatial dimensions. Using conductive atomic force microscope (c-AFM) lithography [1], conductive nanostructures can be reversibly created at the LaAlO3/SrTiO3 interface, showing superconductivity at sub-Kelvin temperatures. Here we focus on the effects of uniaxial stress on the transport of superconducting quantum wires formed at the LaAlO3/SrTiO3 interface. Preliminary results show that superconductivity is strongly affected by uniaxial strain applied parallel to the nanowire direction, with much less influence for strain applied in the transverse directions. We will discuss the implications of possible electron-pairing mechanisms in SrTiO3. |
Tuesday, March 16, 2021 2:06PM - 2:18PM On Demand |
F47.00014: The Zeeman, Spin-Orbit, and Quantum Spin Hall Interactions in Anisotropic and Low-Dimensional Conductors Aiying Zhao The Dirac equation is extended to an orthorhombically anisotropic system with three effective masses. It exhibits the full relativistic and non-relativistic physical properties in low dimension self-consistently. We show the anisotropic Dirac equation satisfies the most general proper Lorentz transformations and improper Lorentz transformations . The appropriate Foldy-Wouthuysen transformations are extended to expand the Hamiltonian near the non-relativistic limit to fourth order in (mc2)-1, and accurate expressions for Zeeman, spin-orbit and quantum spin Hall interactions for low dimension are obtained. We note that When an electron or hole is traveling in an atomically thin one-dimensional conduction band, its Zeeman and spin-orbit interactions are vanishingly small. In two dimensions, its Zeeman interaction depends strongly on the magnetic field direction, and it nearly vanishes when the field is parallel to the conducting layer. We suppose this might be one of the reasons the upper critical field can greatly exceed the standard Pauli limit in clean monolayer and bilayer superconductors at low temperature. |
Tuesday, March 16, 2021 2:18PM - 2:30PM On Demand |
F47.00015: Role of the pinning effect on quantum phase transition in superconducting Ta thin films with the addition of artificial periodic pinning centers Junghyun Shin, Sungyu Park, Suhyeon Noh, Eunseong Kim In order to study the influence of vortex pinning effect on the superconductor-insulator transition, we introduced periodic hole arrays as strong pinning centers into superconducting tantalum thin films which are representative weakly disordered films where metallic behavior was reported. The low temperature transport characteristics of the perforated tantalum thin films with various areal number hole densities were investigated under perpendicular magnetic fields. The increase of strong pinning centers leads that the strongly trapped flux density increases, and thus causes that the superconducting state expands and the metallic behavior is suppressed. In addition, we found that flux distance between weakly pinned interstitial vortex and its adjacent vortex is constant regardless of areal number hole density. One of possible interpretations for understanding this observation is that the constant flux distance for the appearance of metallic behavior is related to vortex localization length of quantum tunneling of vortices. |
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