Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M48: Superconductivity: Materials, Growth, Structure |
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Sponsoring Units: DCMP Chair: Ulrich Welp, Argonne Natl Lab Room: Mile High Ballroom 1A |
Wednesday, March 4, 2020 11:15AM - 11:27AM |
M48.00001: An Investigation into the Characteristics of the Superconductive Phase in Heavily P-doped Germanium Kasra Sardashti, Tri D Nguyen, Mehdi Hatefipour, Joseph Yuan, William Mayer, Javad Shabani Realization of superconductivity in group IV semiconductors is anticipated to be the key in the scalability of the qubit devices. Such materials are promising candidates for fault-tolerant hybrid semiconductor-superconductor quantum systems due to their high purity and ease of processing. In this study, superconducting Ge is realized via ion implantation of Ga, followed by activation annealing. For all annealing temperatures, transport measurements showed an abrupt normal-superconductor transitions at 2.5–3.5 K, with residual resistances < 50 mΩ at 20 mK. Typical values for critical magnetic fields were about 0.6 to 0.8 T, corresponding to coherence lengths of 20 to 25 nm. Microscopy measurements revealed presence of a 20nm thick polycrystalline Ga-rich Ge layer near the top surface. To localize the superconducting region, implantation energy was reduced. The resulting superconducting layer showed no grain structure in micrometer scale, but Raman measurements confirmed its nanocrystalline nature. By reducing the implantation energy and the annealing temperatures, coherence length only decreased to ~18 nm. To further characterize the superconducting Ge films, strategies for their integration into all-Ge Josephson junctions and transistors will be discussed. |
Wednesday, March 4, 2020 11:27AM - 11:39AM |
M48.00002: Physical properties of Li-based LiPd2M Heusler compounds (M = Si, Ge, Sn) Karolina Górnicka, Gabriel Kuderowicz, Bartomiej Wiendlocha, Elizabeth M. Carnicom, Robert J. Cava, Tomasz Klimczuk We synthesized and studied LiPd2M, M = Si, Ge and Sn, Heusler-type compounds. All three compounds crystallize in the cubic Fm-3m crystal structure with estimated lattice parameters a = 5.9016 Å (LiPd2Si), 6.0105 Å (LiPd2Ge) and 6.2642 Å (LiPd2Sn). The compounds were characterized by means of magnetic susceptibility, heat capacity and resistivity. For LiPd2Ge bulk transition was confirmed by a large HC anomaly at Tc = 1.96 K. Fitting the HC data yields γ = 5.8 mJ mol-1 K-2 and ΘD = 244 K. The electron-phonon coupling λe-p= 0.53 implies weak-coupling superconductivity. Electronic structure, phonons and electron-phonon interaction functions were computed using the density functional theory. LiPd2Ge exhibits the strongest electron-phonon coupling within the studied series, in agreement with the observation of superconductivity. In all the compounds a phonon soft mode is found in the Γ-K direction, and it is most pronounced in the case of the superconducting LiPd2Ge, which suggests its correlation with the electron-phonon interaction. |
Wednesday, March 4, 2020 11:39AM - 11:51AM |
M48.00003: Layered tin pnictides as a new class of layered superconductors Yosuke Goto, Yoshikazu Mizuguchi We report SnPn-based (Pn: pnictogen) materials as a new class of layered superconductors. The crystal structure of these compounds is characterized by two layers of a buckled honeycomb network of SnPn, bound by the van der Waals (vdW) forces and separated by Na ions. Measurements of electrical resistivity and specific heat indicate the bulk nature of superconductivity with transition temperature (Tc) of 1.3 K for NaSn2As2 and 2.0 K for Na1-xSn2P2 [1,2]. Recent studies on temperature-dependent magnetic penetration depth and thermal conductivity show that superconductivity of NaSn2As2 is fully gapped s-wave state in the dirty limit. Because there are various structural analogues containing SnPn conducting layers, our results indicate that SnPn-based layered compounds can be categorized into a novel family of layered superconductors. Furthermore, these compounds have also been gaining interest for application as thermoelectric materials and topological materials. In the conference, we will also report our recent progress for the studies on functionalities of SnPn-based layered materials. |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M48.00004: Interface superconductivity in complex metal-oxide heterostructures Priyanka Brojabasi, Guillaume Hardy, Patrick Fournier Interface superconductivity in oxide superstructures (SS) proposes new paths to explore further the mechanism for high-Tc superconductors allowing the manipulation of their electronic properties, but also discovering novel artificial materials [1], e.g., electron transfer from LaFeO3 (LFO) to electron-doped Sm2CuO4 was explored in SS grown by RF sputtering [2]. In the present study, we have grown SS of infinite-layer SrCuO2 (SCO) and LFO as well as SS of electron-doped (Sr,Nd)CuO2 (SNCO) and LFO by pulsed-laser deposition with various thicknesses and annealing conditions. The coherent growth of SCO/LFO and SNCO/LFO SS has been confirmed by X-ray diffraction. Resistivity and Hall effect measurements confirm superconductivity in selected samples of SNCO/LFO SS, but no superconductivity and little doping by charge transfer has been observed in SCO/LFO SS. However, we observe a strong correlation between the critical temperature and the thickness of the SS subcomponents for SNCO/LFO SS. Our findings indicate that charge transfer may not be playing a significant role behind the superconductivity in these structures. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M48.00005: Electron-Hole Competition and Structural Response in the Two-Band Superconductor Nb2PdxSe5 Jennifer Neu, David E Graf, Kaya Wei, Alyssa Gaiser, Yan Xin, Thomas Albrecht-Schmitt, Ryan Baumbach, David J Singh, Theo Siegrist The superconducting properties of Nb2PdxSe5 are highly dependent on the Pd stoichiometry. We have synthesized single crystals of Nb2PdxSe5 with x in the range of 0.68 to 0.96 and have carried out detailed single crystal x-ray structural studies. We observe a pivotal shift in the atomic positions that depend on palladium occupancy at the threshold for superconductivity. We will discuss the crystal growth process, our recent findings of the subtle but profound structural changes, and present the rich spectrum of electronic behavior observed for different Pd occupancy regions. At the threshold Pd stoichiometry for superconductivity, a miscibility gap is apparent, with commensurate change in the electronic transport properties. Electron-hole competition in this two-band system is thought to be responsible for this behavior. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M48.00006: Characterizating the penetration depth and coherence length of superconductor-normal superlattices Patrick Quarterman, Nathan Satchell, Brian James Kirby, Reza Loloee, Gavin Burnell, Norman Birge, Julie Ann Borchers Ferromagnetic Josephson junctions are a viable candidate for a low power cryogenic memory alternative compared to traditional CMOS technologies. There have been many reports concerning the supercurrent passing through the Josephson junction, including the discovery of spin triplet Cooper pairs in these systems [1]. Previously, we have found that by replacing the bottom Nb layer with a Nb/Al or Nb/Au superlattice, where the Al and Au layers are quite thin, the surface roughness is reduced compared to Nb. This decrease in surface roughness yields improved areal dependence of the critical current [2]. Previously, the effects on the penetration depth and coherence length from the insertion of a thin normal metal between Nb layers have not been fully explored, given that the use of such superlattices in Josephson junctions yielded behavior that was consistent with Nb. In this work, we report on our observation of an increased penetration depth and decreased coherence length in Nb/Al and Nb/Au superlattices utilizing polarized neutron reflectometry and electrical transport, respectively. |
Wednesday, March 4, 2020 12:27PM - 12:39PM |
M48.00007: Study of electronic properties and mechanical dissipation in epitaxially grown La2-xSrxCuO4 thin films using scanning probe microscopy Larissa Little, Xuguang Wang, Wenjie Gong, Dilek Yildiz, Jason Hoffman, Jennifer E. Hoffman Understanding interplay between the superconducting dome and adjacent phases is important to better design and manipulate superconductors with high critical temperatures. Here we use the techniques of non-contact atomic force microscopy (nc-AFM) and scanning tunneling spectroscopy (STS) in ultrahigh vacuum to characterize thin films of La2-xSrxCuO4 (LSCO). We grow the LSCO with molecular beam epitaxy and an oxygen plasma source. We produce high quality LSCO (001) samples with precise control over Sr doping level and choose the level of epitaxial strain our films experience by using different substrates (e.g., SrTiO3 or LaSrAlO4). We use nc-AFM to measure excitation and frequency shift as a function of tip distance from the surface and applied voltage bias. These measurements give us insight into the electronic nature of our films, as well as information about how energy dissipates into the sample. |
Wednesday, March 4, 2020 12:39PM - 12:51PM |
M48.00008: Acoustic Phonon Dynamics and Optical Properties of Bi-2212 Crystals Brad McNiven, G. Todd Andrews, James P. F. LeBlanc Acoustic phonon behaviour and optical properties of bulk Bi-2212 crystals at room temperature were probed using Brillouin light scattering spectroscopy and refined optical contrast methods. Values for the complex refractive index at a wavelength of 532 nm are presented and, along with Brillouin peak frequency shift data, used to determine transverse and longitudinal acoustic phonon mode velocities in these crystals. |
Wednesday, March 4, 2020 12:51PM - 1:03PM |
M48.00009: Electron counting and chemical complexity in theTa-Nb-Hf-Zr-Ti HEA superconductors Fabian Von Rohr, Robert J. Cava High-entropy alloys (HEAs) are a new class of materials that consist of several principal elements arranged on simple lattices. These structures are stabilized by the high configurational entropy of the random mixing of the elements. The recently discovered Ta-Nb-Hf-Zr-Ti HEA superconductor appears to display properties of both crystalline intermetallics and amorphous materials; e.g., it has a well-defined superconducting transition along with an exceptional robustness against disorder. In this presentation, we will show that the properties of these superconducting HEAs are strongly related to the electron count and that the Tcs of these alloys fall between those of analogous crystalline and amorphous materials [1-3]. We find that despite the large degree of randomness and disorder in HEAs, the superconducting properties are nevertheless strongly dependent on the chemical composition and complexity. We argue that HEAs are excellent model systems for understanding how superconductivity evolves from crystals to amorphous solids. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M48.00010: Enhancement of Superconductivity in Monolayer NbSe2 Hemian Yi, Timothy Pillsbury, Run Xiao, Fei Wang, Chengye Dong, Yifan Zhao, Guang Wang, lingjie zhou, ling zhang, JOSHUA ROBINSON, Moses Hung-Wai Chan, Nitin Samarth, Cui-Zu Chang The superconducting transition temperature of single unit cell FeSe on SrTiO3 (STO) heterostructure is known to be significantly enhanced over that of bulk FeSe, presumably due to a combination of the electron charge transfer from the STO substrate to FeSe and an enhanced electron-phonon interaction across the heterointerface. Here, we explored the possibility of similar physics in monolayer NbSe2 on n-type and p-type graphene substrates and found that the transition temperature is much higher in the latter heterostructures than in the former ones. The enhancement of superconductivity in monolayer NbSe2 on p-type graphene is likely a result of the charge transfer effect. We also studied the temperature dependence of the resistance of NbSe2 under an in-plane magnetic field. The extracted in-plane upper critical field of monolayer NbSe2 overcomes the Pauli paramagnetic limit, suggesting Ising pairing property. We will talk about the properties of monolayer NbSe2 films grown on other oxide substrates. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M48.00011: MBE synthesis, ARPES and STM characterization of DyBa2Cu3O7-δ thin films Zebin Wu, Daniel Putzky, Asish Kundu, Hui Li, Gennady Logvenov, Bernhard Keimer, Kazuhiro Fujita, Tonica Valla, Ilya Drozdov Growth and characterization of HTSC cuprate DyBa2Cu3O7-δ has been achieved in an OASIS system[1], combining together ozone-assisted oxide molecular beam epitaxy (OMBE), angle-resolved photoemission spectroscopy (ARPES), and spectroscopic-imaging scanning tunneling microscopy (SI-STM). Superconducting transition temperature (Tc) of over 80K measured in mutual inductance can be routinely achieved by shuttering via a real-time feedback from RHEED in OMBE. Leveraging on the synergistic capabilities of the instrument, the in-situ grown DyBa2Cu3O7-δ are transferred in-vacuo into ARPES and SI-STM modules for characterization of their electronic properties.Dispersing quasi-particles are observed in photoemission and superconductivity is confirmed in tunneling spectroscopy. |
Wednesday, March 4, 2020 1:27PM - 1:39PM |
M48.00012: Growth and electrical transport properties of (110) YBa2Cu3O7 / (110) PrBa2(Cu0.8Ga0.2)3O7 heterostructure Hom Kandel, Nathan D Arndt, Jungwoo Li, Chang-Beom Eom We performed pulsed laser-based thin film deposition and study of electrical transport properties on (110)-oriented YBa2Cu3O7 (YBCO)/ (110)-oriented PrBa2(Cu0.8Ga0.2)3O7 heterostructure for the nanofabrication of Superconductor (S) / Insulator (I) / Superconductor (S) tunneling Josephson junction device which may have many advantages over the conventional low-temperature superconductor-based Josephson junction devices including low cost, cryogenic system simplicity, and high IcRn product (with Ic being the junction critical current and Rn the normal resistance). X-ray diffraction pattern (XRD) analysis, atomic force microscopy (AFM), and electrical transport studies were carried out to check the orientation, thickness, roughness, surface morphology, critical temperature (TC), and electrical resistivities of the heterostructures. Here, we report the optimization process for the layer by layer growth, multi-layer epitaxy, thickness control of the superconductor and insulator layers, and the electrical transport properties of the (110) YBa2Cu3O7 / (110) PrBa2(Cu0.8Ga0.2)3O7 heterostructure. |
Wednesday, March 4, 2020 1:39PM - 1:51PM |
M48.00013: Magnetic and superconducting properties of the Ir – rich compounds MIr3 (M=Ce, Th and Nd) Karolina Górnicka, Elizabeth M. Carnicom, Debarchan Das, Sylwia Gutowska, Bartomiej Wiendlocha, Weiwei Xie, Robert J. Cava, Dariusz Kaczorowski, Tomasz Klimczuk Recently we have synthesized and studied CeIr3, NdIr3 and ThIr3 compounds that are members of the RE2m+nT4m+5n family (m, n > 0). The bulk nature of the superconducting transitions for CeIr3 and ThIr3 are evident from the visible anomalies at Tc = 2.5 K and 4.4 K, respectively. The heat capacity experiment revealed that CeIr3 is a weak-coupling BCS superconductor and ThIr3 is a moderately coupled type-II superconductor. Theoretical calculations indicate a multi-band character for the Fermi surfaces, with the dominating contribution to the density of states at the Fermi level coming from the 5d states of Ir. |
Wednesday, March 4, 2020 1:51PM - 2:03PM |
M48.00014: Effects of heteroepitaxy on the crystal structure in superconducting DyBa2Cu3O7-x thin films Daniel Putzky, Padma Radhakrishnan, Georg Christiani, Peter Wochner, Yi Wang, Peter van Aken, Gennady Logvenov, Eva Benckiser, Bernhard Keimer High-quality DyBa2Cu3O7-x thin films were grown by molecular beam epitaxy (MBE). In contrast to the previous growth by MBE using co-deposition technique, we have employed an atomic-layer-by-layer shuttering sequence with in-situ RHEED feedback. Epitaxial films grown on various oxide substrates have a sharp superconducting transition above 80 K. Scanning-transition electron microscopy (STEM) shows atomically sharp substrate-film interfaces and the absence of stacking faults, unlike films previously grown by pulsed-laser deposition (PLD). |
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M48.00015: Properties of Superconducting R2O2Bi (R = Y, Er) with Anti-ThCr2Si2-type Structure Zhuan Xu A new family of bismuth compounds, R2O2Bi (R = Y, Ce and Er etc.) crystallized in the anti-ThCr2Si2-type structure where Bi ions form a square net, has attracted much attention because this family exhibits varous interesting ground states including antiferromagnetic (AFM) order, heavy fermion behavior and superconductivity (SC). We have investigated two compounds Ce2O2Bi and Er2O2Bi by measuring transport and magnetic properties, as well as specific heat. While Ce2O2Bi behaves as a Kondo lattice and experiences an antiferromagnetic (AFM) transition at TN of about 6.7 K, Er2O2Bi is a superconductor with Tc of 1 K. A coexistence of AFM and SC is found. There is a correlationship between the oxygen content and Tc. This work offers a new candidate material for studying the interplay between SC and 4f electron magnetism. |
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