Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session S25: Focus Session: Search for New Superconductors I |
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Sponsoring Units: DMP Chair: Chenglin Zhang, Rice University Room: 203B |
Thursday, March 5, 2015 8:00AM - 8:36AM |
S25.00001: Superconductivity in single-layer films of FeSe with a transition temperature above 100 K Invited Speaker: Jinfeng Jia Recent experiments on FeSe films grown on SrTiO3 (STO) suggest that interface effects can be used as a means to reach superconducting critical temperatures (Tc) of up to 80 K. This is nearly ten times the Tc of bulk FeSe and higher than the record value of 56 K for known bulk Fe-based superconductors. Together with recent studies of superconductivity at oxides heterostructure interfaces, these results rekindle the long-standing idea that electron pairing at interfaces between two different materials can be tailored to achieve high temperature superconductivity. Subsequent angle-resolved photoemission spectroscopy measurements of the FeSe/STO system revealed an electronic structure distinct from bulk FeSe, with an energy gap vanishing at around 65 K. However, ex situ electrical transport measurements have so far only detected zero-resistance - the key experimental signature of superconductivity - below 30 K. Here we report the observation of superconductivity with Tc above 100 K in the FeSe/STO system by means of in situ 4-point probe electrical transport measurements. This finding confirms FeSe/STO as an ideal material for studying high-Tc superconductivity. [Preview Abstract] |
(Author Not Attending)
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S25.00002: Superconducting property of Sn1-xInxTe compounds Ka-Ryeong Kim SnTe has been known as a topological crystalline insulator (TCI). TCI is produced by the inversion symmetry of crystal, instead of time-reversal symmetry and Z2 invariance. Recently, the superconducting properties were discovered in In-doed Sn1-xInxTe compounds, which is believed to be the first superconductor with TCI. We synthesized Sn1-xInxTe (x $=$ 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7 ) single like crystals by the flux method. From the electrical resistivity, magnetization, and heat capacity measurements, we obtained superconducting properties such as the critical temperature, upper-critical magnetic fields, coherence length, and Ginzburg-Landau parameters with respect to In-doping concentrations of Sn1-xInxTe in terms of Ginzburg-Landau and Bardeen-Cooper-Shrieffer (BCS) theory. [Preview Abstract] |
Thursday, March 5, 2015 8:48AM - 9:00AM |
S25.00003: Magnetic Structure of Superconducting FeTeOx Films by Neutron Scattering L.K. Narangammana, Zhiwei Zhang, J.I. Budnick, W.A. Hines, J.W. Lynn, Christof Niedermayer, B.O. Wells We present the temperature-dependent neutron diffraction studies of superconducting FeTeO$_x$ and non-superconducting FeTe films grown by PLD.\footnote{\textbf{Appl. Phys. Lett.} 103, 102604 (2013)} In both cases we were able to get strong elastic, magnetic neutron peaks even though we were using film samples. Both samples had magnetic scattering similar to that of bulk Fe$_{1.05}$Te, indicating the coexistence of magnetism and superconductivity in the oxidized films. We will present a detailed analysis of the differences in magnetism between the superconducting and non-superconducting samples. [Preview Abstract] |
Thursday, March 5, 2015 9:00AM - 9:12AM |
S25.00004: The local electronic structure of 1T-Ta(S$_{1-x}$Se$_x$)$_2$ studied by scanning tunneling microscopy Xintong Li, Peng Cai, Zhenqi Hao, Cun Ye, Naizhou Wang, Xianhui Chen, Yayu Wang The 1T-TaS$_2$ compound exhibits a series of complex charge density wave (CDW) transitions and an unexpected insulating ground state at low temperature. It is generally considered to be a Mott insulator, thus is a rare example of strongly correlated transition metal dichalcogenide. When a sufficient amount of S is substituted by Se, the system becomes a superconductor. The evolution of the electronic structure and CDW order across the insulator and superconductor transition has attracted much attention. In this talk, we report scanning tunneling microscopy studies of the atomic scale electronic structure of 1T-Ta(S$_{1-x}$Se$_x$)$_2$ with varied Se contents. In pristine 1T-TaS$_2$, we observe the $\sqrt{13} \times \sqrt{13}$ commensurate CDW order at low temperature, as well as a well-defined insulating energy gap. With increasing Se content, the commensurate CDW order becomes a nearly commensurate CDW order, and a finite electron density of state appears at the Fermi level. Spectroscopic imaging reveals close correlations between the electronic density of states at various energies. We will discuss the implications of these results on the local electronic structure of doped Mott insulators and superconductors in correlated transition metal dichalcogenides. [Preview Abstract] |
Thursday, March 5, 2015 9:12AM - 9:24AM |
S25.00005: ABSTRACT WITHDRAWN |
Thursday, March 5, 2015 9:24AM - 9:36AM |
S25.00006: Engineering superconductivity in metal/spin ice heterostructures Jian-Huang She, Choong Hyun Kim, Craig Fennie, Michael Lawler, Eun-Ah Kim How to understand and control unconventional superconductivity is among the most fundamental and pressing challenges in modern condensed matter physics. Although spin fluctuation induced pairing has long been discussed as a mechanism for unconventional superconductivity, it has been challenging to prove the mechanism or use such insight to control superconductivity. We propose an artificial heterostructure consisting of metallic layer deposited on top of quantum spin ice which could exhibit unconventional superconductivity mediated by the spin fluctuations in the spin ice. We will discuss material candidates that are amenable for film growth and their expected band structure as well as their potential for topological superconductivity. [Preview Abstract] |
Thursday, March 5, 2015 9:36AM - 9:48AM |
S25.00007: Is Sodium a Superconductor Under Pressure? Roxanne Tutchton, Xiao-Jia Chen, Zhigang Wu Superconductivity has been discovered in compressed Li with a critical temperature ($T_{\rm c}$) of 14 K. The other alkali metals are, theoretically, predicted to become superconductors under pressure. Sodium (Na) is the notable exception. Previous {\it ab initio} calculations considered superconductivity only in the BCC and FCC structures of alkali metals; however, Na goes through complicated, structural phase transitions at higher pressures until it becomes an insulator around 260 GPa. We have performed first-principles linear response calculations for four metallic phases (BCC, FCC, cI16 and tI19) of Na to compute lattice dynamics and the electron-phonon spectral function. The electron-phonon coupling parameter as well as $T_{\rm c}$ were then determined as functions of pressure. Our results suggest that the critical temperature for Na rises with increasing pressure to a maximum $T_{\rm c}$ of 1.2 K in the cI16 phase, then it decreases rapidly to zero K at higher pressures. [Preview Abstract] |
Thursday, March 5, 2015 9:48AM - 10:00AM |
S25.00008: Searching for new superconductors using perspectives from both chemistry and physics Robert Cava Although some may claim otherwise, the view from the lab bench is that it remains very difficult if not impossible to make reasonable predictions for what will be an entirely new superconducting material. This lends a considerable amount of drama to this field, as spectacular superconductors are periodically known to appear out of the blue sky. Nonetheless if ones business is to find new superconductors, a rational approach has to be taken to the discovery process. In our research we try both chemistry and physics-based perspectives to guide us. Mostly, our searches fail but sometimes we have discovered new superconductors, and not by accident. In this talk I will describe some examples of searches from our current work that have yielded new (Low Tc) superconductors based on both chemical and physical ideas. The postdoctoral fellows in my research group who have had primary responsibility for the searches that I will describe are Huixia Luo and Weiwei Xie. [Preview Abstract] |
Thursday, March 5, 2015 10:00AM - 10:12AM |
S25.00009: Search for superconductivity and novel phenomena in natural minerals Renxiong Wang, Xiangfeng Wang, J.R. Jeffries, S.R. Saha, R.L. Greene, J. Paglione, C. Santelli, J. Post In a unique venture in collaboration with the Smithsonian Institution's National Museum of Natural History, we present ongoing work from a project focusing on the search for superconductivity in mineral specimens provided by the Department of Mineral Sciences. Including magnetization and transport studies of Bornite(Cu5FeS4), Berthierite(FeSb2S4), Nagyagite(Pb5Au(Te,Sb)4S5-8) and other related compounds, we report low temperature physical properties and ab initio calculations of electronic structure of these compounds, including several unreported magnetic transitions and unconventional transport properties. We focus on an in-depth study of transport and structural properties of Sperrylite (PtAs2) under high pressures up to 120 GPa utilizing a designer diamond anvil cell, as well as artificial synthesis using chemical substitutions to tune structural and electronic properties. We will discuss the evolution of resistivity, from semiconducting to metallic behavior as a function of applied pressure and substitution, with indications that superconductivity is induced at the highest pressures. [Preview Abstract] |
Thursday, March 5, 2015 10:12AM - 10:24AM |
S25.00010: Search for Superconductivity in Extraterrestrial Materials: An Electro-Magnetic Phase Transition with Spin-Glass Characteristics S. Gu\'enon, J.G. Ramirez, Ali C. Basaran, J. Wampler, S. Taylor, M. Thiemens, Ivan K. Schuller We have established a very sensitive, selective, and non-destructive microwave absorption technique to screen a wide range of different materials for superconductivity. This technique allows for the detection of minute amounts of superconducting material in a non-superconducting matrix and it is an ideal tool for searching for superconducting phases in materials found in nature. Here, we report on electro-magnetic phase transitions in extraterrestrial materials formed under very extreme conditions difficult to replicate in a laboratory. Of particular interest is a phase with a transition temperature of 110 K. The associated field scans are characteristic of a frustrated system. Frustrated systems were reported in magnetic systems (spin glasses) as well as in granular high Tc superconductors (frustrated Josephson Junction networks). We will discuss a procedure to discriminate between those two cases. [Preview Abstract] |
Thursday, March 5, 2015 10:24AM - 10:36AM |
S25.00011: Material Specific Characterization Dataset (MSCD): A Novel Computational System for Searching for High-Tc Superconductors Michael Schaffer, O'Paul Isikaku-Ironkwe The search for novel high-Tc superconductors, HTSCs, involves billions of potential permutations and combinations in over 80 potential elements with thousands of structures. The need arises therefore for a quick-search system with predictive power. Using correlations of superconductivity with electronegativity, valence electrons, atomic number, formula weight, number of atoms and number of elements in the stoichiometry of superconductors, we have developed a simple predictive computational system called MSCD: Material Specific Characterization Dataset. MSCD of a superconductor defines and describes its stoichiometric structure in terms of averages of electronegativity, valence electrons, atomic number, formula weight, atoms-to-element ratio, ionic radii, first ionization energy and other associated ratios. We found that when the valence electrons and atomic numbers are the same, the materials have close Tcs. Also when the electronegativity and valence electrons are the same, they share the same crystal structure. Conversely, by tuning a material's stoichiometry to correspond to a known superconductor's MSCD, the material will become superconducting with close enough Tc. We give many examples of MSCD of superconductors and demonstrate the quick-search predictive power of MSCD in the search for novel HTSCs. [Preview Abstract] |
Thursday, March 5, 2015 10:36AM - 10:48AM |
S25.00012: Generalized Periodic System (GPS) for Superconductors O'Paul Isikaku-Ironkwe, Micheal Schaffer In the search for new superconductors, the need arises for a periodic classification system with predictive power that includes all classes, types and families of superconductors. Using the Mendeleevian model of the Periodic Table of elements, based on increasing mass per atom, we reduce all superconductors to ``super-atoms, super-elements,'' and classify them into the same seven periods as the periodic table. We discover that for both pure elements and multi-element superconductors, the highest Tcs occur in period 4 superconductors with an argon shell core. The key difference between low Tc and high-Tc superconductors (HTSCs) in Period 4 is the presence of anions in the HTSCs. We observe that superconductors in the other periods lacking anions have a maximum Tc of about 40K; also at least three elements, with an average electronegativity of 2.0 or higher in a material is required for Tcs above 40K. The detailed GPS for superconductors which we have developed has predictive power and should be a guide in the design and search for high-Tc superconductivity. [Preview Abstract] |
Thursday, March 5, 2015 10:48AM - 11:00AM |
S25.00013: Tunable cobalt vacancies and related properties in LaCoxAs2 Gang Wang, Shijie Shen, Shifeng Jin, Qingzhen Huang, Tianping Ying, Dandan Li, Xiaolong Chen The ThCr2Si2-type structure, composed of covalently bonded transition metal-metalloid layers and the intermediate metals, is a common structure to around 1000 compounds. However the origin of transition metal vacancies and their effects on the properties of corresponding compounds have been poorly understood. Here we will report the investigation of structure, physical properties, and electronic structure for a series of nominal LaCoxAs2 (1.6 ? x ? 2.1). It is revealed that the Co occupancy can be tuned between 1.98(1) and 1.61(1). The structural analyses show that the existence of Co vacancies results from charge balance due to the formation of bond between As-As. These Co vacancies adjust the Curie temperature from 205 K to 47 K and increase the resistivity by more than 100\%. First-principles calculations indicate that the Co vacancies weaken the spin polarization and reduce the density of states at the Fermi level, resulting in decreased Curie temperature and increased resistivity, respectively. The results address the importance of transition metal vacancies in ThCr2Si2-type structure and offer a reliable route to tune the magnetism of ThCr2Si2-type structure. [Preview Abstract] |
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