Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M40: Matter in Extreme Environments IV: SuperconductivityFocus
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Sponsoring Units: DCOMP DMP Chair: Antonio dos Santos, Oak Ridge National Lab Room: 705 |
Wednesday, March 4, 2020 11:15AM - 11:51AM |
M40.00001: Room-Temperature Superconductivity in High-Pressure Hydrides: An electronic structure perspective Invited Speaker: Lilia Boeri Conventional Superconductivity near Room Temperature was observed for the first time almost fifty years after its theoretical prediction, when a superconducting critical temperature (Tc) of 203 K was reported in sulfur hydride, SH3.[1] Tc’s exceeding 200 K have later been reported also in lanthanum and yttrium hydrides.[2] |
Wednesday, March 4, 2020 11:51AM - 12:03PM |
M40.00002: Design of Ternary Ca-S-H System that are Superconducting Under Pressure Yan Yan, Tiange Bi, Nisha Geng, Xiaoyu Wang, Eva Zurek Hydrogen-rich compounds are promising candidates as high pressure superconductors under high compression. Among the most promising hydrides for high temperture superconductivity are those of sulphur and calcium. The high pressure phase transition of S-H system has resulted in the second highest Tc to date, 203 K at 160 GPa, while a Tc of 220-235K has been predicted for CaH6 at 150 GPa. Here, we present a systematic investigation of Ca-S-H phases with various stoichiometries. We find that CaSH2, CaSH6 and CaSH20 are thermodynamically stable at pressures accessible in diamond anvil cells. In these structures hydrogen still exists in its molecular form, and all of these phases are semiconductors with small band gaps. However, an interesting phase with the composition CaSH3 has been found, which is metastable and metallic, and does not contain any H-H bonds. This unique structure has a Tc up to 46 K at 250 GPa. Analysis of its electronic structure, including the sulphur and hydrogen contributions, reveals a van Hove singularity in the density of states near the Fermi Energy. This feature may be important for the superconductivity. Our approach may pave the way for finding high-Tc superconductors in various ternary hydrides. |
Wednesday, March 4, 2020 12:03PM - 12:15PM |
M40.00003: Quantum Crystal Structure in the 250 K Superconducting Lanthanum Hydride Ion Errea, Francesco Belli, Lorenzo Monacelli, Antonio Sanna, Takashi Koretsume, Terumasa Tadano, Raffaello Bianco, Matteo Calandra, Ryotaro Arita, Francesco Mauri, Jose A. Flores Livas Hydrogen-rich materials at high pressures are at the verge of reaching room-temperature superconductivity. Electrical and x-ray diffraction measurements determined a weakly pressure-dependent Tc for LaH10 between 137 and 218 gigapascals in a structure with a fcc arrangement of La atoms. Here we show that quantum atomic fluctuations stabilize in this pressure range a high-symmetry Fm-3m crystal structure consistent with experiments. Even if ab initio classical calculations predict this structure to distort below 230 GPa, the inclusion of quantum effects evidences the Fm-3m as the true ground state. The agreement between the calculated and experimental Tc values further supports this phase as responsible for the 250 K superconductivity. The relevance of quantum fluctuations questions many of the crystal structure predictions made for hydrides within a classical approach that at the moment guide experiments. Furthermore, quantum effects are revealed to be crucial to stabilize solids with extraordinary electron-phonon coupling, reducing the pressures needed for their synthesis. |
Wednesday, March 4, 2020 12:15PM - 12:27PM |
M40.00004: High field phase diagram of LaH10 Dan Sun, Vasily S Minkov, Panpan Kong, Alexander Drozdov, Shirin Mozaffari, Luis Balicas, Mikhail Eremets, Fedor Balakirev Recent research on the hydrogen-rich hydrides pushes the superconducting transition temperature (Tc) near the limit of room temperature. In the hydrides family, LaH10 keeps the current record of Tc of 250 K. Using a pulsed magnet, we mapped out the phase diagram of LaH10 under pressure of 140 GPa. The normal state has a linear temperature dependence and high resistance. Hc2 has been measured above 60 T. The information on the vortex liquid region, coherence length and density of states are obtained by our measurement, providing valuable information for theoretical and experimental hydride development. |
Wednesday, March 4, 2020 12:27PM - 1:03PM |
M40.00005: Effect of pressure on the noncentrosymmetric antiferromagnet CeNiC2 Invited Speaker: Yoshiya Uwatoko Recently, the pressure-induced superconductivity in the CeNiC2 polycrystal has been discovered at 3.5 K around 11 GPa, the highest superconducting transition temperature in a Ce-based heavy-Fermion compound [1]. The intermetallic CeNiC2 crystalizes in orthorhombic structure (space group Amm2) where the lattice lacks the inversion symmetry along c-axis. With decreasing temperature CeNiC2 displays multiple magnetic transitions, an incommensurate antiferromagnetic (iAFM) order at TN1 = 20 K followed by a commensurate AFM order at TN2 = 10 K and a ferromagnetic order at TC = 2 K [2]. In this talk, I will present the pressure phase diagram of CeNiC2 single crystal based on our recent pressure dependence of transport and magnetic data. We observed superconductivity in a narrow pressure range in the vicinity of the vanishing point of TN1. The remarkable coincidence of non-Fermi liquid behavior and the optimal , coupled with moreover, the non-centrosymmetric crystal structure suggest that superconductivity in CeNiC2 is unconventional and exotic in nature. |
Wednesday, March 4, 2020 1:03PM - 1:15PM |
M40.00006: AB3Si3 (A= Na, K, Rb, Cs), the alkali metal borosilicide in sodalite structure with superconductivity under high pressure Miao Zhang, Eva Zurek Prediction of high-temperature superconductivity in clathrate-like hydrogen cage under high pressure has generated an irresistible interest of searches for clathrate-like superconductors. However, when the pressure is released, atomic hydrogens will decompose into H2, accompanying the disappearance of superconductivity. We herein report the structural and physical properties of AB3Si3 (A= Na, K, Rb and Cs) in clathrate-based sodalite structure, whose frameworks consist of covalent B-Si bonds, by first-principles calculations. Our results show that KB3Si3 and RbB3Si3 are thermally stable within pressure ranges of 6.9-37.0 GPa and 7.3-34.2 GPa, respectively. Phonon calculations confirm that RbB3Si3 is dynamically stable at both ambient and high pressures, while KB3Si3 is not at ambient pressure. Electron-phonon calculations predict that RbB3Si3 possess a Tc of 14.5 K at ambient pressure. Moreover, RbB3Si3 is mechanically stable, and its estimated Vickers hardness values are between 11.8 – 15.2 GPa, which are in good agreement with the ideal strength results. |
Wednesday, March 4, 2020 1:15PM - 1:27PM |
M40.00007: Charge Transfer Induced Band Gap Closure: Trend in Rare Earth Tetrahydrides Discovered under Pressure Tiange Bi, Eva Zurek The recent success of the high-pressure synthesis of CaH4 inspired this analysis of a plethora of previously predicted high-pressure rare-earth metal tetrahydrdes: MH4 (M = Ca, Sr, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu). This type of structure, assuming the space group of I4/mmm and resembling the ThCr2Si2 structure type, contains layers of edge-sharing tetrahedra in the xy plane comprised by the negatively charged atomistic hydrogen layers and molecular H2 layers. When this set of structures are optimized to 0 GPa, while the pressure-induced band broadening is eliminated, the H-H distances within the H2 units are inversely associated with the charges transferred to it, which leads to bandgap closure. The existence of quasi-molecular H2 is stabilized by the electron donation from H2 σ bonding state to the vacant metal d states and the back donation from occupied metal d states to the H2 σ* anti-bonding states. The analysis of the electronic properties and stabilization mechanisms of these high-pressure rare earth metal tetrahydrides would potentially benefit the understanding of their exotic physical properties: i.e. superconductivity novel, magnetic behavior. |
Wednesday, March 4, 2020 1:27PM - 2:03PM |
M40.00008: Fermiology Study of YBCO Invited Speaker: Audrey Grockowiak
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M40.00009: Superconductivity in Li6P electride Guochun Yang Electrides are unique compounds where most of the electrons reside at interstitial regions of the crystal behaving as anions, which strongly determines its physical properties. Interestingly, the magnitude and distribution of interstitial electrons can be effectively modified either by modulating its chemical composition or external conditions (e.g. pressure). Most of the electrides under high pressure are non-metallic, and superconducting electrides are very rare. Here, we report that a pressure-induced stable Li6P electride, identified by first-principles swarm structure calculations, becomes a superconductor with a predicted superconducting transition temperature Tc of 39.3 K, which is the highest among already known electrides. The interstitial electrons in Li6P, with dumbbell-like connected electride states, play a dominant role in the superconducting transition. Our work opens up the interest to explore high-temperature superconductivity in similar binary compounds. |
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