Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session T25: Focus Session: Search for New Superconductors II |
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Sponsoring Units: DMP Chair: Jiaqing Yan, University of Tennessee at Knoxville Room: 203B |
Thursday, March 5, 2015 11:15AM - 11:51AM |
T25.00001: Superconductivity in the vicinity of antiferromagnetic order in CrAs and related materials Invited Speaker: Jianlin Luo Transition-metal oxides or pnictides are in rich of novel and intriguing electronic behaviors due to multiple quantum orders and competing phenomena. Among the different electronic states, the emergence of superconductivity in the vicinity of other quantum orders is at the heart of the rich physics. Superconductivity has been observed in a majority of 3d transition-metal compounds except for the Cr- and Mn- based compounds. It is thus of high interest in exploring possible superconductivity in those systems. In this talk, I will present the discovery of superconductivity on the verge of antiferromagnetic order in CrAs via the application of external high pressure. Bulk superconductivity with T$_{\mathrm{c}}\approx $ 2 K emerges at the critical pressure P$_{\mathrm{c}}\approx $8 kbar, where the first-order antiferromagnetic transition at T$_{\mathrm{N}}\approx $265 K under ambient pressure is completely suppressed. In addition, quantum criticality and non-Fermi liquid behavior are observed near P$_{\mathrm{c}}$, which we interpret as originating from a nearly second-order magnetic quantum phase transition that is concomitant with a first-order structural transition. The present finding opens a new avenue for searching novel superconductors in the Cr and other 3d transitional-metal based systems. \\[4pt] In collaboration with Wei Wu, Jinguang Cheng, Kazuyuki Matsubayashi, Panpan Kong, Fukun Lin, Changqing Jin, Nanlin Wang, Yoshiya Uwatoko, Rong Yi, and Qimiao Si. [Preview Abstract] |
Thursday, March 5, 2015 11:51AM - 12:03PM |
T25.00002: Nodal and multi-gap superconductivity in Ta$_{4}$Pd$_{3}$Te$_{16}$ with weakly ferromagnetic normal state Guang-Han Cao, Wen-He Jiao, Chun-Mu Feng, Zhu-An Xu We recently discovered bulk superconductivity at $T_{\mathrm{c}}=$4.6 K in a transition metal telluride Ta$_{4}$Pd$_{3}$Te$_{16}$ [W. H. Jiao et al., J. Am. Chem. Soc. 136, 1284 (2014)]. This material has a layered structure with one-dimensional PdTe$_{2}$ chains. Significant electron correlations are indicated by the enhanced Sommerfeld coefficient. Here we report the measurements of magnetoresistance, Hall effect, magnetization and specific heat using high-quality crystals. Our results show that Ta$_{4}$Pd$_{3}$Te$_{16}$ is an anisotropic type-II superconductor. The anisotropy of upper critical fields $H_{\mathrm{c2}}(T)$ is strongly $T$-dependent, resulted from the multi-band effect. The zero-field electronic specific heat $C_{\mathrm{e}}(T)$ far below the $T_{\mathrm{c}}$ is found to be proportional to $T^{3}$, suggestive of presence of point nodes in at least one of the superconducting gaps, which is further supported by a nonlinear ($\propto H^{1/2})$ field dependence of Sommerfeld coefficient in the mixed state. Notably, the material shows anisotropic weak-ferromagnetism above $T_{\mathrm{c}}$, implying that spin-triplet superconductivity is likely in this material. [Preview Abstract] |
Thursday, March 5, 2015 12:03PM - 12:15PM |
T25.00003: Search for superconductivity in ternary chalcogenides Bi$_{2} $Rh$ _{3}$S$ _{2}$ Udhara Kaluarachchi, Weiwei Xie, Qisheng Lin, Valentin Taufour, Sergey Bud'ko, Gordon Miller, Paul Canfield Recently Sakamoto and co-workers reported$[1]$ that parkerite-type Bi$_{2} $Rh$ _{3}$Se$ _{2}$ is a new superconducting ($\sim$0.7\,K) compound with the charge density wave ($\sim$250\,K) behavior. In this work we present the physical properties of iso-structural compound$[2]$ Bi$_{2} $Rh$ _{3}$S$ _{2}$. For the first time we have been able to grow single crystals of Bi$_{2} $Rh$ _{3}$S$ _{2}$ and separate them from excess melt via high temperature decanting. We will present the detailed characterization of Bi$_{2} $Rh$ _{3}$S$ _{2}$ and a new, closely related phase by mean of resistivity, magnetization, specific heat and single crystals diffraction measurements.\\[4pt] [1] T. Sakamoto, M. Wakeshima, Y. Hinatsu, and K. Matsuhira, Phys. Rev. B \textbf{75}, 060503 (2007) \\[0pt] [2] S. Natarajan, G. Rao, R. Baskaran, and T. Radhakrishnan, Journal of the Less Common Metals \textbf{138}, 215 (1988) [Preview Abstract] |
Thursday, March 5, 2015 12:15PM - 12:27PM |
T25.00004: Superconductivity in non-centrosymmetric BiPd Ana Maldonado, Zhi-Xiang Sun, Mostafa Enayat, Calum Lithgow, Ed Yelland, Darren Peets, Alexander Yaresko, Andreas Schnyder, Peter Wahl In non-magnetic bulk materials, inversion symmetry protects the spin degeneracy. If the bulk crystal structure lacks a center of inversion, however, Rashba-type spin-orbit interactions lift the spin-degeneracy, leading to a Rashba metal whose Fermi surfaces exhibit a intricate spin texture. In superconducting Rashba metals a pairing wavefunction constructed from these complex spin structures will generally contain both singlet and triplet character. We examine possible triplet components of the order parameter in non-centrosymmetric BiPd, combining macroscopic characterization, atomic-scale ultra-low temperature scanning tunneling spectroscopy and relativistic first-principles calculations. The superconducting state of BiPd appears topologically trivial, consistent with Bardeen-Cooper-Schrieffer theory with an order parameter governed by a single isotropic s-wave gap. [Preview Abstract] |
Thursday, March 5, 2015 12:27PM - 12:39PM |
T25.00005: Evidence for a superconducting surface state in the half-heusler alloy LuPtBi Abhimanyu Banerjee, Alan Fang, Carolina Adamo, Phil Wu, Eli Levenson-Falk, Aharon Kapitulnik, Shekhar Chandra, Binghai Yan, Claudia Felser The half-Heusler alloy LuPtBi is predicted by band structure calculations to be a potential candidate for topological superconductivity. We present experimental evidence for a superconducting surface state at much higher temperatures than the bulk $T_c$ of $0.9$K (seen from transport). STM measurements of the $111$ surface show a well developed superconducting gap at temperatures below $2.4 K$, with an IV curve consistent with d-wave superconductivity. The ratio of $\frac{\Delta}{k_bTc}$ is about $12.0$ as opposed to the BCS value of $1.76$, implying that the true $T_c$ is about $6-7$ K. This result is supported SQUID magnetization measurements as well as theoretical predictions for enhanced surface superconductivity due to a Van-Hove singularity in a Bi-terminated [111] surface. We discuss implications of our measurements and possible future experiments. [Preview Abstract] |
Thursday, March 5, 2015 12:39PM - 12:51PM |
T25.00006: Beyond annealing: A revealing story of electron doped cuprate superconductors Yoshiharu Krockenberger, Masafumi Horio, Hiroshi Irie, Hideki Yamamoto High superconducting transition temperatures are a unique feature of cuprate superconductors. The standard phase diagram randomly combines cuprates with various Cu coordinations, e.g., octahedral vs. square-planar, thus violates electron-hole symmetry arguments. In contrast to hole-doped cuprates, the concept of doping dependency is disobeyed on the electron-doped side. Doping alone fails to induce superconductivity and a process commonly referred to as ``annealing'' is required. We have shown that an elaborate annealing process, i.e. 2-step annealing process, is capable to induce superconductivity into Pr$_{2-x}$Ce$_{x}$CuO$_{4}$ with $x$ as low as $x=0.00$. Here we show that appropriate synthesis conditions allow for the growth of as-grown superconducting Pr$_{2}$CuO$_{4}$ and T$^{\prime}$-La$_{2}$CuO$_{4}$ thin films by molecular beam epitaxy. We observe a hole-like Hall coefficient being linear up to high magnetic fields. Hence, high quality thin films of electron doped cuprate superconductors still show a positive Hall coefficient even at optimal doping level. Finally, the transition from a Mott insulator in T-La$_{2}$CuO$_{4}$ to a superconducting metal in T$^{\prime}$-La$_{2}$CuO$_{4}$ at $x=0.00$ is solely associated to the coordination of Cu. [Preview Abstract] |
Thursday, March 5, 2015 12:51PM - 1:03PM |
T25.00007: Superconductivity in the Tungsten Bronzes Phillip Wu, Satoshi Ishii, Kenji Tanabe, Ko Munakata, Robert H. Hammond, Kazuyasu Tokiwa, Theodore H. Geballe, Malcolm R. Beasley Via pulsed laser deposition and post-annealing, high quality K-doped WO$_{\mathrm{3-y}}$ films with reproducible transport properties are obtained. A home built two-coil mutual inductance setup is used to probe the behavior of the films in the superconducting and normal state. The inverse penetration depths and dissipation peaks are measured as a function of temperature and field. Separately, via thin film deposition techniques, we report for the first time stable crystalline hexagonal WO$_{\mathrm{3}}$ on substrates. In order to tune the physical properties of the undoped material, we utilized an ionic liquid gating technique. We observe an insulator-to-metal transition, showing the ionic liquid gate to be a viable technique to alter the electrical transport properties of this material. By comparing the alkali and ionic liquid gated WO$_{\mathrm{3}}$, we conclude with some remarks regarding how superconductivity arises in this system. [Preview Abstract] |
Thursday, March 5, 2015 1:03PM - 1:15PM |
T25.00008: Prediction of Superconductivity in Potassium-Doped Benzene Hai-Qing Lin, Guohua Zhong, Xiao-Jia Chen To explore underline mechanism for the superconducting phase in recent discovered aromatic hydrocarbons, we carry out the first-principles calculations on benzene, the basic and the simplest unit of the series and examine the structural and phase stability when doped by potassium, K$_x$C$_6$H$_6$, $x=1,2,3$. We found that K$_2$C$_6$H$_6$ with the space group of $Pbca$ is the most stable phase with superconducting transition temperature T$_c$ around 6.2K. Moreover, we argue that all existing hydrocarbons should have superconducting phase in the same range, 5K $<$ T$_c$ $<$ 7K, when doped by potassium atoms. [Preview Abstract] |
Thursday, March 5, 2015 1:15PM - 1:27PM |
T25.00009: ESR and Microwave Absorption in Boron Doped Diamond Single Crystals Christopher Timms Superconductivity has been reportedly found in boron-doped diamond. Most research to date has only studied superconductivity in polycrystalline and thin film boron-diamonds, as opposed to a single crystal. In fact, only one other group has examined a macro scale boron-doped diamond crystal. Our group has successfully grown large single crystals by using the High Temperature High Pressure method (HTHP) and observed a transition to metallic and superconducting states for high B concentrations. For the present, we are studying BDD crystal using Electron Spin Resonance. We conducted our ESR analysis over a range of temperatures (2K to 300K) and found several types of signals, proving the existence of charge carriers with spin 1/2 in BDD. Moreover, we have found that with increasing B concentrations, from n $\sim$ 10$^{18}$ cm$^{-3}$ to n of over 10$^{20}$ cm$^{-3}$, the ESR signal changes from that of localized spins to the Dysonian shape of free carriers. The low magnetic field microwave absorption has also been studied in BDD samples at various B concentrations and the clear transition to superconducting state has been found below Tc that ranges from 2K to 4 K depending on concentration and quality of crystal. [Preview Abstract] |
Thursday, March 5, 2015 1:27PM - 1:39PM |
T25.00010: Detection of pairing in a new high-T$_{\mathrm{c}}$ system: Density of states in nanoclusters Avik Halder, Vitaly Kresin A unique property of metal nanocluster particles is the ``superatom''-like shell structure of the delocalized electrons. The electronic shell levels are highly degenerate, i.e., present sharp peaks in the density of states, which can enable exceptionally strong electron pairing in certain clusters composed of just tens to hundreds of atoms. This offers the potential of using them as building blocks for high-T$_{\mathrm{c}}$ materials. But how can one verify the onset of a superconducting transition in a free nanocluster? To answer this question we demonstrate the production of an intense flux of size-resolved nanoclusters with an adjustable internal temperature, and show that an accurate spectroscopic measurement of their photoelectron yield curves reveals the density of states near the Fermi level and strong changes which can occur upon reaching T$_{\mathrm{c}}$. This has enabled our observation of a new family of high-temperature superconductors. [Preview Abstract] |
Thursday, March 5, 2015 1:39PM - 1:51PM |
T25.00011: High-T$_{\mathrm{c}}$ superconducting state of metal nanoclusters: Experimental observation Vitaly Kresin, Avik Halder A spectroscopic investigation of size-resolved aluminum nanoclusters, Al$_{\mathrm{n}}$, has revealed a novel phenomenon: a rapid rise in the near-threshold density of states of several specific clusters with decreasing temperature. The effect is especially prominent in the closed-shell ``magic'' cluster Al$_{66}$. The characteristics of this behavior are fully consistent with a pairing transition, implying a high-temperature superconducting state with T$_{\mathrm{c}}>\sim $100 K. This value exceeds that of bulk aluminum by two orders of magnitude. This is the first experimental observation of high temperature superconductivity in nanocluster particles. Our results highlight the promise of metal nanoclusters as high-T$_{\mathrm{c}}$ building blocks for materials and networks. [Preview Abstract] |
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