Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q1: Novel Superconductivity: Insights from a Materials Perspective |
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Sponsoring Units: DCMP Chair: Aharon Kapitulnik, Stanford University Room: Oregon Ballroom 201 |
Wednesday, March 17, 2010 11:15AM - 11:51AM |
Q1.00001: Enhanced Superconductivity in Sr$_{2}$CuO$_{(4-x)}$ Invited Speaker: The cause of the enhanced Tc of Sr$_{2}$CuO$_{(4-x)}$ which is almost a factor of two larger than optimally doped La 214 superconductors has remained a challenge since its discovery by Hiroi et al [1]. Lack of progress is due to the difficulties in synthesis which require a strong oxidizing agent at hight pressure and temperature. The resulting superconductor sample is multiphase leading to some ambiguity in interpretation. An unjustified suggestion that the results are spurious is negated by recent experiments in which similar behavior is found but with samples prepared using a different synthesis [2]. This has led us to reconsider the available data in the literature [3]. The experimental value of x = $\sim $ 0.6 suggests that the superconductivity originates in very heavily overdoped CuO$_{2}$ layers containing ordered oxygen vacancies. The data support the idea that there is an exciting region of the cuprate phase diagram waiting to be understood but better samples are needed before the possible pairing mechanisms we can think of, or others yet to be determined, can be investigated. \\[4pt] [1] Z. Hiroi e,t al., Nature 364 (1993) 315 \\[0pt] [2] Q..Q. Liu et al., Phys Rev B 74 (2006) 100506 \\[0pt] [3] T.H. Geballe and M. Marezio Physica C 469 (2009) 680 [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:27PM |
Q1.00002: Superconductivity, Magnetism and High T$_{c}$ Invited Speaker: Maximum T$_{c}$ in a related group of materials often appears in the vicinity of some kind of quantum critical point. This is particularly clear in the case of heavy Fermion superconductivity. The competition between superconductivity and magnetism in these materials appears as the conflict between local and itinerant f-electrons. The magnetic fluctuation spectrum can be variously the source of antiferromagnetic order or superconductivity, and the low energy part of this fluctuation spectrum is gapped in the superconducting state, providing a mechanism for strengthening pair coupling. We show how this plays out in prototypic CeCoIn$_{5}$ and related materials, and discuss the relevance to cuprate and other superconducting materials. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 1:03PM |
Q1.00003: Struggle to find higher-Tc superconductors-No night without dawn Invited Speaker: Superconductors can be categorized into 3 groups depending on its $T$c's ; Matsu ( Pines: Tc$>$160K),Tak\'{e} Bamboo: 150K$>$\textit{Tc}$>$77K) and Um\'{e} (Um\'{e} blossoms: 77K $> T$c). At present stage, no``Matsu''superconductor exists, and only Cu-oxide superconductors are realized as a ``Tak\'{e}'' group. Another all superconductors including MgB$_{2}$, Fe-pnictide etc belong to the``Um\'{e}''group. Therefore, our next target is to find a new ``Tak\'{e}'' compound, new non Cu-oxide superconductor above 77K. We have many approaches to find higher-$T$c superconductors within the conventional synthesis conditions. In this conference, we review a personal struggle-successes and disappointments- how to find the higher-$T$c material. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:39PM |
Q1.00004: Intercalation and superconductivity in ternary layer structured metal nitride halides ($M$N$X$: $M$ = Ti, Zr, Hf; $X$ = Cl, Br, I ) Invited Speaker: There are two types of layer structured polymorphs in the title ternary compounds: the $\alpha $-form with the FeOCl structure and the $\beta $-form with the SmSI structure.$^{ }$These crystals are semiconductors with band gaps of about 2-4 eV. The $\beta $-form has a honeycomb-like metal nitride ($M$N) layered network, and is changed into superconductors by electron doping. The superconducting transition temperatures ($T_{c}$s) are 13-15 K, and about 25 K for $\beta $-ZrNCl and $\beta $-HfNCl, respectively. The electron doping can be done by intercalation of alkali metals or deintercalation of chlorine atoms from the interlayer space between the nitride layers. The alkali metal intercalated compounds can be co-intercalated with various solvent molecules; the $T_{c}$ increases upon swelling with solvent molecules, the anisotropy of the superconductivity being significantly increased. TiNCl adopts only the $\alpha $-form structure. In contrast to the honeycomb network of $\beta $-ZrNCl and HfNCl, TiNCl has orthogonal nitride layers. TiNCl can also be changed into superconductors with $T_{c}$s of 8.6 and $\sim $16.3 K upon electron-doping by means of intercalation of pyridine, and alkali metals, respectively. Superconductivity of TiNCl intercalated with a series of amines will also be introduced. [Preview Abstract] |
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