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Superconductivity in HgBa 2 Ca m-1 Cu m O 2m+2+δ (m=1,2, and 3) under quasihydrostatic pressures. L. Gao et al ., Phys. Rev. B 50 , 4260 (1994) C. Ambrosch-Draxl et al ., Phys. Rev. Lett. 92 , 187004 (2004). Shimizu-group Hanzawa Akinori. Introduction Cuprates series
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Superconductivity in HgBa2Cam-1CumO2m+2+δ (m=1,2, and 3) under quasihydrostatic pressures L. Gao et al., Phys. Rev. B 50, 4260 (1994) C. Ambrosch-Draxl et al., Phys. Rev. Lett. 92, 187004 (2004) Shimizu-group Hanzawa Akinori
Introduction Cuprates series HgBa2Cam-1CumO2m+2+δ CuO2 layer hole concentration Motivation Experiments Results & Discussions Summary Contents
Cuprates series Most of high-temperature superconductors belong to cuprates series. La-Ba-Cu-O Tc= 32 K Tc= 40 K at 1.4 GPa Y-Ba-Cu-O Tc= 90 K Tc= 91 K at 1.8 GPa Tl-Ba-Ca-Cu-O Tc= 116 K Tc= 131 K at 7.5 GPa Hg-Ba-Ca-Cu-O Tc=134 K
HgBa2Cam-1CumO2m+2+δ CuO2 layer For High Temperature cuprate Superconductor (HTS), CuO2 Layer is very important factor. m=1 m=2 m=3 http://hiroi.issp.u-tokyo.ac.jp/Pages/crystal%20gallery.html
CuO2 layer Mott Insulator:Spins are alternately up and down. When coulomb repulsion for two electrons in a Cu is big, Electrons cannot move freely. antiferromagnetism Cu (Insulator) Carriers are doped metalization valence : +2 → +3 The origin of occurring superconductivity.
hole concentration Solid Symbols(●, ▲, and ■) are optimally doped. Tc is the highest on optimally doped at ambient pressure. Tc vs n, where n is the number of carriers per CuO2 layer: △ Hg-1201, ○ Hg-1212, □ Hg-1223; solid symbols: samples used in this study. Temperature under dope over dope metal optimal dope Anti Ferro super-conductor △ ○ □ Carrier concentration
Motivation High pressure is employed in the study of HTS. ・ Ceiling of Tc under high pressure ? ・ The cause for pressure-induced Tc increase in these optimally doped compounds ?
Experiment Electrical resistance measurement Diamond Anvil Cell (DAC) diamond pressure medium : MgO insulator : Al2O3 + epoxy tungsten leads 0.3μm gasket : stainless sample (~300×300×25 ) ruby pseude four-lead resistance measurement 300μm
Results Tc reached ・・・ Hg-1223 : 164 K at 31 GPa Hg-1212 : 154 K at 29 GPa Hg-1201 : 118 K at 24 GPa Tc=164 K for Hg-1223 is the highest Tc in the world !
Discussion 1 Si (semiconductor) Based on the results of・・・ ② carriers are doped “modulation doping” ① amount of oxygen change gap is narrow ③ electrical current flow ③ enhance more Tceffectively ② electrons move into another semiconductor gap is wide ① impurity is doped http://ja.wikipedia.org/wiki/%E5%8D%8A%E5%B0%8E%E4%BD%93
Discussion 2 n vs P (theory) Tc vs P (experiment) outer plane inner plane Pressure perpendicular to the CuO2 layer moves a CuO2 layer close to another CuO2 layer. This effect induces a charge transfer.
Discussion 3 Each phase purity by X-ray data. ~80% ~90% ~95% These samples were the highest purity at that time. Tc can raise much more ! Now the purity is more improved ・・・
Summary ・ Universal large Tc enhancement was observed in HgBa2Cam-1CumO2m+2+δ. ・ A record high temperature of 164 K was reached in Hg-1223 at 31 GPa. ・ If we use high purity sample, Tc will make a record high.