Pressure effect on the superconductivity of HgBa 2 Ca 2 Cu 3 O 8+  Shimizu Lab. M1 KAMADA Yukihiro

Contents Introduction –The world record of the T c –Pressure effect on HgBa 2 Ca 2 Cu 3 O 8+  (previous work) –T c depends on… –Motivation Experiment –About diamond-anvil cell (DAC) –High purity of the samples –The amount of the doping carriers –Method of measuring electrical resistance under high pressure with DAC –Method of cooling & determination of the pressure –Experimental result –Discussion Summary

The world record of the T c Introduction T c = GPa World record of high-T c ! ※ Superconductivity ・ Electrical resistance is Zero ・ Meissner effect (perfect diamagnetism) Its superconductivity can’t be explained with BCS theory. The mechanism of superconductivity still has many mysteries.

Pressure effect on HgBa 2 Ca 2 Cu 3 O 8+  (previous work) The electrical resistivity of Hg-1223 under high pressure Pressure dependence of the T c of Hg-series cuprate L. Gao et al., Phys. Rev. B 50, 4260 (1994) Introduction

SC AFM quasi- gap SC under dope over dope optimal dope Temperature ～ 0.20 electronhole T c depends on…  >0, supplying holes into the CuO 2 layers HgBa 2 Ca m-1 Cu m O 2m+2+  m = 3 is the best for high-T ambient pressure. a a c The carrier concentration Pressure effect is not only changing lattice constant but also changing hole distribution between CuO 2 layers etc… Introduction

T c depends on… F.Nakamura, J.Hori, T.Goko, Y.Uno, N.Kikugawa and T.Fujita, Journal of Low Temperature Physics, Vol Nos. 5/6, 1999 Xiao-Jia Chen, Viktor V. Struzhkin, Yong Yu, Alexander F. Goncharov, Cheng-Tian Lin, Ho-kwang Mao & Russell J. Hemley, Nature 466, (2010) 950–953 La 2-x Sr x CuO 4 Bi 2 Sr 2 Ca 2 Cu 3 O 10+  Introduction

Motivation Try to make a new world record! – High purity of the sample – The amount of the doping carriers – To control the pressure condition – Higher pressure – And so on… Introduction

About diamond-anvil cell (DAC) gasket pressure medium sample Diamond Anvil Cell (DAC) 6 cm 3 cm diamond To explain easily, this picture is the DAC which keeps the pressure by screw. In this experiment, I used the DAC which apply the pressure by gas-pressure system. ※ Experiment

SC AFM quasi- gap SC under dopeover dope optimal dope Temperature ～ 0.20 electronhole High purity of the samples Sample 1 (S1) & Sample 2 (S2) – Purity (Hg-1223 : 90%~) Sample 1 (S1) : T c = 134 ambient pressure –To control a little under doped (annealing in a vacuum) Sample 2 (S2) : T c = 130 ambient pressure –Not to control doping carriers Experiment The amount of the doping carriers

To control the pressure condition Sample 2 (S2) –Hydrostatic With pressure medium (NaCl) –Non-hydrostatic Without pressure medium Experiment

Method of measuring electrical resistance under high pressure with DAC Gasket (SUS310S) Electrical probe (Pt foil) Pressure Medium (NaCl) sample Pressure marker (Ruby chip) Insulator (c-BN powder + epoxy) Electrical probe (Au wire) 300  m 100  m 1.8 GPa Sample 2 Hydrostatic (with NaCl) (Sample 1, Sample 2) ※ with microscope. AC four probe method ※ S1:pserud four probe method Experiment

Method of measuring electrical resistance under high pressure with DAC Gasket (SUS310S) Electrical probe (Pt foil) sample Pressure marker (Ruby chip) Insulator (c-BN powder + epoxy) 300  m Non-hydrostatic (without pressure medium) (Sample 2) Sample  m 0.85 GPa ※ with microscope. AC four probe method Experiment

Method of cooling & determination of the pressure Low temperature generator : Pulse Tube refrigerator (low vibration) Gas type DAC different type Gas type DAC can change the pressure at low temperature. (DAC in the refrigerator) Measured with PC Camera Pressure determination: Ruby fluorescence method Raman shift of diamond Experiment

Experimental result Hg-1223 (S1) with NaCl Hg-1223 (S2) with NaCl Experiment Hydrostatic (with NaCl) (Sample 1, Sample 2)

Experimental result Hg-1223 (S2) with no pressure medium T co TcTc Hg-1223 (S1) at 0.7 GPa The T c was defined by same method of the world record Definition of the T c Experiment Non-hydrostatic (without pressure medium) (Sample 2)

Experimental result Pressure dependence of T c about Sample 1 (carrier controlled) and Sample 2 (non-controlled) Hg-1223 (S1 and S2) with NaCl The pressure effect of the T c depends on the sample Experiment

Experimental result Pressure dependence of T c with pressure medium and without pressure medium about Sample 2 ? The pressure effect of the T c depends on the way how to apply the pressure Hg-1223 (S2) Experiment

Discussion L. Gao et al., Phys. Rev. B 50, 4260 (1994) Comparing the previous work to my work Hg-1223 (S1 and S2) with NaCl Carrier density? But, can’t find any clear reasons.

Discussion Phase transition? The change of the T c by applying the pressure is not continuous The other discussion… Hg-1223 (S1 and S2) with NaCl

Summary From this experiment –Can’t make the new world record… –Phase transition? Future –1. Higher pressure –2. X-ray diffraction measurement –3. Uniaxial pressure –4. Best condition of the pressure The new world record of the T c !?