Superconductivity in HgBa2Cam-1CumO2m+2+δ (m=1,2, and 3) un

der 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

Contents

• Introduction Cuprates series

HgBa2Cam-1CumO2m+2+δ

CuO2 layer

hole concentration

Motivation

• Experiments

• Results & Discussions

• Summary

Cuprates series

La-Ba-Cu-O

Tc= 32 K

Tc= 40 K at 1.4 GPa

Hg-Ba-Ca-Cu-O

Tc=134 K

Most of high-temperature superconductors belong to cuprates series.

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

HgBa2Cam-1CumO2m+2+δ

CuO2 layer

m=1 m=2 m=3

http://hiroi.issp.u-tokyo.ac.jp/Pages/crystal%20gallery.html

For High Temperature cuprate Superconductor (HTS),

CuO2 Layer is very important factor.

CuO2 layerMott Insulator ： Spins are alternately up and down. When coulomb repulsion for two electrons in a Cu is big, Electrons cannot move freely.

antiferromagnetismCu

Carriers are doped

valence : +2 → +3

metalization

The origin of occurring superconductivity.

(Insulator)

hole concentration

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.

△ ○ □

under dope over dope

super-conductor

metal

Carrier concentration

Tem

pera

ture

Anti Ferro

Solid Symbols(●, ▲, and ■) are optimally doped. Tc is the highest on optimally doped at ambient pressure.

optimal dope

MotivationHigh pressure is employed in the study of HTS.

・ The cause for pressure-induced Tc increase in these optimally doped compounds ?

・ Ceiling of Tc under high pressure ?

ExperimentElectrical resistance measurement

300μm

0.3μm

diamond

pressure medium : MgO

insulator : Al2O3 + epoxy

gasket : stainless

sample (～ 300×300×25 　　 )3mμ

Diamond Anvil Cell (DAC)

ruby

pseude four-lead resistance measurement

tungsten leads

ResultsTc 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

http://ja.wikipedia.org/wiki/%E5%8D%8A%E5%B0%8E%E4%BD%93

Si (semiconductor)

“modulation doping”

① impurity is doped

② electrons move into another semiconductor

gap is wide

gap is narrow

③ electrical current flow

Based on the results of・・・

① amount of oxygen change

② carriers are doped

③ enhance more Tc effectively

Discussion 2n vs P (theory) Tc vs P (experiment)

Pressure perpendicular to the CuO2 layer moves a CuO2 layer close to another CuO2 layer. This effect induces a charge transfer.

outer plane

inner plane

Discussion 3Each phase purity by X-ray data.

～ 95%～ 90%

～ 80%

These samples were the highest purity at that time.

Now the purity is more improved ･･･

Tc can raise much more !

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.