LLNL-PRES-674032

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. Lawrence Livermore National Security, LLC

Discovery of superconductivity in Bi2Te: Evidence

of universal behavior in an infinitely adaptive

series under compression

Ryan L. StillwellInternational Conference on Magnetism

Friday, July 10, 2015

Lawrence Livermore National Laboratory LLNL-PRES-6740322

Coauthors, collaborators and

contributors

Lawrence Livermore

National Laboratory

• Jason Jeffries

• Zsolt Jenei

• Scott McCall

• Sam Weir

• Dave Ruddle

University of Alabama

at Birmingham

Yogesh Vohra

National Institute of

Standards and Technology

Nicholas Butch

Lawrence Livermore National Laboratory LLNL-PRES-6740323

Turning topological insulators into

superconductors with high pressure: the (A2)m (A2Q3)n, A=Bi,Sb: Q=Se,Te series and related materials

Materials Pc (GPa) max. Tc (K) T.I.

Bi 7.6 8.4 No

Bi2Te3 11.9 9.4 Yes

Bi4Te3 16.2 8.4 Unconfirmed

Sb2Te3 30 7.3 Yes

Bi2Se3 30 7 Yes

Cux Bi2Se3 0 3.8 Yes

Lawrence Livermore National Laboratory LLNL-PRES-6740324

Infinitely adaptive (Bi2)m(Bi2Te3)n series

J.W.G. Bos et al., PRB, 75 (2007) 195203

Te

Bi

Lawrence Livermore National Laboratory LLNL-PRES-6740325

High temperature flux growth of

Bi2Te crystals

• High purity Bi and Te starting metals

• Grown using excess Bi as flux

• Alumina crucible

• Argon atmosphere

• 420oC soak, centrifuged at 318oC

• Confirmed structure with PXRD

Lawrence Livermore National Laboratory LLNL-PRES-6740326

Evidence of universal convergence to bcc phase at high pressure

O. Degtyareva et al., H.P.R. 24, 319 (2004)

M. Einaga et al., P.R.B 83, 092102 (2011)

J. Jeffries et al., P.R.B 84, 092205 (2011)

Lawrence Livermore National Laboratory LLNL-PRES-6740327

100 μm

Weir et al., APL, 77 (2000), 3400

Designer diamond anvil with diamond

encapsulated resistivity microprobes

• Steatite pressure medium

• Ruby fluorescence pressure calibration

• MP35N gasket

Sample at 2.6 GPa

ruby

steatite

Lawrence Livermore National Laboratory LLNL-PRES-6740328

Hall effect shows multiple carrier

changes as pressure is increased

T= 25K

Lawrence Livermore National Laboratory LLNL-PRES-6740329

Pressure induced metallization of

Bi2Te near 6 GPa

Lawrence Livermore National Laboratory LLNL-PRES-67403210

Onset of superconductivity at 11.5 GPa

with Tc max= 8.6 K at 14.5 GPa.

Lawrence Livermore National Laboratory LLNL-PRES-67403211

Sharp increase in Tc leads to

universal high pressure SC state

J.R. Jeffries et al., PRB, 84 092505 (2011)

Il’ina and Itskevitch, JETP Lett. 11, 218 (1970)

C. Zhang et al., PRB, 83, 140504(R) (2011)J. Jeffries et al., P.R.B 84, 092205 (2011)

C. Zhang et al., P.R.B 83, 140504(R) (2011)

M. Il’ina and E. Itskevich, JETP Lett. 11, 218 (1970)

Lawrence Livermore National Laboratory LLNL-PRES-67403212

Conclusions

Bi2Te XRD suggests universal high pressure convergence of

(Bi2)m(Bi2Te)n series into bcc phase from disparate ground states.

Bi2Te discovered to be a high pressure superconductor

Tc,onset(P=11.5 GPa) ~ 4K

Tc,max (P=14.5 GPa) = 8.6K

Bi2Te implies high pressure SC is universal in (Bi2)m(Bi2Te)n

Pressure is a good tool for exploring TI/SC physics.

Lawrence Livermore National Laboratory LLNL-PRES-67403214

Linear suppression of Tc by application

of magnetic field at 16.2 GPa

Lawrence Livermore National Laboratory LLNL-PRES-67403215

Hc has linear dependence over

accessible phase space