Siddharth S Saxena Siddharth S Saxena Quantum Matter Group - PowerPoint PPT Presentation

F From Quantum Critical Magnets to Q t C iti l M t t Superconducting Graphite Siddharth S Saxena Siddharth S Saxena Quantum Matter Group Cavendish Laboratory University of Cambridge

Collaborators University College London M. Ellerby, C. Howard, T. Weller, N. Skipper, A. Waters, K. Rahnejat, N. Shuttleworth, D. McMorrow Cambridge Sam Brown, P. Alireza, M. Dean, R. Smith, M. Sutherland, A. Kusmartseva, G. Lonzarich G L i h G. Csanyi, P. Littlewood, A. Nevidomskyy, C. Pickard and B. Simons Lausanne A Akrap and Laszlo Forro Paris and Milan Matteo d’Astuto, Claudia Dallera , Sherbrooke Nicolas Doiron-Leyraud, Louis Taillefer

Quantum Phase Transitions Temperature Ordered State Ordered State Magnetism Magnetism SC Pressure Pressure Unconventional Superconductivity discovered N.D. Mathur et al, Nature, Vol. 394, 39, (1998) S.S. Saxena et al, Nature, Vol. 406, 587, (2000)

Clamped pressure cell

Adiabatic Demagnetisation Refrigerator

Quantum Phase Transitions e mperature Tem Novel order Magnetism Pressure Pressure Unconventional Unconventional Superconductivity

Saxena, Agarwal, Ahilan, et. al. Nature, 2000 Huxley et. al. PRB, 2001 y Tateiwa et. al. J.Phys Con. Mat 2001

P. Monthoux and G G Lonzarich, p-wave and d-wave superconductivity in quasi-two-dimensional metals 1999 Phys. Rev. B 59 14598 2-D CeMIn 5 systems are a nice test of this idea Ce 5 syste s a e a ce test o t s dea

Petrovic, Sarrao, Thompson, Fisk et al.

Graphite Intercalates Graphite Intercalates • Two dimensional T di i l hexagonal sheets of Carbon are held Carbon are held together by van der Waals forces Waals forces. • Can introduce metal atoms in between the atoms in between the sheets. • This process can produce superconductivity For This process can produce superconductivity. For example C 8 K superconducts at 0.15K. • Reports on superconductivity in Graphite Reports on superconductivity in Graphite Sulpher Composites and Nanotubes

Motivating Factors Motivating Factors • Why choose Yb? - Role of magnetism and dimensionality key issues in unconventional superconductivity. i i ti l d ti it -Yb has a propensity to from magnetic ions and graphite is quasi two dimensional g p q -Yb forms triangular array in C 6 Yb Yb forms triangular array in C Yb

a C 6 Yb Yb b b

Superconductivity in C 6 Yb Superconductivity in C Yb 25000 c*-axis 80 Basal plane 20000 20000 60 Ω cm 15000 Ω cm ρ / µΩ ρ / µΩ 40 10000 20 20 5000 5000 0 0 0 0 10 10 20 20 30 30 40 40 50 50 60 60 70 70 80 80 0 0 10 10 20 20 30 30 40 40 50 50 60 60 70 70 80 80 T / K T / K Weller, T., Ellerby, M., Saxena, S. S., Smith, R. & Skipper, N. Nature Phys. 1, 39–41 (2005)

Superconductivity in C 6 Yb p y 6 FC ZFC Temperature (K) Weller, T., Ellerby, M., Saxena, S. S., Smith, R. & Skipper, N. Nature Phys. 1, 39–41 (2005)

Change of Anisotropy? Change of Anisotropy? • H c2 (ab)/H c2 (c*) ~ 2 H ( b)/H ( *) 2 suggests a mass H c2 // ab C 6 Yb anisotropy of around 4 anisotropy of around 4, however for pure graphite the mass graphite the mass H c2 // c anisotropy is calculated to be around 50. • The ratio ρ c (300K)/ ρ ab (300K) ρ c ( ) ρ ab ( ) reduced to 100 from 10000. Weller, T., Ellerby, M., Saxena, S. S., Smith, R. & Skipper, N. Nature Phys. 1, 39–41 (2005)

C Ca C 6 Ca • Ca is similar to Yb except there are no f electrons. • Therefore fabricate C 6 Ca where we can Th f f b i t C C h rule out possible magnetism

Superconductivity in C Ca Superconductivity in C 6 Ca Weller, T., Ellerby, M., Saxena, S. S., Smith, R. & Skipper, N. Nature Phys. 1, 39–41 (2005)

Why is this interesting? Why is this interesting? Compound Electron T c doping C K C 8 K 1/8 1/8 0 15K 0.15K C 6 Li C 6 Li 1/6 1/6 - C 6 Ca 1/3 11.5K C 6 Yb 1/3 6.5K C 3 Li 1/3 - C 2 Li C 2 Li 1/2 1/2 1 9K 1.9K

Band Structure Calculations Band Structure Calculations • G. Csanyi, P. B. Littlewood, A. H. N Nevidomskyy, C. J. Pickard and B. D. id k C J Pi k d d B D Simons, Nature Phys. 1, 42–45 (2005).

Graphite band structure Graphite band structure Csányi, G., Littlewood, P. B., Nevidomskyy, A. H., Pickard, C. J. & Simons, B. D. Nature Phys. 1, 42–45 (2005).

Band Structure Band Structure – interlayer band interlayer band Csányi, G., Littlewood, P. B., Nevidomskyy, A. H., Pickard, C. J. & Simons, B. D. Nature Phys. 1, 42–45 (2005).

Position of interlayer band Position of interlayer band Not superconducting All All superconducting Csányi, G., Littlewood, P. B., Nevidomskyy, A. H., Pickard, C. J. & Simons, B. D. Nature Phys. 1, 42–45 (2005).

Bulk evidence for single-gap s-wave superconductivity in the intercalated graphite superconductor C6Yb superconductor C6Yb Mike Sutherland, Nicolas Doiron-Leyraud, Louis Taillefer,Thomas Weller, Mark Ellerby, S.S. Saxena Thermal conductivity of C 6 Yb at T = 300mK as a function of applied field. The dotted line is a fit to the expected behaviour for an s-wave superconductor.

The normalized residual linear term κ 0 /T of C 6 Yb plotted as a function of H=Hc 2 , Th li d id l li t /T f C Yb l tt d f ti f H H with the small contribution from graphite impurities subtracted off. For comparison we also display low-temperature data for the clean s -wave superconductor Nb, the dirty s wave superconducting alloy InBi the multi gap superconductor MgB and an dirty s -wave superconducting alloy InBi, the multi-gap superconductor MgB 2 and an overdoped sample of the d -wave superconductor Tl-2201

Specific Heat of the Ca-Intercalated Graphite Superconductor C 6 Ca Specific Heat of the Ca-Intercalated Graphite Superconductor C 6 Ca C 6 Ca 6 J. S. Kim, R. K. Kremer, and L. Boeri, F. S. Razavi, April 17, 2006 Cond-Mat , , , , p ,

Pressure Cell for DC Magnetization in SQUID 25 mm Developed by S.S. Saxena, K. Ahilan and S. Brown Now available commercially from CamCell http://www.camcell.co.uk

Anna Akrap, Robert P. Smith, Thomas E. Weller, Mark Ellerby, Neal T. Skipper, Lazlo Forro, Siddharth S Saxena C Yb C 6 Yb Upper panel : Superconducting transition temperature for three samples of C6Yb The initial linear increase in T c of 0.4K/GPa is followed by a saturation above 1.8GPa. above 1 8GPa Lower panel: δρ / δΤ calculated from the resistivity data above 50K for the same resistivity data above 50K, for the same three samples as above. Inset shows the pressure dependence of Inset shows the pressure dependence of the residual resistivity ( ρ 0 ) . The connecting lines are eye guides. R.P. Smith et. al. Phys. Rev. B 774 (2): Art. No. 024505 JUL 2006

C Y C 6 Y b ?

Transition in C Yb may be attributable to a shift in the Transition in C 6 Yb may be attributable to a shift in the charge state as observed in other Yb compounds. Tentative Resonant X-ray scattering by Claudia Dalleria and Matteo d’A t t d’Astuto reveals a shift in the charge state between 1.4 and l hift i th h t t b t 1 4 d 2.7 GPa from 2+ to 3+ .

CaC 6 A. Gauzzi, S. Takashima, N. Takeshita, C. Terakura, H. Takagi, N. Emery, C. H´erold, P. Lagrange, and G. Loupias PRL vol.98, no.6, 067002/1-4, 2007

A Gauzzi et al arXiv:0802 3273v1 [cond-mat supr-con] 22 Feb 2008 A.Gauzzi, et.al. arXiv:0802.3273v1 [cond mat.supr con] 22 Feb 2008

Possible Mechanisms ? Possible Mechanisms ? • Acoustic Plasmons? • Intercalant phonon modes ? G. Csanyi, P. B. Littlewood, A. H. Nevidomskyy, C. J. Pickard and B. D Simons D. Simons, Nature Physics 1 49, 2005 Nature Physics 1 49 2005 I.Mazin PRL 95 (22): Art. No. 227001 NOV 25 2005 M.Calandra, F. Mauri, PRL 95 (23): Art. No. 237002 DEC 2 2005 B. Uchoa, A. H. Castro Neto Superconductivity in metal coated graphene cond-mat/0608515 co d a /06085 5

Further work on graphite Further work on graphite • Study of anisotropy • dHvA and photoemission studies • Carbon Nanotubes • Intercalation of graphene sheets • Pressure driven inducement of Yb 2+ to Yb 3+ transition

Transition in C Yb may be attributable to a shift in the Transition in C 6 Yb may be attributable to a shift in the charge state as observed in other Yb compounds. Tentative Resonant X-ray scattering by Claudia Dalleria and Matteo d’A t t d’Astuto reveals a shift in the charge state between 1.4 and l hift i th h t t b t 1 4 d 2.7 GPa from 2+ to 3+ .

Diamond Anvil Cell Diamond Anvil Cell P.Alireza

0.5 mm In collaboration with Univ. of Edinburgh

Focused Ion Bean and Omniprobe Focused Ion Bean and Omniprobe

Focused Ion Bean and Omniprobe p D. Pickard, R. Sinclair (Stanford), S.S. Saxena (Cambridge)

TiClO is a 2D S=1/2 Mott Insulator TiClO is a 2D, S=1/2, Mott Insulator S.S. Saxena, Search for superconductivity in MClO compounds, EPSRC, ARF Proposal J A Wilson (Bristol) S T Bramwell A Wills (UCL Chemistry) A Green (Royal Institution) J.A.Wilson (Bristol), S.T Bramwell, A. Wills (UCL, Chemistry), A. Green (Royal Institution)