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

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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,

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F Q t C iti l M t t From Quantum Critical Magnets to Superconducting Graphite

Siddharth S Saxena Siddharth S Saxena

Quantum Matter Group Cavendish Laboratory

University of Cambridge

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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 L i h

  • G. Lonzarich
  • 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

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Quantum Phase Transitions

Temperature

Ordered State

Magnetism

Ordered State

Magnetism SC

Pressure

Unconventional Superconductivity discovered

Pressure

N.D. Mathur et al, Nature, Vol. 394, 39, (1998) S.S. Saxena et al, Nature, Vol. 406, 587, (2000)

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Clamped pressure cell

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Adiabatic Demagnetisation Refrigerator

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Quantum Phase Transitions

e mperature Tem Magnetism Novel order Pressure Pressure Unconventional Unconventional Superconductivity

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

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  • 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 CeMIn5 systems are a nice test of this idea Ce

5 syste

s a e a ce test o t s dea

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Petrovic, Sarrao, Thompson, Fisk et al.

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Graphite Intercalates Graphite Intercalates

T di i l

  • Two dimensional

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 C8K superconducts at 0.15K.

  • Reports on superconductivity in Graphite

Reports on superconductivity in Graphite Sulpher Composites and Nanotubes

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Motivating Factors Motivating Factors

  • Why choose Yb?
  • Role of magnetism and dimensionality key

i i ti l d ti it issues in unconventional superconductivity.

  • Yb has a propensity to from magnetic ions and

graphite is quasi two dimensional g p q Yb forms triangular array in C Yb

  • Yb forms triangular array in C6Yb
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a b

C6Yb Yb

b

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Superconductivity in C Yb Superconductivity in C6Yb

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

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Superconductivity in C6Yb p y

6

FC ZFC Temperature (K)

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

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Change of Anisotropy? Change of Anisotropy?

H ( b)/H ( *) 2

  • Hc2(ab)/Hc2(c*) ~ 2

suggests a mass anisotropy of around 4

C6Yb Hc2 // ab

anisotropy of around 4, however for pure graphite the mass graphite the mass anisotropy is calculated to be around 50.

Hc2 // c

  • The ratio

ρc(300K)/ρab(300K) ρc( ) ρab( ) reduced to 100 from 10000.

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

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C Ca C6Ca

  • Ca is similar to Yb except there are no f

electrons. Th f f b i t C C h

  • Therefore fabricate C6Ca where we can

rule out possible magnetism

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Superconductivity in C Ca Superconductivity in C6Ca

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

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Why is this interesting? Why is this interesting?

Compound Electron doping

Tc C K 1/8 0 15K C8K 1/8 0.15K C6Li 1/6

  • C6Li

1/6 C6Ca 1/3 11.5K C6Yb 1/3 6.5K C3Li 1/3

  • C2Li

1/2 1 9K C2Li 1/2 1.9K

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Band Structure Calculations Band Structure Calculations

  • G. Csanyi, P. B. Littlewood, A. H.

N id k C J Pi k d d B D Nevidomskyy, C. J. Pickard and B. D. Simons, Nature Phys. 1, 42–45 (2005).

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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).

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Band Structure interlayer band Band Structure – interlayer band

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

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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).

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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 C6Yb at T = 300mK as a function of applied field. The dotted line is a fit to the expected behaviour for an s-wave superconductor.

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Th li d id l li t /T f C Yb l tt d f ti f H H The normalized residual linear term κ0/T of C6Yb plotted as a function of H=Hc2, 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 MgB2 and an

  • verdoped sample of the d-wave superconductor Tl-2201
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Specific Heat of the Ca-Intercalated Graphite Superconductor C6Ca Specific Heat of the Ca-Intercalated Graphite Superconductor C6Ca C6Ca

6

  • J. S. Kim, R. K. Kremer, and L. Boeri, F. S. Razavi, April 17, 2006 Cond-Mat

, , , , p ,

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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

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Anna Akrap, Robert P. Smith, Thomas E. Weller, Mark Ellerby, Neal T.

C Yb

Skipper, Lazlo Forro, Siddharth S Saxena

C6Yb

Upper panel: Superconducting transition temperature for three samples of C6Yb The initial linear increase in Tc of 0.4K/GPa is followed by a saturation above 1 8GPa above 1.8GPa. Lower panel: δρ/δΤcalculated 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 (ρ0 ). The connecting lines are eye guides.

R.P. Smith et. al. Phys. Rev. B 774 (2): Art. No. 024505 JUL 2006

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C Y C6Y b

?

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Transition in C Yb may be attributable to a shift in the Transition in C6Yb 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 l hift i th h t t b t 1 4 d d’Astuto reveals a shift in the charge state between 1.4 and 2.7 GPa from 2+ to 3+ .

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CaC6

  • 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

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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

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Possible Mechanisms ? Possible Mechanisms ?

  • Acoustic Plasmons?
  • Intercalant phonon modes ?
  • G. Csanyi, P. B. Littlewood, A. H. Nevidomskyy, C. J. Pickard and B.

D Simons

Nature Physics 1 49 2005

  • D. Simons, 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

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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 Yb2+ to Yb3+ transition
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Transition in C Yb may be attributable to a shift in the Transition in C6Yb 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 l hift i th h t t b t 1 4 d d’Astuto reveals a shift in the charge state between 1.4 and 2.7 GPa from 2+ to 3+ .

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Diamond Anvil Cell Diamond Anvil Cell

P.Alireza

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0.5 mm

In collaboration with

  • Univ. of Edinburgh
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Focused Ion Bean and Omniprobe Focused Ion Bean and Omniprobe

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Focused Ion Bean and Omniprobe p

  • D. Pickard, R. Sinclair (Stanford), S.S. Saxena (Cambridge)
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TiClO is a 2D S=1/2 Mott Insulator TiClO is a 2D, S=1/2, Mott Insulator

J A Wilson (Bristol) S T Bramwell A Wills (UCL Chemistry) A Green (Royal Institution) 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)

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TiOCl

is a 2D, Spin ½ mott insulator under ambient conditions is a 2D, Spin ½ mott insulator under ambient conditions

500 µm

C A Kuntscher et al cond mat (2006) and

  • C. A. Kuntscher et. al. cond-mat (2006) and

S.S. Saxena, EPSRC ARF proposal (2001)

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Summary Summary

Quantum Critical Regime offers frame work for new discoveries Quantum Critical Regime offers frame work for new discoveries. Led to the case of magnetically mediated superconductivity and first example of itinerant electron ferromagntic superconductor is discovered example of itinerant electron ferromagntic superconductor is discovered. Magnetism and Low Dimensionality are found as physical attributes which aid superconductivity at elevated temperatures. aid superconductivity at elevated temperatures. This road map has led us to the very different case of Graphite Intercalates. Non invasive tuning parameter like high-pressure not only makes new physics tractable, but can also serve as a tool for new material design. p

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Key Publications Key Publications

Superconductivity in graphite intercalated compound C6Yb at 6.5K and C6Ca at 12K (Highest of any graphite and Ce, Yb or U based compound)

  • T. Weller et al. Nature Physics, Vol. 1, pp 39-41

Superconductivity in itinerant electron ferromagnet UGe2 (First example of superconducting pairing of electrons in an itinerant ferromagnet) S.S. Saxena et, al. Nature, Vol. 406, pp. 587-92 pp Prediction and possible explanation of superconductivity in high pressure phase of Iron (Anisotropic pairing as only very pure specimen superconduct. High magnetic susceptibility) S S Saxena P B Littlewood Nature Vol 412 pp 290 291 S.S. Saxena, P.B. Littlewood, Nature, Vol. 412, pp. 290-291 Possible explanation of superconductivity in non centro-symmetric magnet CePt3Si (Magnetic non centro-symmetric materials possibly have exotic mixed-state pairing ) ( g y p y p g ) S.S. Saxena, P. Monthoux, Nature, Vol. 427 pp 799-799