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Spin liquids in condensed matter

Spin liquids in condensed matter. A.V.Mahajan Physics Dept IIT Bombay. “Traditional” electrons. Metallic or magnetic (Ferro/Antiferro) systems have been studied for long. A large number of such systems have been made and characterised. Reasonably good theoretical understanding exists.

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Spin liquids in condensed matter

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  1. Spin liquids in condensed matter A.V.Mahajan Physics Dept IIT Bombay

  2. “Traditional” electrons • Metallic or magnetic (Ferro/Antiferro) systems have been studied for long. • A large number of such systems have been made and characterised. • Reasonably good theoretical understanding exists. • Typically the magnetic systems are 3-dim. • Quantum fluctuations are small…LRO

  3. J J Uniform spin-chain (HAF) S = ½ : power-law spin correlations cspin(T = 0) 0 (no spin-gap) S = 1 : exponentially decaying spin correlations cspin(T = 0) = 0 (spin-gap) JR JL “Exotic” spin systems S = ½ spin-ladder has a gap if number of legs is even Placed between 1D and 2D, the Physics of ladders might be important to understanding high-Tc cuprates

  4. Physics issues • What are the properties of the pristine system? • Can one vary some control parameter across a “quantum critical point”? • Can one induce “order through disorder” • Effect of non-magnetic and magnetic impurities? • Effect of carrier doping? • Comparison with theory.

  5. Ba/Sr O P Cu (Ba, Sr)2Cu(PO4)2 BaCuP2O7 S = ½ HAF chains

  6. (Ba,Sr)2Cu(PO4)2 are one of the BEST examples of isolated S = ½ 1D HAF R. Nath et al. PRB 2005 NMR done with N. Buettgen, A. Loidl at Augsburg Collaboration with Prof. I. Dasgupta for theoretical modeling using DFT (ongoing)

  7. S = ½ 2-LEG LADDER BiCu2PO6 O Cu Bi P

  8. JL JR

  9. D.C.Johnston et al. cond-mat/000147

  10. JR JL Electronic structure calculations done by Sarita Salunke and Indra Dasgupta to determine the hopping parameter t between various Cu atoms. JR/JL = 1 J’’/JL = 0.75 Jnnn/JL = 0.3 J’’ Jnnn

  11. J’’

  12. Specific heat of BiCu2PO6

  13. Doping effects in the 2-leg ladder BiCu2PO6 At Cu2+ site Non-magnetic Zn2+ Magnetic Ni2+ At Bi3+ site Sr2+, Na+ ….hole doping a la high-Tc??

  14. Zn (S = 0) substitution effects in BiCu2PO6

  15. Specific heat data of Zn doped BiCu2PO6

  16. Ni (S=1) doping effects in BiCu2PO6

  17. Specific heat of Ni doped BiCu2PO6

  18. Na+ doping at Bi3+ site in BiCu2PO6

  19. SUMMARY • We have demonstrated that BiCu2PO6 is an example of coupled 2-leg spin ladders. • Zn (non-magnetic) and Ni (magnetic) substitutions at Cu site destroy the spin-gap and induce disordered magnetism. • Na1+ doping at Bi3+ site appears to result in a phase transition to an AF state (with weak ferromagnetic moment) • Continuing effort to check if the coupled ladders can be doped to become metallic

  20. B. Koteswararao Ramesh Nath Sarita Salunke Indra Dasgupta Collaborators LADDER CHAIN • J. Bobroff • H. Alloul • P. Mendels • Labo de Physique des Solides • Orsay, FRANCE • N. Buettgen • A. Krimmel • A. Loidl • EKM, Universitaet Augsburg • GERMANY Indo-French Center for the Promotion Of Advanced Research Alexander von Humboldt foundation DST

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