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Exploring Spin Liquids and Exotic Spin Systems in Condensed Matter Physics

This study investigates the properties of spin liquids and exotic spin systems, focusing on compounds such as (Ba,Sr)2Cu(PO4)2 and BiCu2PO6. Traditional metallic and magnetic systems have well-established theories and characterizations. However, the interplay between quantum critical points, magnetic impurities, and carrier doping in isolated S=½ systems remain crucial for understanding high-Tc superconductivity. The research also explores specific heat measurements and phase transitions caused by doping, contributing to the broader understanding of coupled spin ladders and their potential metallic behavior.

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Exploring Spin Liquids and Exotic Spin Systems in Condensed Matter Physics

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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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