Spin liquids in condensed matter

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Spin liquids in condensed matter

• A.V.Mahajan
• Physics Dept
• IIT Bombay

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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 smallLRO

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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
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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.

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S ½ HAF chains
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(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)
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S ½ 2-LEG LADDER BiCu2PO6
O
Cu
Bi
P
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JL
JR
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D.C.Johnston et al. cond-mat/000147
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(No Transcript)
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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
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J
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Specific heat of BiCu2PO6
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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??
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Zn (S 0) substitution effects in BiCu2PO6
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Specific heat data of Zn doped BiCu2PO6
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Ni (S1) doping effects in BiCu2PO6
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Specific heat of Ni doped BiCu2PO6
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Na doping at Bi3 site in BiCu2PO6
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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

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Collaborators

• B. Koteswararao
• Ramesh Nath

• Sarita Salunke
• Indra Dasgupta

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