Quantum spin glasses and quantum transitions in disordered systems

A large number of disordered transition metal and intermetallic compounds freeze into spin glass states at low temperatures: the frustrating RKKY interactions between the local moments on the d or f orbitals lead to a large number of metastable low energy ground states with a random polarization of spin. However, it is often possible to increase quantum fluctuations of the spins and destroy the average moment on every site: this can be done by applying a magnetic field transverse to the crystalline axis along which the spins prefer to align, or by making the Kondo screening of spins more effective by increasing the Fermi level density of states of the itinerant electrons. The papers below describe theories for such quantum transitions. It is necessary to distinguish transitions in insulators with Ising (papers 2, 4, 6) or Heisenberg (papers 1, 10, 11) spin symmetry, and in metals (papers 5 and 9).

Experimental studies of relevance to the theories described below are in W. Wu et al., Physical Review Letters 71, 1919 (1993), Y. Tabata et al., Physical Review Letters 86, 524 (2001), C. Urano et al., Physical Review Letters 85, 1052 (2000), and D. E. MacLaughlin et al., Physical Review Letters 87, 066402 (2001).

PAPERS

  1. Gapless spin-fluid ground state in a random quantum Heisenberg magnet, S. Sachdev and J. Ye, Physical Review Letters 70, 3339 (1993); cond-mat/9212030
  2. A solvable spin glass of quantum rotors, J. Ye, S. Sachdev, and N. Read, Physical Review Letters 70, 4011 (1993); cond-mat/9212027.
  3. Spin glasses enter the quantum regime, S. Sachdev, Physics World 7, No. 10, 25 (October 1994).
  4. Landau theory of quantum spin glasses of rotors and Ising spins, N. Read, S. Sachdev, and J. Ye, Physical Review B 52, 384 (1995); cond-mat/9412032.
  5. Quantum field theory of metallic spin glasses, S. Sachdev, N. Read, and R. Oppermann, Physical Review B 52, 10286 (1995); cond-mat/9504036.
  6. Landau theory of quantum spin glasses of rotors and Ising spins, N. Read and S. Sachdev, Nuclear Physics B -- Proceedings Supplements, 45A, 38 (1996).
  7. Metallic spin glasses, S. Sachdev and N. Read, Journal of Physics: Condensed Matter 8, 9723 (1996); cond-mat/9609153.
  8. Higher dimensional realizations of activated dynamic scaling at random quantum transitions, T. Senthil and S. Sachdev, Physical Review Letters 77, 5292 (1996); cond-mat/9609030.
  9. Magnetic properties of strongly disordered electronic systems, S. Sachdev, Royal Society Discussion Meeting on The Metal-Non Metal Transition in Macroscopic and Microscopic Systems, Philosophical Transactions of the Royal Society of London, Series A 356, 173 (1998); cond-mat/9705074.
  10. Mean field theory of a quantum Heisenberg spin glass, A. Georges, O. Parcollet, and S. Sachdev, Physical Review Letters 85, 840 (2000); cond-mat/9909239.
  11. Quantum fluctuations of a nearly critical Heisenberg spin glass, A. Georges, O. Parcollet, and S. Sachdev, Physical Review B 63, 134406 (2001); cond-mat/0009388.
  12. Quantum spin glass transition in the two dimensional electron gas, S. Sachdev, Pramana 58, 285 (2002); cond-mat/0109309.
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