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DR Grempel

Publications and source records attributed to DR Grempel.

12 recordsLinked to original sources
PubMed2000

From second to first order transitions in a disordered quantum magnet

We study the spin-glass transition in a disordered quantum model. In a region of the phase diagram quantum effects are small and the phase transition is second order, as in the classical case. In another region, quantum fluctuations drive the transition to first order. Across the first order line the susceptibility is discontinuous and shows hysteresis. Our findings qualitatively reproduce observations on LiHoxY1-xF4. We also discuss a marginally stable spin-glass state and derive some results previously obtained from the real-time dynamics of the model coupled to a bath.

Journal Article↗
PubMed2000

Coherence scale of the kondo lattice

It is shown that the large- N approach yields two energy scales for the Kondo lattice model. The single-impurity Kondo temperature, T(K), signals the onset of local singlet formation, while Fermi-liquid coherence sets in only below a lower scale, T small star, filled. At low conduction electron density n(c) ("exhaustion" limit), the ratio T small star, filled/T(K) is much smaller than unity, and is shown to depend only on n(c) and not on the Kondo coupling. The physical meaning of these two scales is demonstrated by computing several quantities as a function of n(c) and temperature.

Journal Article↗