| 1. |
- Isakov, S V, et al.
(författare)
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Interplay of quantum and thermal fluctuations in a frustrated magnet
- 2003
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Ingår i: Physical Review B. - : American Physical Society. - 1098-0121. ; 68:10, s. 104409-
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate the presence of an extended critical phase in the transverse field Ising magnet on the triangular lattice, in a regime where both thermal and quantum fluctuations are important. We map out a complete phase diagram by means of quantum Monte Carlo simulations, and find that the critical phase is the result of thermal fluctuations destabilising an order established by the quantum fluctuations. It is separated by two Kosterlitz-Thouless transitions from the paramagnet on one hand and the quantum-fluctuation driven three-sublattice ordered phase on the other. Our work provides further evidence that the zero temperature quantum phase transition is in the three-dimensional XY universality class.
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| 2. |
- Isakov, S V, et al.
(författare)
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Magnetization process of spin ice in a [111] magnetic field
- 2004
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Ingår i: Physical Review B. - : American Physical Society. - 1550-235X. ; 70:10, s. 104418-
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Tidskriftsartikel (refereegranskat)abstract
- Spin ice in a magnetic field in the [111] direction displays two magnetization plateaus: one at saturation and an intermediate one with finite entropy. We study the crossovers between the different regimes from a point of view of (entropically) interacting defects. We develop an analytical theory for the nearest-neighbor spin ice model, which covers most of the magnetization curve. We find that the entropy is nonmonotonic, exhibiting a giant spike between the two plateaus. This regime is described by a monomer-dimer model with tunable fugacities. At low fields, we develop an RG treatment for the extended string defects, and we compare our results to extensive Monte Carlo simulations. We address the implications of our results for cooling by adiabatic (de)magnetization.
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| 3. |
- Wang, X., et al.
(författare)
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Weak first-order quantum phase transition in the spin-tetrahedron system Cu(2)Te(2)O(5)Br(2) without lattice contributions
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 83:13, s. 134403-
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Tidskriftsartikel (refereegranskat)abstract
- Under pressure the spin tetrahedron system Cu(2)Te(2)O(5)Br(2) shows a softening of the collective magnetic mode whereas the energy of local spin-exchange processes increases. This apparent contradiction is due to the system's proximity to a quantum critical point induced by competing interactions that effectively decouple the tetrahedra. The high-pressure state is therefore nonmagnetic and dominated by valence bond excitations. Anomalies in the frequency and the intensity of magnetic Raman scattering are evidence for a weakly discontinuous evolution of the quantum critical state. In contrast, structural parameters as well as optical phonon modes evolve continuously with pressure without any sign for discontinuous criticality. No new low-energy excitations are observed. In contrast, the expected fingerprints of the spin-liquid phase are broadened due to Dzyaloshinskii-Moriya interactions.
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