Maximally random systems, maximally degenerate ordering, and lower lower-critical spin-glass dimension

Atalay, Bora (2018) Maximally random systems, maximally degenerate ordering, and lower lower-critical spin-glass dimension. [Thesis]

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Discrete-spin systems with maximally random nearest-neighbor interactions that is symmetric or asymmetric, ferromagnetic or antiferromagnetic, including off-diagonal disorder, are studied, for q=3,4 states in d dimensions. Using renormalization-group theory, for all d≥1 and all noninfinite temperatures, the system eventually renormalizes to a random single state, thus signaling q×q degenerate ordering, which is maximally degenerate ordering. For high-temperature initial conditions, the system crosses over to this highly degenerate ordering only after spending many renormalization-group iterations near the disordered (infinite-temperature) fixed point. Thus, a temperature range of short-range disorder in the presence of long-range order is identified, as previously seen in underfrustrated Ising spin-glass systems. The entropy behaves similarly for ferromagnetic and antiferromagnetic interactions, and shows a derivative maximum at the short-range disordering temperature. As expected, the system is disordered at all temperatures for d=1 . By quenched-randomly mixing local units of different spatial dimensionalities, we also have studied Ising spin-glass systems on hierarchical lattices continuously in dimensionalities 1≤d≤3. The global phase diagram in temperature, antiferromagnetic bond concentration, and spatial dimensionality is calculated. We found, the spin-glass phase disappears to zero temperature at the lower-critical dimension d c=2.431. This sets an upper limit to the lower-critical dimension in general for the Ising spin-glass phase. As dimension is lowered towards dc, the spin-glass critical temperature continuously goes to zero, but the spin-glass chaos fully sustains to the brink of the disappearance of the spin-glass phase. The Lyapunov exponent, measuring the strength of chaos, is thus largely unaffected by the approach to dc and shows a discontinuity to zero at dc
Item Type: Thesis
Uncontrolled Keywords: Renormalization-group theory. -- Quenched random systems. -- Maximal randomness. -- Maximal degeneracy. -- Mixed-spatial dimensions. -- Lower-critical dimension. -- Renormalizasyon-grup teorisi. -- Donmuş rastgele sistemler. -- Azami rastgelelilik. -- Azami yozluk. -- Birleştirilmiş uzamsal boyutlar. -- Altkritik boyut.
Subjects: Q Science > QC Physics
Divisions: Faculty of Engineering and Natural Sciences > Basic Sciences > Physics
Faculty of Engineering and Natural Sciences
Depositing User: IC-Cataloging
Date Deposited: 10 Oct 2018 21:44
Last Modified: 26 Apr 2022 10:26

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