Ahmet Nihat Berker

Berker, Ahmet Nihat

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https://hdl.handle.net/20.500.12469/6148

Name Variants

Nihat Berker A.
BERKER, Ahmet Nihat
Ahmet Nihat, Berker
Berker,Ahmet Nihat
Berker, AHMET NIHAT
A. Berker
B.,Ahmet Nihat
Berker,A.N.
Berker, A.
Berker, Ahmet Nihat
Berker N.
Ahmet Nihat Berker
Ahmet Nihat BERKER
Berker, A. N.
B., Ahmet Nihat
AHMET NIHAT BERKER
A. N. Berker
BERKER, AHMET NIHAT
Berker A.
Berker, A. Nihat

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Prof. Dr.

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[email protected]

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Electrical-Electronics Engineering

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Current Staff

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15

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6

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17

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11

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3

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2

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Documents

160

Citations

6800

h-index

42

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Documents

136

Citations

6632

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Scholarly Output

32

Articles

32

Views / Downloads

9/0

Supervised MSc Theses

0

Supervised PhD Theses

0

WoS Citation Count

124

Scopus Citation Count

130

WoS h-index

7

Scopus h-index

7

Patents

0

Projects

0

WoS Citations per Publication

3.88

Scopus Citations per Publication

4.06

Open Access Source

24

Supervised Theses

0

Journal	Count
Physical Review E	17
Physica A: Statistical Mechanics and its Applications	4
Physica A-Statistical Mechanics and Its Applications	3
Chaos Solitons & Fractals	2
Turkish Journal of Biology	1

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Scholarly Output Search Results

Now showing 1 - 10 of 32

Metastable Potts droplets
(AMER PHYSICAL SOC, 2021) Artun, E. Can; Berker, A. Nihat
The existence and limits of metastable droplets have been calculated using finite-system renormalization-group theory, for q-state Potts models in spatial dimension d = 3. The dependence of the droplet critical sizes on magnetic field, temperature, and number of Potts states q has been calculated. The same method has also been used for the calculation of hysteresis loops across first-order phase transitions in these systems. The hysteresis loop sizes and shapes have been deduced as a function of magnetic field, temperature, and number of Potts states q. The uneven appearance of asymmetry in the hysteresis loop branches has been noted. The method can be extended to criticality and phase transitions in metastable phases, such as in surface-adsorbed systems and water.
Merged Potts-Clock Model: Algebraic and Conventional Multistructured Multicritical Orderings in Two and Three Dimensions
(Amer Physical Soc, 2023) Artun, E. Can; Berker, A. Nihat
A spin system is studied with simultaneous permutation-symmetric Potts and spin-rotation-symmetric clock interactions in spatial dimensions d = 2 and 3. The global phase diagram is calculated from the renormalization-group solution with the recently improved (spontaneous first-order detecting) Migdal-Kadanoff approximation or, equivalently, with hierarchical lattices with the inclusion of effective vacancies. Five different ordered phases are found: Conventionally ordered ferromagnetic, quadrupolar, antiferromagnetic phases and algebraically ordered antiferromagnetic, antiquadrupolar phases. These five different ordered phases and the disordered phase are mutually bounded by first-and second-order phase transitions, themselves delimited by multicritical points: Inverted bicritical, zero-temperature bicritical, tricritical, second-order bifurcation, and zero-temperature highly degenerate multicritical points. One rich phase diagram topology exhibits all of these phenomena.
Citation - WoS: 2
Citation - Scopus: 2
Maximally Random Discrete-Spin Systems With Symmetric and Asymmetric Interactions and Maximally Degenerate Ordering
(Amer Physical Soc., 2018) Atalay, Bora; Berker, A. Nihat
Discrete-spin systems with maximally random nearest-neighbor interactions that can be symmetric or asymmetric ferromagnetic or antiferromagnetic including off-diagonal disorder are studied for the number of states q = 34 in d dimensions. We use renormalization-group theory that is exact for hierarchical lattices and approximate (Migdal-Kadanoff) for hypercubic lattices. For all d > 1 and all nonmfimte temperatures the system eventually renormalizes to a random single state thus signaling q x q degenerate ordering. Note that this is the 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 is calculated for all temperatures behaves similarly for ferromagnetic and antiferromagnetic interactions and shows a derivative maximum at the short-range disordering temperature. With a sharp immediate contrast of infinitesimally higher dimension 1 + epsilon the system is as expected disordered at all temperatures for d = 1.
Axial, planar-diagonal, body-diagonal fields on the cubic-spin spin glass in d=3: A plethora of ordered phases under finite fields
(Amer Physical Soc, 2024) Artun, E. Can; Sarman, Deniz; Berker, A. Nihat
A nematic phase, previously seen in the d = 3 classical Heisenberg spin-glass system, occurs in the n-component cubic-spin spin-glass system, between the low-temperature spin-glass phase and the hightemperature disordered phase, for number of spin components n >= 3, in spatial dimension d = 3, thus constituting a liquid-crystal phase in a dirty (quenched-disordered) magnet. Furthermore, under application of a variety of uniform magnetic fields, a veritable plethora of phases is found. Under uniform magnetic fields, 17 different phases and two spin-glass phase diagram topologies (meaning the occurrences and relative positions of the many phases), qualitatively different from the conventional spin-glass phase diagram topology, are seen. The chaotic rescaling behaviors and their Lyapunov exponents are calculated in each of these spin-glass phase diagram topologies. These results are obtained from renormalization-group calculations that are exact on the d = 3 hierarchical lattice and, equivalently, approximate on the cubic spatial lattice. Axial, planar-diagonal, or body-diagonal finite-strength uniform fields are applied to n = 2 and 3 component cubic-spin spin-glass systems in d=3.
Citation - WoS: 5
Citation - Scopus: 5
Driven and Non-Driven Surface Chaos in Spin-Glass Sponges
(Pergamon-elsevier Science Ltd, 2023) Pektas, Yigit Ertac; Artun, E. Can; Berker, A. Nihat
A spin-glass system with a smooth or fractal outer surface is studied by renormalization-group theory, in bulk spatial dimension d = 3. Independently varying the surface and bulk random-interaction strengths, phase diagrams are calculated. The smooth surface does not have spin-glass ordering in the absence of bulk spin-glass ordering and always has spin-glass ordering when the bulk is spin-glass ordered. With fractal (d > 2) surfaces, a sponge is obtained and has surface spin-glass ordering also in the absence of bulk spin-glass ordering. The phase diagram has the only-surface-spin-glass ordered phase, the bulk and surface spin-glass ordered phase, and the disordered phase, and a special multicritical point where these three phases meet. All spin-glass phases have distinct chaotic renormalization-group trajectories, with distinct Lyapunov and runaway exponents which we have calculated.
Citation - WoS: 2
Citation - Scopus: 2
6-Point Tripled Ashkin-Teller Global Phase Diagrams in Two and Three Dimensions
(Elsevier, 2025) Zeynioglu, Deniz Ipek; Berker, A. Nihat
The tripled Ashkin-Teller model including 6-point interactions is solved in d = 2 and 3 by renormalization-group theory that is exact on the hierarchical lattice and approximate on the recently first/second-order-transition improved Migdal-Kadanoff procedure. Five different ordered phases occur in the dimensionally distinct global phase diagrams. 16 different phase diagram cross-sections in the 2-point and 4-point interaction space are obtained, with first-and second-order phase transitions, multiple tricritical points and critical endpoints.
Citation - WoS: 2
Citation - Scopus: 6
Global Ashkin-Teller Phase Diagrams in Two and Three Dimensions: Multicritical Bifurcation Versus Double Tricriticality-Endpoint
(Elsevier, 2023) Kecoglu, Ibrahim; Berker, A. Nihat
The global phase diagrams of the Ashkin-Teller model are calculated in d = 2 and 3 by renormalization-group theory that is exact on the hierarchical lattice and approximate on the recently improved Migdal-Kadanoff procedure. Three different ordered phases occur in the dimensionally distinct phase diagrams that reflect three-fold order-parameter permutation symmetry, a closed symmetry line, and a quasi-disorder line. First- and second-order phase boundaries are obtained. In d = 2, second-order phase transitions meeting at a bifurcation point are seen. In d = 3, first- and second-order phase transitions are separated by tricritical and critical endpoints.
Citation - WoS: 13
Citation - Scopus: 12
Phase Transitions Between Different Spin-Glass Phases and Between Different Chaoses in Quenched Random Chiral Systems
(Amer Physical Soc., 2017) Çağlar, Tolga; Berker, A. Nihat
The left-right chiral and ferromagnetic-antiferromagnetic double-spin-glass clock model with the crucially even number of states q = 4 and in three dimensions d = 3 has been studied by renormalization-group theory. We find for the first time to our knowledge four spin-glass phases including conventional chiral and quadrupolar spin-glass phases and phase transitions between spin-glass phases. The chaoses in the different spin-glass phases and in the phase transitions of the spin-glass phases with the other spin-glass phases with the non-spin-glass ordered phases and with the disordered phase are determined and quantified by Lyapunov exponents. It is seen that the chiral spin-glass phase is the most chaotic spin-glass phase. The calculated phase diagram is also otherwise very rich including regular and temperature-inverted devil's staircases and reentrances.
XY-Ashkin Phase Diagram in D=3
(Elsevier, 2025) Turkoglu, Alpar; Berker, A. Nihat
The phase diagram of the Ashkin-Tellerized XY model in spatial dimension d = 3 is calculated by renormalization-group theory. In this system, each site has two spins, each spin being an XY spin, that is having orientation continuously varying in 2 pi radians. Nearest-neighbor sites are coupled by two-spin and four-spin interactions. The phase diagram has ordered phases that are ferromagnetic and antiferromagnetic in each of the spins, and phases that are ferromagnetic and antiferromagnetic in the multiplicative spin variable. The phase diagram distinctively exhibits a pair of symmetrically situated direct bifurcation points and a pair of symmetrically situated reverse bifurcation points of the phase boundaries. The renormalization-group flows are in terms of the doubly composite Fourier coefficients of the exponentiated energy of nearest-neighbor spins.
Citation - WoS: 3
Citation - Scopus: 3
Renormalization-Group Theory of the Heisenberg Model in D Dimensions
(Elsevier, 2022) Tunca, Egemen; Berker, A. Nihat
The classical Heisenberg model has been solved in spatial d dimensions, exactly in d = 1 and by the Migdal-Kadanoff approximation in d > 1, by using a Fourier-Legendre expansion. The phase transition temperatures, the energy densities, and the specific heats are calculated in arbitrary dimension d. Fisher's exact result is recovered in d = 1. The absence of an ordered phase, conventional or algebraic (in contrast to the XY model yielding an algebraically ordered phase) is recovered in d = 2. A conventionally ordered phase occurs at d > 2. This method opens the way to complex-system calculations with Heisenberg local degrees of freedom.(c) 2022 Elsevier B.V. All rights reserved.

Berker, Ahmet Nihat

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6

CLEAN WATER AND SANITATION

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INDUSTRY, INNOVATION AND INFRASTRUCTURE

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17

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GOOD HEALTH AND WELL-BEING