Browsing by Subject "Order parameters"

Now showing 1 - 3 of 3

Open Access
Columnar antiferromagnetic order of a MBene monolayer
(American Physical Society, 2021-04-16) Ozdemir, I.; Kadioglu, Y.; Yüksel, Y.; Akıncı, Ü.; Üzengi Aktürk, O.; Aktürk, E.; Çıracı, Salim
First-principles density functional theory, combined with the Monte Carlo method, predicts that the Fe2B2 monolayer of the MBene family has a stable columnar antiferromagnetic (AFM) ground state. Below the critical temperature, Tc=115 K in equilibrium, the spins rotate by the same amount in every other column of Fe atoms, but they retain the same direction in the same column. Under applied tensile strains, Tc and the order parameter can increase nonmonotonically. The onset of the columnar order can result in a transition from two dimension (2D) to 1D in magnetic, electronic, and conduction properties. The ordered magnetic state itself can be tuned by external magnetic field, whereby the columnar magnetic order changes to ferromagnetic order with a double hysteresis behavior. When terminated by Fluorine atoms, the columnar order changes to the AFM order with Tc rising above room temperature. This situation is rather unusual and insofar is fundamental for a realistic, strictly 2D monolayer and can have critical consequences in spin conduction.
Open Access
Phase transitions and renormalization-group theory
(1989-07) Berker, A. Nihat
The study of critical phenomena targets the qualitatively new phenomena that occur through the interactions of very large numbers of degrees of freedom. Such situations are typically realized near the onset of the transition between two thermodynamic phases. The special challenge of this field is thus due to the truly many-body nature of its subject. Another motivating challenge of the field has been the feasibility of immediate comparisons between the outcomes of sophisticated experiments and sophisticated theories, especially in condensed matter systems. Adding to this the wide variety of experimental and theoretical methods, it is seen that many cultures meet and exchange under the aegis of critical phenomena and phase transitions, contributing to the dynamism and intellectual enrichment of the field.
Open Access
Quantum phase transitions from analysis of the polarization amplitude
(American Physical Society, 2019) Hetenyi, Balazs; Dora, B.
In the modern theory of polarization, polarization itself is given by a geometric phase. In calculations for interacting systems the polarization and its variance are obtained from the polarization amplitude. We interpret this quantity as a discretized characteristic function and derive formulas for its cumulants and moments. In the case of a noninteracting system, our scheme leads to the gauge-invariant cumulants known from polarization theory. We study the behavior of such cumulants for several interacting models. In a one-dimensional system of spinless fermions with nearest neighbor interaction the transition at which gap closure occurs can be clearly identified from the finite size scaling exponent of the variance. When next nearest neighbor interactions are turned on a model with a richer phase diagram emerges, but the finite size scaling exponent is still an effective way to identify the localization transition.