Related papers: Generalized Cubic Model for BaTiO$_3$-like Ferroel…
We present a group theoretic analysis of several classes of organic superconductors. We argue that highly frustrated half-filled layered organic superconductors, such as kappa-(ET)_2Cu2(CN)_3 (where ET is BEDT-TTF) and…
We performed first principles calculations for epitaxially strained orthorhombic CaTiO$_3$. The computational results reveal the existence of a metastable ferroelectric phase at compressive strain with unexpected in-plane polarization.…
A model that merges the Potts, cubic, and clock models is studied in spatial dimension d=3 by renormalization-group theory. Effective vacancies are included in the renormalization-group initial conditions. In the global phase diagram, 5…
We studied structural, electronic and magnetic properties of a cubic perovskite BaFeO$_{3-\delta}$ ($0 \le \delta \le 0.5$) within the density functional theory using a generalized gradient approximation and a GGA+U method. According to our…
A four-state model is proposed for description of the sequence of phase transitions in ferroelectric crystals of DMAGaS and DMAAlS type. The ordering processes in the subsystems of DMA groups are considered as a main reason of such…
Proximity to phase transitions (PTs) is frequently responsible for the largest dielectric susceptibilities in ferroelectrics. The impracticality of using temperature as a control parameter to reach those large responses has motivated the…
We discuss the results of a study of restricted solid-on-solid models for fcc (110) surfaces. These models are simple modifications of the exactly solvable BCSOS model, and are able to describe a $(2\times 1)$ missing-row reconstructed…
Pure SrTiO3 in bulk form is known to be an incipient ferroelectric where the quantum fluctuations of lattice positions prevent long range ferroelectric ordering at a finite temperature. We show evidence and identify the origin of…
The structural transformation of multiferroic EuTiO$_3$ has been intensively investigated by synchrotron x-ray diffraction at pressures up to 50.3 GPa and temperatures from 50 to 500 K. An antiferrodistortive phase transition from cubic…
The three-state Potts model with antiferromagnetic nearest-neighbor (n.n.) and ferromagnetic next-nearest-neighbor (n.n.n) interaction is investigated within a mean-field theory. We find that the phase-diagram contains two kind of ordered…
A method for evaluating the piezoelectric response of unpoled ferroelectric ceramics from elastic and dielectric measurements is proposed and tested on BaTiO$_3$. The method is based on the observation that the softening in a ferroelectric…
Molecular-dynamics simulations of KNbO$_3$ reveal preformed dynamic chain-like structures, present even in the paraelectric phase, that are related to the softening of phonon branches over large regions of the Brillouin zone. The phase…
In this special issue of Physica A in memory of Professor Dietrich Stauffer, I first recall my impression on him while being his postdoc for a year at HLRZ. In the following scientific part, I discuss the theory of soft phonons with quartic…
Using ab initio calculations, we have investigated a cubic perovskite BaOsO3 and a few related compounds that have been synthesized recently and formally have a metallic d^4 configuration. In BaOsO3, which shows obvious 3-dimensional…
For the past decades, the low-temperature phase of Ca$_3$Ru$_2$O$_7$ below the 48K first-order phase transition remains a puzzle with controversial suggestions involving metallic ferroelectric, orbital or magnetic ordering. Through analysis…
A complete mapping in the Brillouin zone of the structural instability associated with the ferroelectric phase transitions of KNbO$_3$ has been obtained by first-principles calculations using an LAPW linear response approach. The wavevector…
We propose the Landau model for lock-in phase transitions in uniaxially modulated improper ferroelectric incommensurate-commensurate systems of class I. It includes Umklapp terms of third and fourth order and secondary order parameter…
Liquid crystal materials exhibiting up to three nematic phases are reported. Dielectric response measurements show that while the lower temperature nematic phase has ferroelectric order and the highest temperature nematic phase is apolar,…
By mapping the hamiltonian of the spin one ferromagnet onto that of the classical spherical model we investigate the possible phase transitions and the phase diagram of the spin one ferromagnet. Similarly to what happens in the spherical…
We report a molecular dynamics study of ab initio quality of the ferroelectric phase transition in crystalline PbTiO3. We model anharmonicity accurately in terms of potential energy and polarization surfaces trained on density functional…