Strong electronic interactions can drive a system into a state with a symmetry breaking. Lattice frustration or competing interactions tend to prevent symmetry breaking, leading to quantum disordered phases. In spin systems frustration can produce a spin liquid state. Frustration of a charge degree of freedom also can result in various exotic states, however, experimental data on these effects is scarce. In this work we demonstrate how in a Mott insulator on a weakly anisotropic triangular lattice a charge ordered state melts on cooling down to low temperatures. Raman scattering spectroscopy finds that
Intrinsic local symmetry-breaking in nominally cubic paraelectric BaTiO3
Whereas low-temperature ferroelectrics have a well-understood ordered spatial dipole arrangement, the fate of these dipoles in paraelectric phases remains poorly understood. Using density functional theory (DFT), we find that unlike the case in conventional non-polar ABO3 compounds illustrated here for cubic BaZrO3, the origin of the distribution of the B site off-centering in cubic paraelectric such as BaTiO3 is an intrinsic, energy stabilizing symmetry breaking. Minimizing the internal energy E of a constrained cubic phase already reveals the formation of a distribution of intrinsic local displacements that (i) mimic the symmetries of the low-temperature phases, while (ii) being the precursors of what finite temperature DFT Molecular Dynamics finds as thermal motifs. The implications of such symmetry breaking on the microscopic structures and anomalous properties in these kinds of PE materials are discussed.
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- Award ID(s):
- 1921949
- NSF-PAR ID:
- 10311424
- Date Published:
- Journal Name:
- ArXivorg
- ISSN:
- 2331-8422
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract $$\kappa$$ $${}_{2}$$ $${}_{2}$$ $$T=30\,{\mathrm{K}}$$ $$T=15\,{\mathrm{K}}$$ -
Density functional theory (DFT) prescribes the existence of a ground-state configuration at 0 K for a given system. However, the ground-state configuration alone is insufficient to describe a phase at finite temperatures as symmetry-breaking non-ground-state configurations are excited statistically at temperatures above 0 K. Our multiscale entropy approach, Zentropy, postulates that the entropy of a phase is composed of the sum of the entropy of each configuration weighted by its probability plus the configurational entropy among all configurations. Consequently, the partition function of each configuration in statistical mechanics needs to be evaluated by its free energy rather than total energy. The combination of the ground-state and symmetry-breaking non-ground-state configurations represents the building blocks of materials and can be used to quantitatively predict free energy of individual phases with the free energy of each configuration predicted from DFT as well as all properties derived from free energy of individual phases.more » « less
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