Electronic Structures and Magnetic Order of Ordered-Fe-Vacancy Ternary Iron Selenides TlFe 1.5 Se 2 and A Fe 1.5 Se 2 ( A = K , Rb, or Cs)Yan, Xun-Wang ; Gao, Miao ; Lu, Zhong-Yi ; Xiang, Tao
doi: 10.1103/PhysRevLett.106.087005pmid: 21405594
By the first-principles electronic structure calculations, we find that the ground state of the Fe-vacancies ordered TlFe 1.5 Se 2 is a quasi-two-dimensional collinear antiferromagnetic semiconductor with an energy gap of 94 meV, in agreement with experimental measurements. This antiferromagnetic order is driven by the Se-bridged antiferromagnetic superexchange interactions between Fe moments. Similarly, we find that crystals A Fe 1.5 Se 2 ( A = K , Rb, or Cs) are also antiferromagnetic semiconductors but with a zero-gap semiconducting state or semimetallic state nearly degenerated with the ground states. Thus, rich physical properties and phase diagrams are expected.
Site-Specific Recoil Diffraction of Backscattered Electrons in CrystalsWinkelmann, Aimo
doi: 10.1103/PhysRevLett.106.085503pmid: 21405583
A novel diffraction effect in high-energy electron backscattering is demonstrated: the formation of element-specific diffraction patterns via nuclear recoil. For sapphire ( Al 2 O 3 ), the difference in recoil energy allows us to determine if an electron scattered from aluminum or from oxygen. The angular electron distribution obtained in such measurements is a strong function of the recoiling lattice site. These element-specific recoil diffraction features are explained using the dynamical theory of electron diffraction. Our observations open up new possibilities for local, element-resolved crystallographic analysis using quasielastically backscattered electrons in scanning electron microscopy.
Reentrant Phase Diagram of Network FluidsRusso, J; Tavares, J. M; Teixeira, P. I; Telo da Gama, M. M; Sciortino, F. M
doi: 10.1103/PhysRevLett.106.085703pmid: 21405587
We introduce a microscopic model for particles with dissimilar patches which displays an unconventional “pinched” phase diagram, similar to the one predicted by Tlusty and Safran in the context of dipolar fluids Science 290 , 1328 ( 2000 ) SCIEAS 0036-8075 10.1126/science.290.5495.1328 . The model—based on two types of patch interactions, which account, respectively, for chaining and branching of the self-assembled networks—is studied both numerically via Monte Carlo simulations and theoretically via first-order perturbation theory. The dense phase is rich in junctions, while the less-dense phase is rich in chain ends. The model provides a reference system for a deep understanding of the competition between condensation and self-assembly into equilibrium-polymer chains.
Hybridization Wave as the “Hidden Order” in URu 2 Si 2Dubi, Yonatan ; Balatsky, Alexander V
doi: 10.1103/PhysRevLett.106.086401pmid: 21405588
A phenomenological model for the “hidden order” transition in the heavy-Fermion material URu 2 Si 2 is introduced. The hidden order is identified as an incommensurate, momentum-carrying hybridization between the light hole band and the heavy electron band. This modulated hybridization appears after a Fano hybridization at higher temperatures takes place. We focus on the hybridization wave as the order parameter in URu 2 Si 2 and possibly other materials with similar band structures. The model is qualitatively consistent with numerous experimental results obtained from, e.g., neutron scattering and scanning tunneling microscopy. Specifically, we find a gaplike feature in the density of states and the appearance of features at an incommensurate vector Q * ∼ 0.6 π / a 0 . Finally, the model allows us to make various predictions which are amenable to current experiments.
Soliton Blueshift in Tapered Photonic Crystal FibersStark, S. P; Podlipensky, A. P; Russell, P. St. J
doi: 10.1103/PhysRevLett.106.083903pmid: 21405574
We show that solitons undergo a strong blueshift in fibers with a dispersion landscape that varies along the direction of propagation. The experiments are based on a small-core photonic crystal fiber, tapered to have a core diameter that varies continuously along its length, resulting in a zero-dispersion wavelength that moves from 731 nm to 640 nm over the transition. The central wavelength of a soliton translates over 400 nm towards a shorter wavelength. This is accompanied by strong emission of radiation into the UV and IR spectral regions. The experimental results are confirmed by numerical simulation.
Phonon Emission Induced Dynamic Fracture PhenomenaAtrash, F; Hashibon, A; Gumbsch, P; Sherman, D
doi: 10.1103/PhysRevLett.106.085502pmid: 21405582
We use molecular dynamics simulations to calculate the phonon energy emitted during rapid crack propagation in brittle crystals. We show that this energy is different for different crack planes and propagation directions and that it is responsible for various phenomena at several length scales: energetically preferred crack systems and crack deflection at the atomic scale, reduced maximum crack speed with volume at the micrometer scale, and the inability of a crack to attain the theoretical limiting speed at the macroscale. We propose to include the contribution of this energy in the Freund equation of motion of a dynamically propagating crack.
Defect-Induced Magnetism in Neutron Irradiated 6 H -SiC Single CrystalsLiu, Yu ; Wang, Gang ; Wang, Shunchong ; Yang, Jianhui ; Chen, Liang ; Qin, Xiubo ; Song, Bo ; Wang, Baoyi ; Chen, Xiaolong
doi: 10.1103/PhysRevLett.106.087205pmid: 21405599
Defect-induced magnetism is firstly observed in neutron irradiated SiC single crystals. We demonstrated that the intentionally created defects dominated by divacancies ( V Si V C ) are responsible for the observed magnetism. First-principles calculations revealed that defect states favor the formation of local moments and the extended tails of defect wave functions make long-range spin couplings possible. Our results confirm the existence of defect-induced magnetism, implying the possibility of tuning the magnetism of wide band-gap semiconductors by defect engineering.