| 1761. |
- Springell, R., et al.
(författare)
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Elemental engineering : Epitaxial uranium thin films
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:19
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial films of the well-known alpha (orthorhombic) structure and an unusual hcp form of uranium have been grown on Nb and Gd buffers, respectively, by sputtering techniques. In a 5000 A film of alpha-U a charge-density wave has been observed, and its properties are different from those found in the bulk. The 500 A hcp-U film has a c/a ratio of 1.90(1), which is unusually large for the hcp structure. Theoretical calculations show that this hcp form is metastable and predict that it orders magnetically.
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| 1762. |
- Sque, S. J., et al.
(författare)
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Carbon nanotubes and their interaction with the surface of diamond
- 2007
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 75:11
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Tidskriftsartikel (refereegranskat)abstract
- Calculations based on density-functional theory have been used to model armchair carbon nanotubes existing in isolation, close-packed into nanoropes, and lying prone on both the hydrogen-terminated and clean (001) surfaces of diamond. In the combined nanotube:diamond systems, the electronic band structures are indicative of electron transfer from the hydrogen-terminated diamond to the physisorbed nanotubes; that is, carbon nanotubes-like C60-appear to be capable of transfer doping diamond p type. Total-energy comparisons with separated systems suggest that the nanotubes are positively bound to the diamond substrate. Diffusion techniques have been used to model movement of the (7,7) nanotube across the hydrogen-terminated diamond surface, with the results suggesting that this substrate presents a rather smooth energy surface to the nanotube; this is consistent with the fact that no covalent bonding across the interface has been found. For comparison, the same nanotube has been modeled above a completely clean diamond (001) surface, and while the nanotube remains bound to the diamond substrate, there is no charge transfer across such an interface.
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| 1763. |
- Sreejith, Ganesh Jaya, et al.
(författare)
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Critical behavior in the cubic dimer model at nonzero monomer density
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:1, s. 014404-
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Tidskriftsartikel (refereegranskat)abstract
- We study critical behavior in the classical cubic dimer model (CDM) in the presence of a finite density of monomers. With attractive interactions between parallel dimers, the monomer-free CDM exhibits an unconventional transition from a Coulomb phase to a dimer crystal. Monomers act as charges (or monopoles) in the Coulomb phase and, at nonzero density, lead to a standard Landau-type transition. We use large-scale Monte Carlo simulations to study the system in the neighborhood of the critical point, and find results in agreement with detailed predictions of scaling theory. Going beyond previous studies of the transition in the absence of monomers, we explicitly confirm the distinction between conventional and unconventional criticality, and quantitatively demonstrate the crossover between the two. Our results also provide additional evidence for the theoretical claim that the transition in the CDM belongs in the same universality class as the deconfined quantum critical point in the SU(2) JQ model.
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| 1764. |
- Sreejith, Ganesh Jaya, et al.
(författare)
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Tripartite composite fermion states
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:24, s. 245125-
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Tidskriftsartikel (refereegranskat)abstract
- The Read-Rezayi wave function is one of the candidates for the fractional quantum Hall effect at filling fraction nu = 2 + (3/5), and thereby also its hole conjugate at 2 + (2/5). We study a general class of tripartite composite fermion wave functions, which reduce to the Rezayi-Read ground state and quasiholes for appropriate quantum numbers, but also allow a construction of wave functions for quasiparticles and neutral excitations by analogy to the standard composite fermion theory. We present numerical evidence in finite systems that these trial wave functions capture well the low energy physics of a four-body model interaction. We also compare the tripartite composite fermion wave functions with the exact Coulomb eigenstates at 2 + (3/5), and find reasonably good agreement. The ground state as well as several excited states of the four-body interaction are seen to evolve adiabatically into the corresponding Coulomb states for N = 15 particles. These results support the plausibility of the Read-Rezayi proposal for the 2 + (2/5) and 2 + (3/5) fractional quantum Hall effect. However, certain other proposals also remain viable, and further study of excitations and edge states will be necessary for a decisive establishment of the physical mechanism of these fractional quantum Hall states.
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| 1765. |
- Srepusharawoot, Pornjuk, et al.
(författare)
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One-dimensional polymeric carbon structure based on five-membered rings in alkaline earth metal dicarbides BeC2 and MgC2
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:12, s. 125439-
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Tidskriftsartikel (refereegranskat)abstract
- We studied five alkaline earth dicarbide systems MAEC2 (where M-AE = Be-Ba) by using ab initio random structure search. For BeC2 and MgC2, the lowest energy and dynamically stable configuration consists of five-membered carbon rings connected to each other via an individual carbon atom, stabilized through the donation of electrons from the surrounding alkaline earth ions. For CaC2, SrC2, and BaC2, our study shows that the chain crystal structure is more stable than the predicted structure due to strains induced by the increasing size of alkaline earth metal ions. The reaction energies of the typical synthesis pathway are comparable to those calculated for the experimental reaction of the known chain-type structure. Finally, the proposed structure should be optically distinguishable due to a significantly narrower band gap.
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| 1766. |
- Srinivas, V., et al.
(författare)
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Electronic transport properties of high-resistivity icosahedral AlPdRe below 1 K
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:9
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Tidskriftsartikel (refereegranskat)abstract
- The temperature dependence of the conductivity, sigma(T), and the magnetoresistance up to B = 6 T have been studied in the temperature range 0.01 Kless than or equal toTless than or equal to1 K for two differently prepared i-AlPdRe samples on the insulating side of the metal-insulator transition. sigma(T) for both samples was observed to saturate in zero magnetic field below about 20 mK. With increasing magnetic field the temperature dependence of the conductivity increased, and at 6 T, or(T,B = 6 T) was found to decrease linearly with decreasing temperature down to the lowest measurement temperature of 10 mK. The estimated value of the conductivity at T=0 K, sigma(0 K), was found to decrease strongly with increasing resistance ratio R [ = rho(4 K)/rho(295 K)] over a wide range of R values and for differently prepared samples, suggesting that a finite sigma(0,R) is a characteristic property of the icosahedral phase of high-resistivity i-AlPdRe. The magnetoresistance is positive below 1 K. The relation Deltarho(B)/rhosimilar toB(2) is followed at larger fields by a B-2/3 dependence. With decreasing temperature these characteristic field regions are successively depressed towards smaller magnetic fields and eventually become unobservable. A scaling of the magnetoresistance is found for data in the region Tless than or equal to1 K, Bless than or equal to6 T of the form [Deltarho(B)/rho]/T-alpha=f(B/T) for each sample, with alpha about 0.3 for both samples.
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| 1767. |
- St Pierre, T. G., et al.
(författare)
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Apparent magnetic energy-barrier distribution in horse-spleen ferritin : Evidence for multiple interacting magnetic entities per ferrihydrite nanoparticle
- 2002
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 65:2
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic viscosity measurements were made on native horse-spleen ferritin in zero applied magnetic field at temperatures between 21 and 21 K. The data have been used to calculate the apparent magnetic-moment-weighted energy barrier distribution for the sample of ferritin. The distribution is composed of a log-normal distribution plus a second distribution that is well described by an exponential decay of barrier frequency with increasing barrier height. The two distributions contribute approximately equally to the overall distribution. The log-normal distribution has its peak at an energy barrier of approximately 3 x 10(-21) J, while the decay constant for the second distribution has a value of approximately 2 x 10(-21) J. The existence of the low-energy barrier distribution with exponentially decaying shape in conjunction with the observation of shifted field-cooled magnetic hysteresis loops is interpreted as strong evidence for the existence of multiple interacting magnetic entities within each ferritin particle.
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| 1768. |
- Stanciu, V., et al.
(författare)
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Influence of annealing parameters on the ferromagnetic properties of optimally passivated (Ga,Mn)As epilayers
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:12
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Tidskriftsartikel (refereegranskat)abstract
- The influence of annealing parameters—temperature (Ta) and time (ta)—on the magnetic properties of As-capped (Ga,Mn)As epitaxial thin films has been investigated. The dependence of the transition temperature (TC) on ta marks out two regions. The TC peak behavior, characteristic of the first region, is more pronounced for thick samples, while for the second ("saturated") region the effect of ta is more pronounced for thin samples. A right choice of the passivation medium, growth conditions along with optimal annealing parameters routinely yield TC-values of ~150 K and above, regardless of the thickness of the epilayers
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| 1769. |
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| 1770. |
- Starikov, Anton, et al.
(författare)
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Scenario for the 0.7-conductance anomaly in quantum point contacts
- 2003
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:23
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Tidskriftsartikel (refereegranskat)abstract
- Effects of spontaneous spin polarization in quantum point contacts (QPC's) are investigated for a realistic semiconductor device structure using the Kohn-Sham local spin-density formalism. At maximal polarization in the contact area, there is a bifurcation into ground-state and metastable solutions. The conduction associated with the metastability is lower than for the normal state. With increasing temperature, the conductance should therefore show an anomalous behavior as observed. For the present device we do not recover resonance or quasibound states.
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