Unified continuum approach to crystal surface morphological relaxation

A continuum theory is used to predict scaling laws for the morphological relaxation of crystal surfaces in two independent space dimensions. The goal is to unify previously disconnected experimental observations of decaying surface profiles. The continuum description is derived from the motion of interacting atomic steps. For isotropic diffusion of adatoms across each terrace, induced adatom fluxes transverse and parallel to step edges obey different laws, yielding a tensor mobility for the continuum surface flux. The partial differential equation (PDE) for the height profile expresses an interplay of step energetics and kinetics, and aspect ratio of surface topography that plausibly unifies observations of decaying bidirectional surface corrugations. The PDE reduces to known evolution equations for axisymmetric mounds and one-dimensional periodic corrugations.Comment: 5 pages, 1 figur

Magnetobiostratigraphy of the Spathian to Anisian (Lower to Middle Triassic) Kçira section, Albania

Magnetobiostratigraphic data are presented from three Early/Middle Triassic Han-Bulog Limestone successions from Kçira, northern Albania. A total of 206 standard palaeomagnetic samples were obtained for thermal demagnetization and statisticalanalysis from the 42, 10 and 5m thick sections. The reversal-bearing characteristic component, carried by haematite and magnetite, defines a composite sequence of six main polarity intervals (Kçln to Kç3r) in which are embedded four short polarity intervals, one at the base of Kçln and three towards the top of Kçlr. The early acquisition of the characteristic remanence is supported by the lateral correlation of magnetozones between sections. The Early/Middle Triassic boundary, approximated by the first occurrence of the conodont Chiosella timorensis, falls close to the Kçlr/Kç2n polarity transition. This is in good agreement with recently published magnetobiostratigraphic data from the coeval Chios (Greece) sections. The palaeomagnetic pole calculated from the Kçira characteristic directions lies close to the Triassic portion of the apparent polar wander path for Laurussia (in European coordinates). However, a 40-45" clockwise rotation of the external zone of the Albano-Hellenic Belt to the south of the Scutari-Pec Line is thought to have occurred since the Early-Middle Miocene. The Kçira pole acquires a West Gondwana affinity when restored for the Neogene clockwise rotation. If the clockwise rotation was entirely related to Neogene tectonics, the Kçira area was evidently associated with West Gondwana and located at 12-16"N of the western Tethys margin

Towards a better definition of the Middle Triassic magnetostratigraphy and biostratigraphy in the Tethyan realm

Magnetostratigraphic and biostratigraphic data for the Middle Triassic (Anisian) were obtained from the Han-Bulog facies in the Nderlysaj section from the Albanian Alps and the Dont and Bivera formations in the Dont–Monte Rite composite section from the Dolomites region of northern Italy. The Nderlysaj section is biochronologically bracketed between the late Bithynian and early Illyrian substages (i.e., late-early and early-late Anisian), whereas the Dont–Monte Rite section comprises the late Pelsonian and the early Illyrian substages. The data from Nderlysaj and Dont–Monte Rite, in conjunction with already published data, allow us to construct a nearly complete composite geomagnetic polarity sequence tied to Tethyan ammonoid and conodont biostratigraphy from the late Olenekian (late-Early Triassic) to the late Ladinian (late-Middle Triassic). New conodont data require revision of the published age of the Vlichos section (Greece)

Vibrational And Electronic Excitations In The (ce,la)m In5 (m=co,rh) Heavy-fermion Family

We present a systematic study at ambient pressure of the phononic and electronic Raman-active excitations in the ab plane of the (Ce,La)M In5 (M=Co,Rh) heavy-fermion family. We found that the characteristic Raman spectra of this family of compounds display two phonon modes at ∼38 and ∼165 cm-1 and a broad electronic background centered at ∼40 cm-1. For CeCoIn5, the temperature dependence of these excitations shows anomalous behavior near T* =45 K that may indicate a nontrivial renormalization of the electronic structure driven by strong correlations between hybridized 4f electrons. © 2007 The American Physical Society.754Heffner, R.H., Norman, M.R., (1996) Comments Condens. Matter Phys., 17, p. 361. , CCMPEB 0885-4483Anderson, P.W., (1961) Phys. Rev., 124, p. 41. , PHRVAO 0031-899X 10.1103/PhysRev.124.41Coqblin, B., Schrieffer, J.R., (1969) Phys. Rev., 185, p. 847. , PHRVAO 0031-899X 10.1103/PhysRev.185.847Rajan, V.T., (1983) Phys. Rev. Lett., 51, p. 308. , PRLTAO 0031-9007 10.1103/PhysRevLett.51.308Rossel, C., Yang, K.N., Maple, M.B., Fisk, Z., Zirngiebl, E., Thompson, J.D., (1987) Phys. Rev. B, 35, p. 1914. , See, for example, PRBMDO 0163-1829 10.1103/PhysRevB.35.1914Nakatsuji, S., Pines, D., Fisk, Z., (2004) Phys. Rev. Lett., 92, p. 016401. , PRLTAO 0031-9007 10.1103/PhysRevLett.92.016401Nakatsuji, S., Yeo, S., Balicas, L., Fisk, Z., Schlottmann, P., Pagliuso, P.G., Moreno, N.O., Thompson, J.D., (2002) Phys. Rev. Lett., 89, p. 106402. , PRLTAO 0031-9007 10.1103/PhysRevLett.89.106402Curro, N.J., Sarrao, J.L., Thompson, J.D., Pagliuso, P.G., Kos, Š., Abanov, At., Pines, D., (2003) Phys. Rev. Lett., 90, p. 227202. , PRLTAO 0031-9007 10.1103/PhysRevLett.90.227202Petrovic, C., Movshovich, R., Jaime, M., Pagliuso, P.G., Hundley, M.F., Sarrao, J.L., Fisk, Z., Thompson, J.D., (2001) Europhys. Lett., 53, p. 354. , EULEEJ 0295-5075 10.1209/epl/i2001-00161-8Petrovic, C., Pagliuso, P.G., Hundley, M.F., Movshovich, R., Sarrao, J.L., Fisk, Z., Thompson, J.D., (2001) J. Phys.: Condens. Matter, 13, p. 337. , JCOMEL 0953-8984 10.1088/0953-8984/13/17/103Sidorov, V.A., Nicklas, M., Pagliuso, P.G., Sarrao, J.L., Bang, Y., Balatsky, A.V., Thompson, J.D., (2002) Phys. Rev. Lett., 89, p. 157004. , PRLTAO 0031-9007 10.1103/PhysRevLett.89.157004Bianchi, A., Movshovich, R., Vekhter, I., Pagliuso, P.G., Sarrao, J.L., (2003) Phys. Rev. Lett., 91, p. 257001. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.257001Bianchi, A., Movshovich, R., Capan, C., Pagliuso, P.G., Sarrao, J.L., (2003) Phys. Rev. Lett., 91, p. 187004. , PRLTAO 0031-9007 10.1103/PhysRevLett.91.187004Singley, E.J., Basov, D.N., Bauer, E.D., Maple, M.B., (2002) Phys. Rev. B, 65, p. 161101. , PRBMDO 0163-1829 10.1103/PhysRevB.65.161101Klein, M.V., (1983) Light Scattering in Solids I, 8, p. 147. , edited by M. Cardona, Topics in Applied Physics, Vol. Springer-Verlag, BerlinZawadowski, A., Cardona, M., (1990) Phys. Rev. B, 42, p. 10732. , PRBMDO 0163-1829 10.1103/PhysRevB.42.10732Menéndez, J., Cardona, M., (1984) Phys. Rev. B, 29, p. 2051. , PRBMDO 0163-1829 10.1103/PhysRevB.29.2051Harrison, N., (2004) Phys. Rev. Lett., 93, p. 186405. , PRLTAO 0031-9007 10.1103/PhysRevLett.93.186405Nayak, P., Ojha, B., Mohanty, S., Behera, S.N., (2002) Int. J. Mod. Phys. B, 16, p. 3595. , IJPBEV 0217-9792Hall, D., (2001) Phys. Rev. B, 64, p. 064506. , PRBMDO 0163-1829 10.1103/PhysRevB.64.064506Razafimandiby, H., Fulde, P., Keller, J., (1989) Z. Phys. B: Condens. Matter, 54, p. 111. , ZPCMDN 0722-3277 10.1007/BF01388062Christianson, A.D., (2004) Phys. Rev. B, 70, p. 134505. , PRBMDO 0163-1829 10.1103/PhysRevB.70.13450

Vibrational and electronic excitations in the (Ce,La)MIn5 (M = Co,Rh) heavy-fermion family

We present a systematic study at ambient pressure of the phononic and electronic Raman-active excitations in the ab plane of the (Ce,La)MIn5 (M=Co,Rh) heavy-fermion family. We found that the characteristic Raman spectra of this family of compounds display two phonon modes at similar to 38 and similar to 165 cm(-1) and a broad electronic background centered at similar to 40 cm(-1). For CeCoIn5, the temperature dependence of these excitations shows anomalous behavior near T-*=45 K that may indicate a nontrivial renormalization of the electronic structure driven by strong correlations between hybridized 4f electrons.75

Profile scaling in decay of nanostructures

The flattening of a crystal cone below its roughening transition is studied by means of a step flow model. Numerical and analytical analyses show that the height profile, h(r,t), obeys the scaling scenario dh/dr = F(r t^{-1/4}). The scaling function is flat at radii r<R(t) \sim t^{1/4}. We find a one parameter family of solutions for the scaling function, and propose a selection criterion for the unique solution the system reaches.Comment: 4 pages, RevTex, 3 eps figure

Surface spin-flop transition in a uniaxial antiferromagnetic Fe/Cr superlattice induced by a magnetic field of arbitrary direction

We studied the transition between the antiferromagnetic and the surface spin-flop phases of a uniaxial antiferromagnetic [Fe(14 \AA)/Cr(11 \AA]$_{\rm x20}$ superlattice. For external fields applied parallel to the in-plane easy axis, the layer-by-layer configuration, calculated in the framework of a mean-field one-dimensional model, was benchmarked against published polarized neutron reflectivity data. For an in-plane field $H$ applied at an angle $\psi \ne 0$ with the easy axis, magnetometry shows that the magnetization $M$ vanishes at H=0, then increases slowly with increasing $H$. At a critical value of $H$, a finite jump in $M(H)$ is observed for $\psi<5^{\rm o}$, while a smooth increase of $M$ $vs$ $H$ is found for $\psi>5^{\rm o}$. A dramatic increase in the full width at half maximum of the magnetic susceptibility is observed for $\psi \ge 5^{\rm o}$. The phase diagram obtained from micromagnetic calculations displays a first-order transition to a surface spin-flop phase for low $\psi$ values, while the transition becomes continuous for $\psi$ greater than a critical angle, $\psi_{\rm max} \approx 4.75^{\rm o}$. This is in fair agreement with the experimentally observed results.Comment: 24 pages, 7 figure

Relaxation of Surface Profiles by Evaporation Dynamics

We present simulations of the relaxation towards equilibrium of one dimensional steps and sinusoidal grooves imprinted on a surface below its roughening transition. We use a generalization of the hypercube stacking model of Forrest and Tang, that allows for temperature dependent next-nearest-neighbor interactions. For the step geometry the results at T=0 agree well with the t^(1/4) prediction of continuum theory for the spreading of the step. In the case of periodic profiles we modify the mobility for the tips of the profile and find the approximate solution of the resulting free boundary problem to be in reasonable agreement with the T=0 simulations.Comment: 6 pages, Revtex, 5 Postscript figures, to appear in PRB 15, October 199

Novel continuum modeling of crystal surface evolution

We propose a novel approach to continuum modeling of the dynamics of crystal surfaces. Our model follows the evolution of an ensemble of step configurations, which are consistent with the macroscopic surface profile. Contrary to the usual approach where the continuum limit is achieved when typical surface features consist of many steps, our continuum limit is approached when the number of step configurations of the ensemble is very large. The model can handle singular surface structures such as corners and facets. It has a clear computational advantage over discrete models.Comment: 4 pages, 3 postscript figure