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Search Results: 1 - 10 of 144447 matches for " F. Baumberger "
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From thermally activated to viscosity controlled fracture of biopolymer hydrogels
T. Baumberger,O. Ronsin
Physics , 2008, DOI: 10.1063/1.3078267
Abstract: We report on rate-dependent fracture energy measurements over three decades of steady crack velocities in alginate and gelatin hydrogels. We evidence that, irrespective of gel thermo-reversibility, thermally activated "unzipping" of the non-covalent cross-link zones results in slow crack propagation, prevaling against the toughening effect of viscous solvent drag during chain pull-out, which becomes efficient above a few mm.s$^{-1}$. We extend a previous model [Baumberger {\it et al.} Nature Materials, {\bf 5}, 552 (2006)] to account for both mechanisms, and estimate the microscopic unzipping rates.
Solid Friction from stick-slip to pinning and aging
Tristan Baumberger,Christiane Caroli
Physics , 2005, DOI: 10.1080/00018730600732186
Abstract: We review the present state of understanding of solid friction at low velocities and for systems with negligibly small wear effects. We first analyze in detail the behavior of friction at interfaces between wacroscopic hard rough solids, whose main dynamical features are well described by the Rice-Ruina rate and state dependent constitutive law. We show that it results from two combined effects : (i) the threshold rheology of nanometer-thick junctions jammed under confinement into a soft glassy structure (ii) geometric aging, i.e. slow growth of the real arrea of contact via asperity creep interrupted by sliding. Closer analysis leads to identifying a second aging-rejuvenation process, at work within the junctions themselves. We compare the effects of structural aging at such multicontact, very highly confined, interfaces with those met under different confinement levels, namely boundary lubricated contacts and extended adhesive interfaces involving soft materials (hydrogels, elastomers). This leads us to propose a classification of frictional junctions in terms of the relative importance of jamming and adsoprtion-induced metastability.
A convective instability mechanism for quasistatic crack branching in a hydrogel
T. Baumberger,O. Ronsin
Physics , 2009,
Abstract: Experiments on quasistatic crack propagation in gelatin hydrogels reveal a new branching instability triggered by wetting the tip opening with a drop of aqueous solvent less viscous than the bulk one. We show that the emergence of unstable branches results from a balance between the rate of secondary crack growth and the rate of advection away from a non-linear elastic region of size $\mathcal G/E$ where $\mathcal G$ is the fracture energy and $E$ the small strain Young modulus. We build a minimal, predictive model that combines mechanical characteristics of this mesoscopic region and physical features of the process zone. It accounts for the details of the stability diagram and lends support to the idea that non-linear elasticity plays a critical role in crack front instabilities.
Spin-orbit splitting of the Shockley surface state on Cu(111)
A. Tamai,W. Meevasana,P. D. C. King,C. Nicholson,A. de la Torre,E. Rozbicki,F. Baumberger
Physics , 2013, DOI: 10.1103/PhysRevB.87.075113
Abstract: We present angle-resolved photoemission data from Cu(111). Using a focused 6 eV continuous wave laser for photo-excitation, we achieve a high effective momentum resolution enabling the first detection of the Rashba spin splitting in the Shockley surface state on Cu(111). The magnitude of the spin-splitting of Delta k ~ 0.006 A^-1 is surprisingly large and exceeds values predicted for the analogous surface state on Ag(111) but is reproduced by first principles calculations. We further resolve a kink in the dispersion which we attribute to electron-phonon coupling.
Extracting the spectral function of the cuprates by a full two-dimensional analysis: Angle-resolved photoemission spectra of Bi2Sr2CuO6
W. Meevasana,F. Baumberger,K. Tanaka,F. Schmitt,W. R. Dunkel,D. H. Lu,S. -K. Mo,H. Eisaki,Z. -X. Shen
Physics , 2008, DOI: 10.1103/PhysRevB.77.104506
Abstract: Recently, angle-resolved photoemission spectroscopy (ARPES) has revealed a dispersion anomaly at high binding energy near 0.3-0.5eV in various families of the high-temperature superconductors. For further studies of this anomaly we present a new two-dimensional fitting-scheme and apply it to high-statistics ARPES data of the strongly-overdoped Bi2Sr2CuO6 cuprate superconductor. The procedure allows us to extract theself-energy in an extended energy and momentum range. It is found that the spectral function of Bi2Sr2CuO6 can be parameterized using a small set of tight-binding parameters and a weakly-momentum-dependent self-energy up to 0.7 eV in binding energy and over the entire first Brillouin zone. Moreover the analysis gives an estimate of the momentum dependence of the matrix element, a quantity, which is often neglected in ARPES analyses.
Control of a two-dimensional electron gas on SrTiO3(111) by atomic oxygen
S. McKeown Walker,A. de la Torre,F. Y. Bruno,A. Tamai,T. K. Kim,M. Hoesch,M. Shi,M. S. Bahramy,P. D. C. King,F. Baumberger
Physics , 2014, DOI: 10.1103/PhysRevLett.113.177601
Abstract: We report on the formation of a two-dimensional electron gas (2DEG) at the bare surface of (111) oriented SrTiO3. Angle resolved photoemission experiments reveal highly itinerant carriers with a 6-fold symmetric Fermi surface and strongly anisotropic effective masses. The electronic structure of the 2DEG is in good agreement with self-consistent tight-binding supercell calculations that incorporate a confinement potential due to surface band bending. We further demonstrate that alternate exposure of the surface to ultraviolet light and atomic oxygen allows tuning of the carrier density and the complete suppression of the 2DEG.
Heavy d-Electron Quasiparticle Interference and Real-space Electronic Structure of Sr3Ru2O7
Jinho Lee,M. P. Allan,M. A. Wang,J. E. Farrell,S. A. Grigera,F. Baumberger,J. C. Davis,A. P. Mackenzie
Physics , 2009, DOI: 10.1038/nphys1397
Abstract: The intriguing idea that strongly interacting electrons can generate spatially inhomogeneous electronic liquid crystalline phases is over a decade old, but these systems still represent an unexplored frontier of condensed matter physics. One reason is that visualization of the many-body quantum states generated by the strong interactions, and of the resulting electronic phases, has not been achieved. Soft condensed matter physics was transformed by microscopies that allowed imaging of real-space structures and patterns. A candidate technique for obtaining equivalent data in the purely electronic systems is Spectroscopic Imaging Scanning Tunneling Microscopy (SI-STM). The core challenge is to detect the tenuous but 'heavy' k-space components of the many-body electronic state simultaneously with its r-space constituents. Sr3Ru2O7 provides a particularly exciting opportunity to address these issues. It possesses (i) a very strongly renormalized 'heavy' d-electron Fermi liquid and (ii) exhibits a field-induced transition to an electronic liquid crystalline phase. Finally, as a layered compound, it can be cleaved to present an excellent surface for SI-STM.
Strong electron correlations in the normal state of FeSe0.42Te0.58
A. Tamai,A. Y. Ganin,E. Rozbicki,J. Bacsa,W. Meevasana,P. D. C. King,M. Caffio,R. Schaub,S. Margadonna,K. Prassides,M. J. Rosseinsky,F. Baumberger
Physics , 2009, DOI: 10.1103/PhysRevLett.104.097002
Abstract: We investigate the normal state of the '11' iron-based superconductor FeSe0.42Te0.58 by angle resolved photoemission. Our data reveal a highly renormalized quasiparticle dispersion characteristic of a strongly correlated metal. We find sheet dependent effective carrier masses between ~ 3 - 16 m_e corresponding to a mass enhancement over band structure values of m*/m_band ~ 6 - 20. This is nearly an order of magnitude higher than the renormalization reported previously for iron-arsenide superconductors of the '1111' and '122' families but fully consistent with the bulk specific heat.
Coupling Of The B1g Phonon To The Anti-Nodal Electronic States of Bi2Sr2Ca0.92Y0.08Cu2O(8+delta)
T. Cuk,F. Baumberger,D. H. Lu,N. Ingle,X. J. Zhou,H. Eisaki,N. Kaneko,Z. Hussain,T. P. Devereaux,N. Nagaosa,Z. -X. Shen
Physics , 2004, DOI: 10.1103/PhysRevLett.93.117003
Abstract: Angle-resolved photoemission spectroscopy (ARPES) on optimally doped Bi2Sr2Ca0.92Y0.08Cu2O(8+delta) uncovers a coupling of the electronic bands to a 40 meV mode in an extended k-space region away from the nodal direction, leading to a new interpretation of the strong renormalization of the electronic structure seen in Bi2212. Phenomenological agreements with neutron and Raman experiments suggest that this mode is the B1g oxygen bond-buckling phonon. A theoretical calculation based on this assignment reproduces the electronic renormalization seen in the data.
Controlling bulk conductivity in topological insulators: Key role of anti-site defects
D. O. Scanlon,P. D. C. King,R. P. Singh,A. de la Torre,S. McKeown Walker,G. Balakrishnan,F. Baumberger,C. R. A. Catlow
Physics , 2012, DOI: 10.1002/adma.201200187
Abstract: The binary Bi-chalchogenides, Bi2Ch3, are widely regarded as model examples of a recently discovered new form of quantum matter, the three-dimensional topological insulator (TI) [1-4]. These compounds host a single spin-helical surface state which is guaranteed to be metallic due to time reversal symmetry, and should be ideal materials with which to realize spintronic and quantum computing applications of TIs [5]. However, the vast majority of such compounds synthesized to date are not insulators at all, but rather have detrimental metallic bulk conductivity [2, 3]. This is generally accepted to result from unintentional doping by defects, although the nature of the defects responsible across different compounds, as well as strategies to minimize their detrimental role, are surprisingly poorly understood. Here, we present a comprehensive survey of the defect landscape of Bi-chalchogenide TIs from first-principles calculations. We find that fundamental differences in the energetics of native defect formation in Te- and Se-containing TIs enables precise control of the conductivity across the ternary Bi-Te-Se alloy system. From a systematic angle-resolved photoemission (ARPES) investigation of such ternary alloys, combined with bulk transport measurements, we demonstrate that this method can be utilized to achieve true topological insulators, with only a single Dirac cone surface state intersecting the chemical potential. Our microscopic calculations reveal the key role of anti-site defects for achieving this, and predict optimal growth conditions to realize maximally-resistive ternary TIs.
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