Publications

2014

• Disorder-induced topological change of the superconducting gap structure in iron pnictides
  
  • Mizukami Y.
  • Konczykowski M.
  • Kawamoto Y.
  • Kurata S.
  • Kasahara S.
  • Hashimoto K.
  • Mishra V.
  • Kreisel A.
  • Wang Y.
  • Hirschfeld P.J.
  • Matsuda Y.
  • Shibauchi T.
  Nature Communications, Nature Publishing Group, 2014, pp.6. In superconductors with unconventional pairing mechanisms, the energy gap in the excitationspectrum often has nodes, which allow quasiparticle excitations at low energies. In manycases, such as in d-wave cuprate superconductors, the position and topology of nodes areimposed by the symmetry, and thus the presence of gapless excitations is protected againstdisorder. Here we report on the observation of distinct changes in the gap structure of iron–pnictide superconductors with increasing impurity scattering. By the successive introductionof nonmagnetic point defects into BaFe2(As1-xPx)2 crystals via electron irradiation, we findfrom the low-temperature penetration depth measurements that the nodal state changes to anodeless state with fully gapped excitations. Moreover, under further irradiation the gappedstate evolves into another gapless state, providing bulk evidence of unconventionalsign-changing s-wave superconductivity. This demonstrates that the topology of the superconductinggap can be controlled by disorder, which is a strikingly unique feature of ironpnictides. (10.1038/ncomms6657)
  DOI : 10.1038/ncomms6657
• Interplay between structure and electronic properties of layered transition-metal dichalcogenides: Comparing the loss function of 1T and 2H polymorphs
  
  • Cudazzo Pierluigi
  • Gatti Matteo
  • Rubio Angel
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 90, pp.205128. Transition-metal dichalcogenides (TMD) share the same global layered structure, but distinct polymorphs are characterized by different local coordinations of the transition-metal atoms. Here we compared the 1T and 2H families of metallic TMD, both in the bulk and in the two-dimensional forms. By means of first-principles time-dependent density functional calculations of the loss function, we established the direct connection between the low-energy plasmon properties and the crystal-structure symmetry. The different atomic environments affect the d − d electron-hole excitations, which are prominent at low energies, resulting in distinct in-plane plasmon dispersions in the two families. Conversely, the different periodicity of the plasmon reappearance along the c axis perpendicular to the layers can be used to distinguish the various crystal structures of TMD. (10.1103/PhysRevB.90.205128)
  DOI : 10.1103/PhysRevB.90.205128
• Effect of Electron Irradiation on Superconductivity in Single Crystals of Ba(Fe1−xRux)2As2 (x = 0.24)
  
  • Prozorov R.
  • Kończykowski M.
  • Tanatar M. A.
  • Thaler A.
  • Bud’ko S. L.
  • Canfield P. C.
  • Mishra V.
  • Hirschfeld P. J.
  Physical Review X, American Physical Society, 2014, 4, pp.7. A single crystal of isovalently substituted BaðFe1−xRuxÞ2As2 (x = 0.24) is sequentially irradiated with2.5 MeV electrons up to a maximum dose of 2.1 × 10^19 e−=cm2. The electrical resistivity is measuredin situ at T =22 K during the irradiation and ex situ as a function of temperature between subsequentirradiation runs. Upon irradiation, the superconducting transition temperature Tc decreases and the residualresistivity ρ0 increases. We find that electron irradiation leads to the fastest suppression of Tc comparedto other types of artificially introduced disorder, probably due to the strong short-range potential of thepointlike irradiation defects. A more detailed analysis within a multiband scenario with variable scatteringpotential strength shows that the observed Tc versus ρ0 is fully compatible with s+/-pairing, in contrast to earlier claims that this model leads to a too rapid suppression of Tc with scattering. (10.1103/PhysRevX.4.041032)
  DOI : 10.1103/PhysRevX.4.041032
• Instantaneous Band Gap Collapse in Photoexcited Monoclinic VO2 due to Photocarrier Doping
  
  • Wegkamp Daniel
  • Herzog Marc
  • Xian Lede
  • Gatti Matteo
  • Cudazzo Pierluigi
  • Mcgahan Christiana L.
  • Marvel Robert E.
  • Haglund Richard
  • Rubio Angel
  • Wolf Martin
  • Stähler Julia
  Physical Review Letters, American Physical Society, 2014, 113, pp.216401. Using femtosecond time-resolved photoelectron spectroscopy we demonstrate that photoexcitation transforms monoclinic VO2 quasi-instantaneously into a metal. Thereby, we exclude an 80 fs structural bottleneck for the photoinduced electronic phase transition of VO2. First-principles many-body perturbation theory calculations reveal a high sensitivity of the VO2 band gap to variations of the dynamically screened Coulomb interaction, supporting a fully electronically driven isostructural insulatorto-metal transition. We thus conclude that the ultrafast band structure renormalization is caused by photoexcitation of carriers from localized V 3d valence states, strongly changing the screening before significant hot-carrier relaxation or ionic motion has occurred. (10.1103/PhysRevLett.113.216401)
  DOI : 10.1103/PhysRevLett.113.216401
• Solution to the many-body problem in one point
  
  • Berger Arjan
  • Romaniello Pina
  • Tandetzky Falk
  • Mendoza Bernardo S.
  • Brouder Christian
  • Reining Lucia
  New Journal of Physics, Institute of Physics: Open Access Journals, 2014, 16, pp.113025. (10.1088/1367-2630/16/11/113025)
  DOI : 10.1088/1367-2630/16/11/113025
• Self-limited underdense microplasmas in bulk silicon induced by ultrashort laser pulses
  
  • Mouskeftaras Alexandros
  • Rode Andrei V.
  • Clady Raphael
  • Sentis Marc
  • Uteza Olivier
  • Grojo David
  Applied Physics Letters, American Institute of Physics, 2014, 105 (19). Two-photon ionization by focused femtosecond laser pulses initiates the development of micrometer-scale plasmas in the bulk of silicon. Using pump-and-probe transmission microscopy with infrared light, we investigate the space-time characteristics of these plasmas for laser intensities up to 10(12) W/cm(2). The measurements reveal a self-limitation of the excitation at a maximum free-carrier density of congruent to 10(19) cm(-3), which is more than one order of magnitude below the threshold for permanent modification. The plasmas remain unchanged in the similar to 100 ps timescale revealing slow carrier kinetics. The results underline the limits in local control of silicon dielectric permittivity, which are inherent to the use of single near-infrared ultrashort Gaussian pulses. (C) 2014 AIP Publishing LLC. (10.1063/1.4901528)
  DOI : 10.1063/1.4901528
• Erratum: Solution to the many-body problem in one point
  
  • Berger Arjan
  • Romaniello Pina
  • Tandetzky Falk
  • Mendoza Bernardo S
  • Brouder Christian
  • Reining Lucia
  New Journal of Physics, Institute of Physics: Open Access Journals, 2014, 16 (11), pp.113025. In this work we determine the one-body Greenʼs function as solution of a set of functional integro-differential equations, which relate the one-particle Greenʼs function to its functional derivative with respect to an external potential. In the same spirit as Lani et al (2012 New J. Phys. 14 013056), we do this in a one-point model, where the equations become ordinary differential equations (DEs) and, hence, solvable with standard techniques. This allows us to analyze several aspects of these DEs as well as of standard methods for determining the one-body Greenʼs function that are important for real systems. In particular: (i) we present a strategy to determine the physical solution among the many mathematical solutions; (ii) we assess the accuracy of an approximate DE related to the $GW$+cumulant method by comparing it to the exact physical solution and to standard approximations such as $GW$; (iii) we show that the solution of the approximate DE can be improved by combining it with a screened interaction in the random-phase approximation. (iv) We demonstrate that by iterating the $GW$ Dyson equation one does not always converge to a $GW$ solution and we discuss which iterative scheme is the most suitable to avoid such errors. (10.1088/1367-2630/16/11/119601)
  DOI : 10.1088/1367-2630/16/11/119601
• The interplay between photo-and radiation-induced darkening in ytterbium-doped fibres
  
  • Duchez Jean-Bernard
  • Mady Franck
  • Mebrouk Yasmine
  • Ollier Nadège
  • Benabdesselam Mourad
  Optics Letters, Optical Society of America - OSA Publishing, 2014. This letter demonstrates a remarkable interplay between photo-and radiation-induced darkening of ytterbium-doped alumino-silica optical fibres operated in amplifying conditions and harsh environments (as e.g. in space-based applications). Influences of the pump power, ionizing dose and dose rate on this interaction are characterized. The pump is capable of accelerating or slowing-down the radiation-induced darkening build-up depending on the ionizing dose. The steady state photo-radio-darkening level is independent of the dose and at least equal to the equilibrium level of pure photo-darkening. This lower limit is notably reached at low dose rates, including those encountered in space. We therefore argue that photo-resistant ytterbium-doped fibres will resist against a space mission, whatever the dose. (10.1364/OL.39.005969)
  DOI : 10.1364/OL.39.005969
• Latent heat and nonlinear vortex liquid in the vicinity of the first-order phase transitionin layered high-Tc superconductors
  
  • Dolz M. I.
  • Fasano Y.
  • Pastoriza H.
  • Mosser V.
  • Li M.
  • Konczykowski M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 90, pp.6. In this work we revisit the vortex matter phase diagram in layered superconductors solving still open questions by means of ac and dc local magnetic measurements in the paradigmatic Bi2Sr2CaCu2O8 compound. We show that measuring with ac magnetic techniques is mandatory in order to probe the bulk response of vortex matter, particularly at high temperatures where surface barriers for vortex entrance dominate. From the TFOT evolution of the enthalpy and latent heat at the transition we find that, contrary to previous reports, the nature of the dominant interlayer coupling is electromagnetic in the whole temperature range. By studying the dynamic properties of the phase located at T TFOT, we reveal spanning in a considerable fraction of the phase diagram of a nonlinear vortex phase suggesting that bulk pinning might play a role even in the liquid vortex phase. (10.1103/PhysRevB.90.144507)
  DOI : 10.1103/PhysRevB.90.144507
• Corrosion of titanium and zirconium under Ar irradiation in the low MeV range: an XPS and SE study
  
  • Gorse-Pomonti D.
  • Dragoe N.
  • Barthes-Labrousse M-G
  • Garcia-Caurel E
  • Bérerd N.
  , 2014.
• New insights on P-related paramagnetic point defects in irradiated phosphate glasses: Impact of glass network type and irradiation dose
  
  • Pukhkaya V.
  • Trompier F.
  • Ollier Nadège
  Journal of Applied Physics, American Institute of Physics, 2014, 116 (12), pp.123517. P-related paramagnetic point defects were studied in irradiated Yb-doped phosphate glasses by electron paramagnetic resonance spectroscopy (X and Q-bands). A strong impact of the glass network type on the defect nature is shown. In all glasses, r-POHC defects formation is in strong correlation with Q(2) tetrahedra amount supporting the structure of r-POHC. Ultra-phosphate glasses contain the larger defect type: Peroxy radicals, P-1, P-2, and P-4 defects whose formation is linked to Q(3) tetrahedra presence. In meta-phosphate and poly-phosphate glasses, peroxy radicals appear with r-POHC thermal recovery. In meta-phosphate glasses, a combination of P-1 and P-3 defects was evidenced for the first time, whereas in poly-phosphate glasses, only P-3 defects were identified. Dose effect as well as defect recovery were analyzed. (C) 2014 AIP Publishing LLC. (10.1063/1.4896876)
  DOI : 10.1063/1.4896876
• Growth and characterization of Cu/Co multi-layered nanowires
  
  • Reyes Vasquez David Fernando
  • Gatel Christophe
  • Biziere Nicolas
  • L. Wade Travis
  • Warot-Fonrose Bénédicte
  , 2014. In this study we elaborate multi-layered Co/Cu nanowires by pulsed electrodeposition technique into polycarbonate membranes, their mean diameter is 50nm. Cobalt and copper maps were obtained by EFTEM to get the position and the average thickness of the layers. Using electron holography we observed the magnetic states in individual cobalt layers.
• Cumulant expansion of the retarded one-electron Green function
  
  • Kas J. J.
  • Rehr John J.
  • Reining Lucia
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, pp.085112. The cumulant expansion is a powerful approach for including correlation effects in electronic structure calculations beyond the GW approximation. However, the expansion is not generally valid, as current implementations ignore terms that mix particle and hole states and lead to partial occupation numbers of one-electron states. These limitations are corrected here using a cumulant expansion of the retarded one-electron Green’s function that includes both particle and hole contributions. The approach provides a consistent framework that improves on the GW approximation to the spectral function without additional computational effort. The method is illustrated with results for the homogeneous electron gas and comparisons to experiment and other methods. (10.1103/PhysRevB.90.085112)
  DOI : 10.1103/PhysRevB.90.085112
• Nanometric Resolved Luminescence in h-BN Flakes: Excitons and Stacking Order
  
  • Bourrellier Romain
  • Amato Michele
  • Galvao Tizei Luiz Henrique
  • Giorgetti Christine
  • Gloter Alexandre
  • I. Heggie Malcolm
  • March Katia
  • Stephan Odile
  • Reining Lucia
  • Kociak Mathieu
  • Zobelli Alberto
  ACS photonics, American Chemical Society, 2014, 1, pp.857-862. The strong excitonic emission of hexagonal boron nitride (h-BN) makes this material one of the most promising candidate for light emitting devices in the far ultraviolet (UV). However, single excitons occur only in perfect monocrystals that are extremely hard to synthesize, while regular h-BN samples present a complex emission spectrum with several additional peaks. The microscopic origin of these additional emissions has not yet been understood. In this work we address this problem using an experimental and theoretical approach that combines nanometric resolved cathodoluminescence, high resolution transmission electron microscopy and state of the art theoretical spectroscopy methods. We demonstrate that emission spectra are strongly inhomogeneus within individual few layer flakes and that additional excitons occur at structural deformations, such as faceted plane folds, that lead to local changes of the h-BN layers stacking order. (10.1021/ph500141j)
  DOI : 10.1021/ph500141j
• Carbon-rich icosahedral boron carbide designed from first principles
  
  • Jay Antoine
  • Vast Nathalie
  • Sjakste Jelena
  • Duparc O. Hardouin
  Applied Physics Letters, American Institute of Physics, 2014, 105, pp.031914. The carbon-rich boron-carbide (B11C)C-C has been designed from first principles within the density functional theory. With respect to the most common boron carbide at 20% carbon concentration B4C, the structural modification consists in removing boron atoms from the chains linking (B11C) icosahedra. With C-C instead of C-B-C chains, the formation of vacancies is shown to be hindered, leading to enhanced mechanical strength with respect to B4C. The phonon frequencies and elastic constants turn out to prove the stability of the carbon-rich phase, and important fingerprints for its characterization have been identified. (10.1063/1.4890841)
  DOI : 10.1063/1.4890841
• Linear and nonlinear stationary ac response of nanomagnets in the presence of thermal agitation and spin-transfer torques
  
  • Coffey William T.
  • Kalmykov Yuri P.
  • Titov Serguey V.
  • Byrne Declan J.
  • Wegrowe Jean-Eric
  , 2014.
• Singular robust room-temperature spin response from topological Dirac fermions
  
  • Zhao Lukas
  • Deng Haiming
  • Korzhovska Inna
  • Chen Zhiyi
  • Konczykowski Marcin
  • Hruban Andrzej
  • Oganesyan Vadim
  • Krusin-Elbaum Lia
  Nature Materials, Nature Publishing Group, 2014, 13, pp.580. Topological insulators are a class of solids in which the non-trivial inverted bulk band structure gives rise to metallic surface states1-6 that are robust against impurity scattering2,3,7- 9. In three-dimensional (3D) topological insulators, however, the surface Dirac fermions intermix with the conducting bulk, thereby complicating access to the low-energy (Dirac point) charge transport or magnetic response. Here we use di erential magnetometry to probe spin rotation in the 3D topological material family (Bi2Se3, Bi2Te3 and Sb2Te3).We report a paramagnetic singularity in the magnetic susceptibility at low magnetic fields that persists up to room temperature, and which we demonstrate to arise from the surfaces of the samples. The singularity is universal to the entire family, largely independent of the bulk carrier density, and consistent with the existence of electronic states near the spin-degenerate Dirac point of the 2D helical metal. The exceptional thermal stability of the signal points to an intrinsic surface cooling process, probably of thermoelectric origin10,11, and establishes a sustainable platform for the singular field-tunable Dirac spin response (10.1038/NMAT3962)
  DOI : 10.1038/NMAT3962
• Effets thermoélectriques anisotropes dans les couches minces ferromagnétiques Py et YIG
  
  • Do Chung Pham
  , 2014. Cette thèse est une étude s'inscrivant dans le domaine de la "Spin Caloritronics". Nous avons étudié le transport thermique anisotrope dans les couches minces ferromagnétiques. Le but de cette étude est de déterminer les relations entre le transport thermique et les états d'aimantation de la couche mince ferromagnétique. Nous présentons tous les protocoles expérimentaux qui permettent de faire les mesures de transports électriques et thermiques. Nous présentons également les outils (le modèle, les calculs et la simulation numérique) nécessaires pour analyser finement les résultats de mesure. Le premier objectif est la caractérisation des états d'aimantations des échantillons en utilisant des mesures de magnétorésistance et des mesures d'effets Hall (planaire et anormal). Tous les paramètres permettant de décrire les états d'équilibres magnétiques sont alors déterminés. Nous pouvons ainsi connaître très précisément les états d'aimantation de la couche mince ferromagnétique. Le deuxième objectif est de déterminer la dépendance angulaire du transport thermique anisotrope et de la comparer à celle du transport électrique anisotrope. Pour cela nous remplaçons le courant électrique par un courant de chaleur et effectuons toutes les mesures de tension transverse. Les résultats obtenus montrent que la tension transverse du courant de chaleur a la même dépendance angulaire que la tension transverse obtenue avec un courant électrique.
• Nucleation stage in supersaturated vapor with inhomogeneities due to nonstationary diffusion onto growing droplets
  
  • Kuchma Anatoly
  • Markov Maxim
  • Shchekin Alexander
  Physica A: Statistical Mechanics and its Applications, Elsevier, 2014, 402, pp.255-265. An analytical description of the nucleation stage in a supersaturated vapor with instantly created supersaturation is given with taking into account the vapor concentration inhomogeneities arising as a result of depletion due to nonstationary diffusion onto growing droplets. This description is based on the fact, that the intensity of the nucleation of new droplets is suppressed in spherical diffusion regions of a certain size surrounding previously nucleated droplets, and remains at the initial level in the remaining volume of the vapor gas medium. The value of the excluded volume (excluded from nucleation) depends on the explicit form of the vapor concentration profile in the space around the growing droplet, and we use for that the unsteady self-similar solution of the time-dependent diffusion equation with a convective term describing the flow of the gas-vapor mixture caused by the moving surface of the single growing droplet. The main characteristics of the phase transition at the end of the nucleation stage are found and compared with those in the theory of nucleation with homogeneous vapor consumption (the theory of mean-field vapor supersaturation). It is shown that applicability of the mean-field approach depends on smallness of the square root of the ratio of the densities of metastable and stable phases. With increasing the temperature of the supersaturated vapor or for liquid or solid solutions, this smallness weakens, and then it would be more correct to use the excluded volume approach. (C) 2014 Elsevier B.V. All rights reserved.
• FanTaaStic: Sustainable management of Future Internet testbed federations
  
  • Willner Alexander
  • Albrecht Stefan
  • Covaci Stefan
  • Schreiner Florian
  • Magedanz Thomas
  • Avessta Susanna
  • Scognamiglio Ciro
  • Fdida Serge
  , 2014, pp.1-4. The global trend of Future Internet related experimentally driven research has gained a strong momentum. In this context sustainability and the best use of developed infrastructures are highly critical. While many facilities have reached a level of maturity that allows them to be opened up to a wider use, mainly the academic sectors have been targeted. The Fanning out Testbeds-as-a-Service for the EIT ICT1 (FanTaaStic) project explores best practices, has performed a gap analysis, investigates applicable business models and works out a concept for the operation of a self-sustainable commercial testbed service offering. For defining the operational model, an analysis of available tools and frameworks from past and current Future Internet testbed projects is being carried out, based on a standard framework that defines the required processes and applications for the carrier grade operation of telecommunication infrastructures and provisioning of services. The business model is defined as a gradually growing service offering, based on categories of a framework for IT Service Management in federated e-infrastructures. The applicability of both, the developed business and operational model for such a sustainable federation will initially be implemented and evaluated in 2014. (10.1109/NOMS.2014.6838379)
  DOI : 10.1109/NOMS.2014.6838379
• Synthesis of Poly(vinyl pyrrolidone)/Silver Nanoprism Composites through Simultaneous Photoinduced Polymerization and Electron Transfer Processes
  
  • Sangermano Marco
  • Vivier Florence
  • Rizza Giancarlo
  • Yagci Yusuf
  Journal of Macromolecular Science Part A Pure and Applied Chemistry, Taylor & Francis: STM, Behavioural Science and Public Health Titles, 2014, 51, pp.511-513. An investigation into the in situ preparation of polymer/silver nanoprism composites is described. Photoinitiated polymerizations of N-vinyl pyrrolidone (NVP) in water using 2-hydroxy-2-methyl-1-phenyl propanone as photoinitiator under nitrogen and simultaneous redox reactions of AgNO3 resulted in the formation of poly(N-vinyl pyrrolidone) (PNVP)/silver nanocomposites. Prolonged irradiations at low photoinitiator concentration and equimolar concentrations of AgNO3 and NVP produced only spherical silver nanoparticles. The nanocomposites produced at high silver and photoiniatiator concentrations with short irradiation times e.g. 5 min contain polygonal (mainly triangular) silver nanoprisms as evidenced by spectral and TEM analysis.
• Positron annihilation spectroscopy investigation of vacancy clusters in silicon carbide: Combining experiments and electronic structure calculations
  
  • Wiktor Julia
  • Kerbiriou Xavier
  • Jomard G.
  • Esnouf Stéphane
  • Barthe Marie-France
  • Bertolus M.
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 89, pp.155203. The temperature dependence of the point defects in 6H-SiC induced by 12-MeV proton irradiation was studied by means of isochronal annealing followed by both positron annihilation spectroscopy and electron paramagnetic resonancemeasurements. The formation energies and positron lifetimes of various vacancy clusters were calculated to help in the interpretation of the experiments. The combination of the experiments and calculations enabled the identification of a negative silicon vacancy, with the lifetime of 218 ps, which is annealed between 400 degrees C and 700 degrees C. This process involves vacancy migration and formation of the V-C + V-Si cluster, with a lifetime of 235 ps. In addition, our calculations confirm the identification of several clusters proposed in previous experimental studies.
• Tunable luminescence from Ce-doped aluminoborosilicate glasses
  
  • Malchukova E
  • Boizot B
  Journal of Rare Earths, Elsevier, 2014, 32, pp.217-220. A series of aluminoborosilicate glasses were prepared using the melt-quenching technique for mixture of stoichiometric amounts of SiO 2 , Al 2 O 3 , H 3 BO 3 , Na 2 CO 3 , and ZrO 2 with adding of different amounts of CeO 2. The samples were investigated by means of luminescence spectroscopy. Tunable luminescence from violet to blue/green was observed from these glasses with different Xe-lamp excitation wavelengths ranging from 370 to 480 nm as well as with laser excitation of 266 and 355 nm. Moreover it was found that the possibility of tuning the light by changing of excitation wavelength was not unique. The same effect was observed by adjusting conditions for luminescence measurements as well as under exposure to β-irradiation. The obtained phenomena could be explained taking into account structural characteristics of this glass and it could be concluded that tunable luminescence results from the presence of different Ce-sites the glass matrix. Thus the results suggest that Ce-doped glasses could be considered as conversion materials for blue light-emitting diode chips to generate white light-emitting diodes. Ce 3+ ions were widely used as activators in various fluoride and oxide materials. The preparation of RE-doped phosphor materials for application in advanced illumination technologies has been the subject of intense research during recent decades. These researches are stimulated by the necessity of increasing the efficiency in white light emitting solid state devices which represent an alternate lightning source [1] (10.1016/S1002-0721(14)60055-7)
  DOI : 10.1016/S1002-0721(14)60055-7
• Anisotropic magnetothermal transport and spin Seebeck effect
  
  • Wegrowe J-E
  • Drouhin H-J
  • Lacour Daniel
  Physical Review B: Condensed Matter and Materials Physics (1998-2015), American Physical Society, 2014, 89 (9). The anisotropic properties of thermal transport in insulating or conducting ferromagnets are derived on the basis of the Onsager reciprocity relations applied to a magnetic system. It is shown that the angular dependence of the temperature gradient takes the same form as that of the anisotropic magnetoresistance, including anomalous and planar Hall contributions. The measured thermocouple generated between the extremities of the nonmagnetic electrode in thermal contact to the ferromagnet follows this same angular dependence. The sign and amplitude of the magnetovoltaic signal is controlled by the difference of the Seebeck coefficients of the thermocouple. (10.1103/PhysRevB.89.094409)
  DOI : 10.1103/PhysRevB.89.094409
• Probing ultrashort-pulse laser excitation of sapphire: From the initial carrier creation to material ablation
  
  • Waedegaard Kristian J.
  • Sandkamm Ditte B.
  • Mouskeftaras Alexandros
  • Guizard Stéphane
  • Balling Peter
  EPL - Europhysics Letters, European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing, 2014, 105 (47001), pp.n/a. Ultrashort-pulse laser excitation of dielectrics has been investigated over a large span of intensities. Experimentally, single-shot studies on single-crystal sapphire samples combine time-resolved spectral interferometry with time-resolved reflectivity and ablation-rate measurements. The complete development of the excitation from the first creation of conduction-band electrons at low intensities to the formation of a highly excited plasma and associated material fragmentation is observed experimentally and explained by a single theoretical model, which combines material excitation in a multiple-rate equation description with light propagation. Copyright (C) EPLA, 2014 (10.1209/0295-5075/105/47001)
  DOI : 10.1209/0295-5075/105/47001