Nicole Elizabeth Constenla Bontemps - Academia.edu (original) (raw)
Papers by Nicole Elizabeth Constenla Bontemps
arXiv (Cornell University), Jan 22, 1998
We have measured the microwave dissipation at 10 GHz in a Bi2Sr2CaCu2O 8+δ single crystal, betwee... more We have measured the microwave dissipation at 10 GHz in a Bi2Sr2CaCu2O 8+δ single crystal, between 75 and 50 K, as a function of the static magnetic field applied parallel to the c axis. We observe a clear-cut onset in the dissipation precisely at the melting field. In the liquid phase, for fields ∼ 1-2 kG, the in-plane and the c-axis resistivities deduced from microwave absorption display a different temperature behavior, in contrast with DC measurements. Our c-axis high frequency data and the DC results can be reconciled by including phase slips due to the motion of pancake vortices, as suggested by Koshelev. The microscopic origin of the c-axis dissipation is thus identified through its frequency dependence.
Physical Review B, 1998
We have measured the microwave dissipation at 10 GHz in a Bi 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal, ... more We have measured the microwave dissipation at 10 GHz in a Bi 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal, between 75 and 50 K, as a function of the static magnetic field applied parallel to the c axis. We observe a clear-cut onset in the dissipation precisely at the melting field. In the liquid phase, for fields ϳ1-2 kG, the in-plane and the c axis resistivities deduced from microwave absorption display a different temperature behavior, in contrast with dc measurements. Our c-axis high-frequency data and the dc results can be reconciled by including phase slips due to the motion of pancake vortices, as suggested by Koshelev. The microscopic origin of the c-axis dissipation is thus identified through its frequency dependence. ͓S0163-1829͑98͒50846-6͔
Le Journal de Physique Colloques, 1988
We review the various experimental approaches for dynamic scaling in spin-glasses. We establish t... more We review the various experimental approaches for dynamic scaling in spin-glasses. We establish the relevant linear susceptibilities to be scaled namely Xes-X' (w) and (w). We put emphasis on the assumptions which are necessary for the scaling relations to hold and we discuss their applicability in view of some discrepancies that can be found among the published results.
Recently, A. V. Boris and colleagues claimed to deduce a decrease of intraband spectral weight (S... more Recently, A. V. Boris and colleagues claimed to deduce a decrease of intraband spectral weight (SW), and a transfer of SW from intraband to inter-band frequencies, when optimally-doped or slightly underdoped cuprates become superconducting [A. V. Boris et al., Science 304, p. 708 (2004)]. We show that, while their data agree with others [H. J. A. Molegraaf et al., Science 295, p. 2239 (2002) ; A.F. Santander-Syro et al., Europhys.Lett 62, p. 568 (2003)], their analysis is flawed. They cannot disprove the results which yield a superconductivity-induced increase of intraband SW, and a transfer of SW from high to low frequencies, in underdoped or nearly optimally doped Bi-2212.
Physical Review B, 1990
The decay of the thermoremanent magnetization (TRM) in the metallic spin-glass 2.6 at. /o Ag:Mn l... more The decay of the thermoremanent magnetization (TRM) in the metallic spin-glass 2.6 at. /o Ag:Mn lessens its dependence on the waiting time as H and T approach the de Almeida-Thouless (AT) line. A waiting-time dependence for the decay of the TRM of the insulating spin-glass Euo 4Sro 6S is only observed at T &0.87T~. Decay of the TRM is described for both by a stretched exponential. These results suggest that equilibrium is being approached in the field-cooled state as one approaches the AT line. The issue of the approach to equilibrium in a spin-glass has been a subject of controversy. Two mutually inconsistent theoretical pictures have emerged: the dynamics' of an ultrametric distribution of pure states [e.g., the dynamics of the states associated with the Sherrington-Kirkpatrick model, or the closely associated generalized random-energy model (GREM)]; or the dynamics of a droplet model modeled on the random field Ising model. The experimental situation has also been clouded. The observation of a "stretched exponential" time dependence for the time decay of the thermoremanent magnetization (TRM) has been argued to be correct for measurement times less than the waiting time, giving rise to a
Springer Series in Solid-State Sciences, 1987
There seems to be now a number of experimental evidences that dynamics in spin-glasses may provid... more There seems to be now a number of experimental evidences that dynamics in spin-glasses may provide informations which are relevant to the equilibrium properties: several groups have successfully performed dynamic scaling in a variety of spin-glasses /1–5/; the dynamic exponent is experimentally found to scale between roughly 7 and 8 which compares very well to the exponent determined in the latest numerical simulations /6/; this can be understood through the occurrence of a phase transition at finite temperature.
Journal de Physique Lettres, 1983
Refu le 28juin 1983, accepte le 20 juillet 1983) Résumé. 2014 Nous avons mesuré la susceptibilité... more Refu le 28juin 1983, accepte le 20 juillet 1983) Résumé. 2014 Nous avons mesuré la susceptibilité longitudinale et transverse dans Eu0,4Sr0,6S (102-105 Hz) sous champ appliqué. L'apparition d'une composante imaginaire permet de relever des lignes de transition champ/température, identiques dans les deux configurations; aux champs faibles, la concavité s'inverse et ce d'autant plus que la fréquence est plus élevée. L'interaction dipôle-dipôle permet d'expliquer l'isotropie de la réponse. Nous discutons les résultats en nous référant à la théorie de champ moyen et aux simulations numériques. Abstract 2014 We report on the transverse and longitudinal response in Eu0.4Sr0.6S with a small a.c. field (102-105 Hz) superimposed to a large static one. From the onset of the imaginary susceptibility, we derive transition lines, identical in both configurations, which exhibit, at low field, a reversed curvature more pronounced with increasing frequency. The isotropy of the response is assigned to the dipolar interaction. Our results are compared to mean field theory and numerical simulations.
Journal de Physique Lettres, 1983
2014 Nous avons analysé le retour à l'équilibre de l'aimantation dans Eu0,4Sr0,6S pour différents... more 2014 Nous avons analysé le retour à l'équilibre de l'aimantation dans Eu0,4Sr0,6S pour différents temps de mesure (1 ms-1 s) après coupure d'un petit champ magnétique superposé à un grand champ statique. Nous déduisons, pour les diverses échelles de temps, différentes lignes de transition champ-température, qui chacune suit la loi de De Almeida-Thouless. L'échelle de champ dépend (ne dépend pas) du temps pour des temps de mesure supérieurs (inférieurs) à 10 ms. Nous proposons une interprétation des résultats au vu de récentes théories. Abstract 2014 The change in magnetization of the insulating spin-glass Eu0.4Sr0.6S has been measured as a function of time (1 ms-1 s) for small magnetic field changes superposed on a larger constant field. A set of field-temperature transition lines has been obtained for different time scales. Each appears to be of the De Almeida-Thouless form but with a field scale which is dependent (independent) of the time scale for times > () 10 ms. The results are analysed in terms of recent theories.
Physical Review B, 1988
The time decay of the thermoremanent magnetization of the insulating spin-glass Euo &Sro 6S has b... more The time decay of the thermoremanent magnetization of the insulating spin-glass Euo &Sro 6S has been measured with use of Faraday rotation to probe shortand long-time regimes (3 ms-3000 s) between 0.86T~and 1. 04Tg. Aging elects are negligible in this compound to within our experimental accuracy, so that equilibrium response is accessible. %e And evidence for two time regimes. The decay is of a power-law form at short times. Beyond a well-defined crossover time, the decay is of a stretched exponential form. The crossover time decreases as the temperature increases from below T~, and drops abruptly at T~. No field dependence of the crossover time is observed for the field range investigated |, '5-40 Oe}. Connection is made with computer simulations of Ogielski, and with the existence of a finite length scale irr the equilibrium spin-glass state.
Journal of Physics C: Solid State Physics, 1982
Electron paramagnetic resonance (EPR), optically detected EPR and magnetic circular dichroism mea... more Electron paramagnetic resonance (EPR), optically detected EPR and magnetic circular dichroism measurements have been performed on a 10% doped holmium amorphous aluminosilicate in the range 20-1.4K. This sample had previously been shown to exhibit spin glass properties (freezing temperature Tf=0.6K). The experimental data strongly suggest a random axial symmetry, with a low-symmetry distortion varying locally from site to site. An effective Hamiltonian H=g mu BHSz+AIzSz+2E(Sx2-Sy2) corresponding to a fictitious spin mod +or-1) allows the authors to account satisfactorily for the experimental spectra and leads to an estimate of both the parameters: g=8.8 and 0<or=2E<or=3 cm-1. This model is discussed in view of the experimental results and some comments are further made on its possible consequences on the magnetic behaviour of this holmium aluminosilicate in the vicinity of the freezing temperature.
Lecture Notes in Physics, 1987
The thermoremanent magnetization of the insulating spin-glass Eu(0.4)Sr(0.6)S has been studied in... more The thermoremanent magnetization of the insulating spin-glass Eu(0.4)Sr(0.6)S has been studied in the range 1.01 Tc down to 0.88 Tc for various initial fields, over 3 decades of time (0.30 – 300 s) by means of Faraday rotation. Within our accuracy, the decay of the TRM is well characterized by a stretched exponential law s</font > = s</font >O exp{ -</font > (t/t</font >)1 -</font > n }\sigma = \sigma _{\rm O} \exp \{ - (t/\tau )^{1 - n} \} We have studied the variation of the parameters n and τ as a function of the temperature and field. Besides the well known acceleration of the decay with increasing initially applied fields, our results in the weakest field H = 0.2 Oe exhibit a clear-cut anomaly right at the temperature Tc(H) where the transition is expected to occur in the field H = 0.2 Oe, as determined from our previous dynamical measurements. It suggests a characteristic field scale for a spin-glass which defines the field range over which linear response theory may be applicable.
Physical Review B, 1992
We have measured the room-temperature reflectivity spectra in the infrared and visible range (500... more We have measured the room-temperature reflectivity spectra in the infrared and visible range (500-25 000 cm-1) of YBa2Cu3O6+x (0&lt;=x&lt;=1) and Nd1+yBa2-yCu3O6+x (0&lt;=y&lt;=0.5) polished ceramics as a function of doping (x and y). We show that the intensity of the entire infrared spectrum increases with the hole doping level (x or y). When separated into a Drude contribution and a mid-infrared
We measured the temperature dependence of the optical conductivity of (Pr,Ce)2CuO4 films from the... more We measured the temperature dependence of the optical conductivity of (Pr,Ce)2CuO4 films from the very underdoped to the overdoped regime between 4 meV and 3 eV. We observed a normal state gap but the presence of a Drude-like peak indicates that this gap is partial. The temperature at which the partial gap opens decreases with increasing Ce content and the
Materials Science Forum, 1990
arXiv (Cornell University), Jan 22, 1998
We have measured the microwave dissipation at 10 GHz in a Bi2Sr2CaCu2O 8+δ single crystal, betwee... more We have measured the microwave dissipation at 10 GHz in a Bi2Sr2CaCu2O 8+δ single crystal, between 75 and 50 K, as a function of the static magnetic field applied parallel to the c axis. We observe a clear-cut onset in the dissipation precisely at the melting field. In the liquid phase, for fields ∼ 1-2 kG, the in-plane and the c-axis resistivities deduced from microwave absorption display a different temperature behavior, in contrast with DC measurements. Our c-axis high frequency data and the DC results can be reconciled by including phase slips due to the motion of pancake vortices, as suggested by Koshelev. The microscopic origin of the c-axis dissipation is thus identified through its frequency dependence.
Physical Review B, 1998
We have measured the microwave dissipation at 10 GHz in a Bi 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal, ... more We have measured the microwave dissipation at 10 GHz in a Bi 2 Sr 2 CaCu 2 O 8ϩ␦ single crystal, between 75 and 50 K, as a function of the static magnetic field applied parallel to the c axis. We observe a clear-cut onset in the dissipation precisely at the melting field. In the liquid phase, for fields ϳ1-2 kG, the in-plane and the c axis resistivities deduced from microwave absorption display a different temperature behavior, in contrast with dc measurements. Our c-axis high-frequency data and the dc results can be reconciled by including phase slips due to the motion of pancake vortices, as suggested by Koshelev. The microscopic origin of the c-axis dissipation is thus identified through its frequency dependence. ͓S0163-1829͑98͒50846-6͔
Le Journal de Physique Colloques, 1988
We review the various experimental approaches for dynamic scaling in spin-glasses. We establish t... more We review the various experimental approaches for dynamic scaling in spin-glasses. We establish the relevant linear susceptibilities to be scaled namely Xes-X' (w) and (w). We put emphasis on the assumptions which are necessary for the scaling relations to hold and we discuss their applicability in view of some discrepancies that can be found among the published results.
Recently, A. V. Boris and colleagues claimed to deduce a decrease of intraband spectral weight (S... more Recently, A. V. Boris and colleagues claimed to deduce a decrease of intraband spectral weight (SW), and a transfer of SW from intraband to inter-band frequencies, when optimally-doped or slightly underdoped cuprates become superconducting [A. V. Boris et al., Science 304, p. 708 (2004)]. We show that, while their data agree with others [H. J. A. Molegraaf et al., Science 295, p. 2239 (2002) ; A.F. Santander-Syro et al., Europhys.Lett 62, p. 568 (2003)], their analysis is flawed. They cannot disprove the results which yield a superconductivity-induced increase of intraband SW, and a transfer of SW from high to low frequencies, in underdoped or nearly optimally doped Bi-2212.
Physical Review B, 1990
The decay of the thermoremanent magnetization (TRM) in the metallic spin-glass 2.6 at. /o Ag:Mn l... more The decay of the thermoremanent magnetization (TRM) in the metallic spin-glass 2.6 at. /o Ag:Mn lessens its dependence on the waiting time as H and T approach the de Almeida-Thouless (AT) line. A waiting-time dependence for the decay of the TRM of the insulating spin-glass Euo 4Sro 6S is only observed at T &0.87T~. Decay of the TRM is described for both by a stretched exponential. These results suggest that equilibrium is being approached in the field-cooled state as one approaches the AT line. The issue of the approach to equilibrium in a spin-glass has been a subject of controversy. Two mutually inconsistent theoretical pictures have emerged: the dynamics' of an ultrametric distribution of pure states [e.g., the dynamics of the states associated with the Sherrington-Kirkpatrick model, or the closely associated generalized random-energy model (GREM)]; or the dynamics of a droplet model modeled on the random field Ising model. The experimental situation has also been clouded. The observation of a "stretched exponential" time dependence for the time decay of the thermoremanent magnetization (TRM) has been argued to be correct for measurement times less than the waiting time, giving rise to a
Springer Series in Solid-State Sciences, 1987
There seems to be now a number of experimental evidences that dynamics in spin-glasses may provid... more There seems to be now a number of experimental evidences that dynamics in spin-glasses may provide informations which are relevant to the equilibrium properties: several groups have successfully performed dynamic scaling in a variety of spin-glasses /1–5/; the dynamic exponent is experimentally found to scale between roughly 7 and 8 which compares very well to the exponent determined in the latest numerical simulations /6/; this can be understood through the occurrence of a phase transition at finite temperature.
Journal de Physique Lettres, 1983
Refu le 28juin 1983, accepte le 20 juillet 1983) Résumé. 2014 Nous avons mesuré la susceptibilité... more Refu le 28juin 1983, accepte le 20 juillet 1983) Résumé. 2014 Nous avons mesuré la susceptibilité longitudinale et transverse dans Eu0,4Sr0,6S (102-105 Hz) sous champ appliqué. L'apparition d'une composante imaginaire permet de relever des lignes de transition champ/température, identiques dans les deux configurations; aux champs faibles, la concavité s'inverse et ce d'autant plus que la fréquence est plus élevée. L'interaction dipôle-dipôle permet d'expliquer l'isotropie de la réponse. Nous discutons les résultats en nous référant à la théorie de champ moyen et aux simulations numériques. Abstract 2014 We report on the transverse and longitudinal response in Eu0.4Sr0.6S with a small a.c. field (102-105 Hz) superimposed to a large static one. From the onset of the imaginary susceptibility, we derive transition lines, identical in both configurations, which exhibit, at low field, a reversed curvature more pronounced with increasing frequency. The isotropy of the response is assigned to the dipolar interaction. Our results are compared to mean field theory and numerical simulations.
Journal de Physique Lettres, 1983
2014 Nous avons analysé le retour à l'équilibre de l'aimantation dans Eu0,4Sr0,6S pour différents... more 2014 Nous avons analysé le retour à l'équilibre de l'aimantation dans Eu0,4Sr0,6S pour différents temps de mesure (1 ms-1 s) après coupure d'un petit champ magnétique superposé à un grand champ statique. Nous déduisons, pour les diverses échelles de temps, différentes lignes de transition champ-température, qui chacune suit la loi de De Almeida-Thouless. L'échelle de champ dépend (ne dépend pas) du temps pour des temps de mesure supérieurs (inférieurs) à 10 ms. Nous proposons une interprétation des résultats au vu de récentes théories. Abstract 2014 The change in magnetization of the insulating spin-glass Eu0.4Sr0.6S has been measured as a function of time (1 ms-1 s) for small magnetic field changes superposed on a larger constant field. A set of field-temperature transition lines has been obtained for different time scales. Each appears to be of the De Almeida-Thouless form but with a field scale which is dependent (independent) of the time scale for times > () 10 ms. The results are analysed in terms of recent theories.
Physical Review B, 1988
The time decay of the thermoremanent magnetization of the insulating spin-glass Euo &Sro 6S has b... more The time decay of the thermoremanent magnetization of the insulating spin-glass Euo &Sro 6S has been measured with use of Faraday rotation to probe shortand long-time regimes (3 ms-3000 s) between 0.86T~and 1. 04Tg. Aging elects are negligible in this compound to within our experimental accuracy, so that equilibrium response is accessible. %e And evidence for two time regimes. The decay is of a power-law form at short times. Beyond a well-defined crossover time, the decay is of a stretched exponential form. The crossover time decreases as the temperature increases from below T~, and drops abruptly at T~. No field dependence of the crossover time is observed for the field range investigated |, '5-40 Oe}. Connection is made with computer simulations of Ogielski, and with the existence of a finite length scale irr the equilibrium spin-glass state.
Journal of Physics C: Solid State Physics, 1982
Electron paramagnetic resonance (EPR), optically detected EPR and magnetic circular dichroism mea... more Electron paramagnetic resonance (EPR), optically detected EPR and magnetic circular dichroism measurements have been performed on a 10% doped holmium amorphous aluminosilicate in the range 20-1.4K. This sample had previously been shown to exhibit spin glass properties (freezing temperature Tf=0.6K). The experimental data strongly suggest a random axial symmetry, with a low-symmetry distortion varying locally from site to site. An effective Hamiltonian H=g mu BHSz+AIzSz+2E(Sx2-Sy2) corresponding to a fictitious spin mod +or-1) allows the authors to account satisfactorily for the experimental spectra and leads to an estimate of both the parameters: g=8.8 and 0<or=2E<or=3 cm-1. This model is discussed in view of the experimental results and some comments are further made on its possible consequences on the magnetic behaviour of this holmium aluminosilicate in the vicinity of the freezing temperature.
Lecture Notes in Physics, 1987
The thermoremanent magnetization of the insulating spin-glass Eu(0.4)Sr(0.6)S has been studied in... more The thermoremanent magnetization of the insulating spin-glass Eu(0.4)Sr(0.6)S has been studied in the range 1.01 Tc down to 0.88 Tc for various initial fields, over 3 decades of time (0.30 – 300 s) by means of Faraday rotation. Within our accuracy, the decay of the TRM is well characterized by a stretched exponential law s</font > = s</font >O exp{ -</font > (t/t</font >)1 -</font > n }\sigma = \sigma _{\rm O} \exp \{ - (t/\tau )^{1 - n} \} We have studied the variation of the parameters n and τ as a function of the temperature and field. Besides the well known acceleration of the decay with increasing initially applied fields, our results in the weakest field H = 0.2 Oe exhibit a clear-cut anomaly right at the temperature Tc(H) where the transition is expected to occur in the field H = 0.2 Oe, as determined from our previous dynamical measurements. It suggests a characteristic field scale for a spin-glass which defines the field range over which linear response theory may be applicable.
Physical Review B, 1992
We have measured the room-temperature reflectivity spectra in the infrared and visible range (500... more We have measured the room-temperature reflectivity spectra in the infrared and visible range (500-25 000 cm-1) of YBa2Cu3O6+x (0&lt;=x&lt;=1) and Nd1+yBa2-yCu3O6+x (0&lt;=y&lt;=0.5) polished ceramics as a function of doping (x and y). We show that the intensity of the entire infrared spectrum increases with the hole doping level (x or y). When separated into a Drude contribution and a mid-infrared
We measured the temperature dependence of the optical conductivity of (Pr,Ce)2CuO4 films from the... more We measured the temperature dependence of the optical conductivity of (Pr,Ce)2CuO4 films from the very underdoped to the overdoped regime between 4 meV and 3 eV. We observed a normal state gap but the presence of a Drude-like peak indicates that this gap is partial. The temperature at which the partial gap opens decreases with increasing Ce content and the
Materials Science Forum, 1990