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Swarm of lightsail nanosatellites for Solar System exploration
Authors:
Giovanni Santi,
Alain J. Corso,
Denis Garoli,
Giuseppe Emanuele Lio,
Marco Manente,
Giulio Favaro,
Marco Bazzan,
Giampaolo Piotto,
Nicola Andriolli,
Lucanos Strambini,
Daniele Pavarin,
Leonardo Badia,
Remo Proietti Zaccaria,
Philip Lubin,
Roberto Ragazzoni,
Maria G. Pelizzo
Abstract:
This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for the heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be…
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This paper presents a study for the realization of a space mission which employs nanosatellites driven by an external laser source impinging on an optimized lightsail, as a valuable technology to launch swarms of spacecrafts into the Solar System. Nanosatellites propelled by laser can be useful for the heliosphere exploration and for planetary observation, if suitably equipped with sensors, or be adopted for the establishment of network systems when placed into specific orbits. By varying the area-to-mass ratio (i.e., the ratio between the sail area and the payload weight) and the laser power, it is ossible to insert nanosatellites into different hyperbolic orbits with respect to Earth, thus reaching the target by means of controlled trajectories in a relatively short amount of time. A mission involving nanosatellites of the order of 1 kg of mass is envisioned, by describing all the on-board subsystems and satisfying all the requirements in term of power and mass budget. Particular attention is paid to the telecommunication subsystem, which must offer all the necessary functionalities. To fabricate the lightsail, the thin films technology has been considered, by verifying the sail thermal stability during the thrust phase. Moreover, the problem of mechanical stability of the lightsail has been tackled, showing that the distance between the ligthsail structure and the payload plays a pivotal role. Some potential applications of the proposed technology are discussed, such as the mapping of the heliospheric environment.
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Submitted 15 September, 2022; v1 submitted 23 August, 2022;
originally announced August 2022.
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Phonon Mode Spectroscopy, Electron-Phonon Coupling and the Metal-Insulator Transition in Quasi-One-Dimensional M2Mo6Se6
Authors:
A. P. Petrović,
R. Lortz,
G. Santi,
M. Decroux,
H. Monnard,
L. Boeri,
O. K. Andersen,
J. Kortus,
D. Salloum,
P. Gougeon,
M. Potel,
Ø. Fischer
Abstract:
We present electronic structure calculations, electrical resistivity data and the first specific heat measurements in the normal and superconducting states of quasi-one-dimensional M2Mo6Se6 (M = Tl, In, Rb). Rb2Mo6Se6 undergoes a metal-insulator transition at ~170K: electronic structure calculations indicate that this is likely to be driven by the formation of a dynamical charge density wave. Howe…
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We present electronic structure calculations, electrical resistivity data and the first specific heat measurements in the normal and superconducting states of quasi-one-dimensional M2Mo6Se6 (M = Tl, In, Rb). Rb2Mo6Se6 undergoes a metal-insulator transition at ~170K: electronic structure calculations indicate that this is likely to be driven by the formation of a dynamical charge density wave. However, Tl2Mo6Se6 and In2Mo6Se6 remain metallic down to low temperature, with superconducting transitions at Tc = 4.2K and 2.85K respectively. The absence of any metal-insulator transition in these materials is due to a larger in-plane bandwidth, leading to increased inter-chain hopping which suppresses the density wave instability. Electronic heat capacity data for the superconducting compounds reveal an exceptionally low density of states DEF = 0.055 states eV^-1 atom^-1, with BCS fits showing 2Delta/kBTc >= 5 for Tl2Mo6Se6 and 3.5 for In2Mo6Se6. Modelling the lattice specific heat with a set of Einstein modes, we obtain the approximate phonon density of states F(w). Deconvolving the resistivity for the two superconductors then yields their electron-phonon transport coupling function a^2F(w). In Tl2Mo6Se6 and In2Mo6Se6, F(w) is dominated by an optical "guest ion" mode at ~5meV and a set of acoustic modes from ~10-30meV. Rb2Mo6Se6 exhibits a similar spectrum; however, the optical phonon has a lower intensity and is shifted to ~8meV. Electrons in Tl2Mo6Se6 couple strongly to both sets of modes, whereas In2Mo6Se6 only displays significant coupling in the 10-18meV range. Although pairing is clearly not mediated by the guest ion phonon, we believe it has a beneficial effect on superconductivity in Tl2Mo6Se6, given its extraordinarily large coupling strength and higher Tc compared to In2Mo6Se6.
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Submitted 30 July, 2010;
originally announced July 2010.
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Multi-band Superconductivity in the Chevrel Phases SnMo6S8 and PbMo6S8
Authors:
A. P. Petrović,
R. Lortz,
G. Santi,
C. Berthod,
C. Dubois,
M. Decroux,
A. Demuer,
A. B. Antunes,
A. Paré,
D. Salloum,
P. Gougeon,
M. Potel,
Ø. Fischer
Abstract:
Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2 ~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap distribution is strongly anisotropic, with Delta_2 predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well-fitted by an…
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Sub-Kelvin scanning tunnelling spectroscopy in the Chevrel Phases SnMo6S8 and PbMo6S8 reveals two distinct superconducting gaps with Delta_1 = 3 meV, Delta_2 ~ 1.0 meV and Delta_1 = 3.1 meV, Delta_2 ~ 1.4 meV respectively. The gap distribution is strongly anisotropic, with Delta_2 predominantly seen when scanning across unit-cell steps on the (001) sample surface. The spectra are well-fitted by an anisotropic two-band BCS s-wave gap function. Our spectroscopic data are confirmed by electronic heat capacity measurements which also provide evidence for a twin-gap scenario.
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Submitted 30 June, 2010;
originally announced June 2010.
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The de Haas - van Alphen Effect Study of the Fermi Surface of ZrB12
Authors:
V. A. Gasparov,
I. Sheikin,
F. Levy,
J. Teyssier,
G. Santi
Abstract:
The de Haas - van Alphen (dHvA) effect in the cluster superconductor ZrB12 was studied by magnetic torque measurements in magnetic fields up to 28 T at temperatures down to 0.35 K. The dHvA oscillations due to orbits from the Neck sections and "Cubic Box" of the Fermi surface were detected. We measured cyclotron effective masses of 0.5m_0 for Neck section of the FS. The dHvA frequencies as well…
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The de Haas - van Alphen (dHvA) effect in the cluster superconductor ZrB12 was studied by magnetic torque measurements in magnetic fields up to 28 T at temperatures down to 0.35 K. The dHvA oscillations due to orbits from the Neck sections and "Cubic Box" of the Fermi surface were detected. We measured cyclotron effective masses of 0.5m_0 for Neck section of the FS. The dHvA frequencies as well as the cyclotron effective masses were calculated using the full potential Linear Muffin-Tin Orbital (LMTO) method within the Generalized Gradient Approximation. Comparison of the angular dependence of the dHvA frequencies with the band-structure calculations implies overall agreement with theoretical model, while one section could not be definitely identified.
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Submitted 25 October, 2007;
originally announced October 2007.
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Scanning Tunneling Spectroscopy in the Superconducting State and Vortex Cores of the beta-pyrochlore KOs2O6
Authors:
C. Dubois,
G. Santi,
I. Cuttat,
C. Berthod,
N. Jenkins,
A. P. Petrović,
A. A. Manuel,
Ø. Fischer,
S. M. Kazakov,
Z. Bukowski,
J. Karpinski
Abstract:
We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully-gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fi…
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We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above 1.95 K. This material presents atomically flat surfaces, yielding spatially homogeneous spectra which reveal fully-gapped superconductivity with a gap anisotropy of 30%. Measurements performed at fields of 2 and 6 T display a hexagonal Abrikosov flux line lattice. From the shape of the vortex cores, we extract a coherence length of 31-40 Å, in agreement with the value derived from the upper critical field Hc2. We observe a reduction in size of the vortex cores (and hence the coherence length) with increasing field which is consistent with the unexpectedly high and unsaturated upper critical field reported.
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Submitted 4 April, 2007;
originally announced April 2007.
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Node-like excitations in superconducting PbMo6S8 probed by scanning tunneling spectroscopy
Authors:
C. Dubois,
A. P. Petrovic,
G. Santi,
C. Berthod,
A. A. Manuel,
M. Decroux,
O. Fischer,
M. Potel,
R. Chevrel
Abstract:
We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature depend…
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We present the first scanning tunneling spectroscopy study on the Chevrel phase PbMo6S8, an extreme type II superconductor with a coherence length only slightly larger than in high-Tc cuprates. Tunneling spectra measured on atomically flat terraces are spatially homogeneous and show well-defined coherence peaks. The low-energy spectral weight, the zero bias conductance and the temperature dependence of the gap are incompatible with a conventional isotropic s-wave interpretation, revealing the presence of low-energy excitations in the superconducting state. We show that our data are consistent with the presence of nodes in the superconducting gap.
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Submitted 12 February, 2007;
originally announced February 2007.
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Fermi surface nesting and charge-density wave formation in rare-earth tritellurides
Authors:
J. Laverock,
S. B. Dugdale,
Zs. Major,
M. A. Alam,
N. Ru,
I. R. Fisher,
G. Santi,
E. Bruno
Abstract:
The Fermi surface of rare-earth tri-tellurides ({\it R}Te$_{3}$) is investigated in terms of the nesting driven charge-density wave formation using positron annihilation and first-principles LMTO calculations. Fermi surface nesting is revealed as a strong candidate for driving charge-density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on…
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The Fermi surface of rare-earth tri-tellurides ({\it R}Te$_{3}$) is investigated in terms of the nesting driven charge-density wave formation using positron annihilation and first-principles LMTO calculations. Fermi surface nesting is revealed as a strong candidate for driving charge-density wave formation in these compounds. The nesting vector obtained from positron annihilation experiments on GdTe$_{3}$ is determined to be ${\mathbf q} = (0.28\pm0.02,0,0) {\mathbf a}^{*}$, (${\mathbf a}^{*}=2π/{\mathbf a}$), in excellent agreement with previous experimental and theoretical studies.
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Submitted 5 January, 2005;
originally announced January 2005.
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The role of intra-atomic non-collinear magnetization density in weak ferromagnetism
Authors:
Robert Laskowski,
Gilles Santi
Abstract:
We investigate the mechanism behind the breakdown of the compensation of large magnetic moments leading to weak ferromagnetism. For this we use first-principles calculations within density functional theory and we focus on the weak ferromagnetic compound Mn3Sn. Our new implementation allows for an exact treatment of the spin-density matrix and non-collinearity. In order to gain some insight, our…
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We investigate the mechanism behind the breakdown of the compensation of large magnetic moments leading to weak ferromagnetism. For this we use first-principles calculations within density functional theory and we focus on the weak ferromagnetic compound Mn3Sn. Our new implementation allows for an exact treatment of the spin-density matrix and non-collinearity. In order to gain some insight, our results are compared to the ones obtained by using the atomic moment approximation (AMA) and its role is discussed. We find that the appearance of the weak ferromagnetic moment in this compound originates not so much as an effect of spin-orbit coupling as suggested previously from AMA calculations, as from the non-collinearity of the Sn atom magnetization density. This is confirmed by non-collinear calculations in which the SOC effects are neglected.
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Submitted 10 August, 2004;
originally announced August 2004.
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Electronic Structure of Samarium Monopnictides and Monochalcogenides
Authors:
A. Svane,
V. Kanchana,
G. Vaitheeswaran,
G. Santi,
W. M. Temmerman,
Z. Szotek,
P. Strange,
L. Petit
Abstract:
The electronic structures of SmX (X=N, P, As, Sb, Bi, O, S, Se, Te, Po)compounds are calculated using the self-interaction corrected local-spin density approximation. The Sm ion is described with either five or six localized $f$-electrons while the remaining electrons form bands, and the total energies of these scenarios are compared. With five localized $f$-electrons a narrow $f$-band is formed…
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The electronic structures of SmX (X=N, P, As, Sb, Bi, O, S, Se, Te, Po)compounds are calculated using the self-interaction corrected local-spin density approximation. The Sm ion is described with either five or six localized $f$-electrons while the remaining electrons form bands, and the total energies of these scenarios are compared. With five localized $f$-electrons a narrow $f$-band is formed in the vicinity of the Fermi level leading to an effective intermediate valence. This scenario is the ground state of all the pnictides as well as SmO. With six localized $f$-electrons, the chalcogenides are semiconductors, which is the ground state of SmS, SmSe and SmTe. Under compression the Sm chalcogenides undergo first order transitions with destabilization of the $f$ states into the intermediate valence state, the bonding properties of which are well reproduced by the present theory.
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Submitted 14 July, 2004;
originally announced July 2004.
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Heavy quasiparticles in the ferromagnetic superconductor ZrZn2
Authors:
S. J. C. Yates,
G. Santi,
S. M. Hayden,
P. J. Meeson,
S. B. Dugdale
Abstract:
We report a study of the de Haas-van Alphen effect in the normal state of the ferromagnetic superconductor ZrZn2. Our results are generally consistent with an LMTO band structure calculation which predicts four exchange-split Fermi surface sheets. Quasiparticle effective masses are enhanced by a factor of about 4.9 implying a strong coupling to magnetic excitations or phonons. Our measurements p…
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We report a study of the de Haas-van Alphen effect in the normal state of the ferromagnetic superconductor ZrZn2. Our results are generally consistent with an LMTO band structure calculation which predicts four exchange-split Fermi surface sheets. Quasiparticle effective masses are enhanced by a factor of about 4.9 implying a strong coupling to magnetic excitations or phonons. Our measurements provide insight in to the mechanism for superconductivity and unusual thermodynamic properties of ZrZn2.
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Submitted 11 July, 2002;
originally announced July 2002.
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Longitudinal spin-fluctuations and superconductivity in ferromagnetic ZrZn$_{2}$ from ab initio calculations
Authors:
G. Santi,
S. B. Dugdale,
T. Jarlborg
Abstract:
The recent discovery of superconductivity coexisting with weak itinerant ferromagnetism in the $d$-electron intermetallic compound ZrZn$_{2}$ strongly suggests spin-fluctuation mediated superconductivity. {\it Ab initio} electronic structure calculations of the Fermi surface and generalized susceptibilities are performed to investigate the viability of longitudinal spin-fluctuation-induced spin-…
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The recent discovery of superconductivity coexisting with weak itinerant ferromagnetism in the $d$-electron intermetallic compound ZrZn$_{2}$ strongly suggests spin-fluctuation mediated superconductivity. {\it Ab initio} electronic structure calculations of the Fermi surface and generalized susceptibilities are performed to investigate the viability of longitudinal spin-fluctuation-induced spin-triplet superconductivity in the ferromagnetic state. The critical temperature is estimated to be of the order of 1 K. Additionally, it is shown that in spite of a strong electron-phonon coupling ($λ_{ph}=0.7$), conventional s-wave superconductivity is inhibited by the presence of strong spin-fluctuations.
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Submitted 13 July, 2001;
originally announced July 2001.
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Nesting properties and anisotropy of the Fermi surface of LuNi$_{2}$B$_{2}$C
Authors:
S. B. Dugdale,
M. A. Alam,
I. Wilkinson,
R. J. Hughes,
I. R. Fisher,
P. C. Canfield,
G. Santi,
T. Jarlborg
Abstract:
The rare earth nickel borocarbides, with the generic formula $R$Ni$_{2}$B$_{2}$C, have recently been shown to display a rich variety of phenomena. Most striking has been the competition between, and even coexistence of, antiferromagnetism and superconductivity. We have measured the Fermi surface (FS) of LuNi$_{2}$B$_{2}$C, and shown that it possesses nesting features capable of explaining some o…
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The rare earth nickel borocarbides, with the generic formula $R$Ni$_{2}$B$_{2}$C, have recently been shown to display a rich variety of phenomena. Most striking has been the competition between, and even coexistence of, antiferromagnetism and superconductivity. We have measured the Fermi surface (FS) of LuNi$_{2}$B$_{2}$C, and shown that it possesses nesting features capable of explaining some of the phenomena experimentally observed. In particular, it had previously been conjectured that a particular sheet of FS is responsible for the modulated magnetic structures manifest in some of the series. We report the first direct experimental observation of this sheet.
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Submitted 13 July, 1999;
originally announced July 1999.
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Fermi surface of the colossal magnetoresistance perovskite La_{0.7}Sr_{0.3}MnO_{3}
Authors:
E. A. Livesay,
R. N. West,
S. B. Dugdale,
G. Santi,
T. Jarlborg
Abstract:
Materials that exhibit colossal magnetoresistance (CMR) are currently the focus of an intense research effort, driven by the technological applications that their sensitivity lends them to. Using the angular correlation of photons from electron-positron annihilation, we present a first glimpse of the Fermi surface of a material that exhibits CMR, supported by ``virtual crystal'' electronic struc…
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Materials that exhibit colossal magnetoresistance (CMR) are currently the focus of an intense research effort, driven by the technological applications that their sensitivity lends them to. Using the angular correlation of photons from electron-positron annihilation, we present a first glimpse of the Fermi surface of a material that exhibits CMR, supported by ``virtual crystal'' electronic structure calculations. The Fermi surface is shown to be sufficiently cubic in nature that it is likely to support nesting.
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Submitted 17 December, 1998;
originally announced December 1998.
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s and d-wave symmetries of the solutions of the Eliashberg equations
Authors:
G. Santi,
T. Jarlborg,
M. Peter,
M. Weger
Abstract:
We examine the different possible symmetries of the superconducting gap obtained by solving the Eliashberg equations. We consider an electron-phonon interaction in a strong coupling scenario. The Coulomb pseudopotential plays the crucial role of providing the repulsion needed to favour the d-wave symmetry. But the key parameter that allows very anisotropic solutions even with very strong couplin…
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We examine the different possible symmetries of the superconducting gap obtained by solving the Eliashberg equations. We consider an electron-phonon interaction in a strong coupling scenario. The Coulomb pseudopotential plays the crucial role of providing the repulsion needed to favour the d-wave symmetry. But the key parameter that allows very anisotropic solutions even with very strong coupling is the small angular range of the interaction due to predominantly electron-phonon forward scattering that is found in the high-Tc superconductors. We find both s and d-wave solutions whose stability depends mainly on the angular range of the interaction.
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Submitted 23 February, 1996;
originally announced February 1996.
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Transport Properties, Thermodynamic Properties, and Electronic Structure of SrRuO3
Authors:
P. B. Allen,
H. Berger,
O. Chauvet,
L. Forro,
T. Jarlborg,
A. Junod,
B. Revaz,
G. Santi
Abstract:
SrRuO$_3$ is a metallic ferromagnet. Its electrical resistivity is reported for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K; its specific heat for temperatures up to 230K. The energy bands have been calculated by self-consistent spin-density functional theory, which finds a ferromagnetic ordered moment of 1.45$μ_{\rm B}$ per Ru atom. The measured linear specific he…
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SrRuO$_3$ is a metallic ferromagnet. Its electrical resistivity is reported for temperatures up to 1000K; its Hall coefficient for temperatures up to 300K; its specific heat for temperatures up to 230K. The energy bands have been calculated by self-consistent spin-density functional theory, which finds a ferromagnetic ordered moment of 1.45$μ_{\rm B}$ per Ru atom. The measured linear specific heat coefficient $γ$ is 30mJ/mole, which exceeds the theoretical value by a factor of 3.7. A transport mean free path at room temperature of $\approx 10 Å$ is found. The resistivity increases nearly linearly with temperature to 1000K in spite of such a short mean free path that resistivity saturation would be expected. The Hall coefficient is small and positive above the Curie temperature, and exhibits both a low-field and a high-field anomalous behavior below the Curie temperature.
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Submitted 23 January, 1996;
originally announced January 1996.