| 1. |
- Aleksandrovskii, A. N., et al.
(author)
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Negative thermal expansion of fullerite C60 at helium temperatures
- 1997
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In: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 23:11, s. 943-946
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Journal article (peer-reviewed)abstract
- The thermal expansion of fullerite C60 has been measured in the temperature range 2–9 K. A compacted fullerite sample with a diameter of about 6 mm and height of 2.4 mm was used. It was found that at temperatures below ~ 3.4 K the linear thermal expansion coefficient becomes negative. At temperatures above 5 K our results are in good agreement with the available literature data. A qualitative explanation of the results is proposed
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| 2. |
- Aleksandrovskii, A. N., et al.
(author)
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Thermal expansion of single-crystal fullerite C60 at helium temperatures
- 2000
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In: Low temperature physics (Woodbury, N.Y., Print). - : AIP Publishing. - 1063-777X .- 1090-6517. ; 26:1, s. 75-80
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Journal article (peer-reviewed)abstract
- The thermal expansion of single-crystal fullerite C60 has been studied in the range of liquid-helium temperatures (2–10 K). At temperatures below ~4.5 K the thermal expansion of fullerite C60 becomes negative, in agreement with the previous results on polycrystalline materials. A qualitative explanation of the results is proposed.
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| 3. |
- Andersson, Ove, et al.
(author)
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Reorientational relaxation in C60 following a pressure induced change in the pentagon/hexagon equilibrium ratio
- 1995
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In: Physics Letters A. - : Elsevier Science B.V.. - 0375-9601 .- 1873-2429. ; 206:3-4, s. 260-264
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Journal article (peer-reviewed)abstract
- The orientational structure of C60 depends on pressure and temperature. Pressurization below the glass transition temperature Tg can freeze in non-equilibrium orientational structures. The relaxation of such structures on heating through Tg has been studied through thermal conductivity measurements and the effects observed are explained in a simple model.
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| 4. |
- Lundin, Anders, et al.
(author)
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Compressibility and Structure of C70
- 1995
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In: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 30:8, s. 469-474
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Journal article (peer-reviewed)abstract
- The compressibility of C70 has been investigated by means of direct piston and cylinder measurements in the temperature range 150 to 365 K and up to 1 GPa. At 296 and 343 K we find a very rapid change of volume with pressure below 0.15 GPa. We tentatively interpret this as a continuous molecular reorientation with pressure, probably resulting in a transformation from a mixture of face-centred cubic (f.c.c.) and rhombohedral (r.h.) phases to mainly pure r.h. phase. At 365 K as well as at 236 K and below we see no anomalies indicating any structural or rotational anomalies in the pressure range investigated. The zero-pressure bulk modulus decreases with increasing temperature, from 13.1 GPa at 185 K to 7.9 GPa at 365 K. Our volumetric measurements confirm a recently proposed phase diagram for C70.
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| 5. |
- Lundin, Anders, et al.
(author)
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Compressibility of C61D2 up to 1 GPa in the temperature range 175 - 345 K
- 1996
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In: Carbon. - : Elsevier Science Ltd.. - 0008-6223 .- 1873-3891. ; 34:9, s. 1119-1121
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Journal article (peer-reviewed)abstract
- We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175–343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.
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| 6. |
- Nagel, Peter, et al.
(author)
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C60 one- and two-dimensional polymers, dimers, and hard fullerite: Thermal expansion, anharmonicity, and kinetics of depolymerization
- 1999
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In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 60:24, s. 16920-16927
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Journal article (peer-reviewed)abstract
- We report on high-resolution thermal expansion measurements of high-temperature-pressure treated C60 [one-dimensional (1D) and (2D) polymers and “hard fullerite”], as well as of C60 dimers and single crystal monomer C60 between 10 and 500 K. Polymerization drastically reduces the thermal expansivity from the values of monomeric C60 due to the stronger and less anharmonic covalent bonds between molecules. The expansivity of the “hard” material approaches that of diamond. The large and irreversible volume change upon depolymerization between 400 and 500 K makes it possible to study the kinetics of depolymerization, which is described excellently by a simple activated process, with activation energies of 1.9±0.1 eV (1D and 2D polymers) and 1.75±0.05 eV (dimer). Although the activation energies are very similar for the different polymers, the depolymerization rates differ by up to four orders of magnitude at a given temperature, being fastest for the dimers. Preliminary kinetic data of C70 polymers are presented as well.
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| 7. |
- Persson, Per-Axel, et al.
(author)
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NMR and Raman characterization of pressure polymerized C-60
- 1996
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In: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 258:5-6, s. 540-546
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Journal article (peer-reviewed)abstract
- Bulk C60 has been treated at 1.1 GPa and 550–585 K, producing a dense insoluble material which on heating to above 600 K reverts to normal C60. Raman and IR studies on modified material show a large number of new lines, and the Raman pentagon pinch mode shifts from 1469 to 1458 cm−1 as on photopolymerization. MAS NMR shows one broadened line at the original C60 shift 144 ppm and a small peak at about 77 ppm due to the bridging carbons. None of the new resonances observed for C60 polymerized by other methods were observed. The results verify previously suggested polymeric structures where the fullerence cages are connected by four-membered rings.
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| 8. |
- Persson, Per-Axel, et al.
(author)
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The physical properties of high-pressure polymerized C60
- 1997
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In: Journal of Physics and Chemistry of Solids, volume 58, issue 11. - : Elsevier B.V.. ; 58:11, s. 1881-1885
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Conference paper (peer-reviewed)abstract
- We have studied the structural, thermophysical, and spectroscopic properties of polymeric C60 obtained by high pressure treatment at pressures and temperatures near 1 GPa and 600 K. We present here a brief overview of our results for the structural and thermophysical properties and a more detailed report on recent results obtained by Raman spectroscopy on both thin films, polycrystalline, and single crystal material. The results presented include a comparison between Raman results for photopolymerized and pressure polymerized thin films and a preliminary estimate of the binding energy of polymeric C60.
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| 9. |
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| 10. |
- Sing, M., et al.
(author)
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Electronic structure studies of pressure-polymerized C60
- 1999
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In: Synthetic Metals vol. 103. - : Elsevier B.V.. ; 103:1-3, s. 2454-2455
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Conference paper (peer-reviewed)abstract
- We have investigated the electronic structure of one and two-dimensional C60 polymers with regard to both their low-lying excitations and C 1s excitation spectra by means of electron energy-loss spectroscopy in transmission. We compare the results with those for pristine C60. In general, the spectra for the polymers resemble those for pristine C60 but show a broadening due to both the lowering of the symmetry and the increased intermolecular overlap. This is also reflected by a reduction of the optical gap in comparison with pristine C60.
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| 11. |
- Soldatov, Alexander, et al.
(author)
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Molecular rotation in C70 at high pressures: a thermal conductivity study
- 1996
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In: Journal of Physics and Chemistry of Solids. - : Elsevier Science Ltd. - 0022-3697 .- 1879-2553. ; 57:9, s. 1371-1375
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Journal article (peer-reviewed)abstract
- We have measured the thermal conductivity ε and the heat capacity per unit volume varrhocp of highly pure C70 in the temperature interval 100–450 K under pressures up to 1 GPa. Anomalies indicating freezing of uniaxial molecular rotation were observed in λ and varrhocp upon both cooling and increasing pressure. The phase boundary for this transition has an approximate slope dT/dp = 70 K Gpa−1. The temperature and pressure dependence of λ indicate a substantial amount of structural defects in the sample and strong metastability effects.
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| 12. |
- Soldatov, Alexander, et al.
(author)
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Polymeric fullerenes: from C60 to C70
- 1999
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In: AIP Conference Proceedings vol. 486. - Melville, NY : American Institute of Physics (AIP). - 1563969009 ; , s. 12-15
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Conference paper (peer-reviewed)abstract
- For the first time polymerization of both powder and single crystals of C70 fullerene was established after their subjection to high pressure (1.1 - 2 GPa) at elevated temperature (500 - 580 K). High-resolution capacitance dilatometry, FTIR/Raman spectroscopy and thermal conductivity were employed to characterise the polymeric phase of C70. The results demonstrate drastic changes in the physical properties of C70 on polymerization. We report on a reverse transformation to the monomeric state on heating the polymer to 500 K at ambient pressure. The activation energy of depolymerization was determined to be 1.8(1) eV. We discuss our results in terms of existing structural models for polymerization of C70 and compare the physical properties of C70 and C60 polymers.
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| 13. |
- Soldatov, Alexander, et al.
(author)
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Transport and vibrational properties of pressure polymerized C60
- 1998
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In: Molecular Materials (Molecular Crystals and Liquid Crystals, Section C), vol. 11. - Amsterdam : Overseas Publishers Association. ; 11:1-2, s. 1-6
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Conference paper (peer-reviewed)abstract
- The vibrational spectrum of polycrystalline C60 polymerized at 1.1 GPa and 585 K was studied by inelastic neutron scattering. We find drastic changes in the spectrum compared to the vibrational spectrum of pristine C60: the appearance of a new, broad vibrational band at low energies, and splitting and significant changes in the peak positions of various modes. The thermal conductivity lambda of polymerized C60 was measured in the temperature range 150-320 K and was found to increase with a rise in temperature, which reflects strong phonon scattering. A high degree of structural disorder in the crystalline lattice of the polymeric phase is most probably responsible for the glass-like beahviour of lambda(T).
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| 14. |
- Sundqvist, Bertil, et al.
(author)
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Phase diagram, structure, and disorder in C60 below 300 K and 1 GPa
- 1995
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In: Solid State Communications. - : Elsevier Science Ltd. - 0038-1098 .- 1879-2766. ; 93:2, s. 109-112
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Journal article (peer-reviewed)abstract
- Earlier structural studies have shown that the pentagon-to-hexagon orientation ratio in the orientationally ordered simple cubic phase of C60 decreases under pressure. From anomalies observed in the compressibility and thermal conductivity of C60 under pressure we have deduced a pressure-temperature phase diagram for this substance in the range below 300 K and 1 GPa (10 kbar). We conclude that C60 forms a new, completely “hexagon” ordered structural phase above about 0.6 GPa at 150 K (1.2 GPa at 300 K), and that the glass transition shifts upwards in T under pressure by 54 K GPa−1. However, above 0.1 GPa, pentagon-to-hexagon orientation relaxation seems to occur on heating at an almost pressure independent temperature near 100 K.
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| 15. |
- Sundqvist, Bertil, et al.
(author)
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Structural and physical properties of pressure polymerized C60
- 1998
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In: Carbon, vol. 36 issue 5-6. - : Elsevier B.V.. ; 36:5-6, s. 657-660
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Conference paper (peer-reviewed)abstract
- We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under these conditions arise from nucleation of molecular chains in random directions because of the quasi-free molecular rotation under standard reaction conditions in the fcc phase of C60. Polymerization in He gives results qualitatively different from those obtained in other media.
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| 16. |
- Wågberg, Thomas, et al.
(author)
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2D polymerization and doping of fullerenes under pressure
- 2000
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In: High Pressure Research vol. 18. - : Gordon & Breach. ; 18:1-6, s. 139-143
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Conference paper (peer-reviewed)abstract
- Tetragonal polymeric C60 has been studied by Raman spectroscopy and other methods. Attempts have been made to transform samples from the tetragonal to the orthorhom-bic phase and vice versa. The results suggest that the transformation is direct with no intermediate stage with free molecules. Tetragonal C60 has also been intercalated by potassium metal.
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| 17. |
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| 18. |
- Larson, Jonas, et al.
(author)
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Spin-orbit-coupled Bose-Einstein condensate in a tilted optical lattice
- 2010
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In: Physical Review A. Atomic, Molecular, and Optical Physics. - : APS. - 1050-2947 .- 1094-1622. ; 82:4, s. 043620-
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Journal article (peer-reviewed)abstract
- Bloch oscillations appear for a particle in a weakly tilted periodic potential. The intrinsic spin Hall effect is an outcome of a spin-orbit coupling. We demonstrate that both of these phenomena can be realized simultaneously in a gas of weakly interacting ultracold atoms exposed to a tilted optical lattice and to a set of spatially dependent light fields inducing an effective spin-orbit coupling. It is found that both the spin Hall and the Bloch oscillation effects may coexist, showing, however, a strong correlation between the two. These correlations are manifested as a transverse spin current oscillating in-phase with the Bloch oscillations. On top of the oscillations originating from the periodicity of the model, a trembling motion is found which is believed to be atomic Zitterbewegung. It is argued that the damping of these Zitterbewegung oscillations may to a large extent be prevented in the present setup considering a periodic optical lattice potential.
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| 19. |
- Lebegue, Sebastien, et al.
(author)
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Ab initio study of the electronic properties and Fermi surface of the uranium dipnictides
- 2006
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In: PHYSICAL REVIEW B. - 1098-0121. ; 73:4, s. 045119-
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Journal article (peer-reviewed)abstract
- The electronic structure of the uranium dipnictides UX2 (X=As, Sb, and Bi) is investigated by means of ab initio calculations based on density functional theory. The calculated Fermi surfaces are presented and compared to available experimental models obtained from de Haas-van Alphen experiments. In agreement with experiments they are found to have a significant two-dimensional character. Also, the change of the electronic properties through the series is discussed.
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| 20. |
- Andersson, Ove, et al.
(author)
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Thermal conductivity of C60 at pressures up to 1 GPa and temperatures in the range 50-300 K
- 1996
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:5, s. 3093-3100
-
Journal article (peer-reviewed)abstract
- The thermal conductivity λ of C60 shows anomalies near 260 K and 90 K which are associated with the well-established phase transition and glass transition, respectively. Both transition temperatures increase with pressure, at the rates 120 K GPa-1 and 62 K GPa-1, respectively. With increasing temperature, λ of the simple cubic (sc) phase increased below 170 K (glasslike behavior) but decreased above. The glasslike behavior of λ is probably due to a substantial amount of lattice defects. Possible reasons for the change of sign of dλ/dT near 170 K are discussed. In the face centered cubic (fcc) phase (T≳260 K at atmospheric pressure) λ was almost independent of temperature, a behavior which is far from that of an ordered crystal (λ∝T-1 for T≳Debye temperature). This result can be attributed to the molecular orientational disorder of the fcc phase. The relaxation behavior associated with the glassy state and its unusually strong dependence on thermal history are discussed briefly, and data which support a previously reported relaxation model are presented. At room temperature, the density dependencies of λ, (∂ lnλ/∂ lnρ)T, were 5.5 and 9.5 for the fcc and sc phases, which are values typical for an orientationally disordered phase and a normal crystal phase, respectively.
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| 21. |
- Azimi Mousolou, Vahid, 1982-
(author)
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Quantum Holonomy for Many-Body Systems and Quantum Computation
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- The research of this Ph. D. thesis is in the field of Quantum Computation and Quantum Information. A key problem in this field is the fragile nature of quantum states. This be comes increasingly acute when the number of quantum bits (qubits) grows in order to perform large quantum computations. It has been proposed that geometric (Berry) phases may be a useful tool to overcome this problem, because of the inherent robustness of such phases to random noise. In the thesis we investigate geometric phases and quantum holonomies (matrix-valued geometric phases) in many-body quantum systems, and elucidate the relationship between these phases and the quantum correlations present in the systems. An overall goal of the project is to assess the feasibility of using geometric phases and quantum holonomies to build robust quantum gates, and investigate their behavior when the size of a quantum system grows, thereby gaining insights into large-scale quantum computation. In a first project we study the Uhlmann holonomy of quantum states for hydrogen-like atoms. We try to get into a physical interpretation of this geometric concept by analyzing its relation with quantum correlations in the system, as well as by comparing it with different types of geometric phases such as the standard pure state geometric phase, Wilczek-Zee holonomy, Lévay geometric phase and mixed-state geometric phases. In a second project we establish a unifying connection between the geometric phase and the geometric measure of entanglement in a generic many-body system, which provides a universal approach to the study of quantum critical phenomena. This approach can be tested experimentally in an interferometry setup, where the geometric measure of entanglement yields the visibility of the interference fringes, whereas the geometric phase describes the phase shifts. In a third project we propose a scheme to implement universal non-adiabatic holonomic quantum gates, which can be realized in novel nano-engineered systems such as quantum dots, molecular magnets, optical lattices and topological insulators. In a fourth project we propose an experimentally feasible approach based on “orange slice” shaped paths to realize non- Abelian geometric phases, which can be used particularly for geometric manipulation of qubits. Finally, we provide a physical setting for realizing non-Abelian off-diagonal geometric phases. The proposed setting can be implemented in a cyclic chain of four qubits with controllable nearest-neighbor interactions. Our proposal seems to be within reach in various nano-engineered systems and therefore opens up for first experimental test of the non-Abelian off-diagonal geometric phase.
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| 22. |
- Castelain, Mickaël, et al.
(author)
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Fast uncoiling kinetics of F1C pili expressed by uropathogenic Escherichia coli are revealed on a single pilus level using force-measuring optical tweezers
- 2011
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In: European Biophysics Journal. - : Springer Science and Business Media LLC. - 0175-7571 .- 1432-1017. ; 40:3, s. 305-316
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Journal article (peer-reviewed)abstract
- Uropathogenic Escherichia coli (UPEC) expressvarious kinds of organelles, so-called pili or fimbriae, thatmediate adhesion to host tissue in the urinary tract throughspecific receptor-adhesin interactions. The biomechanicalproperties of these pili have been considered important forthe ability of bacteria to withstand shear forces from rinsingurine flows. Force-measuring optical tweezers have beenused to characterize individual organelles of F1C typeexpressed by UPEC bacteria with respect to such properties.Qualitatively, the force-versus-elongation response wasfound to be similar to that of other types of helix-like piliexpressed by UPEC, i.e., type 1, P, and S, with force-inducedelongation in three regions, one of which represents theimportant uncoiling mechanism of the helix-like quaternarystructure. Quantitatively, the steady-state uncoiling forcewas assessed as 26.4 ±1.4 pN, which is similar to those ofother pili (which range from 21 pN for SI to 30 pN for type 1).The corner velocity for dynamic response (1,400 nm/s) wasfound to be larger than those of the other pili (400–700 nm/sfor S and P pili, and 6 nm/s for type 1). The kinetics werefound to be faster, with a thermal opening rate of 17 Hz, afew times higher than S and P pili, and three orders ofmagnitude higher than type 1. These data suggest that F1Cpili are, like P and S pili, evolutionarily selected to primarilywithstand the conditions expressed in the upper urinary tract.
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| 23. |
- Persson, Per-Axel, et al.
(author)
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High-pressure polymerized C60
- 1996
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In: Extended Abstracts of Carbon´96, European Carbon Conference, Newcastle-upon-Tyne 1996, volume 2. - : The British Carbon Group. ; , s. 746-747, s. 746-747
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Conference paper (other academic/artistic)
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| 24. |
- Soldatov, Alexander, et al.
(author)
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Topochemical polymerization of C70 controlled by monomer crystal packing
- 2001
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In: Science. - : American Association for the Advanement of Science. - 0036-8075 .- 1095-9203. ; 293:5530, s. 680-683
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Journal article (peer-reviewed)abstract
- Polymeric forms of C60 are now well known, but numerous attempts to obtain C70 in a polymeric state have yielded only dimers. Polymeric C70 has now been synthesized by treatment of hexagonally packed C70 single crystals under moderate hydrostatic pressure (2 gigapascals) at elevated temperature (300°C), which confirms predictions from our modeling of polymeric structures of C70. Single-crystal x-ray diffraction shows that the molecules are bridged into polymeric zigzag chains that extend along the c axis of the parent structure. Solid-state nuclear magnetic resonance and Raman data provide evidence for covalent chemical bonding between the C70 cages.
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| 25. |
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