L. Forró - Profile on Academia.edu (original) (raw)
Papers by L. Forró
Neurobiology of Aging, 2006
The pathological hallmarks of Alzheimer's disease (AD) consist of -amyloid plaques and neurofibr... more The pathological hallmarks of Alzheimer's disease (AD) consist of -amyloid plaques and neurofibrillary tangles in affected brain areas. The processes, which drive this host reaction are unknown. To determine whether an analogous host reaction to that occurring in AD could be induced by infectious agents, we exposed mammalian glial and neuronal cells in vitro to Borrelia burgdorferi spirochetes and to the inflammatory bacterial lipopolysaccharide (LPS). Morphological changes analogous to the amyloid deposits of AD brain were observed following 2-8 weeks of exposure to the spirochetes. Increased levels of -amyloid presursor protein (APP) and hyperphosphorylated tau were also detected by Western blots of extracts of cultured cells that had been treated with spirochetes or LPS. These observations indicate that, by exposure to bacteria or to their toxic products, host responses similar in nature to those observed in AD may be induced.
Solid State Communications, 1988
The effect of fast electron irradiation induced disorder on the high Tc (~ 8 K) superconducting t... more The effect of fast electron irradiation induced disorder on the high Tc (~ 8 K) superconducting transition in [3 -(BEDT-TTF)213, and on the metal -semiconductor u-ansition at Tp = 137 K in ct -(BEDT-TTF)213 was studied by resistivity measurements. Defects suppress both transitions at a rate of dTc/dc ~ -40 K/ %. The BEDT-TFF molecules with monovalent anions or iodine complexes form conducting salts, which are less onedimensional (1D) than the compounds of the TTF-TCNQ or (TMTSF)2X families. For example in the c~and 13 modifications of (BEDT-
Synthetic Metals, 1997
We have conducted reflectivity measurements on carbon nanotubes from the far-infrared up to the u... more We have conducted reflectivity measurements on carbon nanotubes from the far-infrared up to the ultraviolet (from 20 cm-t up to 3~10~ cm-'), in order to achieve the complete excitation spectrum. We have analysed our experimental findings in terms of the Maxwell-Gamett (MG) effective medium model, where small conducting particles are dispersed in a dielectric host-medium. We establish that carbon nanotubes have an intrinsic and anisotropic metallic behaviour.
Pressure and doping dependence of electronic properties of carbon nanotube ropes
AIP Conference Proceedings, 2000
We have performed DC transport and optical measurements on purified and doped thick films of sing... more We have performed DC transport and optical measurements on purified and doped thick films of single walled carbon nanotubes (SWNT) in the temperature range 4–300 K. The resistivity under hydrostatic pressure at room temperature shows nonmonotonic variation which is a manifestation of the symmetry change first seen in Raman scattering by Venkateswaran et al.(Phys. Rev. B [bold 59], 10928 (1999)). Despite the non-metallic temperature dependence of the dc resistivity the optical conductivity shows Drude- ...
Physical Review B, 1997
We report Hall coefficient ͑R H ͒ and magnetoresistance ͑⌬/͒ measurements on thin films of aligne... more We report Hall coefficient ͑R H ͒ and magnetoresistance ͑⌬/͒ measurements on thin films of aligned carbon nanotubes. R H is positive in the whole temperature range ͑1.7-300 K͒ showing the predominance of hole transport in the electronic conduction. The upper limit of the carrier concentration is 1.6ϫ10 19 cm Ϫ3. The resistance of the thin-film samples is governed mainly by the loose tube-tube contacts and this shows up in the ⌬/Ͻ0 at low fields, suggesting a noncoherent transport between the nanotubes. ͓S0163-1829͑97͒03311-0͔
The Journal of Physical Chemistry B, 2001
We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, vi... more We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, via a dissolved metal reduction method in liquid ammonia. The hydrogenated derivatives are thermally stable up to 400°C. Above 400°C, a characteristic decomposition takes place accompanied with the simultaneous formations of hydrogen and a small amount of methane. Transmission electron micrographs show corrugation and disorder of the nanotube walls and the graphite layers due to hydrogenation. The average hydrogen contents determined from the yield of evolved hydrogen correspond to the compositions of C 11 H for both types of nanotubes and C 5 H for graphite. Hydrogenation occurred even on the inner tubes of multiwall nanotubes as shown by the chemical composition and the overall corrugation. The thermal stability and structural results suggest the formation of C-H bonds in nanotubes and graphite.
D'Anna et al. Reply
Physical Review Letters, 1999
ABSTRACT A Reply to the Comment by P. Ao.
physica status solidi (b), 2006
We report new results on the electron spin resonance of single walled carbon nanotubes, peapods a... more We report new results on the electron spin resonance of single walled carbon nanotubes, peapods and double walled carbon nanotubes. A small ESR line is present in well purified samples and its temperature dependence reveals a striking ‘super‐Curie’ paramagnetic rise. In addition, we identify a narrower line in peapod and DWNT samples, which displays similar behavior. The linewidth of both inner and outer species are metallic and the outer tube's resonance broadens upon growth of the inner tubes. We observe a sudden decrease of relaxation rate below 20 K, in accordance with the opening of a spin‐gap. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nano Letters, 2006
We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNT... more We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches. Our switches consist of two open-ended MWNT segments separated by a nanometer-scale gap. Switching occurs through electrostatically actuated sliding of the inner nanotube shells to close the gap, producing a conducting ON state. For double-walled nanotubes in particular, a gate voltage can restore the insulating OFF state. Acting as a nonvolatile memory element capable of several switching cycles, our devices are straightforward to implement, self-aligned, and do not require complex fabrication or geometries, allowing for convenient scalability.
Catalytically grown carbon nanotubes: from synthesis to toxicity
Journal of Physics D: Applied Physics, 2007
Reversible Changes in the Superconducting Transition Temperature of Bi 2 Sr 2 CaCu 2 O 8 Single Crystals by Varying the Oxygen Concentration
Europhysics Letters (EPL), 1989
ABSTRACT We present an oxygen-annealing study on thin single crystals of Bi2Sr2CaCu2O8 which show... more ABSTRACT We present an oxygen-annealing study on thin single crystals of Bi2Sr2CaCu2O8 which shows that the superconducting transition temperature (Tc) can be reduced from 85 K to 40 K by removing oxygen and that this process is reversible.
Field emission from carbon nanotubes: perspectives for applications and clues to the emission mechanism
Applied Physics A: Materials Science & Processing, 1999
... Field emission from carbon nanotubes: perspectives for applications and clues to the emission... more ... Field emission from carbon nanotubes: perspectives for applications and clues to the emission mechanism ... Apart from applica-tions that may be realized in a distant future only,carbon nanotubes have shown great potential in some domains. ...
Magnetic resonance in the antiferromagnetic and normal state of NH3K3C60
Physical Review B, 2000
Chemistry - A European Journal, 2010
Physical Review B, 2001
133 Cs and 13 C-NMR have been used to study the electronic properties of the polymerized phase of... more 133 Cs and 13 C-NMR have been used to study the electronic properties of the polymerized phase of CsC 60 at ambient and under hydrostatic pressure. The salient result of this study is the finding of fluctuations in the local field at 133 Cs site which are independent of the applied pressure and due to thermally activated changes in the local electronic environment of 133 Cs nuclei. We establish that the phase separation between magnetic and nonmagnetic domains observed in the low temperature state at ambient pressure is the result of a slowing down of these fluctuations likely related to polaronic charge excitations on the polymers.
Nature communications, Jan 18, 2016
The time-window for processing electron spin information (spintronics) in solid-state quantum ele... more The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temp...
Topics in Applied Physics
After a short presentation on the preparation and structural properties of Multi-Wall carbon Nano... more After a short presentation on the preparation and structural properties of Multi-Wall carbon NanoTubes (MWNTs), their outstanding electronic, magnetic, mechanical and field emitting properties are reviewed. The manifestation of mesoscopic transport properties in MWNTs is illustrated through the Aharonov-Bohm effect, universal conductance fluctuations, the weak localization effect and its power-law temperature/field dependences. Measurements of the Young's modulus of individual nanotubes show the high strength of tubes having well-graphitized walls. Electron Spin Resonance (ESR) measurements indicate the low-dimensional character of the electronic states even for relatively large diameter tubes. The conducting nature of the tubes, together with their large curvature tip structure, make them excellent electron and light emitters suitable for applications.
EPL (Europhysics Letters), 2013
To identify possible spin texture contributions to thermoelectric transport, we present a detaile... more To identify possible spin texture contributions to thermoelectric transport, we present a detailed temperature and pressure dependence of thermopower S in MnSi, as well as a lowtemperature study of S in a magnetic field. We find that S/T reconstructs the (p, T) phase diagram of MnSi encompassing the Fermi liquid, partially ordered, and non-Fermi liquid phases. Our results indicate that the latter two phases have essentially the same nature. In the partially ordered phase, S(T) is strongly enhanced, which may be understood as a spiral-fluctuation-driven phase. A low temperature upturn in S/T pertaining to the partial order phase persists up to the highest pressure, 24 kbar. Contrarily, a small suppression of S(T) is observed in the ordered skyrmion lattice A phase.
EPL (Europhysics Letters), 2013
To identify possible spin texture contributions to thermoelectric transport, we present a detaile... more To identify possible spin texture contributions to thermoelectric transport, we present a detailed temperature and pressure dependence of thermopower S in MnSi, as well as a lowtemperature study of S in a magnetic field. We find that S/T reconstructs the (p, T) phase diagram of MnSi encompassing the Fermi liquid, partially ordered, and non-Fermi liquid phases. Our results indicate that the latter two phases have essentially the same nature. In the partially ordered phase, S(T) is strongly enhanced, which may be understood as a spiral-fluctuation-driven phase. A low temperature upturn in S/T pertaining to the partial order phase persists up to the highest pressure, 24 kbar. Contrarily, a small suppression of S(T) is observed in the ordered skyrmion lattice A phase.
![Research paper thumbnail of Pressure and temperature dependence of interlayer spin diffusion and electrical conductivity in the layered organic conductors κ-(BEDT-TTF)_{2}Cu[N(CN)_{2}]X (X = Cl, Br)](https://attachments.academia-assets.com/86452973/thumbnails/1.jpg)
](Physical Review B, 2011
Α high frequency (111.2-420 GHz) electron spin resonance study of the inter-layer (perpendicular)... more Α high frequency (111.2-420 GHz) electron spin resonance study of the inter-layer (perpendicular) spin diffusion as a function of pressure and temperature is presented in the conducting phases of the layered organic compounds, κ-(BEDT-TTF) 2-Cu[N(CN) 2 ]X (κ-ET 2-X), X=Cl or Br. The resolved ESR lines of adjacent layers at high temperatures and high frequencies allows for the determination of the inter-layer cross spin relaxation time, T x and the intrinsic spin relaxation time, T 2 of single layers. In the bad metal phase spin diffusion is two-dimensional, i.e. spins are not hopping to adjacent layers within T 2. T x is proportional to the perpendicular resistivity, ρ ⊥ , at least approximately, as predicted in models where spin and charge excitations are tied together. In κ-ET 2-Cl, at zero pressure T x increases as the bad metal-insulator transition is approached. On the other hand, T x decreases as the normal metal and superconducting phases are approached with increasing pressure and/or decreasing temperature.
Neurobiology of Aging, 2006
The pathological hallmarks of Alzheimer's disease (AD) consist of -amyloid plaques and neurofibr... more The pathological hallmarks of Alzheimer's disease (AD) consist of -amyloid plaques and neurofibrillary tangles in affected brain areas. The processes, which drive this host reaction are unknown. To determine whether an analogous host reaction to that occurring in AD could be induced by infectious agents, we exposed mammalian glial and neuronal cells in vitro to Borrelia burgdorferi spirochetes and to the inflammatory bacterial lipopolysaccharide (LPS). Morphological changes analogous to the amyloid deposits of AD brain were observed following 2-8 weeks of exposure to the spirochetes. Increased levels of -amyloid presursor protein (APP) and hyperphosphorylated tau were also detected by Western blots of extracts of cultured cells that had been treated with spirochetes or LPS. These observations indicate that, by exposure to bacteria or to their toxic products, host responses similar in nature to those observed in AD may be induced.
Solid State Communications, 1988
The effect of fast electron irradiation induced disorder on the high Tc (~ 8 K) superconducting t... more The effect of fast electron irradiation induced disorder on the high Tc (~ 8 K) superconducting transition in [3 -(BEDT-TTF)213, and on the metal -semiconductor u-ansition at Tp = 137 K in ct -(BEDT-TTF)213 was studied by resistivity measurements. Defects suppress both transitions at a rate of dTc/dc ~ -40 K/ %. The BEDT-TFF molecules with monovalent anions or iodine complexes form conducting salts, which are less onedimensional (1D) than the compounds of the TTF-TCNQ or (TMTSF)2X families. For example in the c~and 13 modifications of (BEDT-
Synthetic Metals, 1997
We have conducted reflectivity measurements on carbon nanotubes from the far-infrared up to the u... more We have conducted reflectivity measurements on carbon nanotubes from the far-infrared up to the ultraviolet (from 20 cm-t up to 3~10~ cm-'), in order to achieve the complete excitation spectrum. We have analysed our experimental findings in terms of the Maxwell-Gamett (MG) effective medium model, where small conducting particles are dispersed in a dielectric host-medium. We establish that carbon nanotubes have an intrinsic and anisotropic metallic behaviour.
Pressure and doping dependence of electronic properties of carbon nanotube ropes
AIP Conference Proceedings, 2000
We have performed DC transport and optical measurements on purified and doped thick films of sing... more We have performed DC transport and optical measurements on purified and doped thick films of single walled carbon nanotubes (SWNT) in the temperature range 4–300 K. The resistivity under hydrostatic pressure at room temperature shows nonmonotonic variation which is a manifestation of the symmetry change first seen in Raman scattering by Venkateswaran et al.(Phys. Rev. B [bold 59], 10928 (1999)). Despite the non-metallic temperature dependence of the dc resistivity the optical conductivity shows Drude- ...
Physical Review B, 1997
We report Hall coefficient ͑R H ͒ and magnetoresistance ͑⌬/͒ measurements on thin films of aligne... more We report Hall coefficient ͑R H ͒ and magnetoresistance ͑⌬/͒ measurements on thin films of aligned carbon nanotubes. R H is positive in the whole temperature range ͑1.7-300 K͒ showing the predominance of hole transport in the electronic conduction. The upper limit of the carrier concentration is 1.6ϫ10 19 cm Ϫ3. The resistance of the thin-film samples is governed mainly by the loose tube-tube contacts and this shows up in the ⌬/Ͻ0 at low fields, suggesting a noncoherent transport between the nanotubes. ͓S0163-1829͑97͒03311-0͔
The Journal of Physical Chemistry B, 2001
We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, vi... more We have prepared hydrogenated single-wall and multiwall carbon nanotubes, as well as graphite, via a dissolved metal reduction method in liquid ammonia. The hydrogenated derivatives are thermally stable up to 400°C. Above 400°C, a characteristic decomposition takes place accompanied with the simultaneous formations of hydrogen and a small amount of methane. Transmission electron micrographs show corrugation and disorder of the nanotube walls and the graphite layers due to hydrogenation. The average hydrogen contents determined from the yield of evolved hydrogen correspond to the compositions of C 11 H for both types of nanotubes and C 5 H for graphite. Hydrogenation occurred even on the inner tubes of multiwall nanotubes as shown by the chemical composition and the overall corrugation. The thermal stability and structural results suggest the formation of C-H bonds in nanotubes and graphite.
D'Anna et al. Reply
Physical Review Letters, 1999
ABSTRACT A Reply to the Comment by P. Ao.
physica status solidi (b), 2006
We report new results on the electron spin resonance of single walled carbon nanotubes, peapods a... more We report new results on the electron spin resonance of single walled carbon nanotubes, peapods and double walled carbon nanotubes. A small ESR line is present in well purified samples and its temperature dependence reveals a striking ‘super‐Curie’ paramagnetic rise. In addition, we identify a narrower line in peapod and DWNT samples, which displays similar behavior. The linewidth of both inner and outer species are metallic and the outer tube's resonance broadens upon growth of the inner tubes. We observe a sudden decrease of relaxation rate below 20 K, in accordance with the opening of a spin‐gap. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Nano Letters, 2006
We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNT... more We exploit the remarkable low-friction bearing capabilities of multiwalled carbon nanotubes (MWNTs) to realize nanoelectromechanical switches. Our switches consist of two open-ended MWNT segments separated by a nanometer-scale gap. Switching occurs through electrostatically actuated sliding of the inner nanotube shells to close the gap, producing a conducting ON state. For double-walled nanotubes in particular, a gate voltage can restore the insulating OFF state. Acting as a nonvolatile memory element capable of several switching cycles, our devices are straightforward to implement, self-aligned, and do not require complex fabrication or geometries, allowing for convenient scalability.
Catalytically grown carbon nanotubes: from synthesis to toxicity
Journal of Physics D: Applied Physics, 2007
Reversible Changes in the Superconducting Transition Temperature of Bi 2 Sr 2 CaCu 2 O 8 Single Crystals by Varying the Oxygen Concentration
Europhysics Letters (EPL), 1989
ABSTRACT We present an oxygen-annealing study on thin single crystals of Bi2Sr2CaCu2O8 which show... more ABSTRACT We present an oxygen-annealing study on thin single crystals of Bi2Sr2CaCu2O8 which shows that the superconducting transition temperature (Tc) can be reduced from 85 K to 40 K by removing oxygen and that this process is reversible.
Field emission from carbon nanotubes: perspectives for applications and clues to the emission mechanism
Applied Physics A: Materials Science & Processing, 1999
... Field emission from carbon nanotubes: perspectives for applications and clues to the emission... more ... Field emission from carbon nanotubes: perspectives for applications and clues to the emission mechanism ... Apart from applica-tions that may be realized in a distant future only,carbon nanotubes have shown great potential in some domains. ...
Magnetic resonance in the antiferromagnetic and normal state of NH3K3C60
Physical Review B, 2000
Chemistry - A European Journal, 2010
Physical Review B, 2001
133 Cs and 13 C-NMR have been used to study the electronic properties of the polymerized phase of... more 133 Cs and 13 C-NMR have been used to study the electronic properties of the polymerized phase of CsC 60 at ambient and under hydrostatic pressure. The salient result of this study is the finding of fluctuations in the local field at 133 Cs site which are independent of the applied pressure and due to thermally activated changes in the local electronic environment of 133 Cs nuclei. We establish that the phase separation between magnetic and nonmagnetic domains observed in the low temperature state at ambient pressure is the result of a slowing down of these fluctuations likely related to polaronic charge excitations on the polymers.
Nature communications, Jan 18, 2016
The time-window for processing electron spin information (spintronics) in solid-state quantum ele... more The time-window for processing electron spin information (spintronics) in solid-state quantum electronic devices is determined by the spin-lattice and spin-spin relaxation times of electrons. Minimizing the effects of spin-orbit coupling and the local magnetic contributions of neighbouring atoms on spin-lattice and spin-spin relaxation times at room temperature remain substantial challenges to practical spintronics. Here we report conduction electron spin-lattice and spin-spin relaxation times of 175 ns at 300 K in 37±7 nm carbon spheres, which is remarkably long for any conducting solid-state material of comparable size. Following the observation of spin polarization by electron spin resonance, we control the quantum state of the electron spin by applying short bursts of an oscillating magnetic field and observe coherent oscillations of the spin state. These results demonstrate the feasibility of operating electron spins in conducting carbon nanospheres as quantum bits at room temp...
Topics in Applied Physics
After a short presentation on the preparation and structural properties of Multi-Wall carbon Nano... more After a short presentation on the preparation and structural properties of Multi-Wall carbon NanoTubes (MWNTs), their outstanding electronic, magnetic, mechanical and field emitting properties are reviewed. The manifestation of mesoscopic transport properties in MWNTs is illustrated through the Aharonov-Bohm effect, universal conductance fluctuations, the weak localization effect and its power-law temperature/field dependences. Measurements of the Young's modulus of individual nanotubes show the high strength of tubes having well-graphitized walls. Electron Spin Resonance (ESR) measurements indicate the low-dimensional character of the electronic states even for relatively large diameter tubes. The conducting nature of the tubes, together with their large curvature tip structure, make them excellent electron and light emitters suitable for applications.
EPL (Europhysics Letters), 2013
To identify possible spin texture contributions to thermoelectric transport, we present a detaile... more To identify possible spin texture contributions to thermoelectric transport, we present a detailed temperature and pressure dependence of thermopower S in MnSi, as well as a lowtemperature study of S in a magnetic field. We find that S/T reconstructs the (p, T) phase diagram of MnSi encompassing the Fermi liquid, partially ordered, and non-Fermi liquid phases. Our results indicate that the latter two phases have essentially the same nature. In the partially ordered phase, S(T) is strongly enhanced, which may be understood as a spiral-fluctuation-driven phase. A low temperature upturn in S/T pertaining to the partial order phase persists up to the highest pressure, 24 kbar. Contrarily, a small suppression of S(T) is observed in the ordered skyrmion lattice A phase.
EPL (Europhysics Letters), 2013
To identify possible spin texture contributions to thermoelectric transport, we present a detaile... more To identify possible spin texture contributions to thermoelectric transport, we present a detailed temperature and pressure dependence of thermopower S in MnSi, as well as a lowtemperature study of S in a magnetic field. We find that S/T reconstructs the (p, T) phase diagram of MnSi encompassing the Fermi liquid, partially ordered, and non-Fermi liquid phases. Our results indicate that the latter two phases have essentially the same nature. In the partially ordered phase, S(T) is strongly enhanced, which may be understood as a spiral-fluctuation-driven phase. A low temperature upturn in S/T pertaining to the partial order phase persists up to the highest pressure, 24 kbar. Contrarily, a small suppression of S(T) is observed in the ordered skyrmion lattice A phase.
Physical Review B, 2011
Α high frequency (111.2-420 GHz) electron spin resonance study of the inter-layer (perpendicular)... more Α high frequency (111.2-420 GHz) electron spin resonance study of the inter-layer (perpendicular) spin diffusion as a function of pressure and temperature is presented in the conducting phases of the layered organic compounds, κ-(BEDT-TTF) 2-Cu[N(CN) 2 ]X (κ-ET 2-X), X=Cl or Br. The resolved ESR lines of adjacent layers at high temperatures and high frequencies allows for the determination of the inter-layer cross spin relaxation time, T x and the intrinsic spin relaxation time, T 2 of single layers. In the bad metal phase spin diffusion is two-dimensional, i.e. spins are not hopping to adjacent layers within T 2. T x is proportional to the perpendicular resistivity, ρ ⊥ , at least approximately, as predicted in models where spin and charge excitations are tied together. In κ-ET 2-Cl, at zero pressure T x increases as the bad metal-insulator transition is approached. On the other hand, T x decreases as the normal metal and superconducting phases are approached with increasing pressure and/or decreasing temperature.