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The ability to fabricate crystalline monolayers of confined superconducting or magnetic condensate on surfaces is a key issue to realize new functionalities and understand the nature of competing orders in their phase diagram at the nanoscale. Herein, we outline a reliable method to pattern a monolayer of superconducting islands and Kagome lattice of (BETS)2GaCl4 (where BETS = bis(ethylenedithio) tetraselenafulvalene) on Ag(111). At a deposition temperature of 125 K, (BETS)2GaCl4 dimers form Kagome lattice with a pore size of 1.2 nm, making it possible to encapsulate small molecules within the nanoporous network. When deposited at 300 K, the molecules retain their superconducting structure and minimize substrate interaction by aligning their long molecular axis perpendicular to the substrate. These results provide guidelines for facile controllable fabrications of epitaxial superconducting and/or magnetic confined condensates on metal surfaces.

Antiferromagnetic spin-flop transitions in a series of λ-(BETS)2FeBrxCl4-x are observed using piezoresistive AFM microcantilever. The measurements are carried out on a tiny single crystal using a sample rotator and the easy axis changes with increasing the bromine content x. The Neel temperature and spin-flop transition field also rise with increasing the bromine content x, suggesting an enhancement of π-d interactions by replacement of chlorine with bromine atoms in this mixed-halide anion system.

We present scanning probe microscopy investigations of metal dichalcogenide nanotubes and wires (MDNW) in order to explore their structure and electronic properties. Local spectroscopy shows that the electronic properties are very sensitive to the stoichiometry of the nanowires, which can be controlled by adjusting the synthesis conditions. Unlike their carbon counterparts, MDNW can be fabricated to yield mainly single-phase material, which makes their use as devices more feasible. In addition, we find also remarkable mechanical properties, where the molecules can be cut, recombined or deformed without any loss of structural integrity. We demonstrate this by mechanically deforming Mo6SxIy nanowires to highly strained configurations without causing irreversible changes to their structures. The rupturing and/or welding process of these nanowires, using AFM manipulation, shows that the molecules stretch to more than 30% of their relaxed configuration before plastic deformation occurs. Copyright © 2006 John Wiley & Sons, Ltd.

Using a scanning probe microscope, we investigate the structure, electronic and mechanical properties of MoS2–Ix nanotubes and Mo6SxIy nanowires. The electronic properties are interestingly very sensitive to the stoichiometry of the nanowires, which can be controlled by adjusting the synthesis conditions. In addition to that, we find also remarkable mechanical properties where molecules can be cut and recombined or deformed without any loss of structural integrity. We demonstrate this by deforming Mo6SxIy nanowires to highly strained configurations without causing irreversible changes to their structures. The rupturing and/or welding process of these nanowires, using AFM manipulation, shows that the molecules stretch to more than 30% of its relaxed configuration before plastic deformation occurs.

We present a comparative study on supported and suspended carbon nanotubes, using room temperature scanning tunneling microscopy measurement, in order to assess the effect of substrate interactions on the electronic properties. Our results show two remarkable differences between suspended and supported molecules; first there is about 0.1 eV less shift in the band structure toward higher energies which indicates less doping from the Au(1 1 1) substrate; second there are persistent coherent oscillations that are very sensitive to the bias voltage. The undamped behaviour of these oscillations is a manifestation of long coherence length, suggesting that the electron-electron interactions between nanotube and substrate is the main mechanism for phase relaxation. The origin of these oscillations is the constructive interference of electron waves that are scattered from defects on the nanotube. We present a high-resolution topographic image of a unique type of such defects where a void on the wall of a pristine nanotube is observed for the first time.

This work deals with the steady-state and time-resolved photoluminescence study of a well-known red emitting electroluminescent dye, tetraphenylporphyrin (TPP), doped in poly(methylmethacrylate). From the time-resolved photoluminescence (PL) study, exponential decay of TPP emission was observed for these doped films in the studied concentrations region (10~mol/L). At lower doping concentrations below 10 mol/L, PL lifetimes of TPP were relatively constant (∼ 10 ns) and equal to that of TPP in dilute solution. A decrease in PL lifetime was observed at high doping concentration, down to 8 ns at a concentration of 10 mol/L. This observed decrease in PL lifetime of TPP with the increase of TPP concentration was due to the concentration quenching of TPP monomer emission by the TPP dimer/aggregate sites formed at such higher concentrations. The results of concentration quenching in TPP system were compared to that of tetraphenylchlorin system reported earlier.

We dispersed single-wall carbon nanotubes (SWNTs) in polyvinyl alcohol (PVA) film mostly with nanoscale uniformity and mechanically stretched it. Polarized absorption spectra showed strong anisotropy in the near-infrared band gap transition of semiconductor SWNT with a dichroic ratio of 7.4, indicating good alignment of the embedded SWNT. The saturable absorption property of the band gap transition measured using a polarized femtosecond laser showed strong dependence on the polarization angle. When the polarization of the light was parallel to the stretching direction, the saturation power was 2.6 times smaller than that of the unstretched film, which we ascribed to the increased transition probability.

Time-resolved photoluminescence (PL) of a red emitting dye, tetraphenylchlorin (TPC), doped in poly(methylmethacrylate) (PMMA) at various concentrations was studied to clarify the mechanism of concentration quenching often observed in organic electroluminescence devices. At doping concentrations lower than 10−2 mol/L, PL lifetimes of TPC were relatively constant (∼10 ns) and equal to that of TPC in dilute solution. At doping concentrations higher than 10−2 mol/L, PL lifetime decreased rapidly with increasing concentration, down to 2 ns at 8 × 10−2 mol/L. This decrease in PL lifetime was related to the concentration quenching of TPC monomer emission by the increasing number of TPC dimer sites formed at such higher concentrations. Our experimental results of concentration-dependence trapping agree fairly well with the theoretical model of trapping by dimers reported in literature.

We have investigated the electronic structure of Au(tmdt) 2 (tmdt = trimethylenetetrathiafulvalenedithiolate), which is a single-component conductor showing a magnetic phase transition around 100 K...

We report on STM measurements of suspended carbon nanotubes at room temperature. We have found that the substrate–nanotube interactions influence the electronic properties. Bands on supported tubes are shifted toward higher energies, while those on unsupported tubes are symmetric around the Fermi level. We have also observed that interference pattern of electron waves, caused by scattering on defects and edges, is more pronounced on suspended nanotubes. These results highlight the role of substrate interactions and shed some light on their influences on nanotube devices.

A free-standing film made of a single-wall carbon nanotube (SWCNT)–polyvinylalchol (PVA) composite material was fabricated by pretreatment of SWCNTs with ultrasonication in water with the aid of a surfactant that promotes unbundling of aggregated SWNCTs. Characterizations using optical absorption spectroscopy, optical microscopy, and micro-Raman spectroscopy revealed that the film has an optical absorption at approximately 1.5 μm, suitable for the occurrence of saturable absorption (a promising nonlinear optical effect) in optical telecommunication wavelengths, and that SWCNTs in the film are dispersed uniformly with a low scattering loss. The saturable absorption properties of the film at 1.56 μm measured using the Z-scan method was basically similar to those of the SWCNTs deposited on quartz glass, indicating that the free-standing SWCNT–PVA film is as promising as the SWCNT film deposited directly on a substrate.

We investigate the nature of the magnetoresistance in the antiferromagnetic, metallic, and field-induced superconducting ground states of the quasi-two dimensional organic-magnetic conductor λ-BETS 2 Fe x Ga 1-x Cl 4 for several alloy and experimental configurations. These include a consideration of scaling-type behaviour for x = 0.47 where the field is directed in plane along the c-axis. Here we find that both the antiferromagnetic and the superconducting states follow relatively simple scaling laws with magnetic field and temperature respectively over a considerable range of the phase diagram. An investigation of systematic rotation of the magnetic field with respect to both polar and azimuthal directions for x = 0.8 in high magnetic fields is also reported for both the metallic and antiferromagnetic phases.

To further enhance the critical current density ( J c ) and irreversibility field ( H irr ) of (Cu 1− x C x )Ba 2 Ca n −1 Cu n O 2 n +4− δ ( n =4; hereafter described as (Cu,C)-1234), pinning centers were introduced by heavy-ion irradiation. The polycrystalline samples were irradiated with Au 15+ ions (240 MeV energy) at various fluence of 3.5 × 10 10 , 6.5 × 10 10 , 1 × 10 11 , 2.5 × 10 11 and 5 × 10 11 ions/cm 2 . The intragrain J c was determined from M – H curves using Bean’s critical state model. With increase of the fluence, J c shows a rapid increase and reaches a maximum value, 4.1 × 10 6 A/cm 2 (77 K and 1 T) for the fluence of 1 × 10 11 ions/cm 2 and above which it decreases slowly. The maximum value of H irr (77 K), determined by extrapolating J c curves to a 10 3 A/cm 2 criterion, is about 14.5 T for the 2.5 × 10 11 ions/cm 2 . The α value in equation H irr ( T )= H irr (0)(1− T / T c ) α decreases from 2.97 for un-irradiated sample to 1.87 for the fluence of 1 × 10 11 ions/cm 2 . These results indicate the possibility of J c (77 K and 1 T) enhancement and reaching a high H irr (77 K) at the fluence of the 1.5 × 10 11 ions/cm 2 .

A brief review of some of the arguments pointing towards the possibility of organic conductors of the form alpha-(BEDT-TTF)(2)MHg(SCN)(4) (where M = K, Tl and Rb) being candidates for Frohlich superconductivity is given. (C) 2002 Published by Elsevier Science B.V.

We examine magnetic field dependent properties associated with the newly discovered field-induced superconducting state (FISC) in λ-BETS 2 FeCl 4 . These include the metal-to-antiferromagnetic insulator transition, the critical field of the FISC state in tilted magnetic fields, and the low-pressure, magnetic field dependence of the insulating and superconducting phases.

Organic alloys λ-(BETS) 2 Fe x Ga 1- x Cl 4 show superconductivity only under very high magnetic fields parallel to the conducting layer for x ≥0.47. As x decreases, the field induced superconducti...

For further enhancement of critical currents density Jc and irreversibility field Hirr of (Cu1−xCx) Ba2Can−1CunO2n+4−δ ((Cu,C)-(n−1)n, n=3, 4 and 5) family, pinning centers were introduced by ion and neutron irradiation in these compounds. The polycrystalline samples were irradiated with 3.6×1017 neutrons/cm2 or with Au15+ ions (240 MeV energy) at a fluence of 1×1011 ions/cm2. Jc and Hirr were determined for the irradiated samples as well as unirradiated samples. The intragrain Jc was evaluated from M–H curves using Bean's critical state model. In (Cu,C)-12(n−1)n, Jc (77 K, 1 T) shows a remarkable increase from 3.9×104 to 9.1×105 A/cm2 for neutron irradiated (Cu,C)-1234 and from 3.9×104 to 4.1×106 A/cm2 for heavy-ion irradiated (Cu,C)-1234. These results indicate the possibility of further enhancement of Jc and of achieving a very high Hirr of (Cu,C)-1234 in (Cu,C)-12(n−1)n family.

We investigate by electrical transport the field-induced superconducting state (FISC) in the organic conductor λ- (BETS) 2 FeCl 4. Below 4 K, antiferromagnetic-insulator, metallic, and eventually superconducting (FISC) ground states are observed with increasing in-plane magnetic field. The FISC state survives between 18 and 41 T, and can be interpreted in terms of the Jaccarino-Peter effect, where the external magnetic field compensates the exchange field of aligned Fe 3+ ions. We further argue that the Fe 3+ moments are essential to stabilize the resulting singlet, two-dimensional superconducting state. Here we provide experimental evidence indicating that this state, as well as the insulating antiferromagnetic ground state, is extremely sensitive to hydrostatic pressure.

Electronic states have been investigated under high magnetic fields for quasi-two-dimensional organic conductors λ- (BETS) 2 Fe x Ga 1-x Cl 4 (x = 1.0, 0.47, 0.45, 0). Under magnetic field parallel to the c-axis, various electronic states appear, depending on x, field, and temperature. The global phase diagram for this alloy is presented and the evidence of the strong internal field due to the Fe moments is shown.

Owing to the coupling between π and d electron systems, organic conductors based on BETS molecules and magnetic anions such as FeC - 4 and FeBr - 4 exhibit very unique physical properties. The orthorhombic κ-(BETS) 2 FeBr 4 system is the first antiferromagnetic organic superconductor. Due to the metamagnetic nature of Fe spin system, the magnetic field dependence of resistivity shows a strong anisotropy in the ac conduction plane below T c . On the other hand, the triclinic modification, λ-(BETS) 2 FeCl 4 undergoes coupled antiferromagnetic and metal-insulator (MI) transitions at 8.5 K. The easy axis of the antiferromagnetic spin structure was found to be deviated from the c axis ( ∥ needle axis of the crystal) by 30-35°. The field-induced insulator-to-metal transition and pressure-induced superconducting transition of λ-(BETS) 2 FeCl 4 were briefly described from the viewpoint of the role of coupling between π and d electron systems.

Crystals of BETS conductors containing FeX 4 − (X=Cl, Br) anions are polymorphic. λ-BETS 2 FeCl 4 undergoes a π-d coupled antiferromagnetic insulating transition at about 8.5 K. But it exhibits a paramagnetic metal - antiferromagnetic metal transition and superconducting transition at high pressure. κ-BETS 2 FeX 4 (X=Cl, Br) are antiferromagnetic organic superconductors with the transition temperatures of T N =2.4 K (Br), 0.45 K (Cl) and T c =1.1 K (Br) and 0.1 K (Cl). Resistivity step observed at T N is the first direct evidence for π-d interaction in organic metals. No distinct anomaly in the specific heat at T c and the anisotropy of the recovery of resistivity under magnetic field at T

Among six BETS (=bis(ethylenedithio)tetraselenafulvalene) superconductors, the systems with FeX 4 m (X=Cl, Br) anions exhibit salient electronic properties due to the coupling between ~ and d electron systems. u -BETS 2 FeCl 4 undergoes successive transitions as, antiferromagnetic insulating phase M metallic phase with ferromagnetically oriented Fe 3+ spins M superconducting phase ( H //conduction plane) M metallic phase, with increasing magnetic field. s -BETS 2 FeX 4 exhibits successive antiferromagnetic and superconducting transitions with decreasing temperature. Resistivity anomaly observed at antiferromagnetic transition temperature indicates an evidence for the coupling between ~ and d electron systems. antiferromagnetic organic superconductor BETS magnetic organic superconductor organic superconductor

The effect of uniaxial pressure on the superconducting transition temperature, T c , was studied in organic superconductor κ-(BEDT-TTF) 2 Cu(NCS) 2 . When the pressure was applied along the c-axis in the conducting b-c plane, \partial T_c/\partial p was found to show a positive value. In other words, T c increased by application of pressure, in contrast to other cases including the uniaxial pressure perpendicular to the conducting plane and the hydrostatic pressure. Detailed experimental studies on the temperature dependence of magnetization under uniaxial pressure using SQUID magnetometer are presented.

Superconducting compounds of Ba2Can−1CunO2n(O,F)2 (n=2–5) whose apical oxygen is partially substituted by fluorine have been synthesized under high pressure. The nearly single-phase samples of n=3 and 4 were prepared from almost stoichiometric compositions (δ is small) of Ba2Ca2Cu3O6(O1−y±δFy)2 (y=0.6–0.8) and Ba2Ca3Cu4O8(O1−y±δFy)2 (y=0.5–0.7), respectively. The samples showed sharp superconducting transitions in both resistivity and susceptibility measurements. The samples showed typical under-doped behavior (S-shape) in the temperature dependence of resistivity. The Tc for the n=3 phase monotonically increased with decreasing a nominal fluorine content y, which shows the electronic state shifts from under-doped toward optimally one with increasing hole density by substitution of apical O2− for F−. The highest Tc measured so far for n=2, 3, 4 and 5 phases were 90, 120, 105 and 90 K, respectively. This compound shows a maximum Tc at n=3 like in many other homologous series. In spite of a short spacing between superconducting blocks (≈7.36 A), the critical current density (Jc) and irreversibility field (Hirr) of the n=3 phase decreased rapidly with increasing temperature provably due to the small carrier (holes) density.

Two “superconducting transition temperatures” ( T c s) of Cu x Ba 2 Ca 3 Cu 4 O y were examined by the specific heat measurement. Comparing the specific heat under magnetic field (14 T) and that without field, two anomalies were observed in the electronic specific heat. When there are more than two Fermi surfaces (FSs) and the superconducting gaps do not develop simultaneously in these FSs, we can expect two anomalies. Strictly speaking the second anomaly at lower temperature ( T c2 ) is not due to the real phase transition but its vestige. A theoretical inspection indicates the second anomaly means the inter-FS interaction is very weak. If the symmetry of the superconducting gap on one FS is different from that on the other, one can expect a drastic suppression of the inter-FS interaction.

TlBa 2 Ca n −1 Cu n O y ( n =3: Tl-1223 and n =4: Tl-1234) have been found to have comparable T c with Hg-system which is known to show the highest T c in superconductors. Samples were synthesized under a pressure of 3.5 GPa using precursors with small residual carbon concentrations. We found that starting composition of Tl and synthesis temperature also affect the T c . Polycrystalline samples showed T c of 133.5 (Tl-1223) and 127 K (Tl-1234) after the post-annealing in nitrogen flow, respectively. Composition analysis suggested that suppression of the substitution of Tl for Ba- and Ca-site enhances the T c .

A TlBa2Ca2Cu3Oy (Tl-1223) superconductor with an ideal composition has a much higher Tc than the established value (~120 K). The intrinsic Tc arises by suppression of Tl substitution for Ba and Ca sites, which inherently occurs in samples prepared by conventional methods. The substitution of Tl was suppressed by preserving the samples in a heavily over-doped state (Tc~100 K) which was realized by a high-pressure (solid and oxygen) synthesis method. In addition, we found several synthesis conditions for which we could obtain high-Tc samples with good reproducibility. Residual carbon in the precursor was found to be harmful for superconductivity, so that it had to be reduced as much as possible before the high-pressure synthesis. The synthesis temperature and starting concentration of Tl, which also affect Tc, had to be controlled properly to enhance Tc. Samples show that Tc≥130 K by post-annealing in a reducing atmosphere at 650-700 °C for 0.5 h to 12 h. The sample prepared with the starting composition of Tl0.75Ba2Ca2Cu3.25Oy had an almost ideal grain composition and showed a Tc of 133.5 K. This Tc is comparable with that of HgBa2Ca2Cu3Oy (Hg-1223) which is known to have the highest Tc in superconductors.

We measured for the first time the fundamental and higher harmonic components of AC susceptibility of CuBa 2 Ca 3 Cu 4 O y superconductor produced by the high-pressure technique, in various experimental conditions (temperature, DC magnetic field, AC field amplitude and frequency). The results are discussed qualitatively in the frame of the critical state and other models in the literature. By using a very simple frequency-dependent critical state model, we estimated the parameters of practical interest, critical current density and pinning potential at various DC fields and temperatures and the irreversibility field. We also extrapolated our estimations to both practical temperature of 77 K and longer time scale as of DC magnetization and transport measurements. The results appeared to be quite self-consistent.

We have recently found various magnetic organic conductors exhibiting novel electric and magnetic properties, where the interplay between magnetism and conductivity play an essential role. There are mainly two types of crystal modification (λ and κ) in (BETS) 2 FeX 4 [BETS=bis(ethylenedithio)tetraselenafulvalene]. In the triclinic modification, λ-(BETS) 2 FeCl 4 , conduction electrons in the BETS layers interact with spins localized on the FeCl 4 − anions to give an antiferromagnetic insulating ground state. But the system becomes a superconductor at high pressure. In addition, λ-(BETS) 2 Fe x Ga 1− x Cl 4 (0.35 x 2 FeBr 4 , has been revealed to be the first antiferromagnetic organic superconductor ( T N =2.4 K and T c =1.1 K). The specific heat measurements showed evidence for the coexistence of magnetic order and superconductivity below T c . The easy axis of the antiferromagnetic metal phase below T N is parallel to the a axis and the field dependence of the magnetization showed a metamagnetic behavior around 2 T. Recently, we have found that isostructural λ-(BETS) 2 FeCl 4 undergoes similar magnetic and superconducting transitions at lower temperatures.

A detailed angular dependent magneto-transport and magnetization study of the charge transfer salt α-(ET) 2 MHg(SCN) 4 , where M = K, Rb, or Tl, reveals multiple electronic sub-phases with respect to temperature, field strength, and field orientation. We find that the low temperature ground state undergoes two subsequent field-induced phase transitions above a critical angle, θ c , of the magnetic field with respect to the crystallographic axes (θ c ≥ 50°). This new T-B-θ phase diagram may be qualitatively described assuming a charge density wave framework with the field-induced transitions arising from the interplay between orbital and Pauli effects. This implies well (but not perfectly) nested quasi-one-dimensional Fermi sheets.

Magnetoresistance measurements have been performed for the organic conductor -(BETS) FeBr to investigate the Fermi surface. Three fundamental Shubnikov-de Haas oscillations (, and ) were observed. The cross-sectional areas corresponding to the and oscillations are about 20% and 100% in the "rst Brillouin zone, respectively. The oscillations can be assigned to the closed orbit and the magnetic breakdown orbit. The e!ective masses of the conduction electrons are determined to be 5.2m for and 7.9m for . The heavy masses are probably due to the antiferromagnetic #uctuation e!ect of the Fe spins. The origin of the oscillation with very low frequency is not explained by the band calculation. 2001 Elsevier Science B.V. All rights reserved.

ac susceptibility measurements of the charge-density-wave (CDW) compound alpha-(BEDT-TTF)(2)-KHg(SCN)(4) at magnetic fields, mu0H >23 T, above its Pauli paramagnetic limit, reveal unambiguously that the magnetic hysteresis observed previously within this CDW phase is diamagnetic and can only be explained by induced currents. It is argued that the ensemble of experimental techniques amounts to a strong case for dissipationless conductivity within this phase.

Specific heat anomaly was studied on Cu x Ba 2 Ca 3 Cu 4 O y . ΔC/ T c , a height of peak of the specific heat at the superconducting transition ( T c ) divided by T c , is less than 60% of that of optimally doped YBa 2 Cu 3 O 7-δ . This suggests that a large density of states (DOS) remains to prohibit the creation of Bardeen-Cooper-Schrieffer (BCS) pairs at T c . It is much larger than the residual DOS at 0 K. We interpret that the “ missing DOS ” start to become BCS pairs at a temperature lower than T c , as proposed by an NMR study [Phys. Rev. B 61 (2000) 9707], though we have not yet seen clear evidence of this.

Photoluminescence properties were measured for vacuum-deposited thin films of magnesium, chloroaluminum, bromoaluminum, and metal-free phthalocyanines (MgPc, AlClPc, AlBrPc, and H2Pc). For MgPc, Al...

We have performed magnetoresistance measurements on an organic conductor, α-(BEDT-TTF)2KHg(SCN)4, and on a Kondo semiconductor, CeNiSn, at low temperatures and for fields up to 45 T in the hybrid magnet at the National High Magnetic Field Laboratory. We will discuss some new insight into a very controversial high-field phase of α-(BEDT-TTF)2KHg(SCN)4 gained from measurements of the anomalous temperature dependence of the quantum oscillations in the range 25–45 T. New information will also be presented on the temperature dependence of resistivity in the high-field state of CeNiSn, where questions of metallic versus semiconducting ground states arise. To acquaint researchers who anticipate using the facility in the near future, practical details concerning use of this new high-field resource are included.

The electrical and magnetic properties of kappa-(BETS)(2)FeBr(4) salt [where BETS = bis(ethylenedithio)tetraselenafulvalene] showed that this system is the first antiferromagnetic organic metal at ambient pressure (T(N) = 2.5 K). The characteristic field dependence of the magnetization at 2.0 K indicates a clear metamagnetic behavior. The small resistivity drop observed at T(N) clearly shows the existence of the interaction between pi metal electrons and localized magnetic moments of Fe(3+) ions. In addition, this system underwent a superconducting transition at 1.1 K. That is, kappa-(BETS)(2)FeBr(4) is the first antiferromagnetic organic metal exhibiting a superconducting transition below Néel temperature. The magnetic field dependence of the superconducting critical temperature indicated that the superconductivity in this system is strongly anisotropic also in the conduction plane because of the existence of the metamagnetically induced internal field based on the antiferromagnetic ordering of the Fe(3+) 3d spins in contrast to the cases of the other conventional organic superconductors. Furthermore, the specific heat measurement exhibited a lambda-type large peak of zero-field specific heat corresponding to the three-dimensional antiferromagnetic ordering of high-spin Fe(3+) ions. The lack of distinct anomaly in the C(p) vs T curve at T(c) suggests the coexistence of the superconductivity and the antiferromagnetic order below T(c).

We present the results of magnetotransport and magnetic torque measurements on the $\ensuremath{\alpha}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}\mathrm{KHg}(\mathrm{SCN}{)}_{4}$ charge-transfer salt within its high-magnetic-field phase, in magnetic fields extending to 33 T and temperatures as low as 27 mK. While the experimentally determined phase diagram closely resembles that predicted by theoretical models for charge-density waves in strong magnetic fields, the phase that occurs at fields above $\ensuremath{\sim}23 \mathrm{T},$ which is expected to be either a modulated charge-density wave phase or a charge/spin-density wave hybrid, exhibits unusual physical properties that are most atypical of a density wave ground state. Notably, the resistivity undergoes a dramatic drop below $\ensuremath{\sim}3 \mathrm{K}$ within this phase, falling in an approximately exponential fashion at low temperatures, while the magnetic torque undergoes extensive hysteresis. This hysteresis, which occurs over a broad range of fields and gives rise to a large negative differential susceptibility $\ensuremath{\partial}M/\ensuremath{\partial}B$ on reversing the direction of sweep of the magnetic field, is strongly temperature dependent and also has several of the physical characteristics predicted by critical-state models normally used to describe the pinning of vortices in type II superconductors. Such a behavior appears therefore only to be explained consistently in terms of persistent currents within the high-magnetic-field phase of $\ensuremath{\alpha}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}\mathrm{KHg}(\mathrm{SCN}{)}_{4},$ although the origin of these currents remains an open question.

We present angular dependent magneto-transport and magnetization measurements on alpha-(ET)2MHg(SCN)4 compounds at high magnetic fields and low temperatures. We find that the low temperature ground state undergoes two subsequent field-induced density-wave type phase transitions above a critical angle of the magnetic field with respect to the crystallographic axes. This new phase diagram may be qualitatively described assuming a charge density wave ground state which undergoes field-induced transitions due to the interplay of Pauli and orbital effects., 11 pages, 4 figures, shown at the APS march meeting 2000, appears in the Ph.D. thesis of J. S. Qualls (Florida State University, 1999), and submitted to PRL

The conductivity measurements were performed in the spin-density-wave (SDW) phase of (TMTSF) 2 ClO 4 . The electric conductivity increases above the clear threshold electric field E T . The normalized excess electric conductivity [σ(2 E T )-σ(0)]/σ(0) rapidly decreases below about T * ≃0.3 T SDW , where T SDW is the SDW transition temperature. In high electric fields far above E T , the temperature independent electric conduction expressed as the function j = j 0 exp (- E 0 / E ) is observed below T * . It is suggested that the sliding of SDW with the quantum origin occurs in the low temperature. These phenomena are related to the phase transition dividing the SDW phase into two sub-phases in (TMTSF) 2 ClO 4 . The electric conductivity in the low temperature sub-phase is discussed in term of the SDW with the discommensuration.

We have performed the electric conductivity measurements in the spin-density-wave (SDW) phase of (TMTSF) 2 ClO 4 to clarify the dynamics of SDW. The temperature dependence of threshold electric fie...

We report here on an optimised purification method for carbon nanotubes which yields microcrystalline single wall nanotube (SWNT) material. For this work the material is characterised using a scanning tunneling microscope (STM) with atomic resolution at room temperature. In the purified material, tubes with armchair structure prevail (diameter 1.7–2.5 nm), although tubes with other chiralities are also present. Based on STM topographic images the purity of SWNT material in the final step was estimated to be between 70 and 80%. In contrast to well-known ropes of SWNTs, the microcrystalline material is composed of parallel SWNTs which are not twisted, forming a crystalline structure in two dimensions. An interesting point is that tubes from one microcrystal appear from the STM images all to have the same chirality.

We dispersed nanoparticles of Prussian blue (PB) in water using surface modification of the PB nanoparticles. Using spin-coating method, a thin film is easily fabricated with water dispersible ink of PB nanoparticles. The PB film thickness was estimated as 40–430 nm. The PB nanoparticle film on an indium tin oxide glass substrate showed a stable electrochromic response: the color changed repeatedly between blue and colorless without any post-treatment.

A series of metal bis-mnt complexes (mnt = 1,2-dithiolatomaleonitrile) with the trimethylammonium methylferrocene cation have been synthesized and characterized using X-ray diffraction, magnetic susceptibility, and differential scanning calorimetry measurements. The complexes have the formulas (FcCH(2)NMe(3))[Ni(mnt)(2)] (2), (FcCH(2)NMe(3))[Pt(mnt)(2)] (3), and (FcCH(2)NMe(3))(2)[Cu(mnt)(2)] (4) (where Fc = ferrocene). At 300 K, the crystal structures of 1:1 complexes 2 and 3 are very similar. They consist of pairs of [M(mnt)(2)](-) in a slipped configuration packed in stacks. Each [M(mnt)(2)](-) stack is separated from adjacent stacks by two columns of cations. Within the pairs, the [M(mnt)(2)](-) anions interact via short M.S contacts, while there are no short contacts between the pairs. Complex 4, which has a 2:1 stoichiometry, exhibits a markedly different packing arrangement of the anionic units. Due to the special position of the Cu atom in the asymmetric unit cell, [Cu(mnt)(2)](2)(-) dianions are completely isolated from each other. The magnetic susceptibility behavior of the nickel complex is consistent with the presence of magnetically isolated, antiferromagnetically (AF) coupled [Ni(mnt)(2)](-) pairs with the AF exchange parameter, J = -840 cm(-)(1). The platinum complex undergoes an endothermic structural phase transition (T(p)) at 247 K. Below T(p) its structure is characterized by the formation of magnetically isolated [Pt(mnt)(2)](2)(2)(-) dimers in an eclipsed configuration with short Pt.Pt and S.S contacts between monomers. In the magnetic properties, the structural changes reveal themselves as an abrupt susceptibility drop implying a substantial increase of the AF exchange parameter. A mechanism of the phase transition in the platinum compound is proposed. For compound 4, paramagnetic behavior is observed.

Synthesis of ${\mathrm{CuBa}}_{2}{\mathrm{Ca}}_{3}{\mathrm{Cu}}_{4}{\mathrm{O}}_{12\ensuremath{-}y}$ (Cu-1234) with Mg doping at the Ca sites, hitherto unexplored, is attempted and reported here. Different samples with 5%, 10%, 20%, and 33% Mg (in nominal stoichiometry) have been prepared in gold capsules under 3.5 GPa pressure and at about 1000 \ifmmode^\circ\else\textdegree\fi{}C temperature using a cubic anvil-type high-pressure machine. The samples were characterized through x-ray diffractometry, resistivity, dc susceptibility, and Hall effect measurements. The samples were then aligned along their c axis under 10 T field at room temperature. Magnetization (both in $H\ensuremath{\parallel}\mathrm{ab}$ and $H\ensuremath{\parallel}c$) was measured between 120 and 5 K in different field values up to 5 T. The superconducting anisotropy (defined as ${\ensuremath{\xi}}_{\mathrm{ab}}/{\ensuremath{\xi}}_{c}{=H}_{c2}^{\mathrm{ab}}{/H}_{c2}^{c}$), estimated in the reversible magnetization regime, comes out to be about 1.4, and is lower than that of the pristine sample. Improvement in the anisotropy factor obtained has been discussed in light of the observed changes in the lattice parameters and the hole concentration, emanating from Mg doping in the Cu-site vacancies in charge reservoir blocks of the 1234 structure.

The hot press method was employed for the synthesis of a new family of the high T c superconductor (CuTl)Ba 2 Ca n −1 Cu n O 2 n +4− y . By varying the starting composition of the samples, the optimum preparation conditions for the Cu 1− x Tl x Ba 2 Ca 2 Cu 3 O 10− y ( x =0.25–0.75) phases were studied. The highest T c (121 K) sample of (Cu 0.3 Tl 0.7 )-1223 was obtained by hot press sintering at 1000°C for 3 h. Highly oriented (Cu 0.3 Tl 0.7 )-1223 samples along the c -axis were obtained by the same way.

We describe experiments in steady magnetic fields up to 33 T at low-temperatures on low-dimensional organic metals where the Landau level separation becomes greater than either the thermal or the impurity broadening. High precision, simultaneous Shubnikov–de Haas and de Haas–van Alphen measurements allow direct correlation of the oscillations of the magnetization with the dissipation as the Landau levels cross the Fermi level. From these results, we can determine with reasonable certainty the functional form of the density of states, and their relative values in the open- and closed-orbit bands.

Single crystals of CuBa 2 Ca 3 Cu 4 O y (Cu-1234) with dimensions up to 200×100×20 μ m 3 have been synthesized under high pressure using a belt type anvil apparatus. The impurity of Au, emanating from Au capsule, was found in the crystals by SEM–EDS analysis. These crystals showed superconducting transition temperature ( T c ) ranging from 105 K to 68 K and are lower than that of Au-free polycrystals ( T c =118 K). The T c values are found to decrease linearly with Au content at a substantially high rate of 7.0±0.4 K%, indicating the substitution of Au ions for Cu-sites. Superconducting anisotropy γ as estimated from the resistivity data of Cu-1234 single crystal just above T c (=102 K) has been found to be higher ( γ =5.8) than that for the Au-free polycrystals.