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Since the discovery of superconductivity at ~ 200 K in H3S [1], similar or higher transition temperatures, Tcs, have been reported for various hydrogen-rich compounds under ultra-high pressures [2]. Superconductivity was experimentally proved by different methods, including electrical resistance, magnetic susceptibility, optical infrared, and nuclear resonant scattering measurements. The crystal structures of superconducting phases were determined by X-ray diffraction. Numerous electrical transport measurements demonstrate the typical behavior of a conventional phonon-mediated superconductor: zero resistance below Tc, shift of Tc to lower temperatures under external magnetic fields, and pronounced isotope effect. Remarkably, the results are in good agreement with the theoretical predictions, which describe superconductivity in hydrides within the framework of the conventional BCS theory. However, despite this acknowledgement, experimental evidences for the superconducting state in these compounds have recently been treated with criticism [3–7], which apparently stems from misunderstanding and misinterpretation of complicated experiments performed under very high pressures. Here, we describe in greater detail the experiments revealing high-temperature superconductivity in hydrides under high pressures. We show that the arguments against superconductivity [3–7] can be either refuted or explained. The experiments on the high-temperature superconductivity in hydrides clearly contradict the theory of hole superconductivity [8] and eliminate it [3].

The low temperature magnetic properties of nanopowders of CoFe 2 O 4 and of CoFe 2 O 4 /FeCo-FeO with average particle size of about 6 nm were investigated for temperatures down to 5 K and for applied magnetic fields up to 350 kOe. Highly enhanced coercive fields were obtained for the CoFe 2 O 4 nanoparticles. The values of the saturation magnetization M S and of the anisotropy constant K 1 were also found to be enhanced for the nanocomposite powder sample. The overall results are discussed in terms of a particle model which takes into account a thin amorphous layer present in the CoFe 2 O 4 particles and due to a FeCo-FeO layer grown during an annealing procedure. Moreover, the temperature dependence of K 1 was found to be in good agreement with a model proposed by Tachiki.

We report a de Haas-van Alphen (dHvA) effect study on the Dirac type-II semimetallic candidates MAl_{3} (where, M=V, Nb and Ta). The angular dependence of their Fermi surface (FS) cross-sectional areas reveals a remarkably good agreement with our first-principles calculations. Therefore, dHvA supports the existence of tilted Dirac cones with Dirac type-II nodes located at 100, 230 and 250 meV above the Fermi level ϵ_{F} for VAl_{3}, NbAl_{3} and TaAl_{3} respectively, in agreement with the prediction of broken Lorentz invariance in these compounds. However, for all three compounds we find that the cyclotron orbits on their FSs, including an orbit nearly enclosing the Dirac type-II node, yield trivial Berry phases. We explain this via an analysis of the Berry phase where the position of this orbit, relative to the Dirac node, is adjusted within the error implied by the small disagreement between our calculations and the experiments. We suggest that a very small amount of doping could displace ϵ_{F} to produce topologically nontrivial orbits encircling their Dirac node(s).

MoTe

Electronic nematic materials are characterized by a lowered symmetry of the electronic system compared to the underlying lattice, in analogy to the directional alignment without translational order in nematic liquid crystals. Such nematic phases appear in the copper- and iron-based high-temperature superconductors, and their role in establishing superconductivity remains an open question. Nematicity may take an active part, cooperating or competing with superconductivity, or may appear accidentally in such systems. Here we present experimental evidence for a phase of fluctuating nematic character in a heavy-fermion superconductor, CeRhIn

Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

The two-dimensional organic conductor λ-(BETS)2FeCl4 has an unusual phase diagram as a function of temperature and magnetic field that includes a paramagnetic metal (PM) phase, an antiferromagnetic insulating (AFI) phase, and a field-induced superconducting phase (S. Uji, H. Kobayashi, L. Balicas, J. S. Brooks: Adv. Mater. 14: 243, 2002). Here, we report a preliminary investigation of the PM and AFI phases at 9 T over the temperature range of 2.0–180 K that uses proton nuclear magnetic resonance measurements of the spectrum, the spin-lattice relaxation rate 1/T 1, and the spin echo decay rate 1/T 2. The sample is a small single crystal whose mass is about 3 μg (approximately 2·1016 protons). Its small size creates several challenges that include detecting small signals and excluding parasitic proton signals that are not from the sample (H. N. Bachman, I. F. Silvera: J. Magn. Reson. 162: 417, 2003). These strategies and other techniques used to obtain viable signals are described.

The electronic properties of graphene are described by a Dirac Hamiltonian with a four-fold symmetry of spin and valley. This symmetry may yield novel fractional quantum Hall (FQH) states at high magnetic field depending on the relative strength of symmetry-breaking interactions. However, observing such states in transport remains challenging in graphene, as they are easily destroyed by disorder. In this work, we observe in the first two Landau levels the two-flux composite-fermion sequences of FQH states between each integer filling factor. In particular, the odd-numerator fractions appear between filling factors 1 and 2, suggesting a broken-valley symmetry, consistent with our observation of a gap at charge neutrality and zero field. Contrary to our expectations, the evolution of gaps in a parallel magnetic field suggests that states in the first Landau level are not spin-polarized even up to very large out-of-plane fields.

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.

The quantum Hall effect is investigated in the organic conductor (TMTSF${)}_{2}$P${\mathrm{F}}_{6}$ (TMTSF is tetramethyltetraselenafulvalene) under hydrostatic pressure. Under a pressure of $p\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}9$ kbar, the sequence of the quantum Hall numbers $L\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}{\ensuremath{\sigma}}_{\mathrm{xy}}/({\ensuremath{-}2e}^{2}/h)$ with increasing magnetic field is regular: $L\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\dots{},3,2,1,\dots{}$ as reported earlier. At $p\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}8.5$ kbar, however, the irregular sequence $L\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\dots{},3,\ensuremath{-}2,2,1,\dots{}$ is found. The temperature--magnetic field phase diagram is investigated in detail. We discuss our findings in the framework of recent theories of the quantum Hall effect in magnetic-field-induced spin-density waves.

The study of the magnetoresistance in the organic quasi-one-dimensional conductor (TMTSF)2NO3 at a pressure (8 kbar) exceeding the critical pressure required for the stabilization of a conducting state at low temperature has revealed the existence of quantum oscillations with a frequency of 190 T in good agreement with an extended Huckel-type calculation of the band structure. Unlike other members of the (TMTSF)2X series the ambient pressure SDW ground state in (TMTSF)2NO3 can be understood in terms of an instability involving the nesting of 2D semi-metallic Fermi surfaces.

We report magnetotransport measurements in the quasi one dimensional (Q-1-D) organic conductor (TMTTF) 2 Br at pressures up to 26 kbar, down to 0.45 K in magnetic fields up to 19 T along the c * direction. It is found that a superconducting ground state is stabilized under 26 kbar at T c =0.8 K. No magnetic field induced spin density wave (FISDW) transitions are observed below 19T unlike other Q-1-D superconductors pertaining to the selenium series. The computed amplitude of the interchain coupling along transverse directions is unable to explain the missing FISDW instability

Two new gapless quantum spin-liquid candidates with S = 1 (Ni(2+)) moments: the 6H-B phase of Ba(3)NiSb(2)O(9) with a Ni(2+)-triangular lattice and the 3C phase with a Ni(2/3)Sb(1/3)-three-dimensional edge-shared tetrahedral lattice were obtained under high pressure. Both compounds show no magnetic order down to 0.35 K despite Curie-Weiss temperatures θ(CW) of -75.5 (6H-B) and -182.5 K (3C), respectively. Below ~25 K, the magnetic susceptibility of the 6H-B phase saturates to a constant value χ(0) = 0.013 emu/mol, which is followed below 7 K by a linear-temperature-dependent magnetic specific heat (C(M)) displaying a giant coefficient γ = 168 mJ/mol K(2). Both observations suggest the development of a Fermi-liquid-like ground state. For the 3C phase, the C(M) perpendicular T(2) behavior indicates a unique S = 1, 3D quantum spin-liquid ground state.

Using Shubnikov-de Haas oscillations measured in URu2Si2 over a broad range in a magnetic field of 11-45 T, we find a cascade of field-induced Fermi surface changes within the hidden order phase I and further signatures of oscillations within field-induced phases III and V [previously discovered by Kim et al., [Phys. Rev. Lett. 91, 256401 (2003)]. A comparison of kinetic and Zeeman energies indicates a pocket-by-pocket polarization of the Fermi surface leading up to the destruction of the hidden order phase I at ≈35 T. The anisotropy of the Zeeman energy driving the transitions in URu2Si2 points to an itinerant hidden order parameter involving quasiparticles whose spin degrees of freedom depart significantly from those of free electrons.

We uncover a strong anisotropy in both the anomalous Hall effect (AHE) and the magnetoresistance of the chiral spin states of Pr(2)Ir(2)O(7). The AHE appearing below 1.5 K at a zero magnetic field shows hysteresis which is most pronounced for fields cycled along the [111] direction. This hysteresis is compatible with the field-induced growth of domains composed by the 3-in 1-out spin states which remain coexisting with the 2-in 2-out spin ice manifold once the field is removed. Only for fields applied along the [111] direction, we observe a large positive magnetoresistance and Shubnikov-de Haas oscillations above a metamagnetic critical field. These observations suggest the reconstruction of the electronic structure of the conduction electrons by the field-induced spin texture.

The resistivity along the conducting chains, ρ xx , and the Hall resistivity ρ xy are investigated as a function of the electric field in the magnetic-field-induced spin-density wave (FISDW) states of (TMTSF) 2 PF 6 under hydrostatic pressure. Both resistivities decrease with increasing electric field above the same well-defined threshold electric field in the order of 100 μV/cm. We interpret the nonlinearity by the depinning and sliding of the FISDW. The nonlinearity in ρ xy is much stronger than in ρ xx what we attribute to an unusually strong coupling between the FISDW and single-particle excitations

The synthesis and characterization of Ba3CuSb2O9, which has a layered array of Cu2+ spins in a triangular lattice, are reported. The magnetic susceptibility and neutron scattering experiments of this material show no magnetic ordering down to 0.2 K with a θ(CW) = -55 K. The magnetic specific heat reveals a T-linear dependence with a γ = 43.4 mJ K(-2) mol(-1) below 1.4 K. These observations suggest that Ba3CuSb2O9 is a new quantum spin liquid candidate with a S = 1/2 triangular lattice.

We present a detailed quantum oscillation study of the Fermi surface of the recently discovered Yb-based heavy fermion superconductor beta-YbAlB4. We compare the data, obtained at fields from 10 to 45 T, to band structure calculations performed using the local density approximation. Analysis of the data suggests that f holes participate in the Fermi surface up to the highest magnetic fields studied. We comment on the significance of these findings for the unconventional superconducting properties of this material.

In this Letter, we report a new spin ice--Pr2Sn2O7--which appears to have enhanced residual entropy due to the dynamic nature of the spins. Neutron scattering experiments show that at 200 mK, there is a significant amount of magnetic diffuse scattering which can be fit to the dipolar spin-ice model. However, these short-ranged ordered spins have a quasielastic response that is atypical of the canonical spin ices, and suggests that the ground state is dynamic (i.e., composed of locally ordered two-in-two-out spin configurations that can tunnel between energetically equivalent orientations). We report this as an example of a dynamic spin ice down to 200 mK.

Here we report the observation of Fermi surface (FS) pockets via the Shubnikov-de Haas effect in NaxCoO2 for x=0.71 and 0.84, respectively. Our observations indicate that the FS expected for each compound intersects their corresponding Brillouin zones, as defined by the previously reported superlattice structures, leading to small reconstructed FS pockets, but only if a precise number of holes per unit cell is localized. For 0.71or = x0.75 the coexistence of itinerant carriers and localized S=1/2 spins on a paramagnetic triangular superlattice leads at low temperatures to the observation of a deviation from standard Fermi-liquid behavior in the electrical transport and heat capacity properties, suggesting the formation of some kind of quantum spin-liquid ground state.

We employ a combination of chemical substitution and angle resolved photoemission spectroscopy to prove that the Fermi level in the gamma band of Sr(2-y)La(y)RuO(4) can be made to traverse a van Hove singularity. Remarkably, the large mass renormalization has little dependence on either k or doping. By combining the results from photoemission with thermodynamic measurements on the same batches of crystals, we deduce a parametrization of the full many-body quasiparticle dispersion in Sr(2)RuO(4) which extends from the Fermi level to approximately 20 meV above it.

The distorted kagomé system Nd3Ga5SiO14 has been investigated with neutron scattering down to 0.046 K with no evidence of magnetic long range order of the Nd3+ moments in a zero field. Substantial diffuse scattering is observed which is in agreement with nearest-neighbor correlations between the fluctuating spins. Upon the application of a field in the c direction, the diffuse scattering is reduced in intensity while the magnetic Bragg peaks grow in intensity to saturate by 1 T to 1/2 of the expected magnetization. These measurements suggest that a unique spin-liquid state develops in Nd3Ga5SiO14 with a frustration index of f approximately |theta|/T_{C}or =1300.

Angle-dependent magnetoresistance measurements are used to determine the isotropic and anisotropic components of the transport scattering rate in overdoped Tl2Ba2CuO6+delta for a range of Tc values between 15 and 35 K. The size of the anisotropic scattering term is found to scale linearly with Tc, establishing a link between the superconducting and normal state physics. A comparison with results from angle resolved photoemission spectroscopy indicates that the transport and quasiparticle lifetimes are distinct.

Shubnikov-de Haas oscillations reveal at high fields an abrupt reconstruction of the Fermi surface within the hidden-order (HO) phase of URu2Si2. Taken together with reported Hall effect results, this implies an increase in the effective carrier density and suggests that the field suppression of the HO state is ultimately related to destabilizing a gap in the spectrum of itinerant quasiparticles. While hydrostatic pressure favors antiferromagnetism in detriment to the HO state, it has a modest effect on the complex H-T phase diagram. Instead of phase separation between HO and antiferromagnetism our observations indicate adiabatic continuity between both orderings with field and pressure changing their relative weight.

Shubnikov-de Haas oscillations for two well-defined frequencies, corresponding, respectively, to areas of 0.8 and 1.36% of the first Brillouin zone, were observed in single crystals of Na(0.3)CoO2. The existence of Na superstructures in Na0.3CoO2, coupled with this observation, suggests the possibility that the periods are due to the reconstruction of the large Fermi surface around the Gamma point. An alternative interpretation in terms of the long sought-after epsilon'(g) pockets is also considered but found to be incompatible with existing specific heat data.

Transport, magnetic and thermal properties at high magnetic fields (H) and low temperatures (T) of the heavy fermion compound CeAuSb2are reported. At H=0 this layered system exhibits antiferromagnetic order below TN= 6K. Applying B along the inter-plane direction, leads to a continuous suppression of TNand a quantum critical point at Hc≅ 5.4 T. Although it exhibits Fermi liquid behavior within the Neel phase, in the paramagnetic state the fluctuations associated with Hcgive rise to unconventional behavior in the resistivity (sub-linear in T) and to a TlnT dependence in the magnetic contribution to the specific heat. For H > Hc, and low T the electrical resistivity exhibits an unusualT3-dependence. © 2006 American Institute of Physics.

Strongly frustrated magnetism of the metallic pyrochlore oxide Pr2Ir2O7 has been revealed by single crystal study. While Pr 4f moments have an antiferromagnetic RKKY interaction energy scale of /T*/ = 20 K mediated by Ir 5d-conduction electrons, no magnetic long-range order is found except for partial spin freezing at 120 mK. Instead, the Kondo effect, including a lnT dependence in the resistivity, emerges and leads to a partial screening of the moments below /T*/. Our results indicate that the underscreened moments show spin-liquid behavior below a renormalized correlation scale of 1.7 K.

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru0.96Rh0.04)2Si2, which yield irreversible properties similar to those at the valence transition of Yb(1-x)Y(x)InCu4. To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition.

We report an electrical transport study in Ca2-xSrxRuO4 single crystals at high magnetic fields (B). For x=0.2, the Hall constant Rxy decreases sharply at an anisotropic metamagnetic transition, reaching its value for Sr2RuO4 at high fields. A sharp decrease in the coefficient of the resistivity T2 term and a change in the structure of the angular magnetoresistance oscillations for B rotating in the planes confirms the reconstruction of the Fermi surface. Our observations and local-density-approximation calculations indicate a strong dependence of the Fermi surface on Ca concentration and suggest the coexistence of itinerant and localized electronic states in single layered ruthenates.

de Haas-van Alphen measurements on Ce(x)La(1-x)MIn(5) yield contrasting types of behavior that depend on whether M=Co and Ir or M=Rh. A stronger x-dependent scattering in the case of M=Co and Ir is suggestive of a stronger relative coupling, J/W, of the conduction electrons to the 4f electrons, which would then account for the development of a heavy composite Fermi-liquid state as x--1. The failure of a composite Fermi-liquid state to form for any x in the case of M= Rh is shown to be inconsistent with theoretical models that propose antiferromagnetism to result from spin-density-wave formation.

The triple-layered ${\mathrm{Sr}}_{4}{\mathrm{Ru}}_{3}{\mathrm{O}}_{10}$ is characterized by an unexpectedly strong quasi-two dimensional characteristic, and a sharp metamagnetic transition and ferromagnetic behavior occurring within the basal plane and along the c axis, respectively. The interplane resistivity at magnetic field B, up to 32 T, exhibits very low-frequency quantum oscillations associated with the spin polarized state when B is parallel to the c axis, and a large magnetoresistivity accompanied by critical fluctuations governed by the metamagnetic transition when B is perpendicular to the c axis. The complex behavior evidenced in magnetization, specific heat, and resistivity presented is not characteristic of any obvious ground states, and points to a unusual state that shows a delicate balance between fluctuations and order. Implications of these results are discussed.

We report measurements of the de Haas-van Alphen (dHvA) effect for single crystals of MgB2, in magnetic fields up to 32 T. In contrast to our earlier work, dHvA orbits from all four sheets of the Fermi surface were detected. Our results are in good overall agreement with calculations of the electronic structure and the electron-phonon mass enhancements of the various orbits, but there are some small quantitative discrepancies. In particular, systematic differences in the relative volumes of the Fermi-surface sheets and the magnitudes of the electron-phonon coupling constants could be large enough to affect detailed calculations of T(c) and other superconducting properties.

We report the interplane resistivity, ${\ensuremath{\rho}}_{c},$ at high magnetic fields B, with different orientations together with structural and magnetic properties of bilayered ${\mathrm{Ca}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7},$ a Mott-like system with a gap of 0.1 eV. A wide array of conventionally unanticipated phenomena revealed in this work includes (1) a collapse of the c-axis lattice parameter at a metal-nonmetal transition, (2) quantum oscillations in ${\ensuremath{\rho}}_{c}$ in the gapped, nonmetallic state for the $B\ensuremath{\parallel}c$ axis, (3) interplane tunneling magnetoresistivity for the $B\ensuremath{\parallel}a$ or b axis, and yet conspicuously different anisotropies of the colossal magnetoresistivity and magnetization, and (4) a non-Fermi-liquid behavior in a metallic state fully recovered in high magnetic fields. The implications of the coexistence of these conflicting phenomena are discussed.

The phase diagram of FeSi(1-x)Ge(x), obtained from magnetic, thermal, and transport measurements on single crystals, shows a discontinuous transition from Kondo insulator to ferromagnetic metal with x at a critical concentration, x(c) approximately 0.25. The gap of the insulating phase strongly decreases with x. The specific heat gamma coefficient appears to track the density of states of a Kondo insulator. The phase diagram is consistent with an insulator-metal transition induced by a reduction of the hybridization with x in conjunction with disorder on the Si/Ge ligand site.

The interchain resistivity of PrBa(2)Cu(4)O(8) has been measured in high magnetic fields up to 30 T. Co-herent interchain transport at low temperatures is destroyed by a large magnetic field applied perpendicular to the CuO chains. Comparisons with quasiclassical transport theory provide strong experimental support for a three-dimensional Fermi-liquid ground state in PrBa(2)Cu(4)O(8), despite extreme anisotropy in its electronic properties and the presence of strong electron correlations.

We present and analyze the normal phase temperature dependence of resistivity and nuclear spin-lattice relaxation of $(\mathrm{TMTSF}{)}_{2}{\mathrm{ClO}}_{4}$ under strong transverse magnetic fields. From a field-dependent scaling theory we show that the singular enhancement of the one-dimensional electron-electron umklapp scattering and antiferromagnetic spin correlations under field play a fundamental role in the large enhancement of magnetoresistance and nuclear relaxation of Bechgaard salts.

Summary form only given. We studied the Fermi surface of the organic conductor (TMTSF)/sub 2/NO/sub 3/ through the measurements of magnetic quantum oscillations. Two different families of oscillations are observed. Well defined Shuvnikov-de Haas(SdH) oscillations with frequency of ca. 60T can be observed below 8K and above 6T at the ambient pressure. The higher frequency oscillations reported elsewhere is not visible be low 12T. The angular magnetoresistance does not show any structure neither at Yamaji's magic angles nor at Lebed's resonance condition. Only the SdH oscillations for the field scaled by Cos /spl theta/ are added and easily separated. Under a pressure of 10kbar, different oscillations with frequency of ca. 200T is observed above 10T at 450mK. Even though it is the same frequency as so called rapid oscillations observed in other Bechgaard salts, angular dependence of oscillation frequency does not follow the simple cosine law contrary to that of (TMTSF)/sub 2/CIO/sub 4/. The amplitude of oscillations depend very oddly with sample orientation, too. Both suggest that the electron structure at low temperature is strongly modified upon application of pressure which may explain the absence of superconductivity and the field-induced spin-density waves. The angular magnetoresistance shows actually three maxima at angles which are not determined from the known theories.

Summary form only given. The Hall resistance as a function of the current along the conducting chains is investigated in the magnetic-field-induced spin-density wave (FISDW) phases of (TMTSF)/sub 2/PF/sub 6/, (TMTSF stands for tetramethyltetraselenafulvalene). Recently, we have reported/sub 1/ a nonlinear Hall resistance decreasing strongly with increasing current above a well-defined threshold current. Now we present strong evidence that the nonlinearity arises from the depinning of the FISDW. We show that by applying a radio-frequency excitation superimposed on a dc bias, interference features appear in the differential Hall resistance whwnever the phase change rate of the sliding FISDW is equal to the frequency of the rf excitation (Shapiro interference).

Measurements of the Hall effect at low electric fields in the metallic and spin-density wave (SDW) phases in (TMTSF) 2 AsF 6 shows that the scattering of single particles is strongly reduced in the SDW phase. This is attributed to a strong electron-electron scattering present in the metallic phase and absent in the SDW phase. Above the depinning threshold field for the nonlinear SDW conductivity the Hall voltage is a reliable measure of the quasiparticle current. This current is reduced above the depinning threshold because of the backflow of quasiparticles due to the interaction with the moving SDW. At 4.2 K the backflow coefficient is comparable to what is observed in CDW systems

An electrical-transport study, under magnetic field, of the organic low-dimensional conductor (TMTSF)2PF6 in its metallic state is presented. The resistance anisotropies Ryy/Rxx and Rzz/Rxx in a given sample were found to be strongly magnetic field as well as temperature dependent. Clear experimental evidence of a magnetic-field-induced one-dimensionalization of the in-plane electronic motion is provided. These findings are compared with recent experimental results and theories proposed to explain the “anomalous” magnetoresistance observed in the TMTSF compounds in terms of an unconventional or non-classical metal.

We studied the Fermi surface of the organic conductor (TMTSF) 2 NO 3 through the measurements of magnetic quantum oscillations. Well defined Shuvnikov-de Haas(SdH) oscillations with frequency of ca. 60T can be observed below 8K and above 6T at the ambient pressure. Under a pressure of 8kbar, different oscillations with frequency of ca. 180T is observed above 10T at 450mK. Electron structure at low temperature seems strongly modified upon application of pressure which may explain the absence of superconductivity and the field-induced spin-density waves. The angular magnetoresistance could not be fit neither by Yamaji's model nor by Lebed's.