Search

Growth of 2D materials under ultrahigh-vacuum (UHV) conditions allows for an in situ characterization of samples with direct spectroscopic insight. Heteroepitaxy of transition-metal dichalcogenides (TMDs) in UHV remains a challenge for integration of several different monolayers into new functional systems. In this work, we epitaxially grow lateral WS2–MoS2 and vertical WS2/MoS2 heterostructures on graphene. By means of scanning tunneling spectroscopy (STS), we first examined the electronic structure of monolayer MoS2, WS2, and WS2/MoS2 vertical heterostructure. Moreover, we investigate a band bending in the vicinity of the narrow one-dimensional (1D) interface of the WS2–MoS2 lateral heterostructure and mirror twin boundary (MTB) in the WS2/MoS2 vertical heterostructure. Density functional theory (DFT) is used for the calculation of the band structures, as well as for the density of states (DOS) maps at the interfaces. For the WS2–MoS2 lateral heterostructure, we confirm type-II band alignment and determine the corresponding depletion regions, charge densities, and the electric field at the interface. For the MTB, we observe a symmetric upward bend bending and relate it to the dielectric screening of graphene affecting dominantly the MoS2 layer. Quasi-freestanding heterostructures with sharp interfaces, large built-in electric field, and narrow depletion region widths are proper candidates for future designing of electronic and optoelectronic devices.

We present a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals: (TiZrNbNi)1−xCux and (TiZrNbCu)1−xCox in a broad composition range of 0

Growth of 2D materials under ultrahigh-vacuum (UHV) conditions allows for an in situ characterization of samples with direct spectroscopic insight. Heteroepitaxy of transition-metal dichalcogenides (TMDs) in UHV remains a challenge for integration of several different monolayers into new functional systems. In this work, we epitaxially grow lateral WS

We report the temperature and magnetic field dependence of transport properties in epitaxial films of the manganite La$_{1-x}$Ca$_{x}$MnO$_{3}$ in the overdoped region of the phase diagram for $x > 0.5$, where a charge--ordered (CO) and an antiferromagnetic (AF) phase are present. Resistivity, magnetoresistance and angular dependence of magnetoresistance were measured in the temperature interval $4.2 ~\mathrm{K} < T < 300 ~\mathrm{K}$, for three concentrations $x = 0.52, 0.58$ and $0.75$ and in magnetic fields up to 5 T. The semiconductor/insulator--like behavior in zero field was observed in the entire temperature range for all three concentrations \textit{x} and the electric conduction, at lower temperatures, in the CO state obeys 3D Mott's variable--range hopping model. A huge negative magnetoresistance for $x = 0.52$ and $x = 0.58$, a metal--insulator transition for $B > 3 ~\mathrm{T}$ for $x = 0.52$ and the presence of anisotropy in magnetoresistance for $x = 0.52$ and $x = 0.58$ show the fingerprints of colossal magnetoresistance (CMR) behavior implying the existence of ferromagnetic (FM) clusters. The declining influence of the FM clusters in the CO/AF part of the phase diagram with increasing $x$ contributes to a possible explanation that a phase coexistence is the origin of the CMR phenomenon., 33 pages, 7 figures, 1 table, accepted in Thin Solid Films

We present results of comprehensive study of electronic properties of (TiZrNbCu) 1 − x Nix metallic glasses performed in broad composition range x encompassing both, high entropy (HE) range, and conventional Ni-base alloy concentration range, x ≥ 0.35. The electronic structure studied by photoemission spectroscopy and low temperature specific heat (LTSH) reveal a split-band structure of density of states inside valence band with d-electrons of Ti, Zr, Nb and also Ni present at Fermi level N(EF), whereas LTSH and magnetoresistivity results show that variation of N(EF) with x changes in Ni-base regime. The variation of superconducting transition temperatures with x closely follows that of N(EF). The electrical resistivities of all alloys are high and decrease with increasing temperature over most of explored temperature range, and their temperature dependence seems dominated by weak localization effects over a broad temperature range (10–300 K). The preliminary study of Hall effect shows positive Hall coefficient that decreases rapidly in Ni-base alloys.

We investigate the dc resistivity and Hall effect of the quasi-two-dimensional organic materials κ–(ET)2X, where X=Ag2(CN)3 and B(CN)4 and compare them with the results for X=Cu2(CN)3. All three compounds are considered to be quantum-spin-disordered Mott insulators. Despite high similarities in chemical composition and crystal structure, large differences in the dc resistivity and Hall coefficient are found. While around room temperature the dc transport properties are dominantly determined by the strength of the electron correlations, upon reducing the temperature, dc transport happens by hopping due to inherent disorder. The most disordered compound with X=Cu2(CN)3 turns out to have the lowest dc resistivity and the highest charge carrier density, i.e., in the phase diagram it is located closest to the metal-insulator transition. The least disordered compound with X=B(CN)4 shows the highest resistivity and the lowest carrier density, i.e., lies farthest from the metal-insulator transition. We explain such counterintuitive behavior within the theory of Mott-Anderson localization as a consequence of disorder-induced localized states within the correlation gap.

The cobalt-based Heusler alloys are promising for spintronic applications, thanks to their high spin polarization and half-metallic character. This work investigates the spin-dependent transport and thermoelectric effects in epitaxial Co${}_{2}$TiSn thin films, with and without V doping. The anomalous Nernst angle and anomalous Hall angle are both determined, and the relationship between these two important parameters is discussed. These experimental results are a step toward realizing spin-caloritronic devices for efficient on-chip energy harvesting of waste heat.

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition. Conversely, the dielectric response observed in dimer Mott insulator phases with no complete evidence for charge ordering is rather intriguing. We overview our recent results of anisotropic complex conductivity (dc – MHz) in the magnetic phase of κ - ( BEDT - TTF ) 2 Cu [ N ( CN ) 2 ] Cl and in the spin-liquid phase of κ - ( BEDT - TTF ) 2 Cu 2 ( CN ) 3 . We discuss possible explanations for the observed dynamics within current theoretical models and compare them with the well-known fingerprints of the spin density wave response to ac electric fields.

The Mott insulator κ-(BEDT-TTF)2Ag2(CN)3 forms a highly-frustrated triangular lattice of S = 1/2 dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response, and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasidegenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound κ-(BEDT-TTF)2Cu2(CN)3.

We present Hall effect measurements of two-leg ladder Sr 14 - x Ca x Cu 24 O 41 ( 0 ⩽ x ⩽ 11.5 ). In these composite materials charge and spin ordering occur within chain and ladder subsystems. They have been investigated intensively during the last years because of their fascinating physical properties, especially after the discovery of superconductivity under pressure (for x > 10 ). They are the first superconducting copper oxides (superconductivity occurs under pressure for x > 10 ) without the CuO 2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for x 10 . The x = 11.5 compound shows metallic behavior and our Hall effect results match qualitatively the behavior found in high- T c cuprates. We have determined the effective number of carriers and its dependence on composition (x) and compared it to the number of holes in the ladders obtained by other experimental techniques at room temperature.

We report Hall effect measurements performed in the normal phase and at ambient pressure of (TMTSF) 2 ReO 4 and (more anisotropic) (TMTTF) 2 AsF 6 quasi-1D organic conductors. For T>200 K, the Hall coefficient of (TMTSF) 2 ReO 4 is smoothly temperature-dependent, and its value corresponds to a carrier concentration of one hole/unit cell. On the other hand, the Hall coefficient of (TMTTF) 2 AsF 6 is enhanced above 220 K, and the corresponding carrier concentration is almost 100 times lower than the expected one for one hole/unit cell. Our results give evidence for the existence of a high temperature regime above 200 K in (TMTTF)2X salts, where the 1D Luttinger liquid features appear in the transport properties.

We present the measurements of the magnetotransport properties of the spin liquid candidate κ -(BEDT-TTF) 2 Cu 2 (CN) 3 . The temperature dependencies of dc resistivity and Hall coefficient R H as well as magnetoresistance at fixed temperatures in magnetic fields up to 5 T suggest that the charge transport takes place via 2D variable range hopping among localized states.

Magnetoresistance in the spin-density wave (SDW) state of (TMTSF)2PF6 is known to exhibit a rich variety of the angular dependencies when a magnetic field B is rotated in the b'-c*, a-b' and a-c* planes. In the presence of a magnetic field the quasiparticle spectrum in the SDW with imperfect nesting is quantized. In such a case the minimum quasiparticle energy depends both on the magnetic field strength |B| and the angle \theta between the field and the crystal direction a, b' or c*. This approach describes rather satisfactory the magnetoresistance above T*~4K.

It is well documented that SDW in (TMTSF)2PF6 undergoes another phase transition at T* ≈ 4 K , though the nature of the new phase has not been identified. In particular the angular dependence of the magnetoresistance for B ‖( a, b ′) plane below 4.2 K is dramatically different from the one above 4.2 K. We propose that below T* the new phase unconventional SDW (USDW) appears which modifies drastically the quasiparticle spectrum. The present model describes the observed angular dependence of the magnetoresistance reasonably well, which cannot be interpreted in terms of the conventional SDW.

We have in detail characterized the anisotropic charge response of the dimer Mott insulator $\ensuremath{\kappa}\text{\ensuremath{-}}(\text{BEDT-TTF}{)}_{2}{\mathrm{Cu}}_{2}(\text{CN}{)}_{3}$ by dc conductivity, Hall effect, and dielectric spectroscopy. At room temperature, the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity $\ensuremath{\rho}(T)$. Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K, we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also, the relaxation levels off. The observed behavior bears features of relaxorlike ferroelectricity. Because heterogeneities impede its long-range development, only a weak-tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.

We have measured the magnetic susceptibility, resistivity, magnetoresistivity and Hall effect of nonstoichiometric cuprous selenide between 5 and 350 K. Our results show that below 170 K Cu 2− x Se is a mixture of diamagnetic Cu 1.995 Se and paramagnetic Cu 3 Se 2 . The phase diagram of the Cu–Se system, in which 170 K represents the eutectic isotherm, governs the relative content of the two phases. For the Cu 3 Se 2 phase a transition to an antiferromagnetic state is observed at about 50 K, with the corresponding Weiss temperature Θ =120 K. On heating above 170 K Cu 2− x Se becomes completely diamagnetic, but the transformation is slow and strongly time dependent. The complicated magnetic behaviour is ascribed to a broad temperature hysteresis of the process.

We have measured the magnetoresistance and the Hall effect in the spin-density-wave (SDW) state of (TMTSF)_2PF_6 down to 2K and in magnetic fields up to 9T in order to gain an additional insight into the nature of the possible subphases in the SDW state. We have found that the temperature dependent magnetoresistance anisotropy changes below 4K ; this change being maximal for the current in the lowest conductivity direction. The Hall resistivity has showed different magnetic field dependencies for T>4K and T

We report on the magnetotransport properties and spin polarization of Co-doped (La,Sr)TiO 3 (Co-LSTO) thin films in which the host oxide is a strongly correlated metal with a high density of carriers. In order to probe the spin polarization, we have performed tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions associating Co-LSTO and Co electrodes. A large spin polarization of around -80% has been determined at low temperatures, indicating that the carriers in this system are highly spin-polarized. We also report on the planar magnetotransport experiments on Co-LSTO films grown on SrTiO 3 substrates. The electrical properties of these samples are strongly dependent on the growth conditions and large electronic mobilities as high as 10 4 cm 2 /Vs at T< 10 K are observed for specimens grown at the lowest oxygen pressure. We show that this high-mobility state is three-dimensional and we relate it to the doping of the SrTiO 3 substrate with oxygen vacancies.

We present the b'-axis transverse magnetoresistance study of the spin-density-wave (SDW) ground state in the quasi–one-dimensional conductor (TMTSF)2PF6 for temperatures down to 2.2 K and magnetic fields up to 5 T. The magnetoresistance is very large and highly anisotropic. We present the clear change in the activation energy for T > 4.2 K and T < 4.2 K, which depends on magnetic field. The results can be well described by the quasi-particles with the energy gap given in the model with imperfect nesting.

Using a unique home-made cell for four-contact impedance spectroscopy of conductive liquid samples, we establish the existence of two low frequency conductivity relaxations in aqueous solutions of gelatin, in both liquid and gel state. A comparison with diffusion measurements using pulsed field gradient NMR shows that the faster relaxation process is due to gelatin macromolecule self-diffusion. This single molecule diffusion is mostly insensitive to the macroscopic state of the sample, implying that the gelation of gelatin is not a percolative phenomenon, but is caused by aggregation of triple helices into a system-spanning fibre network., 4 figures

We present results of impedance spectroscopy on gelatin solutions using a specially constructed four-electrode impedance spectroscopy cell. Our method enables impedance measurements of conductive liquid samples down to the sub- Hertz frequencies, avoiding electrode polarization effects that usually cripple standard impedance analyzers. This enables conductivity studies of self-diffusion and collective phenomena in biological samples (macromolecules, cells, ...). Our results in aqueous solutions of gelatin reveal two relaxation processes in the dilute and semi-dilute solutions. Using PFG NMR diffusiometry we identify the faster process as a self-diffusion of gelatin molecules. Scaling relations for the self- diffusion indicate that we have a microscopic phase separation distinct from spinodal decomposition. After the formation of triple-helix junction sites and the onset of gelation, these hydrophobic triple-helices aggregate due to the attractive helix-helix interactions. This leads to the formation of microphase separation between gelatin molecules which are part of the gel macrostructure (gel phase) and those which are free (sol phase). The slower process indicates a collective phenomena with anomalous diffusion. This suggests that between the single helical segments joining three chains and the macroscopic gel there exists additional levels of organization. The scales inferred from these experiments lie in the micron range and on the same scale that TEM micrographs reveal polypeptide bundles forming a network.

We have measured the Hall effect on recently synthesized single crystals of quasi-one-dimensional organic conductor TTF-TCNQ, a well known charge transfer complex that has two kinds of conductive stacks: the donor (TTF) and the acceptor (TCNQ) chains. The measurements were performed in the temperature interval 30 K < T < 300 K and for several different magnetic field and current directions through the crystal. By applying the equivalent isotropic sample (EIS) approach, we have demonstrated the importance of the choice of optimal geometry for accurate Hall effect measurements. Our results show, contrary to past belief, that the Hall coefficient does not depend on the geometry of measurements and that the Hall coefficient value is around zero in high temperature region (T > 150 K), implying that there is no dominance of either TTF or TCNQ chain. At lower temperatures, our measurements clearly prove that all three phase transitions of TTF-TCNQ could be identified from Hall effect measurements., Revised version; 7 pages, 5 figures

We present an improved approach to the impedance spectroscopy of conductive liquid samples using four-electrode measurements. Our method enables impedance measurements of conductive liquids down to the sub-Hertz frequencies, avoiding the electrode polarization effects that usually cripple standard impedance analysers. We have successfully tested our apparatus with aqueous solutions of potassium chloride and gelatin. The first substance has shown flat spectra from $\sim$100 kHz down to sub-Hz range, while the results on gelatin clearly show the existence of two distinct low frequency conductive relaxations., 5 pages, 6 figures

We study the extrinsic spin Hall effect induced by Ir impurities in Cu by injecting a pure spin current into a CuIr wire from a lateral spin valve structure. While no spin Hall effect is observed without Ir impurity, the spin Hall resistivity of CuIr increases linearly with the impurity concentration. The spin Hall angle of CuIr, $(2.1 \pm 0.6)$% throughout the concentration range between 1% and 12%, is practically independent of temperature. These results represent a clear example of predominant skew scattering extrinsic contribution to the spin Hall effect in a nonmagnetic alloy., 5 pages, 4 figures

We have studied the influence of the magnetic field in the plane perpendicular to the highly conducting axis on the ohmic and non-ohmic electrical transport in the spin-density wave state of the organic conductor (TMTSF) 2 NO 3 . In particular, we report (1) the angular dependence of the magnetoresistance at different temperatures and in low electric fields and (2) magnetic field dependence of the threshold electric field for the non-ohmic conductivity. We discuss obtained results and compare them with the behaviour found in the spin-density wave state of the other (TMTSF) 2 X compounds.

We have used electric-field-dependent measurements to probe the magnetic-field dependence of the phase-coherence length in the spin-density-wave (SDW) state of the organic conductor tetramethyltetraselenafulvalinium nitrate (TMTSF${)}_{2}$${\mathrm{NO}}_{3}$. The threshold electric field increases if a magnetic field is applied in the plane perpendicular to the highly conducting axis. The magnitude of the increase is angle-dependent and vanishes when the field is applied along the intermediate-conductivity axis. This behavior results from a reduction of the phase-coherence length of the SDW with strongly imperfect nesting in a magnetic field.

Among perovskites, SrTiO_3 (STO) is one of the most widely studied oxides because of its potential in many applications in oxide electronics. Recently it has been shown that irradiated STO surfaces exhibit high-mobility conduction in contrast to the insulating behaviour of stoichiometric STO single crystals. The possibility of modifying the properties of solids just by etching their surfaces opens up new perspectives for engineering of the functional properties of materials. But for that purpose, a deeper knowledge of damage extension and its consequences on the physical properties is highly desired. Bearing this in mind, we have characterized the spatial distribution and the nature of vacancy defects in insulating as-received as well as in ion-irradiated STO substrates exhibiting high-mobility conduction. Because tiny amounts of oxygen vacancies can trigger substantial modifications of the physical properties of STO, positron annihilation spectroscopy techniques appear as an appropriate characterization tool. We show that Ti vacancies are native defects homogeneously distributed in as-received substrates. In contrast, the dominant vacancy defects consist of non-homogeneous distributions of cation-oxygen vacancy complexes in ion-etched substrates. Their spatial extension is tuned over a few microns in ionetched samples. Our results shed light on the transport mechanisms of conductive STO crystals and on strategies for defect-engineered oxide quantum wells, wires and dots.

Using a combination of advanced characterization tools (positron annihilation spectroscopy, conductive-tip atomic force microscopy, and high-field magnetotransport), we have studied the extension, origin and properties of the high mobility electron gas (HMEG) generated by etching the SrTiO(3) surfaces with Ar(+) ions. Contrary to previous assumptions, we show that this HMEG is not confined to nanometric thickness but extends to a few micrometer from the surface. We discuss this unanticipated large spatial extension in terms of the striking large diffusion of oxygen vacancy-related defects. (C) 2010 American Institute of Physics.

We present Hall-effect measurements of two-leg ladder compounds ${\text{Sr}}_{14\ensuremath{-}x}{\text{Ca}}_{x}{\text{Cu}}_{24}{\text{O}}_{41}$ $(0\ensuremath{\le}x\ensuremath{\le}11.5)$ with the aim to determine the number of carriers participating in dc transport. Distribution of holes between the ladder and chain subsystems is one of the crucial questions important for understanding the physics of these compounds. Our Hall-effect and resistivity measurements show typical semiconducting behavior for $xl11.5$. However, for $x=11.5$, the results are completely different, and the Hall coefficient and resistivity behavior are qualitatively similar to that of high-temperature copper-oxide superconductors. We have determined the effective number of carriers at room temperature and compared it to the number of holes in the ladders obtained by other experimental techniques. We propose that going from $x=0$ to $x=11.5$ less than 1 hole per f.u. is added to the ladders and is responsible for a pronounced change in resistivity with Ca doping.

${\text{Ru}}_{1\ensuremath{-}x}{\text{Sn}}_{x}{\text{Sr}}_{2}{\text{EuCu}}_{2}{\text{O}}_{8}$ and ${\text{Ru}}_{1\ensuremath{-}x}{\text{Sn}}_{x}{\text{Sr}}_{2}{\text{GdCu}}_{2}{\text{O}}_{8}$ have been comprehensively studied by microwave and dc resistivity and magnetoresistivity and by the Hall measurements. The ruthenium magnetic ordering temperature ${T}_{m}$ is considerably reduced with increasing Sn content. However, doping with Sn leads to only slight reduction of the superconducting critical temperature ${T}_{c}$ accompanied with the increase in the upper critical field ${B}_{c2}$, indicating an increased disorder in the system and a reduced scattering length of the conducting holes in ${\text{CuO}}_{2}$ layers. In spite of the increased scattering rate, the normal state resistivity and the Hall resistivity are reduced with respect to the pure compound, due to the increased number of itinerant holes in ${\text{CuO}}_{2}$ layers, which represent the main conductivity channel. Most of the electrons in ${\text{RuO}}_{2}$ layers are presumably localized, but the observed negative magnetoresistance and the extraordinary Hall effect lead to the conclusion that there exists a small number of itinerant electrons in ${\text{RuO}}_{2}$ layers that exhibit colossal magnetoresistance.

Systematic study of electrical resistivity of Hf_{100-x}Fe_x (x=20,25), Hf_{100-x}Cu_x (x=30,40,50), and Ti_{65}Cu_{35} metallic glasses has been done in the temperature range 0.3 K - 290 K, and in magnetic fields B = 0.44 K, which is well above T_c of pure crystalline Hf (0.13 K). From the initial slopes of the upper critical fields, (dH_{c2}/dT)_{T_c}, and resistivities we determined the dressed electronic densities of states, N_{\gamma}(E_F), for all alloys. Both T_c and N_{\gamma}(E_F) decrease with increasing x (Fe and Cu content). The results are compared with those for corresponding Zr-base metallic glasses and ion-implanted Hf films., Comment: 9 pages, 4 figures, 1 table

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (PO2

Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied by dc magnetization, microwave measurements, magnetoresistivity and Hall resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron doping by La reduces the hole concentration in the CuO2 planes and completely suppresses superconductivity. Microwave absorption, dc resistivity and ordinary Hall effect data indicate that the carrier concentration is reduced and a semiconductor-like temperature dependence is observed. Two magnetic ordering transitions are observed. The ruthenium sublattice orders antiferromagnetically at 155 K for low applied magnetic field and the gadolinium sublattice antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a complicated temperature dependence due to the combination of the two magnetic orderings and spin fluctuations. It is shown that the ruthenium magnetism influences the conductivity in the RuO2 layers while the gadolinium magnetism influences the conductivity in the CuO2 layers. The magnetoresistivity is isotropic above 4 K, but it becomes anisotropic when gadolinium orders antiferromagnetically., 7 pages, 9 figures, submitted to European Physical Journal B

At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO3/SrTiO3 system. While this state has been predicted and reported to be confined at the interface, some works indicate a much broader spatial extension, thereby questioning its origin. Here we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO3/SrTiO3 samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending upon specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of microns into SrTiO3 to a few nanometers next to the LaAlO3/SrTiO3 interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system., Comment: This updated version contains new experimental data

The study reports on the magnetic properties and spin polarization of (La,Sr)Ti1-xCoxO3 (Co-LSTO) thin films. Tunneling magnetoresistance (TMR) measurements on magnetic tunnel junctions were performed to probe the spin polarisation. A large spin of -80% has been determined at low temperature, indicating that the carriers are highly spin-polarized in this system. Structural analysis was done through use of combining high-resolution transmission electron microscopy, Auger electron spectroscopy and X-ray magnetic circular dichroism. As a result, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Finally a report on planar magnetotransport experiments on Co-LSTO films grown on SrTiO3 (STO) substrates is presented.

We present the high-temperature $(70\phantom{\rule{0.3em}{0ex}}\mathrm{K}lTl300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ resistivity anisotropy and Hall effect measurements of the quasi-one-dimensional (1D) organic conductor $(\mathrm{TMTTF}{)}_{2}{\mathrm{AsF}}_{6}$. The temperature variations of the resistivity are pronouncedly different for the three different directions, with metalliclike at high temperatures for the $\mathbf{a}$ axis only. Above $220\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ the Hall coefficient ${R}_{H}$ is constant, positive, and strongly enhanced over the expected value; and the corresponding carrier concentration is almost 100 times lower than calculated for one hole/unit cell. Our results give evidence for the existence of a high-temperature regime above $200\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ where the 1D Luttinger liquid features appear in the transport properties. Our measurements also give strong evidence of charge ordering in $(\mathrm{TMTTF}{)}_{2}{\mathrm{AsF}}_{6}$. At the charge-ordering transition ${T}_{\mathrm{CO}}\ensuremath{\approx}100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, ${R}_{H}(T)$ abruptly changes its behavior, switches sign, and rapidly increases with further temperature decrease.

We report on the growth of heterostructures composed of layers of the high-Curie temperature ferromagnet Co-doped $(\mathrm{La},\mathrm{Sr}){\mathrm{TiO}}_{3}$ (Co-LSTO) with high-mobility ${\mathrm{SrTiO}}_{3}$ (STO) substrates processed at low oxygen pressure. While perpendicular spin-dependent transport measurements in STO//Co-LSTO/LAO/Co tunnel junctions demonstrate the existence of a large spin polarization in Co-LSTO, planar magnetotransport experiments on STO//Co-LSTO samples evidence electronic mobilities as high as $\ensuremath{\sim}{10}^{4}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{2}∕\mathrm{V}\phantom{\rule{0.2em}{0ex}}\mathrm{s}$ at $T=10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At high enough applied fields and low enough temperatures $(\ensuremath{\mu}\mathrm{H}\ensuremath{\geqslant}6\phantom{\rule{0.3em}{0ex}}\mathrm{T}$, $T\ensuremath{\leqslant}4\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ Shubnikov--de Haas oscillations are also observed. We present an extensive analysis of these quantum oscillations and relate them with the electronic properties of STO, for which we find large scattering rates up to $\ensuremath{\approx}{10}^{\ensuremath{-}11}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. Thus this work opens up the possibility to inject a spin-polarized current from a high-Curie temperature diluted oxide into an isostructural system with high mobility and a large spin diffusion length.

It is well documented that SDW in (TMTSF)2PF6 undergoes another phase transition at T*\approx 4K, though the nature of the new low temperature phase is controversial. We have shown recently that the new phase is well described in terms of unconventional SDW (USDW) which modifies the quasiparticle spectrum dramatically. In this paper we show that the same model describes consistently the Hall resistivity observed in (TMTSF)2PF6., 7 pages, 2 figures

The low temperature phase (LTP) of alpha-(BEDT-TTF)2KHg(SCN)(4) salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyze theoretically ADMR in unconventional (or nodal) charge-density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)2KHg(SCN)(4).

We investigated the transport properties of the quasi one-dimensional organic metal (TMTSF)2ReO4 above the anion-ordering metal-insulator transition (T_{AO} \approx 180K). The pronounced conductivity anisotropy, a small and smoothly temperature dependent Hall effect, and a small, positive and temperature dependent magnetoresistance are analyzed within the existing Fermi-liquid and non-Fermi liquid models. We propose that the transport properties of quasi one-dimensional Bechgaard salts at high temperatures can be described within the Fermi liquid description., Comment: RevTeX4, 8 pages, 5 figures, revised version

The presence of subphases in spin-density wave (SDW) phase of (TMTSF)_2PF_6 below T* \approx 4 K has been suggested by several experiments but the nature of the new phase is still controversial. We have investigated the temperature dependence of the angular dependence of the magnetoresistance in the SDW phase which shows different features for temperatures above and below T* \approx 4 K. For T > 4 K the magnetoresistance can be understood in terms of the Landau quantization of the quasiparticle spectrum in a magnetic field, where the imperfect nesting plays the crucial role. We propose that below T* \approx 4 K the new unconventional SDW (USDW) appears modifying dramatically the quasiparticle spectrum. Unlike conventional SDW the order parameter of USDW depends on the quasiparticle momentum $\Delta_1(\mvk)\propto \cos 2bk_y$. The present model describes many features of the angular dependence of magnetoresistance reasonably well. Therefore, we may conclude that the subphase in (TMTSF)2PF6 below T \approx 4 K is described as SDW plus USDW.

Comprehensive measurements of dc and ac susceptibility, dc resistance, magnetoresistance, Hall resistivity, and microwave absorption and dispersion in fields up to 8 T have been carried out on ${\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ with the aim to establish the properties of ${\mathrm{RuO}}_{2}$ and ${\mathrm{CuO}}_{2}$ planes. At $\ensuremath{\sim}130 \mathrm{K},$ where the magnetic order develops in the ${\mathrm{RuO}}_{2}$ planes, one observes a change in the slope of dc resistance, change in the sign of magnetoresistance, and the appearance of an extraordinary Hall effect. These features indicate that the ${\mathrm{RuO}}_{2}$ planes are conducting. A detailed analysis of the ac susceptibility and microwave data on both ceramic and powder samples show that the penetration depth remains frequency dependent and larger than the London penetration depth even at low temperatures. We conclude that the conductivity in the ${\mathrm{RuO}}_{2}$ planes remains normal even when superconducting order is developed in the ${\mathrm{CuO}}_{2}$ planes below $\ensuremath{\sim}45 \mathrm{K}.$ Thus, experimental evidence is provided in support of theoretical models which base the coexistence of superconductivity and magnetic order on decoupled ${\mathrm{CuO}}_{2}$ and ${\mathrm{RuO}}_{2}$ planes.

Recently many people discuss unconventional density wave (i.e. UCDW and USDW). Unlike in conventional density waves, the quasiparticle excitations in these systems are gapless. The appearence of these systems suggests paradigm shift from quasi ID system to quasi 2D and 3D systems. Here we limit ourselves to the angular dependent magnetoresistance (ADMR) observed in the low temperature phase (LTP) of α-(BEDT-TTF)2KHg(SCN)4. Here we show that UCDW describes successfully many features of ADMR as manifestation of the Landau quantization of the quasiparticle spectrum in magnetic field. Indeed ADMR will provide a unique window to access UDW like the AF phase in URu2Si2, the pseudogap phase in high Tc cuprates and the glassy phase in organic superconductor κ-(ET)2 salts.

In spite of extensive experimental studies of the angular dependent magnetoresistance (ADMR) of the low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 about a decade ago, the nature of LTP remains elusive. Here we present a new study of ADMR of LTP in alpha-(ET)_2 salts assuming that LTP is unconventional charge density wave (UCDW). In the presence of magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to striking ADMR in UCDW. The present model appears to account for many existing ADMR data of alpha-(BEDT-TTF)_2KHg(SCN)_4 remarkably well., 6 pages, 4 figures

We have studied the magnetoresistance anisotropy (at the ambient pressure) for different (TMTSF) 2 X crystals, with the current along the least conducting c direction, and the magnetic field rotated in the (a-b) plane. We compare and contrast the differences between the quenched (Q) and the relaxed (R) state for X=ClO 4 , and discuss the differences in the SDW state of X-PF 6 , X=ClO 4 (Q) and X=AsF 6 .

We present the resistivity and transverse magnetoresistance results for three principal axes of (TMTSF) 2 PF 6 in the SDW ground state ( T ≥2.2 K and B ≤5 T). Our data show a clear change of the activation energy around 4 K and its magnetic field dependence above.

We present the results for the magnetic field dependence of the electrical resistivity in hydrogen-doped Zr 68 Fe 32 metallic glasses. The undoped sample is paramagnetic down to very low temperatures ( < 1 K) because of pronounced spin fluctuations. The observed magnetoresistance is positive and increases with hydrogen concentration. The results have been analyzed using a renormalized expression for the magnetoresistivity which takes into account the exchange enhancement of the spin-splitting contributions (through the Stoner factor) to the usual weak localization and electron-electron interaction terms. The magnetoresistivity enhancement of hydrogen-doped Zr 68 Fe 32 has been attributed to the increase of the Stoner factor (1 - I) -1 , and of the spin-scattering rate τ s -1 . That increase indicates enhancement of spin fluctuations with hydrogen.

We present the influence of a transverse magnetic field on the spin-density wave (SDW) ground state of the organic conductor (TMTSF) 2 NO 3 . Magnetic field increases the single-particle activation energy. A finite magnetic field (H C ) induces discontinuities in the magnetoresistance behaviour and its value is temperature dependent. The threshold electric field (E T ) for the SDW sliding increases in a magnetic field. All observed effects are strongly angle-dependent indicating that they are determined by the magnetic field component along the least-conduction (c * ) direction. We discuss these results in the framework of a theoretical model for the SDW with large imperfect nesting