Angular-dependent Magnetoresistance Oscillations Research Articles

Fermi Surface Structure and Isotropic Stability of Fulde-Ferrell-Larkin-Ovchinnikov Phase in Layered Organic Superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3

The Fermi surface structure of a layered organic superconductor β″-(BEDT-TTF)2SF5CH2CF2SO3 was determined by angular-dependent magnetoresistance oscillations measurements and band-structure calculations. This salt was found to have two small pockets with the same area: a deformed square hole pocket and an elliptic electron pocket. Characteristic corrugations in the field dependence of the interlayer resistance in the superconducting phase were observed at any in-plane field directions. The features were ascribed to the commensurability (CM) effect between the Josephson vortex lattice and the periodic nodal structure of the superconducting gap in the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase. The CM effect was observed in a similar field region for various in-plane field directions, in spite of the anisotropic nature of the Fermi surface. The results clearly showed that the FFLO phase stability is insensitive to the in-plane field directions.

Shubnikov–de Haas Effect and Angular-Dependent Magnetoresistance in Layered Organic Conductor β′′-(ET)(TCNQ)

This paper reports the experimental results of the Shubnikov–de Haas (SdH) effect and angular-dependent magnetoresistance oscillation (AMRO) for the organic conductor β′′-(ET)(TCNQ). We observed several two dimensional (2D) SdH frequencies, whose cross-sectional areas of the Fermi surfaces (FSs) correspond to only a few percent of the first Brillouin zone. Such small 2D FSs are not predicted by band-structure calculations, suggesting that these FS pockets are created by an imperfect nesting of FSs at low temperatures. It is found that the AMRO consists of a long-period oscillation and a short-period one. The long-period oscillation is associated with the Yamaji oscillation corresponding to the α orbit, whose shape and area are consistent with previous magneto-optical measurement. The short-period oscillation is not caused by peaks instead but dips. The dip structure is discussed in terms of the AMRO of a quasi-2D electron system with a periodic potential caused by the possible density-wave related to the ...

Magnetic-field-induced phase transitions in the quasi-one-dimensional organic conductor HMTSF–TCNQ

Motivated by an interest to see if the field-induced (FI) phase in the charge-density wave (CDW) system is similar to the field-induced-SDW (FISDW) in (TMTSF)2X, (TMTSF: tetramethyltetraselenafulvalene), we examined the magnetic-field-induced phases in a quasi-one-dimensional (Q1D) organic conductor HMTSF–TCNQ (hexamethylene- tetraselenafulvalene- tetracyanoquinodimethane) under a pressure of 1.1 GPa, where the CDW occurring at 30 K is suppressed. The work was carried out by measurements of angular-dependent magnetoresistance oscillations and exploratory work on the Hall effect. It turned out that the FI-phase, most likely a FICDW for B > 0.1 T, accompany a quantum Hall effect, and the FI-phase transitions are controlled by the field component along the least conducting axis. Above 10 T, the lowest Landau level of the small 2D Fermi pocket (due to incomplete nesting of Fermi surface) exceeds the Fermi level, reaching the quantum limit. Although there are many differences between the CDW (HMTSF–TCNQ) and SDW ((TMTSF)2X) systems, a similar scenario for field-induced phases seems to hold.

Additional Evidence for the Surface Origin of the Peculiar Angular-Dependent Magnetoresistance Oscillations Discovered in a Topological Insulator Bi1−xSbx

We present detailed data on the unusual angular-dependent magnetoresistance oscillation phenomenon recentiy discovered in a topological insulator Bi0.91Sb0.09. Direct comparison of the data taken before and after etching the sample surface gives compelling evidence that this phenomenon is essentially originating from a surface state. The symmetry of the oscillations suggests that it probably comes from the (111) plane, and obviously a new mechanism, such as a coupling between the surface and the bulk states, is responsible for this intriguing phenomenon in topological insulators.

Quantum transport of two-dimensional Dirac fermions in SrMnBi2

We report two-dimensional quantum transport in SrMnBi${}_{2}$ single crystals. The linear energy dispersion leads to unusual nonsaturated linear magnetoresistance since all Dirac fermions occupy the lowest Landau level in the quantum limit. The transverse magnetoresistance exhibits a crossover at a critical field ${B}^{*}$ from semiclassical weak-field ${B}^{2}$ dependence to the high-field linear-field dependence. With an increase in temperature, the critical field ${B}^{*}$ increases and the temperature dependence of ${B}^{*}$ satisfies the quadratic behavior which is attributed to the Landau-level splitting of the linear energy dispersion. The effective magnetoresistant mobility ${\ensuremath{\mu}}_{\text{MR}}\ensuremath{\sim}3400$ cm${}^{2}$/V s is derived. Angular-dependent magnetoresistance and quantum oscillations suggest dominant two-dimensional (2D) Fermi surfaces. Our results illustrate the dominant 2D Dirac fermion states in SrMnBi${}_{2}$ and imply that bulk crystals with Bi square nets can be used to study low-dimensional electronic transport commonly found in 2D materials such as graphene.

Fermi surface and interlayer transport in the two-dimensional magnetic organic conductor (Me-3,5-DIP)[Ni(dmit)2]2

Resistance and magnetic torque measurements at low temperatures under high magnetic fields have been performed for a magnetic organic conductor (Me-3,5-DIP)[Ni(dmit)${}_{2}$]${}_{2}$ to investigate the electronic state. This conductor contains two types of Ni(dmit)${}_{2}$]${}_{2}$ anion layers, layers I and II. Shubnikov-de Haas and angular-dependent magnetoresistance oscillations clearly show that there exists a two-dimensional Fermi surface in layer II, whose spins are strongly coupled with the localized spins in layer I. When the magnetic field is applied parallel to the layers, the interlayer resistance shows a sharp minimum at $~8$ T and then slow oscillation at higher fields. The minimum is explained by the combined effect of the field-dependent magnetic potential and momentum shift in the interlayer tunneling. The mechanism of the slow oscillation is not clarified yet.

Electrical Transport Properties of Topological Insulators

From a viewpoint of transport properties, topological insulators are the materials that are insulating in the bulk but are metallic at their edge. After briefly introducing the basic phenomena such as Dirac fermions and quantum spin Hall effect for topological insulators, we describe the details of the quantum oscillations originating from the surface state of a three-dimensional topological insulator Bi1-xSbx, which was observed for the first time by our group. Intriguingly, this material was found to exhibit a novel angular-dependent magnetoresistance oscillation phenomenon, whose origin is still unknown but probably reflects a new physics in the surface transport properties of the topological insulator.

Quasi-Two-Dimensional Fermi Surfaces and Coherent Interlayer Transport inKFe2As2

We report the results of the angular-dependent magnetoresistance oscillations (AMROs), which can determine the shape of bulk Fermi surfaces (FSs) in quasi-two-dimensional (Q2D) systems, in a highly hole-doped Fe-based superconductor KFe2As2 with Tc ≈ 3.7 K. From the AMROs, we determined the two Q2D FSs with rounded-square cross sections, correspond to 12% and 17% of the first Brillouin zone. The rounded-squared shape of the FS cross section is also confirmed by the analyses of the interlayer transport under in-plane fields. From the obtained FS shape, we infer the character of the 3d orbitals that contribute to the FSs.

Reply to “Comment on ‘Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation’ ”

In reply to the Comment by Kennett regarding our article [Phys. Rev. B 77, 235123 (2008)], we clarify the key points at which we disagree with Kennett's derivation of the interlayer magnetoconductivity in layered metals and argue that our original derivation of this quantity is valid.

Comment on “Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation”

Recently, Smith and McKenzie [Phys. Rev. B 77, 235123 (2008)] used Boltzmann theory to calculate expressions for the interlayer resistivity in quasi-one-dimensional and quasi-two-dimensional metals for an arbitrary elastic collision integral. In this Comment I point out that their treatment of the equations of motion leads to an error in their expressions, and I derive corrected expressions for the interlayer conductivity in quasi-one-dimensional and quasi-two-dimensional metals in the presence of anisotropic scattering.

Angular-dependent oscillations of the magnetoresistance inBi2Se3due to the three-dimensional bulk Fermi surface

We observed pronounced angular-dependent magnetoresistance (MR) oscillations in a high-quality Bi2Se3 single crystal with the carrier density of 5x10^18 cm^-3, which is a topological insulator with residual bulk carriers. We show that the observed angular-dependent oscillations can be well simulated by using the parameters obtained from the Shubnikov-de Haas oscillations, which clarifies that the oscillations are solely due to the bulk Fermi surface. By completely elucidating the bulk oscillations, this result paves the way for distinguishing the two-dimensional surface state in angular-dependent MR studies in Bi2Se3 with much lower carrier density. Besides, the present result provides a compelling demonstration of how the Landau quantization of an anisotropic three-dimensional Fermi surface can give rise to pronounced angular-dependent MR oscillations.

Role of anion size, magnetic moment, and disorder on the properties of the organic conductor κ-(BETS) 2Ga 1- xFe xCl 4- yBr y

Shubnikov–de Haas and angular dependent magnetoresistance oscillations have been used to explore the role of anion size, magnetic moment, and disorder in the organic conductors κ ‐ ( BETS ) 2 GaBr 4 and κ ‐ ( BETS ) 2 FeCl 2 Br 2 in the isomorphic class κ ‐ ( BETS ) 2 Ga 1 ‐ x Fe x Cl 4 ‐ y Br y . The results, combined with previous work, show correlations between the anion composition ( Ga 1 ‐ x Fe x Cl 4 ‐ y Br y ) and the superconducting transition temperature, effective mass, Fermi surface topology, and the mean free path.

Anisotropic scattering in angular-dependent magnetoresistance oscillations of quasi-two-dimensional and quasi-one-dimensional metals: Beyond the relaxation-time approximation

The electrical resistivity for a current moving perpendicular to layers (chains) in quasi-two-dimensional (2D) [quasi-one-dimensional (1D)] metals under an applied magnetic field of varying orientation is studied using Boltzmann transport theory. We consider the simplest nontrivial quasi-2D and quasi-1D Fermi surfaces but allow for an arbitrary elastic collision integral (i.e., a scattering probability with arbitrary dependence on momentum transfer) and obtain an expression for the resistivity which generalizes that previously found using a single relaxation-time approximation. The dependence of the resistivity on the angle between the magnetic field and current changes depending on the momentum dependence of the scattering probability. So, whereas zero-field intralayer transport is sensitive only to the momentum-averaged scattering probability (the transport relaxation rate), the resistivity perpendicular to layers measured in a tilted magnetic field provides detailed information about the momentum-dependence of interlayer scattering. These results help us to clarify the meaning of the relaxation rate determined from fits of angular-dependent magnetoresistance oscillations (AMROs) experimental data to theoretical expressions. Furthermore, we suggest how AMRO might be used to probe the dominant scattering mechanism.

Pulsed magnetic field study of unconventional magnetoresistance of Q1D superconductors (TMTSF)2ClO4and (DMET)2I3

Quasi-one-dimensional (Q1D) organic conductors with simple open Fermi surfaces have provided novel angular dependent magnetoresistance oscillation (AMRO) phenomena for the last two decades. Both semiclassical and quantum mechanical theories well explain these phenomena, but detailed study of the field dependence probably gives a crucial test. Recently it was proposed that a kind of AMRO that is known as "Lee-Naughton oscillations (LNO)" observed for (TMTSF)2ClO4 is a result of dimensional crossover of electronic system from oneto two-dimension on changing the field orientation. We have studied the field dependence of the magnetoresistance of Q1D superconductors (TMTSF)2ClO4 and (DMET)2I3by using a 46-T pulsed magnetic field system and found the B1/2-behavior at minima of LNO.

Fermiology and superconductivity at high magnetic fields in a completely organic cation radical salt

We report specialized interplane magnetoresistance (MR) measure-ments on the organic superconducting compound β′′-(BEDT-TTF)2SF5CH2CF2SO3 (where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene) in both the superconducting (Tc ∼ 5 K) and normal states versus magnetic field direction. In the normal state, detailed angular-dependent magnetoresistance oscillation (AMRO) studies reveal peculiar features of the Fermi surface topology of this compound, and very high magnetic field studies further support the unusual nature of the electronic structure. In the superconducting state we investigate, through detailed AMRO measurements, the anomalous MR peak that appears within the superconducting field-temperature phase diagram. Our results reveal a direct connection between the superconducting state determined from purely in-plane field, and the vortex lattice produced by the inter-plane magnetic field. We also describe several unique sample rotation instruments used in these high field experiments, including the use of dysprosium pole pieces in combination with a 45 T hybrid magnet to carry out measurements at the highest steady-state resistive magnetic field (47.8 T) yet achieved.

Field- and angular-dependent resistance ofλ−(BETS)2FeCl4under pressure

We measured the field strength and angular dependence in the electrical resistance of the organic conductor $\ensuremath{\lambda}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}\mathrm{Fe}{\mathrm{Cl}}_{4}$ under a pressure of $6\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. In addition to the slow Shubnikov--de Haas (SdH) oscillations similar to those observed at ambient pressure, much faster oscillations are detected and attributed to the magnetic breakdown (MB) orbit. The increase of the SdH frequency indicates an increase in the size of the closed Fermi surface under pressure. The effective masses as determined from the closed and MB orbit oscillations are $(2.9\ifmmode\pm\else\textpm\fi{}0.3){m}_{0}$ and $(5.5\ifmmode\pm\else\textpm\fi{}0.3){m}_{0}$, respectively. The effective mass becomes smaller under pressure most likely due to the broadening of the bandwidth. The estimated internal field increases from $32\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}52\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ under a pressure of $6\phantom{\rule{0.3em}{0ex}}\mathrm{kbar}$. Angular-dependent magnetoresistance oscillations reveal a very small closed orbit which is not detected in the SdH oscillation measurements.

Fermi surface and interlayer transport in high-stageMoCl5graphite intercalation compounds

Shubnikov--de Haas (SdH) and angular-dependent magnetoresistance oscillations (AMRO's) in high-stage $\mathrm{Mo}{\mathrm{Cl}}_{5}$ graphite intercalation compounds are reported. Several SdH oscillations and AMRO's are observed; however, the background of the angular-dependent magnetoresistance cannot be interpreted by the semiclassical model based on the Boltzmann coherent transport theory. A resistance peak in magnetic fields parallel to the conducting layers is clearly observed, demonstrating coherent transport. The results are discussed in terms of an incoherent motion crossing the magnetic intercalate layers and a coherent motion only in the graphite layers.

Quantum features of angular dependent magnetoresistance oscillations in quasi-two-dimensional conductors near high magnetic field quantum limit

We report novel features of angular dependent magnetoresistance oscillations (AMROs) observed in strong magnetic fields where only a few Landau levels are occupied. In order to realize this “near-quantum-limit” in real Q2D systems, we have chosen GaAs/AlGaAs semiconductor superlattices for AMRO experiments. Near the quantum limit, the peak position of AMRO slightly depends on field strength, and it jumps synchronizing Shubnikov-de Haas peaks. AMRO disappears when the parallel field component exceeds a certain value which gives a broad local minimum of interlayer resistance. The observed features are hardly expected from the conventional picture based on the semiclassical Fermi surface topological effect ignoring Landau quantization. We have successfully explained these new features by the quantum mechanical picture which evaluates interlayer conductivity from magnetic eigen states using the Kubo formula. This quantum picture gives the most general and complete description of AMRO in Q2D conductors.

Fermi surface reconstruction in the magnetic-field-induced superconductorκ−(BETS)2FeBr4

Shubnikov-de Haas (SdH) and angular dependent magnetoresistance oscillations (AMROs) are measured in the organic superconductor with magnetic anions, $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BETS})}_{2}\mathrm{Fe}{\mathrm{Br}}_{4}$. In the paramagnetic phase $({\ensuremath{\mu}}_{0}H>{\ensuremath{\mu}}_{0}{H}_{c}=5.5\phantom{\rule{0.3em}{0ex}}\mathrm{T})$, the AMROs and the SdH oscillations are clearly observed, which are basically consistent with the band structure calculation. In the canted antiferromagnetic phase $(H<{H}_{c})$, a low frequency SdH oscillation is observed. The observation of the oscillation is not interpreted by the simple FS reconstruction due to the long range order of the Fe $3d$ spins and implies that the strong correlation between the $\ensuremath{\pi}$ and $d$ electrons modifies the reconstruction. No sign of the enhancement of the critical quantum fluctuation at ${H}_{c}$ is observed in the SdH oscillations, the reason of which is also discussed.

Investigation of interlayer coherency and angular-dependent magnetoresistance oscillations in magnetic graphite intercalation compounds

We investigated the interlayer coherency and angular-dependent magnetoresistance oscillations (AMROs) in magnetic graphite intercalation compounds (GICs), stage-1 FeCl 3 GIC ( S = 5/2) and stage-5 MoCl 5 GIC ( S = 1/2), where sufficiently strong π -d coupling is expected. Shubnikov-de Haas (SdH) oscillations were observable in a limited field-angle region. Standard AMRO was observed for both GICs, but the background of the angular-dependent magnetoresistance cannot be interpreted by the semi-classical model, based on the Boltzmann coherent transport theory. The resistance peak in magnetic fields parallel to the conduction layers is observed only for stage-5 MoCl 5 GIC, demonstrating coherent transport. The results are discussed in terms of magnetic scattering in the characteristic stacking structure of GICs.