Angle-dependent Magnetoresistance Research Articles

A detailed de Haas–van Alphen effect study of the overdoped cuprate Tl2Ba2CuO6+δ

We report a detailed quantum oscillation study of the overdoped cuprate Tl2Ba2CuO6+δ at two different doping levels (Tc=10 and 26 K). The derived Fermi surface size and topology complement earlier angle-dependent magnetoresistance studies and confirm the existence of a large quasi-cylindrical hole-doped Fermi surface with a small, but finite, c-axis warping. An accurate determination of the hole concentration reveals that superconductivity in Tl2Ba2CuO6+δ does not follow the universal Tc(p) parabola for cuprate families and survives up to a larger doping of pc=0.31. The observation of quantum oscillations for both dopings demonstrates that Fermi liquid behaviour is not confined to the edge of the superconducting dome, but is robust up to at least 0.3Tmaxc. Moreover, the observation of such well-resolved oscillations implies that the physical properties of overdoped Tl2Ba2CuO6+δ are determined by a single, spatially homogeneous electronic ground state. Finally, analysis of the different quasiparticle masses points towards a purely magnetic or electronic pairing mechanism.

A Comparative Study of Angle Dependent Magnetoresistance in [001] and [110] La2/3Sr1/3MnO3

The angle dependent magnetoresistance study on [001] and [110] La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ thin films show that the anisotropy energy of [110] films is higher when compared with a [001] oriented La$_{2 / 3}$Sr$_{1 / 3}$MnO$_{3}$ film of similar thickness. The data has been analyzed in the light of multidomain model and it is seen that this model correctly explains the observed behavior.

Two distinct quasiparticle inelastic scattering rates in thet−Jmodel and their relevance for high-Tccuprate superconductors

The recent findings about two distinct quasiparticle inelastic scattering rates in angle-dependent magnetoresistance (ADMR) experiments in overdoped high-$T_c$ cuprates superconductors have motivated many discussions related to the link between superconductivity, pseudogap, and transport properties in these materials. After computing dynamical self-energy corrections in the framework of the $t-J$ model the inelastic scattering rate was introduced as usual. Two distinct scattering rates were obtained showing the main features observed in ADMR experiments. Predictions for underdoped cuprates are discussed. The implicances of these two scattering rates on the resistivity were also studied as a function of doping and temperature and confronted with experimental measurements.

In-plane electronic anisotropy in underdopedBa(Fe1−xCox)2As2revealed by partial detwinning in a magnetic field

We present results of angle-dependent magnetoresistance measurements and direct optical images of underdoped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ which reveal partial detwinning by action of a 14T magnetic field. Driven by a substantial magneto-elastic coupling, this result provides evidence for an electronic origin of the lattice distortion in underdoped iron pnictides. The observed anisotropy in these partially detwinned samples implies a substantial in-plane electronic anisotropy in the broken symmetry state, with a smaller resistivity along the antiferromagnetic ordering direction.

Angle-dependent magnetoresistance oscillations and magnetic breakdown in [formula omitted

We present results of stereographic measurements of interlayer magnetoresistance in the quasi-two-dimensional (Q2D) organic conductor, α ‐ ( BEDT ‐ TTF ) 2 KHg ( SCN ) 4 , at around charge density wave (CDW) transition temperature T c ∼ 8 K . At 2 K in the CDW phase, there exists the anomalous Lebed resonance pattern, the amplitude of which is modulated by Danner–Chaikin oscillations in case of applied magnetic field close to the Q2D conducting plane. On the contrary, at 7 K just below T c , we have found that the Kajita oscillation of the cylindrical Fermi surfaces appears superposed on the anomalous Lebed resonance. A quantum model of interlayer tunneling demonstrates these behaviors qualitatively. These results suggest that magnetic breakdown plays a key role in anomalous angle-dependent magnetoresistance oscillations.

Field-angle dependence of interlayer off-diagonal magnetoresistance in quasi two-dimensional layered conductors

We studied field-angle effects on the interlayer off-diagonal element of the magnetoresistance in a quasi two-dimensional (Q2D) system. We numerically calculated the angle dependence of the off-diagonal resistance ρ xz in the framework of the semiclassical transport theory when the current parallel to the interlayer z-direction was applied and the magnetic field was rotated from the z-direction to the intra-layer x-direction. The calculated ρ xz showed the oscillatory structure analogous to the angle dependent magnetoresistance oscillation (AMRO). This effect which we call “the off-diagonal AMRO” can be explained as the Fermi surface topological effect in the same way as AMRO. The off-diagonal AMRO was experimentally verified in an organic conductor α-(BEDT-TTF) 2NH 4Hg(SCN) 4.

Electronic states of organic quasi-two dimensional conductor β″-(DODHT) 2PF 6: Charge ordering and superconductivity

In the title compound, we made X-ray satellite reflection measurements up to 0.7 GPa and angle-dependent magnetoresistance (AMR) measurements at 1.9 GPa. The purpose of the study is to clarify (1) how large the temperature-pressure regime is for the long-range charge ordering (CO), (2) whether or not the high pressure regime for the superconductivity is really a metallic state, and (3) what the electronic properties are in the intermediate pressure regime between the long-range CO and the superconducting states. The long-range CO was found to be stable up to 0.7 GPa, and its temperature-pressure regime coincides with that expected from transport measurements. AMR at 1.9 GPa, 1.4 K and 12 T suggests the presence of Fermi surfaces consistent with band calculations based on X-ray structural analyses at room temperature and the same pressure. Raman studies by one of the authors (K.Y.) suggest the presence of metallic state in the intermediate pressure regime where the resistance shows apparently insulating properties. Discussion is made on the role of the charge-degree of freedom in causing the superconductivity.

First observation of angle-dependent Stark cyclotron resonance in bulk crystals: High-electric-field interlayer magnetotransport in a layered organic conductor

We report a novel angle-dependent magnetotransport phenomenon in layered conductors under strong interlayer electric fields. Interlayer conduction shows the Stark cyclotron resonance (SCR) when electron orbital motion becomes periodic in k-space. The SCR amplitude oscillates depending on magnetic field orientations. The conventional angle-dependent magnetoresistance oscillation (AMRO) switches to the angle-dependent SCR in high electric fields. We predict angle-dependent SCR due to electron orbital motion in layered conductors with coherent interlayer coupling. In addition, we demonstrate the expected switching from conventional AMRO to angle-dependent SCR in high electric fields using an organic conductor α-(BEDT-TTF) 2NH 4Hg(SCN) 4. This is the first observation of the SCR with orbital origin in bulk crystals.

Magnetic breakdown and angle-dependent magnetoresistance oscillations

We describe how the presence of magnetic breakdown affects the appearance of angle-dependent magnetoresistance oscillations in an organic metal. The model takes account of all the contributions from quasiparticles undergoing both magnetic breakdown and Bragg reflection at each junction and allows extremely efficient simulation of data which can be compared with experimental results on κ − ( BEDT − TTF ) 2 Cu ( NCS ) 2 .

Stereoscopic study of angle-dependent interlayer magnetoresistance in the organic conductorκ−(BEDT-TTF)2Cu(NCS)2

We stereoscopically studied the angle-dependent interlayer magnetoresistance ${R}_{zz}(\ensuremath{\theta},\ensuremath{\phi})$ of the organic conductor $\ensuremath{\kappa}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\text{Cu}{(\text{NCS})}_{2}$. A pressure of 7 kbar was applied to render the sample fully metallic. The stereoscopic view enables us to distinguish between quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) types of mixed angular magnetoresistance oscillations. A crossover between Q1D features and Q2D features is observed at $\ensuremath{\phi}\ensuremath{\sim}35\ifmmode^\circ\else\textdegree\fi{}$ when the field rotates in the conducting plane. While the coherence peak in the Q1D region has a constant angular width, $1.4\ifmmode^\circ\else\textdegree\fi{}$, the width of the humplike peak in the Q2D region grows with inverse $\text{cos}\text{ }\ensuremath{\phi}$ dependence up to $25\ifmmode^\circ\else\textdegree\fi{}$. In addition, differences of the $\ensuremath{\phi}$-dependence of ${R}_{zz}^{\ensuremath{\theta}=0}$ and of its temperature dependence support the crossover behavior between Q1D and Q2D dominance.

Temperature dependence of interlayer magnetoresistance in anisotropic layered metals

Studies of interlayer transport in layered metals have generally made use of zero temperature conductivity expressions to analyze angle-dependent magnetoresistance oscillations (AMRO). However, recent high temperature AMRO experiments have been performed in a regime where the inclusion of finite temperature effects may be required for a quantitative description of the resistivity. We calculate the interlayer conductivity in a layered metal with anisotropic Fermi surface properties allowing for finite temperature effects. We find that resistance maxima are modified by thermal effects much more strongly than resistance minima. We also use our expressions to calculate the interlayer resistivity appropriate to recent AMRO experiments in an overdoped cuprate which led to the conclusion that there is an anisotropic, linear in temperature contribution to the scattering rate and find that this conclusion is robust.

Tracking anisotropic scattering in overdoped Tl2Ba2CuO6+δ above 100 K

The present paper describes new polar angle-dependent magnetoresistance (ADMR) measurements in the overdoped cuprate Tl2Ba2CuO6+δ over an expanded range of temperatures and azimuthal angles. These detailed measurements re-affirm the analysis of earlier data taken over a more restricted temperature range and at a single azimuthal orientation, in particular the delineation of the intraplane scattering rate into isotropic and anisotropic components. These new measurements also reveal additional features in the temperature and momentum dependence of the scattering rate, including anisotropy in the T2 component and the preservation of both the T-linear and T2 components up to 100 K. The resultant form of the scattering rate places firm constraints on the development of any forthcoming theoretical framework for the normal state charge response of high-temperature superconducting cuprates.

Magnetic field induced coherence-incoherence crossover in the interlayer conductivity of a layered organic metal

The angle-dependent interlayer magnetoresistance of the pressurized (to the normal metallic state) layered organic metal $\ensuremath{\alpha}\text{\ensuremath{-}}{(\text{BEDT-TTF})}_{2}\text{KHg}{(\text{SCN})}_{4}$ is found to change from the conventional behavior at low magnetic fields to an anomalous one at high fields. The dependence of this field-induced crossover on the sample purity and temperature reveals parallel contribution of the classical Boltzmann and incoherent channels in the interlayer conductivity. The latter channel, having a metallic temperature dependence but being insensitive to an in-plane magnetic field, may be responsible for magnetoresistance anomalies observed in a number of layered metals. We propose a possible mechanism for the incoherent channel combining interlayer tunneling via local hopping centers and intralayer diffusion.

Angle-Dependent magneto-resistance near the pre-martensitic phase of Ni2MnGa

Angle-dependent magneto-resistance measurements in the vicinity of the pre-martensite phase (TPM∼219 K) in Ni2MnGa are reported. Magneto-resistance measurements detect a change in slope, from positive to negative near TPM that can be suppressed with a modest magnetic field. Mirroring this change in slope, published ARPES data [Opeil et al., Phys. Rev. Lett. 100, 165703 (2008).] show a significant depletion of states (pseudo-gap) forming at 0.3 eV below the Fermi energy.

Magnetotransport properties inK0.50CoO2 single crystals

We have measured susceptibility and angle-dependent magnetoresistance (AMR) onK0.50CoO2 single crystals. A possible magnetic structure similar to that ofNa0.5CoO2,a G-type anti-ferromagnetic (AF) structure (both in-plane and inter-plane are AF), is proposed.At ∼20 K,a loop is observed between zero-field-cooled (ZFC) and field-cooled (FC) susceptibility. The absolutevalue of magnetoresistance (MR) at 20 K is much larger than other cases with H applied within theab plane. This could arise from the magnetic field being applied in theab plane, leading to spin–flop of the small magnetic moment ofCo3.5−δ sites at 20 K to form in-plane ferromagnetic ordering, as observed inNa0.52CoO2.

Orbital origin of field-induced “quantum criticality” in overdoped Tl 2 Ba 2 CuO 6+ x

Shibauchi et al. (1) report high-field c-axis resistivity ρc data for the overdoped cuprate Tl2Ba2CuO6+x citing evidence for a field-induced quantum critical point coincident with Bc2. Such a claim has profound implications for our understanding of the cuprate phase diagram. Our own extensive angle-dependent magnetoresistance studies of Tl2Ba2CuO6+x, however, offer an alternative explanation for their findings based entirely on cyclotron (orbital) effects.

Quantum interference and weak localization effects in the interlayer magnetoresistance of layered metals

Studies of angle-dependent magnetoresistance oscillations (AMRO) in the interlayer conductivity of layered metals have generally considered semi-classical electron transport. We consider a quantum correction to the semi-classical conductivity that arises from what can be described as an interlayer Cooperon. This depends on both the disorder potential within a layer and the correlations of the disorder potential between layers. We compare our results with existing experimental data on organic charge transfer salts that are not explained within the standard semi-classical transport picture. In particular, our results may be applicable to effects that have been seen when the applied magnetic field is almost parallel to the conducting layers. We predict the presence of a peak in the resistivity as the field direction approaches the plane of the layers. The peak can occur even when there is weakly incoherent transport between layers.

Anisotropic scattering and superconductivity in high- [formula omitted] cuprates

The isotropic and anisotropic components of the transport scattering rate in overdoped Tl 2 Ba 2 CuO 6 + δ are determined for a range of T c values between 15 and 35 K by angle-dependent magnetoresistance measurements at T = 40 K . The anisotropic scattering term is found to scale linearly with T c and appears to vanish at the point where superconductivity is destroyed, establishing a clear link between the superconducting and normal state physics. Comparison with results from angle resolved photoemission spectroscopy suggests that the transport and quasi-particle lifetimes are very different.

Effect of magnetic breakdown on angle-dependent magnetoresistance in a quasi-two-dimensional metal: An analytically solvable model

We have developed an analytical model of angle-dependent magnetoresistance oscillations (AMROs) in a quasi-two-dimensional metal in which magnetic breakdown occurs. The model takes account of all the contributions from quasiparticles undergoing both magnetic breakdown and Bragg reflection at each junction and allows extremely efficient simulation of data which can be compared with recent experimental results on the organic metal kappa-ET2Cu(NCS)2. AMROs resulting from both closed and open orbits emerge naturally at low field, and the model enables the transition to breakdown-AMROs with increasing field to be described in detail.

Probing Fermi surface anisotropies in layered metals with AMRO

A layered crystal structure and strong interactions between electrons are common features of many interesting electronic materials. The coherence of interlayer charge transport and origin of intralayer anisotropies in such materials are important questions. We show that angle dependent magnetoresistance oscillations (AMRO) are sensitive to anisotropies around an intralayer Fermi surface, and discuss their asymptotic behaviour in the high field limit.