Colossal transverse magnetoresistance due to nematic superconducting phase fluctuations in a copper oxide (original) (raw)
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Parallel and perpendicular susceptibility above T_{c} in La_{2-x}Sr_{x}CuO_{4} single crystals
Physical Review B, 2012
We report direction-dependent susceptibility and resistivity measurements on La2−xSrxCuO4 single crystals. These crystals have rectangular needle-like shapes with the crystallographic "c" direction parallel or perpendicular to the needle axis, which, in turn, is in the applied field direction. At optimal doping we find finite diamagnetic susceptibility above Tc, namely fluctuating superconductivity (FSC), only when the field is perpendicular to the planes. In underdoped samples we could find FSC in both field directions. We provide a phase diagram showing the FSC region, although it is sample dependent in the underdoped cases. The variations in the susceptibility data suggest a different origin for the FSC between underdoping (below 10%) and optimal doping. Finally, our data indicates that the spontaneous vortex diffusion constant above Tc is anomalously high.
Angle-Resolved Transport Measurements Reveal Electronic Nematicity in Cuprate Superconductors
Journal of Superconductivity and Novel Magnetism
Observations of spontaneous breaking of the rotational symmetry in an electron fluid, the so-called 'electronic nematicity', has been reported in several quantum materials. We have developed several different methods, based on angle-resolved transport measurements, to determine the amplitude and the director of the nematic order. We present methods that are applicable to thin films or single crystals, illustrate them with transport data obtained on copper-oxide superconductors, and discuss their relative advantages and disadvantages.
Spin fluctuations in insulating, weakly metallic and superconducting La2-xSrxCuO4
Physica B: Condensed …, 1994
We review the results of a comprehensive set of neutron scattering experiments on the spin fluctuations in La2_xSrxCuO 4 with x varying between 0 and 0.15. For 0 <x ~< 0.0175 the materials exhibit 3D Nrel order; for x = 0 the spin correlations above T N are accurately described by recent theory for the 2D S= 1/2 Heisenberg antiferromagnet. For 0.02~<x ~<0.04 the spin fluctuations are purely 2D with a spin correlation length which is independent of temperature below-250 K. Remarkably, in this concentration range the spin correlation length follows the simple form ~-l(x, T) = ~ l(x, 0) + ~-1(0, T). Further, the generalized susceptibility integrated around the (Tr, ~r) antiferromagnetic position follows a simple scaling function in the variable w/T thus providing a natural explanation for various normal state properties of the lamellar copper oxides. For x ~> 0.06 the spin fluctuations are incommensurate; we find in a sample with x = 0.15 and T c = 33 K that the spin fluctuations at low energies for T ~< 100 K are quite sharp in momentum space. Further, for energies as low as 1.5 meV the spin fluctuations persist into the superconducting state with no significant change in the incommensurate geometry down to 2 K.
2007
The angle-dependent interlayer magnetoresistance of overdoped Tl2Ba2CuO 6+δ has been measured in high magnetic fields up to 45 Tesla. A conventional Boltzmann transport analysis with no basal-plane anisotropy in the cyclotron frequency ωc or transport lifetime τ is shown to be inadequate for explaining the data. We describe in detail how the analysis can be modified to incorporate in-plane anisotropy in these two key quantities and extract the degree of anisotropy for each by assuming a simple four-fold symmetry. While anisotropy in ωc and other Fermi surface parameters may improve the fit, we demonstrate that the most important anisotropy is that in the transport lifetime, thus confirming its role in the physics of overdoped superconducting cuprates.
Physical Review B, 2011
The interplay between superconducting fluctuations and inhomogeneities presents a renewed interest due to recent works of different groups which apparently support an intrinsically anomalous (beyond the conventional Gaussian-Ginzburg-Landau scenario) diamagnetism above Tc in underdoped cuprates. This conclusion, mainly based in the observation of new anomalies in the isothermal magnetization curves at low field amplitudes, is in contradiction with our earlier results in the underdoped La1.9Sr0.1CuO4 [Phys. Rev. Lett. 84, 3157 (2000)]. These seemingly intrinsic anomalies are being presented in various influential works as a "thermodynamic evidence" for phase incoherent superconductivity in the pseudogap regime, this last being at present a central and debated issue of the cuprate superconductors' physics. To further probe the diamagnetism above Tc in underdoped cuprates, here we have extended our magnetization measurements in La1.9Sr0.1CuO4 to two samples with the same nominal composition but, due to different growth procedures, with different chemical disorder, in one of the samples this disorder being close to the intrinsic-like one, associated with the unavoidable random distribution of the Sr ions (which will be then present even in an ideal La1.9Sr0.1CuO4 crystal). For this sample, the corresponding Tc-inhomogeneities may be approximated as symmetric around the average Tc. In contrast, the most disordered sample presents a pronounced asymmetric Tc-distribution. The comparison between the magnetization measured in both samples provide a crucial check of the chemical disorder origin of the observed diamagnetism anomalies, which are similar to those claimed as due to phase fluctuations by other authors. This conclusion applies also to the sample affected only by the intrinsic-like chemical disorder, providing then a further check that, for all applied magnetic field amplitudes, the intrinsic diamagnetism above the superconducting transition of underdoped cuprates is not affected by the opening of a pseudogap in the normal state. It is also shown here that once these disorder effects are overcome, the remaining precursor diamagnetism may be accounted at a quantitative level in terms of the Gaussian-Ginzburg-Landau approach under a total energy cutoff.
Search for ferromagnetic order in overdoped copper-oxide superconductors
Scientific Reports, 2017
In copper-oxides that show high-temperature superconductivity (HTS), the critical temperature (T c) has a dome-shaped doping dependence. The cause of demise of both T c and superfluid density n s on the overdoped side is a major puzzle. A recent study of transport and diamagnetism in a large number of overdoped La 2−x Sr x CuO 4 (LSCO) films shows that this cannot be accounted for by disorder within the conventional Bardeen-Cooper-Schrieffer theory. This brings to focus an alternative explanationcompetition of HTS with ferromagnetic order, fluctuating in superconducting samples and static beyond the superconductor-to-metal transition. Here, we examine this proposal by growing singlecrystal LSCO thin films with doping on both sides of the transition by molecular beam epitaxy, and using polarized neutron reflectometry to measure their magnetic moments. In a heavily overdoped, metallic but non-superconducting LSCO (x = 0.35) film, the spin asymmetry of reflectivity shows a very small static magnetic moment (~2 emu/cm 3). Less-doped, superconducting LSCO films show no magnetic moment in neutron reflectivity, both above and below T c. Therefore, the collapse of HTS with overdoping is not caused by competing ferromagnetic order. The superconducting temperature T c in cuprates shows an unusual dome-shaped dependence on the doping level, which presumably originates from an unconventional pairing mechanism. On the low-doping side of the dome in the x-T (doping-temperature) phase diagram, the competition of HTS with antiferromagnetism, charge density waves, and the pseudogap phase has been investigated extensively although some details are still debated 1,2. The overdoped side has been studied less and the situation is even more puzzling. It has been speculated that the demise of T c and the superfluid density n s with overdoping originates from pair breaking caused by impurities, disorder, and phase separation, which could be accounted for within the conventional dirty-BCS (Bardeen-Cooper-Schrieffer) picture 3. However, this hypothesis has been thoroughly scrutinized and refuted in the recently released detailed study of penetration depth and magnetoresistance in a huge number of overdoped LSCO films 4 grown by atomic-layer-by layer molecular beam epitaxy (ALL-MBE). In these high-quality single-crystal films, the superfluid seems to be homogeneous and uniform at every doping. This brings to the forefront an alternative explanation that on the high-doping side HTS competes with ferromagnetic order 5. In fact, ferromagnetism does occur in closely related oxides such as La 1−x Sr x CoO 3 (ref. 6). Electronic band calculations show a tendency towards ferromagnetic ordering 7 at high charge doping in La 2− x Ba x CuO 4. The dramatic evolution of Fermi surface with overdoping in LSCO may provide a chance for magnetic moments to be interacting and correlated in a preferred direction, in some composition window. Several experimental observations provide some support to this scenario 8-16. The temperature dependence of magnetic susceptibility (χ) in overdoped LSCO crystals indicated the absence of local magnetic moments below the critical doping x c ≈ 0.18, and dramatic increase in their density with further overdoping 8-12. Muon spin rotation (μ SR) experiments 15 detected the onset of static magnetic moments at low temperature in heavily overdoped (x = 0.33) LSCO, metallic but non-superconducting (in what follows, we refer to such samples simply as 'metallic'). However, no ferromagnetism has been detected so far in the vicinity of the quantum (T = 0) superconductor-to-metal transition (SMT) that occurs at the overdoped dome edge (x c2 ≈ 0.26).
Magnetic Fluctuations of Stripes in the High Temperature Cuprate Superconductors
Physical Review Letters, 2005
Within the time-dependent Gutzwiller approximation for the Hubbard model we compute the magnetic fluctuations of vertical metallic stripes with parameters appropriate for La1.875Ba0.125CuO4 (LBCO). For bond-and site-centered stripes the excitation spectra are similar, consisting of a low-energy incommensurate acoustic branch which merges into a "resonance peak" at the antiferromagnetic wave vector and several high-energy optical branches. The acoustic branch is similar to the result of theories assuming localized spins whereas the optical branches are significantly different. Results are in good agreement with a recent inelastic neutron study of LBCO. PACS numbers: 74.25.Ha,71.28.+d,71.45.lr Since the discovery of cuprate superconductors the elucidation of their magnetic properties has been a subject of intense research in the high-T c community due to their possible relevance for the superconducting mechanism[1]. However, no consensus has been reached yet wether the magnetic excitation spectra in the various cuprate materials can be traced back to some universal phenomenology which could be expected in the face of the robust nature of superconductivity. The insulating parent compounds show long-range antiferromagnetic (AF) order in the CuO 2 planes below the Néel temperature[2]. This static AF order is lost above a concentration of added holes per planar copper x ≈ 0.02 but complex dynamical spin correlations persist up to the overdoped regime .
Competing ferromagnetism in high-temperature copper oxide superconductors
Proceedings of the National Academy of Sciences, 2007
The extreme variability of observables across the phase diagram of the cuprate high-temperature superconductors has remained a profound mystery, with no convincing explanation for the superconducting dome. Although much attention has been paid to the underdoped regime of the hole-doped cuprates because of its proximity to a complex Mott insulating phase, little attention has been paid to the overdoped regime. Experiments are beginning to reveal that the phenomenology of the overdoped regime is just as puzzling. For example, the electrons appear to form a Landau Fermi liquid, but this interpretation is problematic; any trace of Mott phenomena, as signified by incommensurate antiferromagnetic fluctuations, is absent, and the uniform spin susceptibility shows a ferromagnetic upturn. Here, we show and justify that many of these puzzles can be resolved if we assume that competing ferromagnetic fluctuations are simultaneously present with superconductivity, and the termination of the supe...
Transverse Magnetoresistance Induced by the Nonuniformity of Superconductor
Nanomaterials
The transverse magnetoresistance (Rxy) caused by inhomogeneous superconductivity is symmetric about the magnetic field around the critical magnetic field region. This has caused many disturbances during the study of vortex dynamics by Hall signals. Here, we found that the peak of Rxy measured in our samples was induced by the nonuniformity of the superconductors. The peak values of Rxy decrease with increasing applied current and temperature, which can be described by the theory of superconductivity inhomogeneity. Based on this, we have proposed and verified a method for separating the transverse voltage caused by the inhomogeneity of superconductivity. Additionally, quantity ΔB(0) can also be used to characterize the uniformity of superconductivity. This clears up the obstacles for studying vortex motion dynamics and reveals a way to study the influence of the domain wall on superconductivity.