arXiv subjects

S. Ono

Publications and source records attributed to S. Ono.

52 records · Page 3Linked to original sources

arXiv2004

Examination of the c-axis resistivity of Bi_{2}Sr_{2-x}La_xCuO_{6+δ} in magnetic fields up to 58 T

We measure the magnetic-field dependence of the c-axis resistivity, ρ_c(H), in a series of Bi_{2}Sr_{2-x}La_xCuO_{6+δ} (BSLCO) single crystals for a wide range of doping using pulsed magnetic fields up to 58 T. The behavior of ρ_c(H) is examined in light of the recent determination of the upper critical field H_{c2} for this material using Nernst effect measurements. We find that the peak in ρ_c(H) shows up at a field H_p that is much lower than H_{c2} and there is no discernable feature in ρ_c(H) at H_{c2}. Intriguingly, H_p shows a doping dependence similar to that of T_c, and there is an approximate relation k_{B}T_c \simeq {1/2}gμ_{B}H_p. Moreover, we show that the data for the lowest-T_c sample can be used to estimate the pseudogap closing field H_{pg}, but the method to estimate H_{pg} proposed by Shibauchi {\it et al.} [Phys. Rev. Lett. {\bf 86}, 5763 (2001)] must be modified to apply to the BSLCO system.

cond-mat.supr-con↗

arXiv2004

Quantum Phase Transitions in a Cuprate Superconductor Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ}

To elucidate a quantum phase transition (QPT) in Bi_2Sr_{2-x}La_xCuO_{6+δ}, we measure charge and heat transport properties at very low temperatures and examine the following characteristics for a wide range of doping: normal-state resistivity anisotropy under 58 T, temperature dependence of the in-plane thermal conductivity K_{ab}, and the magnetic-field dependence of K_{ab}. It turns out that all of them show signatures of a QPT at the 1/8 hole doping. Together with the recent normal-state Hall measurements under 58 T that signified the existence of a QPT at optimum doping, the present results indicate that there are two QPTs in the superconducting doping regime of this material.

cond-mat.supr-con↗

arXiv2004

Manifestation of the magnetic resonance mode in the nodal quasiparticle lifetime in superconducting cuprates

Studying the nodal quasiparticles in superconducting cuprates by photoemission with highly improved momentum resolution, we show that a new "kink" feature in the scattering rate is a key to uncover the nature of electron correlations in these compounds. Our data provide evidence that the main doping independent contribution to the scattering can be well understood in terms of the conventional Fermi liquid model, while the additional doping dependent contribution has a magnetic origin. This sheds doubt on applicability of a phonon-mediated pairing mechanism to high temperature superconductors.

cond-mat.supr-con↗

arXiv2004

Local Ordering in the Pseudogap State of the High-T$_c$ Superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

We report atomic scale characterization of the pseudogap state in a high-T$_c$ superconductor, Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$. The electronic states at low energies within the pseudogap exhibit spatial modulations having an energy-independent incommensurate periodicity. These patterns, which are oriented along the copper-oxygen bond directions, appear to be a consequence of an electronic ordering phenomenon--the observation of which correlates with the pseudogap in the density of electronic states. Our results provide a stringent test for various ordering scenarios in the cuprates, which have been central in the debate on the nature of the pseudogap and the complex electronic phase diagram of these compounds.

cond-mat.supr-con↗

arXiv2003

Vorticity and the Nernst Effect in Cuprate Superconductors

We present a review of the vortex-Nernst effect in the 3 cuprate families La_{2-x}Sr_xCuO_4, Bi_2Sr_2CaCu_2O_8, and YBa_2Cu_3O_{y}, and discuss the scenario that the superconducting transition in the hole-doped cuprates corresponds to the destruction of long-range phase coherence rather than the vanishing of the order-parameter amplitude.

cond-mat.supr-con↗

arXiv2003

Reply to the "Comment on 'Intrinsic tunneling spectra of Bi_2(Sr_{2-x}La_x)CuO_6' ": Auxiliary information

To better address the heating issue in stacks of intrinsic Josephson junctions, we directly measure temperature of the stack by using a micron-sized thermocouple which is in direct thermal- and electrical contact to the stack, exactly in the place where the bias current is injected. Our measurements have shown that the temperature of the stack can reach 200-300K at the highest bias. Thus, we confirm experimentally that the Joule self-heating is a severe problem in intrinsic-junction-spectroscopy experiments. The pseudogap features reported in our previous paper (A.Yurgens etal, PRL 90, 147005 (2003)) are indeed an artifact of Joule heating. The detailed measurements of the temperature of the stacks at different ambient temperatures T0 allow us to deduce the unique, "heating-free" I(V)-, or dI/dV(V) curves.

cond-mat.supr-con↗

arXiv2003

Reply to the "Comment on 'Intrinsic tunneling spectra of Bi_2(Sr_{2-x}La_x)CuO_6' "

cond-mat.supr-con↗

arXiv2002

Intrinsic tunneling spectra of Bi_2(Sr_{2-x}La_x)CuO_6

We have measured intrinsic-tunneling spectra of a single CuO-layer La-doped Bi_2Sr_{2-x}La_xCuO_{6+δ} (Bi2201-La_x). Despite a difference of a factor of three in the optimal superconducting critical temperatures for Bi2201-La_{0.4} and Bi2212 (32 and 95 K, respectively) and different spectral energy scales, we find that the pseudogap vanishes at a similar characteristic temperature T*\approx 230-300K for both compounds. We find also that in Bi2201-La_x, PG humps are seen as sharp peaks and, in fact, even dominate the intrinsic spectra.

cond-mat.supr-con↗

arXiv2002

Evolution of the resistivity anisotropy in Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} single crystals for a wide range of hole doping

To elucidate how the temperature dependence of the resistivity anisotropy of the cuprate superconductors changes with hole doping, both the in-plane and the out-of-plane resistivities (ρ_{ab} and ρ_{c}) are measured in a series of high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} (BSLCO) single crystals for a wide range of x (x = 0.23 - 1.02), which corresponds to the hole doping per Cu, p, of 0.03 - 0.18. The anisotropy ratio, ρ_{c}/ρ_{ab}, shows a systematic increase with decreasing p at moderate temperatures, except for the most underdoped composition where the localization effect enhances ρ_{ab} and thus lowers ρ_{c}/ρ_{ab}. The exact p dependence of ρ_{c}/ρ_{ab} at a fixed temperature is found to be quite peculiar, which is discussed to be due to the effect of the pseudogap that causes ρ_{c}/ρ_{ab} to be increasingly more enhanced as p is reduced. The pseudogap also causes a rapid growth of ρ_{c}/ρ_{ab} with decreasing temperature, and, as a result, the ρ_{c}/ρ_{ab} value almost reaches 10^6 in underdoped samples just above T_c. Furthermore, it is found that the temperature dependence of ρ_{c} of underdoped samples show two distinct temperature regions in the pseudogap phase, which suggests that the divergence of ρ_{c} below the pseudogap temperature is governed by two different mechanisms.

cond-mat.supr-con↗

arXiv2001

Zn-doping effect on the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ} single crystals

We report the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}Cu_{1-z}Zn_{z}O_{6+δ} (Zn-doped BSLCO) single crystals with z of up to 2.2%. Besides the typical Zn-doping effects on the in-plane resistivity and the Hall angle, we demonstrate that the nature of the low-temperature normal state in the Zn-doped samples is significantly altered from that in the pristine samples under high magnetic fields. In particular, we observe nearly-isotropic negative magnetoresistance as well as an increase in the Hall coefficient at very low temperatures in non-superconducting Zn-doped samples, which we propose to be caused by the Kondo scattering from the local moments induced by Zn impurities.

cond-mat.supr-con↗

arXiv2001

Two mechanisms of pseudogap formation in Bi-2201: Evidence from the c-axis magnetoresistance

Measurements of the c-axis resistivity and magnetoresistance have been used to investigate the pseudogap (PG) behavior in Bi_{2+z}Sr_{2-x-z}La_xCuO_y (Bi-2201) crystals at various hole densities. While the PG opening temperature T* increases with decreasing hole doping, the magnetic-field sensitivity of the PG is found to have a very different trend: it appears at lower temperatures in more underdoped samples and vanishes in non-superconducting samples. These data suggest that besides the field-insensitive pseudogap emerging at T*, a distinct one is formed above T_c as a precursor to superconductivity.

cond-mat.supr-con↗

arXiv2001

The onset of the vortex-like Nernst signal above Tc in La_{2-x}Sr_xCuO_4 and Bi_2Sr_{2-y}La_yCuO_6

The diffusion of vortices down a thermal gradient produces a Josephson signal which is detected as the vortex Nernst effect. In a recent report, Xu et al., Nature 406, 486 (2000), an enhanced Nernst signal identified with vortex-like excitations was observed in a series of La_{2-x}Sr_xCuO_4 (LSCO) crystals at temperatures 50-100 K above T_c. To pin down the onset temperature T_ν of the vortex-like signal in the lightly doped regime (0.03 < x < 0.07), we have re-analyzed in detail the carrier contribution to the Nernst signal. By supplementing new Nernst measurements with thermopower and Hall-angle data, we isolate the off-diagonal Peltier conductivity α_{xy} and show that its profile provides an objective determination of T_ν. With the new results, we revise the phase diagram for the fluctuation regime in LSCO to accomodate the lightly doped regime. In the cuprate Bi_2Sr_{2-y}La_yCuO_6, we find that the carrier contribution is virtually negligible for y in the range 0.4-0.6. The evidence for an extended temperature interval with vortex-like excitations is even stronger in this system. Finally, we discuss how T_ν relates to the pseudogap temperature T* and the implications of strong fluctuations between the pseudogap state and the d-wave superconducting state.

cond-mat.str-el↗

arXiv2000

Metal-to-Insulator Crossover in the Low-Temperature Normal State of Bi_{2}Sr_{2-x}La_{x}CuO_{6+δ}

We measure the normal-state in-plane resistivity of La-doped Bi-2201 single crystals at low temperatures by suppressing superconductivity with 60-T pulsed magnetic fields. With decreasing hole doping, we observe a crossover from a metallic to insulating behavior in the low-temperature normal state. This crossover is estimated to occur near 1/8 doping, well inside the underdoped regime, and not at optimum doping as reported for other cuprates. The insulating regime is marked by a logarithmic temperature dependence of the resistivity over two decades of temperature, suggesting that a peculiar charge localization is common to the cuprates.

cond-mat.supr-con↗

arXiv2000

Systematic evolution of the magnetotransport properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6} in a wide doping range

Recently we have succeeded in growing a series of high-quality Bi_{2}Sr_{2-x}La_{x}CuO_{6} crystals in a wide range of carrier concentrations. The data of ρ_{ab}(T) and R_H(T) of those crystals show behaviors that are considered to be "canonical" to the cuprates. The optimum zero-resistance T_c has been raised to as high as 38 K, which is almost equal to the optimum T_c of La_{2-x}Sr_{x}CuO_{4}.

cond-mat.supr-con↗

arXiv2000

Carrier concentrations in Bi_{2}Sr_{2-z}La_{z}CuO_{6+δ} single crystals and their relation to Hall coefficient and thermopower

We measured the thermopower S and the Hall coefficients R_H of Bi_{2}Sr_{2-z}La_{z}CuO_{6+δ} (BSLCO) single crystals in a wide doping range, in an effort to identify the actual hole concentrations per Cu, p, in this system. It is found that the "universal" relation between the room-temperature thermopower and T_c does not hold in the BSLCO system. Instead, comparison of the temperature-dependent R_H data with other cuprate systems is used as a tool to identify the actual p value. To justify this approach, we compare normalized R_H(T) data of BSLCO, La_{2-x}Sr_{x}CuO_{4} (LSCO), YBa_{2}Cu_{3}O_{y}, and Tl_{2}Ba_{2}CuO_{6+δ}, and demonstrate that the R_H(T) data of the LSCO system can be used as a template for the estimation of p. The resulting phase diagram of p vs T_c for BSLCO suggests that T_c is anomalously suppressed in the underdoped samples, becoming zero at around p ~ 0.10, while the optimum T_c is achieved at p ~ 0.16 as expected.

cond-mat.supr-con↗

arXiv1999

Systematic Evolution of the Magnetotransport Properties of Bi_{2}Sr_{2-x}La_{x}CuO_{6} with Carrier Concentration

We report that it is possible to obtain a series of high-quality crystals of La-doped Bi-2201, of which the transport properties have been believed to be "dirtier" than those of other cuprates. In our crystals, the normal-state transport properties display behaviors which are in good accord with other cuprates; for example, in the underdoped region the in-plane resistivity ρ_{ab} shows the pseudogap feature and in the overdoped region the T dependence of ρ_{ab} changes to T^n with n > 1. The characteristic temperatures of the pseudogap deduced from the resistivity and the Hall coefficient data are presented.

cond-mat.supr-con↗