arXiv subjects

K. M. Suzuki

Publications and source records attributed to K. M. Suzuki.

9 recordsLinked to original sources

arXiv2020

Magnetism behavior of $T^{\prime}$-type Eu$_2$CuO$_4$ revealed by muon spin rotation/relaxation measurements

We performed muon spin rotation/relaxation measurements to investigate the magnetic behavior of $T^{\prime}$-type Eu$_2$CuO$_4$ (ECO), which is the parent compound of electron-doped cuprate superconductors, and the effects of oxygen-reduction annealing on its magnetism. In as-sintered (AS) ECO, we clarified the development of magnetic correlations upon cooling below $T_\mathrm{N1}$ (= 265 K) as well as the coexistence of a dominant fluctuating spin state and partially ordered spin state in the temperature range between $\sim$150 K and $T_\mathrm{N1}$. Upon further cooling, uniform long-range magnetic order was observed below $T_\mathrm{N2} = 110$ K, which is close to the ordering temperature of 115 K in $T^{\prime}$-type La$_2$CuO$_4$ (LCO) [Phys. Rev. B {\bf 82}, 180508(R) (2010)]. For oxygen-reduction-annealed ECO, a similar ordering sequence with the same $T_\mathrm{N2}$ was observed but without the partially ordered spin state. Therefore, the fluctuating spin state over a wide temperature range and a $T_\mathrm{N2}$ less than the N{é}el temperature ($T_\mathrm{N2} \approx T_\mathrm{N1}$) in $T$-type LCO are common features of the $T^{\prime}$-type parent $R_2$CuO$_4$ ($R$CO, $R$: rare-earth ion). The origin of the partially ordered spin state in AS ECO is discussed from the viewpoint of chemical defect. Furthermore, we discuss the roles of electron doping and repairing defect in the observed effect of annealing on the magnetism of $T^{\prime}$-type $R$CO.

cond-mat.str-el↗

arXiv2019

Distribution of the magnetic environment in charge ordered La$_{1.885}$Sr$_{0.115}$CuO$_{4}$

We report the inverse Laplace transform (ILT) analysis of the $^{139}$La nuclear spin-lattice relaxation rate $1/T_1$ in charge ordered La$_{1.885}$Sr$_{0.115}$CuO$_4$ ($T_{charge} \sim 80$K, $T_{c} \simeq T_{spin}^{neutron}=30$K), and shed new light on its magnetic inhomogeneity. We deduce the probability density function $P(1/T_{1})$ of the distributed $1/T_1$ (i.e. the histogram of distributed $1/T_1$) by taking the inverse Laplace transform of the experimentally observed nuclear magnetization recovery curve $M(t)$. We demonstrate that spin freezing sets in in some domains precisely below the onset of charge order at $T_{charge}$, but their volume fraction grows only gradually toward $T_{c}$. Nearly a half of the sample volume exhibits properties expected for canonical high $T_c$ cuprates without charge order even near $T_c$. Our findings explain why charge order does not suppress $T_c$ of La$_{1.885}$Sr$_{0.115}$CuO$_4$ as significantly as in La$_{1.875}$Ba$_{0.125}$CuO$_4$.

cond-mat.supr-con↗

arXiv2019

Observation of two types of charge density wave orders in superconducting La$_{2-x}$Sr$_x$CuO$_4$

The discovery of charge- and spin-density-wave (CDW/SDW) orders in superconducting cuprates has altered our perspective on the nature of high-temperature superconductivity (SC). However, it has proven difficult to fully elucidate the relationship between the density wave orders and SC. Here using resonant soft X-ray scattering we study the archetypal cuprate, La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) over a broad doping range. We reveal the existence of two types of CDW orders in LSCO, namely CDW stripe order and CDW short-range order (SRO). While the CDW-SRO is suppressed by SC, it is partially transformed into the CDW stripe order with developing SDW stripe order near the superconducting $T_{\rm c}$. These findings indicate that the stripe orders and SC are inhomogeneously distributed in the superconducting CuO$_2$ planes of LSCO. This further suggests a new perspective on the putative pair-density-wave order that coexists with SC, SDW, and CDW orders.

cond-mat.supr-con↗

arXiv2019

Successive magnetic ordering sequence observed from muon spin rotation in T'-structured R2CuO4 (R = Eu, Nd)

The magnetic behavior and effects of oxygen-reduction annealing on the magnetism of T'-structured R2CuO4 (R = Eu and Nd), which is the parent compound of electron-doped cuprate superconductors, have been investigated from muon spin rotation (muSR) measurements. In the muon time spectra of as-sintered R2CuO4, an oscillation component with a small amplitude and a dominant exponential-type decay component were observed for the temperature range between 150 K and TN1 (=250-270 K). This observation suggests an inhomogeneous magnetic phase of a fluctuating spin state and a locally ordered spin state at these temperatures. With decreasing temperature,the small oscillation component disappears, and the exponential one develops below 150 K. Upon further cooling, well-defined oscillation spectra corresponding to uniform long-ranged magnetic order emerge below TN2 = 110 K. Except for the absence of the small oscillation component, similar magnetic behavior is confirmed for the annealed compounds. Therefore, the successive development of magnetism characterized by the fluctuating spin state over a wide temperature range is a common feature for T'-R2CuO4. We discuss a possible picture for the ordering sequence in T'-R2CuO4 and the origin of the small oscillation component in the as-sintered compounds from the viewpoint of local defects.

cond-mat.str-el↗

arXiv2015

Strong electron correlation behind the superconductivity in Ce-free and Ce-underdoped high-Tc T'-cuprates

In order to investigate the electronic state of Ce-free and Ce-underdoped high-Tc cuprates with the so-called T' structure, we have performed muon-spin-relaxation (muSR) and specific-heat measurements of Ce-free T'-La_1.8_Eu_0.2_CuO_4+d_ (T'-LECO) polycrystals and Ce-underdoped T'-Pr_1.3-x_La_0.7_Ce_x_CuO_4+d_ (T'-PLCCO) single crystals with x=0.10. The muSR spectra of the reduced superconducting samples of both T'-LECO with Tc=15K and T'-PLCCO with x=0.10 and Tc=27K have revealed that a short-range magnetic order coexists with the superconductivity in the ground state. The formation of a short-range magnetic order due to a tiny amount of excess oxygen in the reduced superconducting samples strongly suggest that the Ce-free and Ce-underdoped T'-cuprates are regarded as strongly correlated electron systems.

cond-mat.supr-con↗

arXiv2015

Single-crystal growth of underdoped Bi-2223

To investigate the origin of the enhanced Tc ({\approx} 110 K) of the trilayer cuprate superconductor Bi2Sr2Ca2Cu3O10+δ (Bi-2223), its underdoped single crystals are a critical requirement. Here, we demonstrate the first successful in-plane resistivity measurements of heavily underdoped Bi-2223 (zero-resistivity temperatures {\approx} 20~35 K). Detailed crystal growth methods, the annealing process, as well as X-ray diffraction (XRD) and magnetic susceptibility measurement results are also reported.

cond-mat.supr-con↗

arXiv2012

Distinct Fe-induced magnetic states in the underdoped and overdoped regimes of La2-xSrxCu1-yFeyO4 revealed by muon spin relaxation

Zero-field and longitudinal-field muon-spin-relaxation measurements have been performed in partially Fe-substituted La2-xSrxCu1-yFeyO4 in a wide range of hole concentration, to investigate the magnetic state induced by the Fe substitution recently suggested from the neutron-scattering measurements [Phys. Rev. Lett. 107, 127002 (2011)]. It has been found that the magnetic transition temperature is notably enhanced through the 1% Fe substitution in a wide range of hole concentration where superconductivity appears in Fe-free La2-xSrxCuO4. In the underdoped regime, the Fe-induced magnetic order can be understood in terms of the concept of stripe pinning by Fe as in the case of the Zn-induced one in La2-xSrxCu1-yZnyO4. In the overdoped regime, on the other hand, the Fe-induced magnetic order is short-ranged, which is distinct from the stripes. It is plausible that a spin-glass state of Fe spins derived from the Ruderman-Kittel-Kasuya-Yosida interaction is realized in the overdoped regime, suggesting a change of the ground state from the strongly correlated state to the Fermi-liquid state with hole doping in La-214 high-Tc cuprates.

cond-mat.supr-con↗

arXiv2010

Inherent spin density wave instability by vortices in superconductors with strong Pauli effects

A novel spin density wave (SDW) instability mechanism enhanced by vortices under fields is proposed to explain the high field and low temperature (HL) phase in CeCoIn$_5$. In the vortex state the strong Pauli effect and the nodal gap conspire to enhance the momentum resolved spectral weight exclusively along the nodal direction over the normal value, providing a favorable nesting condition for SDW with ${\bf Q}=(2k_F, 2k_F, 0.5)$ only under high field ($H$). Observed mysteries of the field-induced SDW confined within $H_{c2}$ are understood consistently, such facts that ${\bf Q}$ is directed to the nodal direction independent of $H$, SDW diminishes under tilting field from the $ab$ plane, and the SDW transition line in $(H,T)$ has a positive slope.

cond-mat.supr-con↗

arXiv2008

Magnetization profile and core level spectroscopy in a multiply quantized vortex of imbalanced Fermi superfluids

The core structure of multiply quantized vortices is theoretically investigated in fermionic superfluid near Feshbach resonance. Under population imbalance in two hyperfine spin states, the vortex core is filled in by the ``paramagnetic moment''. Here, we find the spatial oscillation of the magnetization inside the core sensitively due to the topological structure of the pairing field, in the range from the weak coupling regime to the unitary limit. This magnetization inside the giant core reveals the winding number of the vortex and directly results from the low-lying quasiparticle states bound inside the core. It is therefore proposed that the density profile experiment using phase contrast imaging can provide the spectroscopy of novel core level structures in giant vortices. To help the understanding on these outcomes, we also derive the analytic solution for the low-lying quasiparticle states inside the core of a multiply quantized vortex.

cond-mat.supr-con↗