Large Wilson Ratio Research Articles

Normal-state properties of the quasi-one-dimensional superconductor Ta4Pd3Te16

We examined the physical properties of the quasi-one-dimensional superconductor Ta4Pd3Te16 in the normal state by detailed measurements of susceptibility, in-plane anisotropic resistivity, magnetoresistance, Hall resistivity, and Seebeck coefficient. The large Wilson ratio, as inferred from normal-state susceptibility, indicates strong electron–electron interaction. The Hall and Seebeck coefficients show not only significant temperature-dependent behavior, indicating the multiband effect, but also an obvious anomaly around T1 = 40 K. Analyses of both the Hall resistivity and thermopower using a two-band model indicate that the electrons dominate the electrical transport at low temperatures. Our results imply that it is the quantum fluctuations of the charge order taking place in the temperature range 30–50 K that may result in the abnormal normal-state properties of Ta4Pd3Te16.

High-Pressure Synthesis of Fully Occupied Tetragonal and Cubic Tungsten Bronze Oxides.

A high-pressure reaction yielded the fully occupied tetragonal tungsten bronze K3 W5 O15 (K0.6 WO3 ). The terminal phase shows an unusual transport property featuring slightly negative temperature-dependence in resistivity (dρ/dT<0) and a large Wilson ratio of RW =3.2. Such anomalous metallic behavior possibly arises from the low-dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze Kx WO3 -K0.6-y Bay WO3 phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO3 phase was also identified as a line phase-in marked contrast to Nax WO3 and Lix WO3 with varying quantities of x (<1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended.

High‐Pressure Synthesis of Fully Occupied Tetragonal and Cubic Tungsten Bronze Oxides

AbstractA high‐pressure reaction yielded the fully occupied tetragonal tungsten bronze K3W5O15 (K0.6WO3). The terminal phase shows an unusual transport property featuring slightly negative temperature‐dependence in resistivity (dρ/dT&lt;0) and a large Wilson ratio of RW=3.2. Such anomalous metallic behavior possibly arises from the low‐dimensional electronic structure with a van Hove singularity at the Fermi level and/or from enhanced magnetic fluctuations by geometrical frustration of the tungsten sublattice. The asymmetric nature of the tetragonal tungsten bronze KxWO3‐K0.6−yBayWO3 phase diagram implies that superconductivity for x≤0.45 originates from the lattice instability because of potassium deficiency. A cubic perovskite KWO3 phase was also identified as a line phase—in marked contrast to NaxWO3 and LixWO3 with varying quantities of x (&lt;1). This study presents a versatile method by which the solubility limit of tungsten bronze oxides can be extended.

Superconductivity in Ba2/3Pt3B2 with the Kagome lattice

Resistivity, magnetization and low temperature specific heat (down to 0.4 K) of Ba2/3Pt3B2 with the Kagome lattice of the transition metal Pt atoms have been investigated. The magnetization hysteresis loops measured on the sample indicate that it belongs to a type-II superconductor. The specific heat exhibits ΔC/γnT|Tc≈1.7, showing a moderate coupling superconductivity. Furthermore, the magnetic field dependence of the electronic specific heat coefficient in the low temperature limit demonstrates a linear relation γe∝H, suggesting an s-wave gap. Surprisingly, the Wilson ratio determined here is about 34, which may be explained by short range magnetic correlation. Compared with the compound LaRu3Si2, we intend to attribute the extraordinarily large Wilson ratio to the deficiency of Ba atoms. Further theoretical and experimental efforts are required to clarify this issue.

Superconductivity and physical properties of strongly electron correlated compounds LanRu3n−1B2n (n = 1, 2, and 3)

We examined the physical properties of homologous LanRu3n−1B2n (n = 1−3) series including a new compound of n = 2. All of these compounds showed strong electron-electron correlation characterized by large Wilson ratio. In contrast to LaRu2B2 and La2Ru5B4 that show normal metal behaviors down to 1.8 K, we discover La3Ru8B6 is an intermediately coupled BCS superconductor with . The experimental and theoretical calculation results suggest that the emergence of superconductivity in La3Ru8B6 can be attributed to the rather large density of states at EF when compared to other two compounds.

Strong magnetic instability in correlated metallic Bi2Ir2O7

We report an experimental/theoretical study of single-crystal Bi2Ir2O7 that possesses a metallic state with strongly exchange-enhanced paramagnetism. The ground state of Bi2Ir2O7 is characterized by the following features: (1) a divergent low-temperature magnetic susceptibility that indicates no long-range order down to 50 mK; (2) strongly field-dependent coefficients of the low-temperature T and T3 terms of the specific heat; (3) a conspicuously large Wilson ratio RW ≈ 53.5; and (4) unusual temperature and field dependences of the Hall resistivity that abruptly change below 80 K, without any clear correlation with the magnetic behavior. All these unconventional properties suggest the existence of an exotic ground state in Bi2Ir2O7.

Anisotropic heavy-Fermi-liquid formation in valence-fluctuatingα-YbAlB4

$\alpha$-YbAlB$_4$ is the locally isostructural polymorph of $\beta$-YbAlB$_4$, the first example of an Yb-based heavy fermion superconductor which exhibits pronounced non-Fermi-liquid behavior above $T_{\rm c}$. Interestingly, both $\alpha$-YbAlB$_4$ and $\beta$-YbAlB$_4$ have strongly intermediate valence. Our single crystal study of the specific heat, magnetization and resistivity has confirmed the Fermi liquid ground state of $\alpha$-YbAlB$_4$ ~in contrast with the quantum criticality observed in $\beta$-YbAlB$_4$. Both systems exhibit Kondo lattice behavior with the characteristic temperature scale $T^* \sim$ 8 K in addition to a valence fluctuation scale $\sim 200$ K. Below $T^*$, $\alpha$-YbAlB$_4$ a heavy Fermi liquid state with an electronic specific heat coefficient $\gamma\sim$ 130 mJ/mol K$^2$ and a large Wilson ratio more than 7, which indicates ferromagnetic correlation between Yb moments. A large anisotropy in the resistivity suggests that the hybridization between 4$f$ and conduction electrons is much stronger in the $ab$-plane than along the c-axis. The strongly anisotropic hybridization as well as the large Wilson ratio is the key to understand the unusual Kondo lattice behavior and heavy fermion formation in mixed valent compounds.

Local moment behaviors of the valence fluctuating systems β-YbAlB4 and α-YbAlB4

β-YbAlB4 is the first example of an Yb-based heavy Fermion superconductor with Tc = 80 mK and exhibits pronounced non-Fermi-liquid behavior above Tc. On the other hand, recent hard x-ray photoemission spectroscopy measurements have revealed strong intermediate valence of both β-YbAlB4 and its locally isostructural polymorph α-YbAlB4 . Here we present the results of the specific heat and magnetization measurements of β-YbAlB4 and α-YbAlB4 . The results indicate a Fermi liquid ground state for α-YbAlB4 in contrast to the quantum criticality found in β-YbAlB4 . Interestingly, both systems exhibit Kondo lattice behavior with large Wilson ratio below T* ~ 8K, through the renormalization of a high valence fluctuation scale ~ 200 K.

Unusual heavy-mass nearly ferromagnetic state with a surprisingly large Wilson ratio in the double layered ruthenates(Sr1−xCax)3Ru2O7

We report an unusual nearly ferromagnetic, heavy-mass state with a surprisingly large Wilson ratio $R_{\textrm{w}}$ (e.g., $R_{\textrm{w}}\sim$ 700 for $x =$ 0.2) in double layered ruthenates (Sr$_{1-x}$Ca$_{x}$)$_{3}$Ru$_{2}$O$_{7}$ with 0.08 $< x <$ 0.4. This state does not evolve into a long-range ferromagnetically ordered state despite considerably strong ferromagnetic correlations, but freezes into a cluster-spin-glass at low temperatures. In addition, evidence of non-Fermi liquid behavior is observed as the spin freezing temperature of the cluster-spin-glass approaches zero near $x \approx$ 0.1. We discuss the origin of this unique magnetic state from the Fermi surface information probed by Hall effect measurements.

Ferromagnetic spin fluctuation inLaFeAsO1−xFx

The F-doped LaFeAsO---a recently discovered superconductor with the high ${T}_{c}$ of 26 K---has been studied using the resistivity $(\ensuremath{\rho})$, magnetic-susceptibility $(\ensuremath{\chi})$, and heat-capacity $({C}_{p})$ measurements in the F doping range $0\ensuremath{\le}x\ensuremath{\le}0.14$ $({\text{LaFeAsO}}_{1\ensuremath{-}x}{\text{F}}_{x})$. In the low-temperature region, a ${T}^{3}\text{ }\text{ln}\text{ }T$ term in ${C}_{p}$ and a ${T}^{2}$ term in $\ensuremath{\chi}$---which are derived from the spin fluctuation---are observed. The nearly ferromagnetic nature evidenced by a large Wilson ratio (6.5 for $x=0$ and 11.2 for $x=0.025$) suggests that the superconductivity in the LaFeAsO system is mediated by ferromagnetic spin fluctuation.

Non-Fermi-liquid behavior in nearly ferromagneticSrIrO3single crystals

We report transport and thermodynamic properties of single-crystal SrIrO3 as a function of temperature T and applied magnetic field H. We find that SrIrO3 is a non-Fermi-liquid metal near a ferromagnetic instability, as characterized by the following properties: (1) small ordered moment but no evidence for long-range order down to 1.7 K; (2) strongly enhanced magnetic susceptibility that diverges as T or T1/2 at low temperatures, depending on the applied field; (3) heat capacity C(T,H) ~ -Tlog T that is readily amplified by low applied fields; (4) a strikingly large Wilson ratio at T< 4K; and (5) a T3/2-dependence of electrical resistivity over the range 1.7 < T < 120 K. A phase diagram based on the data implies SrIrO3 is a rare example of a stoichiometric oxide compound that exhibits non-Fermi-liquid behavior near a quantum critical point (T = 0 and H = 0.23 T).

Structural and physical properties of the 6H BaRuO 3 polymorph synthesized under high pressure

The single-phase 6H BaRuO 3 with the hexagonal BaTiO 3 structure was synthesized at 5 GPa and 1000 °C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) Å and c=14.0499(2) Å; the average Ru–O distance and direct Ru–Ru distance in the Ru 2O 9 dioctahedron being 1.992(6) and 2.5658(14) Å, respectively. The electrical resistivity of the 6H BaRuO 3 follows a relationship of ρ versus T 3/2 below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO 3 is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio R W and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO 3 was discussed.

Physical properties of the β-Ti6Sn5 system

The current work reports the specific heat, the resistivity and the magnetic susceptibility of both single-crystal and polycrystalline β-Ti6Sn5 at cryogenic temperatures. The effects of small additions of magnetic and non-magnetic impurities were examined. Resistivity and magnetic susceptibility measurements reveal that the undoped material is a Pauli paramagnet displaying Fermi-liquid behaviour, while ferromagnetic ordering was observed at T150K with small additions of Ce, La or Co. Analysis of the electronic specific heat γ and magnetic susceptibility gives an unexpectedly large Wilson ratio R w of 1.76, a value indicative of correlated electron behaviour. We present the general physical properties and based on the sensitivity of the magnetic properties to doping, show evidence that β-Ti6Sn5 exhibits a ground state in close proximity to a non-magnetic and magnetic phase boundary.

Ferromagnetic correlations in heavy fermion compounds

Recent work has stressed the role of antiferromagnetic correlations in heavy fermion compounds. In this paper we show that ferromagnetic correlations are also present. As primary evidence we exhibit data for Ce 3In, showing that it has an enhanced low temperature susceptibility and large Wilson ratio R = 11.5. By comparing with neutron scattering results for CeAl and CeM 2Si 2 we show that antiferro- and ferromagnetic correlations are expected to coexist when the heavy fermion system is in the vicinity of a transition to a magnetically ordered state where ferromagnetic sheeys are antiferromagnetically coupled. We also show that the onsets of the magnetic correlations, of the coherence in the resistivity, and of the heavy mass in the specific heat all coincide in Ce 3In.