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Register a new userMultiband electronic transport in $alpha$-Yb$_{1-x}$Sr$_{x}$AlB$_{4}$ [x = 0, 0.19(3)] single crystals
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We report on the evidence for the multiband electronic transport in $alpha$-YbAlB$_{4}$ and $alpha$-Yb$_{0.81(2)}$Sr$_{0.19(3)}$AlB$_{4}$. Multiband transport reveals itself below 10 K in both compounds via Hall effect measurements, whereas anisotropic magnetic ground state sets in below 3 K in $alpha$-Yb$_{0.81(2)}$Sr$_{0.19(3)}$AlB$_{4}$. Our results show that Sr$^{2+}$ substitution enhances conductivity, but does not change the quasiparticle mass of bands induced by heavy fermion hybridization.
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A laboratory hard X-ray photoelectron spectroscopy (HXPS) system equipped with a monochromatic Cr K$alpha$ ($h u = 5414.7$ eV) X-ray source was applied to an investigation of the core-level electronic structure of La$_{1-x}$Sr$_x$MnO$_3$. No appreciable high binding-energy shoulder in the O $1s$ HXPS spectra were observed while an enhanced low binding-energy shoulder structure in the Mn $2p_{3/2}$ HXPS spectra were observed, both of which are manifestation of high bulk sensitivity. Such high bulk sensitivity enabled us to track the Mn $2p_{3/2}$ shoulder structure in the full range of $x$, giving us a new insight into the binding-energy shift of the Mn $2p_{3/2}$ core level. Comparisons with the results using the conventional laboratory XPS ($h u = 1486.6$ eV) as well as those using a synchrotron radiation source ($h u = 7939.9$ eV) demonstrate that HXPS is a powerful and convenient tool to analyze the bulk electronic structure of a host of different compounds.
Single crystals of A$_{1-x}$K$_x$Fe$_2$As$_2$ (A=Ba, Sr) with high quality have been grown successfully by FeAs self-flux method. The samples have sizes up to 4 mm with flat and shiny surfaces. The X-ray diffraction patterns suggest that they have high crystalline quality and c-axis orientation. The non-superconducting crystals show a spin-density-wave (SDW) instability at about 173 K and 135 K for Sr-based and Ba-based compound, respectively. After doping K as the hole dopant into the BaFe$_2$As$_2$ system, the SDW transition is smeared, and superconducting samples with the compound of Ba$_{1-x}$K$_x$Fe$_2$As$_2$ (0 $< x leqslant$ 0.4) are obtained. The superconductors characterized by AC susceptibility and resistivity measurements exhibit very sharp superconducting transition at about 36 K, 32 K, 27 K and 23 K for x= 0.40,0.28,0.25 and 0.23, respectively.
We present the electronic structure of Sr_{1-(x+y)}La_{x+y}Ti_{1-x}Cr_{x}O_{3} investigated by high-resolution photoemission spectroscopy. In the vicinity of Fermi level, it was found that the electronic structure were composed of a Cr 3d local state with the t_{2g}^{3} configuration and a Ti 3d itinerant state. The energy levels of these Cr and Ti 3d states are well interpreted by the difference of the charge-transfer energy of both ions. The spectral weight of the Cr 3d state is completely proportional to the spin concentration x irrespective of the carrier concentration y, indicating that the spin density can be controlled by x as desired. In contrast, the spectral weight of the Ti 3d state is not proportional to y, depending on the amount of Cr doping.
We have examined an isovalent Rh substitution effect on the transport properties of the thermoelectric oxide Ca$_3$Co$_{4}$O$_9$ using single-crystalline form. With increasing Rh content $x$, both the electrical resistivity and the Seebeck coefficient change systematically up to $x=0.6$ for Ca$_3$Co$_{4-x}$Rh$_{x}$O$_9$ samples. In the Fermi-liquid regime where the resistivity behaves as $rho=rho_0+AT^2$ around 120 K, the $A$ value decreases with increasing Rh content, indicating that the correlation effect is weakened by Rh $4d$ electrons with extended orbitals. We find that, in contrast to such a weak correlation effect observed in the resistivity of Rh-substituted samples, the low-temperature Seebeck coefficient is increased with increasing Rh content, which is explained with a possible enhancement of a pseudogap associated with the short-range order of spin density wave. In high-temperature range above room temperature, we show that the resistivity is largely suppressed by Rh substitution while the Seebeck coefficient becomes almost temperature-independent, leading to a significant improvement of the power factor in Rh-substituted samples. This result is also discussed in terms of the differences in the orbital size and the associated spin state between Co $3d$ and Rh $4d$ electrons.
We report a study on the thermal conductivity of CuFe$_{1-x}$Ga$_x$O$_2$ ($x =$ 0--0.12) single crystals at temperatures down to 0.3 K and in magnetic fields up to 14 T. CuFeO$_2$ is a well-known geometrically frustrated triangular lattice antiferromagnet and can be made to display multiferroicity either by applying magnetic field along the $c$ axis or by doping nonmagnetic impurities, accompanied with rich behaviors of magnetic phase transitions. The main experimental findings of this work are: (i) the thermal conductivities ($kappa_a$ and $kappa_c$) show drastic anomalies at temperature- or field-induced magnetic transitions; (ii) the low-$T$ $kappa(H)$ isotherms exhibit irreversibility in a broad region of magnetic fields; (iii) there are phonon scattering effect caused by magnetic fluctuations at very low temperatures. These results demonstrate strong spin-phonon coupling in this material and reveal the non-negligible magnetic fluctuations in the ground state of pure and Ga-doped samples.
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