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Register a new userGrowth and characterization of HgBa2CaCu2O6+d and HgBa2Ca2Cu3O8+d crystals
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We report the successful synthesis of single-crystalline cuprate superconductors HgBa$_{2}$CaCu$_{2}$O$_{6+delta}$ and HgBa$_{2}$Ca$_{2}$Cu$_{3}$O$_{8+delta}$. These compounds are well-known for their high optimal superconducting critical temperatures of $T_mathrm{c}$ = 128 K and 134 K at ambient pressure, respectively, and for their challenging synthesis. Using a conventional quartz-tube encapsulation method and a two-layer encapsulation method that utilizes custom-built high-pressure furnaces, we are able to grow single crystals with linear dimensions up to several millimeters parallel to the CuO$_2$ planes. Extended post-growth anneals are shown to lead to sharp superconducting transitions, indicative of high macroscopic homogeneity. X-ray diffraction and polarized Raman spectroscopy are identified as viable methods to resolve the seemingly unavoidable inter-growth of the two compounds. Our work helps to remove obstacles toward the study of these model cuprate systems with experimental probes that require sizable high-quality crystals.
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Recent experiments in multiband Fe-based and heavy-fermion superconductors have challenged the long-held dichotomy between simple $s$- and $d$-wave spin-singlet pairing states. Here, we advance several time-reversal-invariant irreducible pairings that go beyond the standard singlet functions through a matrix structure in the band/orbital space, and elucidate their naturalness in multiband systems. We consider the $stau_{3}$ multiorbital superconducting state for Fe-chalcogenide superconductors. This state, corresponding to a $d+d$ intra- and inter-band pairing, is shown to contrast with the more familiar $d +text{i}d$ state in a way analogous to how the B- triplet pairing phase of enhe superfluid differs from its A- phase counterpart. In addition, we construct an analogue of the $stau_{3}$ pairing for the heavy-fermion superconductor CeCu$_{2}$Si$_{2}$, using degrees-of-freedom that incorporate spin-orbit coupling. Our results lead to the proposition that $d$-wave superconductors in correlated multiband systems will generically have a fully-gapped Fermi surface when they are examined at sufficiently low energies.
Solution growth of single crystals of the recently reported new compound Ce2PdIn8 was investigated. When growing from a stoichiometry in a range 2:1:20 - 2:1:35, single crystals of CeIn3 covered by a thin (~50 um) single-crystalline layer of Ce2PdIn8 were mostly obtained. Using palladium richer compositions the thickness of the Ce2PdIn8 layers were increased, which allowed mechanical extraction of single-phase slabs of the desired compound suitable for a thorough study of magnetism and superconductivity. In some solution growth products also CePd3In6 (LaNi3In6 - type of structure) and traces of phases with the stoichiometry CePd2In7, Ce1.5Pd1.5In7 (determined only by EDX) have been identified. Magnetic measurements of the Ce2PdIn8 single crystals reveal paramagnetic behaviour of the Ce3+ ions with significant magnetocrystalline anisotropy. Above 70 K the magnetic susceptibility follows the Curie-Weiss law with considerably different values of the paramagnetic Curie temperature, for the magnetic field applied along the a- (-90 K) and c-(-50 K) axis. Below the reported critical temperature for superconductivity Tc (0.69 K) the electrical resistivity drops to zero. Comparative measurements of the electrical resistivity, heat capacity and AC susceptibility of several crystals reveal that the superconducting transition is strongly sample-dependent.
Electronic Raman scattering with in and out of (ab) plane polarizations have been performed on HgBa2Ca2Cu3O8+d in a slightly underdoped single crystal with a critical temperature Tc=122 K. We find that the d-wave pairing gap at the antinodes is higher in energy (14 kBTc) than in other cuprates and that it varies very slowly up to Tc. This hints at a strong coupling nature of the pairing mechanism. Interestingly, we reveal that the pairing-gap feature in the Raman response displays a complex peak-dip-hump structure, in a fashion reminiscent of what observed by angle resolved photo-emission spectroscopy in Bi2Sr2CaCu2O8+d (Bi-2212). We detect two other distinct superconducting peaks at 5kBTc and 7kBTc when probing respectively around the nodes and on the whole Fermi surface. Finally we establish that the pairing gap at the antinodes is detected both for (ab) plane and for c-axis light polarizations. This shows that the quasiparticle dynamics along the c-axis is intimately connected to the antinodal one in the (ab) plane.
Bi$_2$Sr$_{2-x}$La$_x$CuO$_{6+delta}$ (0$leq x leq$1.00) single crystals with high-quality have been grown successfully using the travelling-solvent floating-zone technique. The patterns of X-ray diffraction suggest high crystalline quality of the samples. After post-annealing in flowing oxygen at 600 $^o$C, the crystals show sharp superconducting transitions revealed by AC susceptibility. The hole concentration $p$ is deduced from superconducting transition temperature ($T_c$), which exhibits a linear relation with La doping level $x$. It ranges from the heavily overdoped regime ($p approx$ 0.2) to the extremely underdoped side ($p approx$ 0.08) where the superconductivity is absent. Comparing with the superconducting dome in Bi$_{2+x}$Sr$_{2-x}$CuO$_{6+delta}$ system, the effects from out-of-plane disorders show up in our samples. Besides the La doping level $x$, the superconductivity is also sensitive to the content of oxygen which could be tuned by post-annealing method over the whole doping range. The post-annealing effects on $T_c$ and $p$ for each La doping level are studied, which give some insights on the different nature between overdoped and underdoped regime.
Being homologue to the new, Fe-based type of high-temperature superconductors, CeFePO exhibits magnetism, Kondo and heavy-fermion phenomena. We experimentally studied the electronic structure of CeFePO by means of angle-resolved photoemission spectroscopy. In particular, contributions of the Ce 4f-derived states and their hybridization to the Fe 3d bands were explored using both symmetry selection rules for excitation and their photoionization cross-section variations as a function of photon energy. It was experimentally found - and later on confirmed by LDA as well as DMFT calculations - that the Ce 4f states hybridize to the Fe 3d states of d_{3z^2-r^2} symmetry near the Fermi level that discloses their participation in the occurring electron-correlation phenomena and provides insight into mechanism of superconductivity in oxopnictides.
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