It has recently been established that the high temperature (high-Tc(between atomic and macroscopic scale). Here we report micro X-ray diffraction imaging of the spatial distribution of both the charge-density-wave 'puddles' (domains with only a few wavelengths) and quenched disorder in HgBa 2 CuO 4+y , the single layer cuprate with the highest T c , 95 kelvin [26][27][28] . We found that the charge-density-wave puddles, like the steam bubbles in boiling water, have a fat-tailed size distribution that is typical of selforganization near a critical point 19 . However, the quenched disorder, which arises from oxygen interstitials, has a distribution that is contrary to the usual assumed random, uncorrelated distribution 12, 13 . The interstitials-oxygen-rich domains are spatially anticorrelated with the charge-density-wave domains, leading to a complex emergent geometry of the spatial landscape for superconductivity. 2Although it is known that the incommensurate charge-density-wave (CDW) order in cuprates (copper oxides) is made of ordered, stripy, nanoscale puddles with an average of only 3-4 oscillations, information about the size distribution and spatial organization of these puddles has so far not been available. We present experiments that demonstrate that CDW puddles, have a complex spatial distribution and coexist with, but are spatially anticorrelated to, quenched disorder in HgBa 2 CuO 4+y (Hg1201). The sample we studied is a layered perovskite at optimum doping with oxygen interstitials y=0.12, tetragonal symmetry P4/mmm and a low misfit strain [14][15][16] . The X-ray diffraction (XRD) measurements (see Methods) show diffuse CDW satellites (secondary peaks surrounding a main peak) at q CDW =(0.23a*, 0.16c*), in the b*=0 plane and q CDW =(0.23b*, 0.16c*) in the a*=0 plane (where a*, b*, and c* are the reciprocal lattice units) around specific Bragg peaks, such as (1 0 8), below the onset temperature T CDW =240 K (see Fig. 1a). The component of the momentum transfer q CDW in the CuO 2 plane (0.23a*) in this case is smaller than it is in the underdoped case (0.28a*) 5 . The temperature evolution of CDW-peak profile along a* (in the h direction; Fig. 1b) shows a smeared, glassy-like evolution below T CDW .The CDW-peak intensity reaches a maximum at T=100 K, followed by a drop associated with the onset of superconductivity at T=T c . We investigated the isotropic character of the CDW, in the a-b plane using azimuthal scans, as shown in Fig. 1c. We observed an equal probability of vertical and horizontally striped CDW puddles.Our main result is the discovery of the statistical spatial distribution of the CDW-puddle size and density throughout the sample, which shows an emergent complex network geometry for the superconducting phase. We performed scanning micro X-ray diffraction (SµXRD) measurements (see Methods) to extend the imaging of spatial inhomogeneity previously obtained by scanning tunneling microscopy [7][8][9] , from the surface to the bulk of the sample and from nanoscale to mesoscale spatial inh...

We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 (lambda{1}/xi{1}<1/sqrt[2]) and type-2 (lambda{2}/xi{2}>1/sqrt[2]) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamerlike vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations.

The growth of carbon-substituted magnesium diboride Mg͑B 1−x C x ͒ 2 single crystals with 0 ഛ x ഛ 0.15 is reported, and the structural, transport, and magnetization data are presented. The superconducting transition temperature decreases monotonically with increasing carbon content in the full investigated range of substitution. By adjusting the nominal composition, T c of substituted crystals can be tuned in a wide temperature range between 10 and 39 K. Simultaneous introduction of disorder by carbon substitution and significant increase of the upper critical field H c2 is observed. Comparing with the nonsubstituted compound, H c2 at 15 K for x = 0.05 is enhanced by more than a factor of 2 for H oriented both perpendicular and parallel to the ab plane. This enhancement is accompanied by a reduction of the H c2 -anisotropy coefficient ␥ from 4.5 ͑for the nonsubstituted compound͒ to 3.4 and 2.8 for the crystals with x = 0.05 and 0.095, respectively. At temperatures below 10 K, the single crystal with larger carbon content shows H c2 ͑defined at zero resistance͒ higher than 7 and 24 T for H oriented perpendicular and parallel to the ab plane, respectively. Observed increase of H c2 cannot be explained by the change in the coherence length due to the disorder-induced decrease of the mean free path only.

Spin-orbit coupling (SOC) is a fundamental interaction in solids which can induce a broad spectrum of unusual physical properties from topologically non-trivial insulating states to unconventional pairing in superconductors. In iron-based superconductors (IBS) its role has so far been considered insignificant with the models based on spin-or orbital fluctuations pairing being the most advanced in the field. Using angle-resolved photoemission spectroscopy we directly observe a sizeable spin-orbit splitting in all main families of IBS. We demonstrate that its impact on the lowenergy electronic structure and details of the Fermi surface topology is much stronger than that of possible nematic ordering. Intriguingly, the largest pairing gap is always supported exactly by SOCinduced Fermi surfaces.In the presence of spin-orbit coupling, the electron's spin quantized along any fixed axis is no longer a good quantum number, but its total angular momentum is. This basic fact alone or in combination with a particular symmetry breaking may lead to a splitting of otherwise degenerate energy bands and is the origin of fascinating phenomena such as spin Hall effects A special role has been played by SOC in the field of superconductors. In low-dimensional or noncentrosymmetric systems it can promote and stabilize superconductivity [6], allow ferromagnetism to coexist with superconductivity [7] or even rise T c [8]. If SOC is large, some superconductors can host an elusive Fulde-Ferrell-Larkin-Ovchinnikov state [9] or topological superconductivity [4]. It is anticipated that SOC could be a very important ingredient in describing the superconducting state in Sr 2 RuO 4 [10]. Since k-dependent spin-orbit splitting is larger than the superconducting gap in this material, the SOC-induced spin anisotropy together with the orbital mixing should directly influence the orbital and spin angular momentum of the Cooper pairs. Singlet and triplet states could be strongly mixed, blurring the distinction between spin-singlet and spintriplet pairing [11].In multiband iron-based superconductors, where the low energy electronic structure is composed of different orbitals, the situation is even more complicated because of the presence of the sizeable Hund's coupling. When the electronic structure near the Fermi energy is composed of different orbitals and spins mixed via spin-orbit coupling, determination of the pairing symmetry becomes non-trivial. However, up to now SOC in iron pnictides and chalcogenides was considered weak.We start with the example of LiFeAs, which is a special representative of iron-based family of superconductors [12]. This material is one of the most studied due to its stoichiometry and non-polar surfaces. Its electronic structure is believed to be well understood from numerous angle-resolved photoemission experiments (ARPES) and the parameterization of its electronic dispersions has been used to test the most developed theoretical approaches [13][14][15]. To detect spin-orbit coupling in LiFeAs experimentally we first ne...

a b s t r a c tA review of our investigations on single crystals of LnFeAsO 1Àx F x (Ln = La, Pr, Nd, Sm, Gd) and Ba 1Àx -Rb x Fe 2 As 2 is presented. A high-pressure technique has been applied for the growth of LnFeAsO 1Àx F x crystals, while Ba 1Àx Rb x Fe 2 As 2 crystals were grown using a quartz ampoule method. Single crystals were used for electrical transport, structure, magnetic torque and spectroscopic studies. Investigations of the crystal structure confirmed high structural perfection and show incomplete occupation of the (O, F) position in superconducting LnFeAsO 1Àx F x crystals. Resistivity measurements on LnFeAsO 1Àx F x crystals show a significant broadening of the transition in high magnetic fields, whereas the resistive transition in Ba 1Àx Rb x Fe 2 As 2 simply shifts to lower temperature. The critical current density for both compounds is relatively high and exceeds 2 Â 10 9 A/m 2 at 15 K in 7 T. The anisotropy of magnetic penetration depth, measured on LnFeAsO 1Àx F x crystals by torque magnetometry is temperature dependent and apparently larger than the anisotropy of the upper critical field. Ba 1Àx Rb x Fe 2 As 2 crystals are electronically significantly less anisotropic. Point-Contact Andreev-Reflection spectroscopy indicates the existence of two energy gaps in LnFeAsO 1Àx F x . Scanning Tunneling Spectroscopy reveals in addition to a superconducting gap, also some feature at high energy ($20 meV).

Type-II Dirac/Weyl semimetals are characterized by strongly tilted Dirac cones such that the Dirac/Weyl node emerges at the boundary of electron and hole pockets as a new state of quantum matter, distinct from the standard Dirac/Weyl points with a point-like Fermi surface which are referred to as type-I nodes. The type-II Dirac fermions were recently predicted by theory and have since been confirmed in experiments in the PtSe 2 -class of transition metal dichalcogenides. However, the Dirac nodes observed in PtSe 2 , PdTe 2 and PtTe 2 candidates are quite far away from the Fermi level, making the signature of topological fermions obscure as the physical properties are still dominated by the non-Dirac quasiparticles. Here we report the synthesis of a new type-II Dirac semimetal NiTe 2 in which a pair of type-II Dirac nodes are located very close to the Fermi level. The quantum oscillations in this material reveal a nontrivial Berry's phase associated with these Dirac fermions. Our first principles calculations further unveil a topological Dirac cone in its surface states. Therefore, NiTe 2 may not only represent an improved system to formulate the theoretical understanding of the exotic consequences of type-II Dirac fermions, it also facilitates possible applications based on these topological carriers.

No abstract

Single crystals of SmFeAsO1−xFy of a size up to 120 × 100 µm2 have been grown from NaCl/KCl flux at a pressure of 30 kbar and temperature of 1350-1450 °C using the cubic anvil high-pressure technique. The superconducting transition temperature of the obtained single crystals varies between 45 and 53 K. Obtained crystals are characterized by a full diamagnetic response in low magnetic fields and by a high critical current density in high magnetic fields. Structural refinement has been performed on the single crystal. Differential thermal analysis investigations at 1 bar Ar pressure show decomposition of SmFeAsO1−xFy at 1302 °C.Abstract. Single crystals of SmFeAsO 1-x F y of a size up to 120x100 μm 2 have been grown from NaCl/KCl flux at pressure of 30 kbar and temperature of 1350-1450 °C using cubic anvil high-pressure technique. Superconducting transition temperature of the obtained single crystals varies between 45 and 53 K. Obtained crystals are characterized by full diamagnetic response in low magnetic field and by high critical current density in high magnetic field. Structure refinement has been performed on single crystal. Differential thermal analysis investigations at 1 bar Ar pressure show decomposition of SmFeAsO 1-x F y at 1302 °C.