Invasive pancreatic ductal adenocarcinoma is an almost uniformly fatal disease. Several distinct noninvasive precursor lesions can give rise to invasive adenocarcinoma of the pancreas, and the prevention, detection, and treatment of these noninvasive lesions offers the potential to cure early pancreatic cancers. Noninvasive precursors of invasive ductal adenocarcinoma of the pancreas include pancreatic intraepithelial neoplasias (PanINs), intraductal papillary mucinous neoplasms (IPMNs), and mucinous cystic neoplasms. Diagnostic criteria, including a distinct ovarian-type stroma, and a consistent nomenclature are well established for mucinous cystic neoplasms. By contrast, consistent nomenclatures and diagnostic criteria have been more difficult to establish for PanINs and IPMNs. Because both PanINs and IPMNs consist of intraductal neoplastic proliferations of columnar, mucin-containing cells with a variable degree of papilla formation, the distinction between these two classes of precursor lesions remains problematic. Thus, considerable ambiguities still exist in the classification of noninvasive neoplasms in the pancreatic ducts. A meeting of international experts on precursor lesions of pancreatic cancer was held at The Johns Hopkins Hospital from August 18 to 19, 2003. The purpose of this meeting was to define an international acceptable set of diagnostic criteria for PanINs and IPMNs and to address a number of ambiguities that exist in the previously reported classification systems for these neoplasms. We present a consensus classification of the precursor lesions in the pancreatic ducts, PanINs and IPMNs.
This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr 2 RuO 4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr 2 RuO 4 . After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr 2 RuO 4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr 2 RuO 4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr 2 RuO 4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr 2 RuO 4 .KEYWORDS: Sr 2 RuO 4 , ruthenate, spin-triplet superconductivity, topological superconductor Spin-Triplet Superconductors Candidates of spin-triplet superconductorsIn the last three decades, and particularly since the discovery of high-transition-temperature (high-T c ) superconductivity of the cuprates, 1) studies of ''unconventional'' superconductivity have been one of the main topics in condensed-matter physics. Here we designate the term ''unconventional'' as the pairing based on non-phonon mechanisms.2) The unconventional superconductivity is mainly found in heavy-fermion superconductors (since 1978), 3) Unconventional superconductivity is characterized by the anisotropic gap function or order parameter which is integrated to be zero or a small value due to the variations of the wave function ''phase'', in contrast to an ordinary s-wave state. In many of them, including high-T c cuprates and iron pnictides, the electrons are clearly paired in spinsinglet states. In this point of view, they are similar to conventional s-wave superconductors, in which the spindegrees of freedom is lost in the charged superfluids. Spintriplet superfluid states are fully established in the Fermi liquid 3 He, 7,8) for which spin and mass supercurrents emerge in the charge-neutral superfluids. The question is then whether or not spin-triplet superconductors exist, and what novel superconducting properties they may exhibit due to their charge and spin supercurrents.There are several classes of candidates of spin-triplet superconductors represented in Table I. W...
Now that more than two decades have passed since the first reports of intraductal papillary-mucinous neoplasms (IPMNs), it has become clear that IPMN consists of a spectrum of neoplasms with both morphological and immunohistochemical variations. At a meeting of international experts on pancreatic precursor lesions held in 2003, it was agreed that a consensus classification of IPMN subtypes should be established to enable a more detailed analysis of the clinicopathological significance of the variations. Based on our experience and on information from the literature, we selected representative histological examples of IPMNs and defined a consensus nomenclature and criteria for classifying variants as distinctive IPMN subtypes including gastric type, intestinal type, pancreatobiliary type, and oncocytic type. These definitions can be used for further analyses of the clinicopathological significance of the variations of IPMN.
A long-standing question in the field of superconductivity is whether pairing of electrons can arise in some cases as a result of magnetic interactions instead of electron-phonon-induced interactions as in the conventional Bardeen-Cooper-Schrieffer theory 1 . A major challenge to the idea of magnetically mediated superconductivity has been the dramatically different behaviour of the cerium and ytterbium heavy-fermion compounds. The cerium-based systems are often found to be superconducting 1-6 , in keeping with a magnetic pairing scenario, but corresponding ytterbium systems, or hole analogues of the cerium systems, are not. Despite searches over two decades there has been no evidence of heavy-fermion superconductivity in an ytterbium system, casting doubt on our understanding of the electron-hole parallelism between the cerium and the ytterbium compounds. Here we present the first empirical evidence that superconductivity is indeed possible in an ytterbium-based heavy-fermion system. In particular, we observe a superconducting transition at T c = 80 mK in high-purity single crystals of YbAlB 4 in the new structural β phase 7 . We also observe a novel type of non-Fermi-liquid state above T c that arises without chemical doping, in zero applied magnetic field and at ambient pressure, establishing β-YbAlB 4 as a unique system showing quantum criticality without external tuning.First we present the bulk magnetic and electronic properties of β-YbAlB 4 , a new morphology of the previously known α-YbAlB 4 (refs 7,8). Shown in Fig. 1a is the orthorhombic crystal structure of β-YbAlB 4 and the temperature dependence of the d.c. magnetic susceptibility χ = M/H. Here, M and H represent the magnetization and external field, respectively. The magnetic susceptibility shows the strong uniaxial anisotropy of an Ising system with moments aligned along the c axis. Above 100 K the c-axis susceptibility has a Curie-Weiss form χ c (T ) = C/(T − θ W ), with θ W ∼ −210 K and a Curie constant C corresponding to an effective Ising moment µ eff = g J J Z ∼ 3.1 µ B , where g J is the Landé g factor and J Z is the c-axis component of the total angular momentum. The in-plane susceptibility, on the other hand, is almost temperature independent, showing a weak peak around 200 K.Shown in Fig. 1b is the temperature dependence of the in-plane resistivity, ρ ab , along with the estimated 4f -electron contribution ρ m (defined in the figure caption), which shows a coherence peak at about 250 K. The low residual resistivity ρ ab (0) ∼ 0.4 µ cm and correspondingly high residual resistivity ratio, ρ ab (300 K)/ρ ab (0) ∼ 300, suggest that the electronic mean free path is of the order of 0.1 µm.In contrast to most other heavy-fermion compounds, the resistivity does not show a Fermi liquid (FL) regime characterized by a T 2 temperature variation (Fig. 1b). As shown in Fig. 1b insets, ρ ab is linear between 4 and 1 K and varies as T 1.5 below T 0 ∼ 1 K down to 80 mK. Below 80 mK our highest-purity samples are superconducting (Fig. 1b, insets). We shall...
In condensed matter physics, spontaneous symmetry breaking has been a key concept, and discoveries of new types of broken symmetries have greatly increased our understanding of matter 1,2 . Recently, electronic nematicity, novel spontaneous rotational-symmetry breaking leading to an emergence of a special direction in electron liquids, has been attracting significant attention 3-6 . Here, we show bulk thermodynamic evidence for nematic superconductivity, in which the nematicity emerges in the superconducting gap amplitude, in Cu x Bi 2 Se 3 . Based on high-resolution calorimetry of single-crystalline samples under accurate two-axis control of the magnetic field direction, we discovered clear two-fold symmetry in the specific heat and in the upper critical field despite the trigonal symmetry of the lattice. Nematic superconductivity for this material should possess a unique topological nature associated with odd parity 7-9 . Thus, our findings establish a new class of spontaneously symmetry-broken states of matter-namely, odd-parity nematic superconductivity.
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