Search

Copyright of Crítica is the property of Instituto de Investigaciones Filosoficas and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A 2×2×1 superstructure of the P63/mmc NiAs structure is reported in which kagome nets are stabilized in the octahedral transition metal layers of the compounds Ni0.7Pd0.2Bi, Ni0.6Pt0.4Bi, and Mn0.99Pd0.01Bi. The ordered vacancies that yield the true hexagonal kagome motif lead to filling of trigonal bipyramidal interstitial sites with the transition metal in this family of "kagome‐NiAs" type materials. Further ordering of vacancies within these interstitial layers can be compositionally driven to simultaneously yield kagome‐connected layers and a net polarization along the c axes in Ni0.9Bi and Ni0.79Pd0.08Bi, which adopt Fmm2 symmetry. The polar and non‐polar materials exhibit different electronic transport behaviour, reflecting the tuneability of both structure and properties within the NiAs‐type bismuthide materials family. [ABSTRACT FROM AUTHOR]

Major depressive disorder (MDD) is a serious condition with a large disease burden. It is often claimed that MDD is a "brain disease." What would it mean for MDD to be a brain disease? I argue that the best interpretation of this claim is as offering a substantive empirical hypothesis about the causes of the syndrome of depression. This syndrome-causal conception of disease, combined with the idea that MDD is a disease of the brain, commits the brain disease conception of MDD to the claim that brain dysfunction causes the symptoms of MDD. I argue that this consequence of the brain disease conception of MDD is false. It incorrectly rules out genuine instances of content-sensitive causation between adverse conditions in the world and the characteristic symptoms of MDD. Empirical evidence shows that the major causes of depression are genuinely psychological causes of the symptoms of MDD. This rules out, in many cases, the "brute" causation required by the brain disease conception. The existence of cases of MDD with non-brute causes supports the reinstatement of the old nosological distinction between endogenous and exogenous depression. [ABSTRACT FROM AUTHOR]

The article discusses the author's response to criticisms of their paper on philosophy of psychiatry. The author addresses the accusation of postmodern tendencies in philosophy of psychiatry and argues that these claims are unsubstantiated. They also clarify their use of terminology and emphasize the importance of understanding in the field. The author disagrees with the suggestion that philosophy should be more practical and instead believes that delivering useful knowledge in collaboration with science is the key. [Extracted from the article]

It is a mistake to think that any philosophical contribution to the study of psychopathology is otiose. I identify three non-exhaustive roles that philosophy can and does occupy in the study of mental disorder, which I call the agenda-setting role, the synthetic role, and the regulative role. The three roles are illustrated via consideration of the importance of Jaspers' notion of understanding and its application to specific examples of mental disorder, including delusions of reference, Capgras delusion and other monothematic delusions, and clinical depression. Together the three roles assign to philosophy of psychopathology the task of determining how to situate the varieties of mental disorder within the system of interpretive and evaluative concepts that partially make up the dynamic but indispensable manifest image. [ABSTRACT FROM AUTHOR]

Monothematic delusions are delusions whose contents pertain to a single subject matter. Examples include Capgras delusion, the delusion that a loved one has been replaced by an impostor, and Cotard delusion, the delusion that one is dead or does not exist. Two-factor accounts of such delusions hold that they are the result of both an experiential deficit—for instance, flattened affect—coupled with an aberrant cognitive response to that deficit. In this article, we develop a new expressivist two-factor account of delusion. In contrast to existing endorsement and explanationist accounts, which treat delusions as either explanations or endorsements of the contents of these disordered experiences, we hold that delusional beliefs have an expressive function: they characterize, in impressionistic terms, what the subject's experience is like for them. We show how our account improves upon existing two-factor views in explaining the central features of monothematic delusions, in particular how delusional subjects fall short of the ideal of rationality. [ABSTRACT FROM AUTHOR]

Understanding the structure–property relationships of materials in order to supress thermal conductivity is crucial for developing efficient thermoelectric generators and thermal barrier coatings. Low thermal conductivity materials can often contain a single dominant phonon scattering mechanism. Here, we highlight how combining different structural features into one material can aid in the design and identification of new materials with low thermal conductivities. We synthesise two new mixed-anion materials, Bi8CsO8SeX7 (X = Cl and Br), with low thermal conductivities of 0.27(2) and 0.22(2) W m−1 K−1 respectively, measured along their c-axes at room temperature. The Bi8CsO8SeX7 materials possess a combination of bond strength hierarchies, Cs+ vacancies, and low frequency Cs+ rattling. These different features significantly inhibit phonon transport along different crystallographic directions. Due to sharp bond strength contrast between the van der Waals gaps and [Bi2O2]2+ layers, the Bi8CsO8SeX7 materials exhibit thermal conductivities <50% of the theoretical minimum when measured along the stacking direction. Conversely, the thermal conductivity associated with the ab-plane is reduced by Cs+ rattling when compared to the structurally and compositionally related BiOCl. [ABSTRACT FROM AUTHOR]

Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors (1), in magnetic memory (2), and in hard drives (3) at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures (4). Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide W[Te.sub.2]: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of W[Te.sub.2], will represent a significant new direction in the study of magnetoresistivity., Large magnetoresistance (MR) is an uncommon property, mostly of magnetic compounds. Giant magnetoresistance (GMR) (5) and colossal magnetoresistance (CMR) (6,7) occur in thin-film metals and manganese-based perovskites, for example. In [...]

The thermal conductivity of crystalline materials cannot be arbitrarily low, as the intrinsic limit depends on the phonon dispersion. We used complementary strategies to suppress the contribution of the longitudinal and transverse phonons to heat transport in layered materials that contain different types of intrinsic chemical interfaces. BiOCl and Bi2O2Se encapsulate these design principles for longitudinal and transverse modes, respectively, and the bulk superlattice material Bi4O4SeCl2 combines these effects by ordering both interface types within its unit cell to reach an extremely low thermal conductivity of 0.1 watts per kelvin per meter at room temperature along its stacking direction. This value comes within a factor of four of the thermal conductivity of air. We demonstrated that chemical control of the spatial arrangement of distinct interfaces can synergically modify vibrational modes to minimize thermal conductivity. [ABSTRACT FROM AUTHOR]

We report the aperiodic titanate Ba10Y6Ti4O27 with a room‐temperature thermal conductivity that equals the lowest reported for an oxide. The structure is characterised by discontinuous occupancy modulation of each of the sites and can be considered as a quasicrystal. The resulting localisation of lattice vibrations suppresses phonon transport of heat. This new lead material for low‐thermal‐conductivity oxides is metastable and located within a quaternary phase field that has been previously explored. Its isolation thus requires a precisely defined synthetic protocol. The necessary narrowing of the search space for experimental investigation was achieved by evaluation of titanate crystal chemistry, prediction of unexplored structural motifs that would favour synthetically accessible new compositions, and assessment of their properties with machine‐learning models. [ABSTRACT FROM AUTHOR]

The consideration of the problem of healthcare allocation as a special case of distributive justice is especially alluring when we only consider consequentialist theories. I articulate here an alternative Rawlsian non-consequentialist theory which prioritizes the fairness of healthcare allocation procedures rather than directly setting distributive parameters. The theory in question stems from Rawlsian commitments that, it is argued, have a better Rawlsian pedigree than those considered as such by Tännsjö. The alternative framework is worthy of consideration on its own merits, but it also casts light on two related difficulties with Tännsjö's approach: (i) the limits of his supposedly ecumenical methodology, which is revealed to be dialectically suspect and (ii) issues with the type of abstraction and idealization from actual judgements and preferences which the approach requires. [ABSTRACT FROM AUTHOR]

In this paper, I argue against three leading accounts of self-deception and propose a heretofore overlooked route to self-deception. The central problem with extant accounts is that they are unable to balance two crucial desiderata: (a) to make the dynamics of self-deception (e.g., the formation of self-deceptive beliefs) psychologically plausible, and (b) to capture self-deception as an intentional phenomenon for which the self-deceiver is responsible. I argue that the three leading views all fail on one or both counts. However, I claim that many or most cases of self-deception conform to a different model, which I call 'self-deception as omission.' In these cases, the process of self-deceptive belief formation and the intentional act for which the self-deceiver is responsible come apart, allowing us to meet both desiderata. Self-deceptive beliefs are often formed by unconscious mechanisms closely analogous to "System 1" processes of dual-systems psychology, or by other mechanisms of motivated reasoning. The nascently self-deceptive subject then acquiesces in the comforting belief and commits an epistemic failure by allowing it to persist. If this is done for motivationally biased reasons – for example, preferring that the belief in question be true – then the subject is self-deceived and is blameworthy for her epistemic omission. [ABSTRACT FROM AUTHOR]

Materials with giant spin splitting are desired for spintronic applications. The fabrications of spintronic devices from half metals with one spin direction are often hampered, however, by stray magnetic fields, domain walls, short spin coherence times, scattering on magnetic atoms or magnetically active interfaces, and other characteristics that come along with the magnetism. The surfaces of topological insulators, or Dirac/Weyl semimetals, could be an alternative, but production of high‐quality thin films without the presence of the bulk states at the Fermi energy remains very challenging. Here, by utilizing angle‐resolved photoemission spectroscopy, a record‐high Dresselhaus spin–orbit splitting of the bulk state in the nonmagnetic IrBiSe is found. The band structure calculations indicate that the splitting band is fully spin‐polarized with 3D chiral spin texture. As a source of spin‐polarized electrons, lightly doped IrBiSe is expected to generate electric‐field‐controlled spin‐polarized currents, free from back scattering, and could host triplet and Fulde–Ferrel–Larkin–Ovchinnikov (FFLO) superconductivity. [ABSTRACT FROM AUTHOR]

Layered two-anion compounds are of interest for their diverse electronic properties. The modular nature of their layered structures offers opportunities for the construction of complex stackings used to introduce or tune functionality, but the accessible layer combinations are limited by the crystal chemistries of the available anions. We present a layered three-anion material, Bi4O4Cu1.7Se2.7Cl0.3, which adopts a new structure type composed of alternately stacked BiOCuSe and Bi2O2Se-like units. This structure is accessed by inclusion of three chemically distinct anions, which are accommodated by aliovalently substituted Bi2O2Se0.7Cl0.3 blocks coupled to Cu-deficient Bi2O2Cu1.7Se2 blocks, producing a formal charge modulation along the stacking direction. The hypothetical parent phase Bi4O4Cu2Se3 is unstable with respect to its charge-neutral stoichiometric building blocks. The complex layer stacking confers excellent thermal properties upon Bi4O4Cu1.7Se2.7Cl0.3: a room-temperature thermal conductivity (κ) of 0.4(1) W/ mK was measured on a pellet with preferred crystallite orientation along the stacking axis, with perpendicular measurement indicating it is also highly anisotropic. This κ value lies in the ultralow regime and is smaller than those of both BiOCuSe and Bi2O2Se. Bi4O4Cu1.7Se2.7Cl0.3 behaves like a charge-balanced semiconductor with a narrow band gap. The chemical diversity offered by the additional anion allows the integration of two common structural units in a single phase by the simultaneous and coupled creation of charge-balancing defects in each of the units. [ABSTRACT FROM AUTHOR]

We report a reinvestigation of superconducting Sn1-xInxTe at both low and high In doping levels. Considering the system over a broad composition range in a single study allows us to characterize a significant change in the properties as a function of x: The system evolves from a weakly coupled p-type superconductor to a strongly coupled n-type superconductor with increasing indium content. Hall effect measurements show that the carrier density does not vary monotonically with indium content; a change from p-type to n-type is observed near 10% In doping. This is contrary to expectations dictating that In should be a p-type dopant in semiconducting SnTe, because it has one less valance electron than Sn. A crystallographic search for point defects at high x indicates that the material remains ideal NaCl-type over a wide composition range. Density functional theory calculations for In-doped SnTe support a picture where In does not act as a trivial hole dopant but instead forms a distinct, partly filled In 5s-Te5p hybridized state centered around EF, which is very different from what is seen for other nominal hole dopants such as Na, Ag, and vacant Sn sites. [ABSTRACT FROM AUTHOR]

We report the synthesis and crystal structure of a new high-temperature form of Ca3P2. The crystal structure was determined through Rietveld refinements of synchrotron powder x-ray diffraction data. This form of Ca3P2 has a crystal structure of the hexagonal Mn5Si3 type, with a Ca ion deficiency compared to the ideal 5:3 stoichiometry. This yields a stable, charge-balanced compound of Ca2+ and P3-. We also report the observation of a secondary hydride phase, Ca5P3H, which again is a charge-balanced compound. The calculated band structure of Ca3P2 indicates that it is a three-dimensional Dirac semimetal with a highly unusual ring of Dirac nodes at the Fermi level. The Dirac states are protected against gap opening by a mirror plane in a manner analogous to what is seen for graphene. [ABSTRACT FROM AUTHOR]

Dirac and Weyl semimetals are 3D analogues of graphene in which crystalline symmetry protects the nodes against gap formation. Na3Bi and Cd3As2 were predicted to be Dirac semimetals, and recently confirmed to be so by photoemission experiments. Several novel transport properties in a magnetic field have been proposed for Dirac semimetals. Here, we report a property of Cd3As2 that was unpredicted, namely a remarkable protection mechanism that strongly suppresses backscattering in zero magnetic field. In single crystals, the protection results in ultrahigh mobility, 9 × 106 cm2 V−1 s−1 at 5 K. Suppression of backscattering results in a transport lifetime 104 times longer than the quantum lifetime. The lifting of this protection by the applied magnetic field leads to a very large magnetoresistance. We discuss how this may relate to changes to the Fermi surface induced by the applied magnetic field. [ABSTRACT FROM AUTHOR]

Dirac and Weyl semimetals are 3D analogues of graphene in which crystalline symmetry protects the nodes against gap formation. Na3Bi and Cd3As2 were predicted to be Dirac semimetals, and recently confirmed to be so by photoemission experiments. Several novel transport properties in a magnetic field have been proposed for Dirac semimetals. Here, we report a property of Cd3As2 that was unpredicted, namely a remarkable protection mechanism that strongly suppresses backscattering in zero magnetic field. In single crystals, the protection results in ultrahigh mobility, 9 × 106 cm2 V−1 s−1 at 5 K. Suppression of backscattering results in a transport lifetime 104 times longer than the quantum lifetime. The lifting of this protection by the applied magnetic field leads to a very large magnetoresistance. We discuss how this may relate to changes to the Fermi surface induced by the applied magnetic field. [ABSTRACT FROM AUTHOR]

Magnetoresistance is the change in a material's electrical resistance in response to an applied magnetic field. Materials with large magnetoresistance have found use as magnetic sensors, in magnetic memory, and in hard drives at room temperature, and their rarity has motivated many fundamental studies in materials physics at low temperatures. Here we report the observation of an extremely large positive magnetoresistance at low temperatures in the non-magnetic layered transition-metal dichalcogenide WTe2: 452,700 per cent at 4.5 kelvins in a magnetic field of 14.7 teslas, and 13 million per cent at 0.53 kelvins in a magnetic field of 60 teslas. In contrast with other materials, there is no saturation of the magnetoresistance value even at very high applied fields. Determination of the origin and consequences of this effect, and the fabrication of thin films, nanostructures and devices based on the extremely large positive magnetoresistance of WTe2, will represent a significant new direction in the study of magnetoresistivity. [ABSTRACT FROM AUTHOR]

Condensed-matter systems provide a rich setting to realize Dirac and Majorana fermionic excitations as well as the possibility to manipulate them for potential applications. It has recently been proposed that chiral, massless particles known as Weyl fermions can emerge in certain bulk materials or in topological insulator multilayers and give rise to unusual transport properties, such as charge pumping driven by a chiral anomaly. A pair of Weyl fermions protected by crystalline symmetry effectively forming a massless Dirac fermion has been predicted to appear as low-energy excitations in a number of materials termed three-dimensional Dirac semimetals. Here we report scanning tunnelling microscopy measurements at sub-kelvin temperatures and high magnetic fields on the II-V semiconductor Cd3As2. We probe this system down to atomic length scales, and show that defects mostly influence the valence band, consistent with the observation of ultrahigh-mobility carriers in the conduction band. By combining Landau level spectroscopy and quasiparticle interference, we distinguish a large spin-splitting of the conduction band in a magnetic field and its extended Dirac-like dispersion above the expected regime. A model band structure consistent with our experimental findings suggests that for a magnetic field applied along the axis of the Dirac points, Weyl fermions are the low-energy excitations in Cd3As2. [ABSTRACT FROM AUTHOR]

We report the direct observation of the three-dimensional (3D) Dirac semimetal phase in cadmium arsenide (Cd3As2) by means of angle-resolved photoemission spectroscopy. We identify two momentum regions where electronic states that strongly disperse in all directions form narrow conelike structures, and thus prove the existence of the long sought 3D Dirac points. This electronic structure naturally explains why Cd3As2 has one of the highest known bulk electron mobilities. This realization of a 3D Dirac semimetal in Cd3As2 not only opens a direct path to a wide spectrum of applications, but also offers a robust platform for engineering topologically nontrivial phases including Weyl semimetals and quantum spin Hall systems. [ABSTRACT FROM AUTHOR]

The structure of Cd3As2, a high-mobility semimetal reported to host electrons that act as Dirac particles, is reinvestigated by single-crystal X-ray diffraction. It is found to be centrosymmetric rather than noncentrosymmetric as previously reported. It has a distorted superstructure of the antifluorite (M2X) structure type with a tetragonal unit cell of a = 12.633(3) and c = 25.427(7) Å in the centrosymmetric I41/acd space group. The antifluorite superstructure can be envisioned as consisting of distorted Cd6⌗2 cubes (where ⌗ = an empty cube vertex) in parallel columns, stacked with opposing chirality. Electronic structure calculations performed using the experimentally determined centrosymmetric structure are similar to those performed with the inversion symmetry absent but with the important implication that Cd3As2 is a three-dimensional (3D)-Dirac semimetal with no spin splitting; all bands are spin degenerate and there is a 4-fold degenerate bulk Dirac point at the Fermi energy along G-Z in the Brillouin zone. This makes Cd3As2 a 3D electronic analogue of graphene. Scanning tunneling microscopy experiments identify a 2 × 2 surface reconstruction in the (112) cleavage plane of single crystals; needle crystals grow with a [110] long axis direction. [ABSTRACT FROM AUTHOR]

We report on the superconducting properties of the KxWO3 tetragonal tungsten bronze. The highest superconducting transition temperature (Tc=2.1 K) was obtained for K0.38WO3. Tc decreases linearly with increasing K content. Using the measured values for the upper critical field Hc2 and the specific heat C, we estimate the orbital critical field Hc2(0), coherence length ξ(0), Debye temperature ΘD, and coupling constant λe−p. The magnitude of the specific-heat jump at Tc suggests that the KxWO3 tetragonal tungsten bronze is a weakly coupled superconductor. The superconducting phase diagram of the doped tungsten bronze family is presented. [ABSTRACT FROM AUTHOR]

The layered, noncentrosymmetric heavy element PbTaSe2 is found to be superconducting. We report its electronic properties accompanied by electronic-structure calculations. Specific heat, electrical resistivity, and magnetic-susceptibility measurements indicate that PbTaSe2 is a moderately coupled, type-IIBCS superconductor (Tc = 3.72 K, Ginzburg-Landau parameter κ = 17) with an electron-phonon coupling constant of λep = 0.74. Electronic-structure calculations reveal a single bulk three-dimensional Dirac cone at the K point of the Brillouin zone derived exclusively from its hexagonal Pb layer; it is similar to the feature found in graphene except there is a 0.8 eV gap opened by spin-orbit coupling. The combination of large spin-orbit coupling and lack of inversion symmetry also results in large Rashba splitting on the order of tenths of an eV. [ABSTRACT FROM AUTHOR]

Spectroscopic detection of Dirac and Weyl fermions in real materials is vital for both, promising applications and fundamental bridge between high-energy and condensed-matter physics. While the presence of Dirac and noncentrosymmetric Weyl fermions is well established in many materials, the magnetic Weyl semimetals still escape direct experimental detection. In order to find a time-reversal symmetry breaking Weyl state we design two materials and present here experimental and theoretical evidence of realization of such a state in one of them, YbMnBi2. We model the time-reversal symmetry breaking observed by magnetization and magneto-optical microscopy measurements by canted antiferromagnetism and find a number of Weyl points. Using angle-resolved photoemission, we directly observe two pairs of Weyl points connected by the Fermi arcs. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties. Candidate materials containing magnetic Weyl fermions remain rare. Here, the authors report evidence of a magnetic Weyl state and observe the surface Fermi arcs in YbMnBi2. [ABSTRACT FROM AUTHOR]

We report on electronic transport measurements of electrostatically gated nanodevices of the semimetal WTe2. High mobility metallic behavior is achieved in the 2D limit by encapsulating thin flakes in an inert atmosphere. At low temperatures, we find that a large magnetoresistance can be turned on and off by electrostatically doping the system between a semimetallic state and an electron-only metallic state, respectively. We confirm the nature of the two regimes by analyzing the magnetoresistance and Hall effect with a two-carrier model, as well as by analysis of Shubnikov-de Haas oscillations, both of which indicate depletion of hole carriers via the electrostatic gate. This confirms that semiclassical transport of two oppositely charged carriers accurately describes the exceptional magnetoresistance observed in this material. Finally, we also find that the magnetoresistance power law is subquadratic and density independent, suggesting new physics specifically in the semimetallic regime. [ABSTRACT FROM AUTHOR]