In metals, orbital motions of conduction electrons on the Fermi surface are quantized in magnetic fields, which is manifested by quantum oscillations in electrical resistivity. This Landau ...quantization is generally absent in insulators. Here, we report a notable exception in an insulator-ytterbium dodecaboride (YbB
). The resistivity of YbB
, which is of a much larger magnitude than the resistivity in metals, exhibits distinct quantum oscillations. These unconventional oscillations arise from the insulating bulk, even though the temperature dependence of the oscillation amplitude follows the conventional Fermi liquid theory of metals with a large effective mass. Quantum oscillations in the magnetic torque are also observed, albeit with a lighter effective mass.
Quantum oscillations in transport and thermodynamic parameters at high magnetic fields are an unambiguous signature of the Fermi surface, the defining characteristic of a metal. Recent observations ...of quantum oscillations in insulating SmB6 and YbB12, therefore, have been a big surprise—despite the large charge gap inferred from the insulating behaviour of the resistivity, these compounds seemingly host a Fermi surface at high magnetic fields. However, the nature of the ground state in zero field has been little explored. Here, we report the use of low-temperature heat-transport measurements to discover gapless, itinerant, charge-neutral excitations in the ground state of YbB12. At zero field, sizeable linear temperature-dependent terms in the heat capacity and thermal conductivity are clearly resolved in the zero-temperature limit, indicating the presence of gapless fermionic excitations with an itinerant character. Remarkably, linear temperature-dependent thermal conductivity leads to a spectacular violation of the Wiedemann–Franz law: the Lorenz ratio is 104–105 times larger than that expected in conventional metals, indicating that YbB12 is a charge insulator and a thermal metal. Moreover, we find that these fermions couple to magnetic fields, despite their charge neutrality. Our findings expose novel quasiparticles in this unconventional quantum state.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We report the in situ preparation of surfaces of the proposed topological Kondo insulator SmB
by controlled cycles of Ar ion sputtering and annealing. The procedure provides a reproducible way for ...the preparation of Sm- or B-rich surface terminations by low (
1080
C) or high (
1200
C) temperature annealing. The surface quality and termination were checked by low energy electron diffraction and Auger electron spectroscopy. Photoemission studies were carried out using momentum microscopy and two laboratory light sources providing polarised radiation with an energy of 6 eV (fourth harmonic of a pulsed Ti:Sapphire laser) and unpolarised radiation with an energy of 21.2 eV (He-I line of a gas discharge lamp). Full dispersions of electronic states in a wide two-dimensional momentum space were obtained by momentum microscopy from the in situ prepared Sm-terminated surface. The shape of the Fermi surface is discussed based on the sections through the bulk Brillouin zone sampled by the different photon energies.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb1−xZrxB12 (0 x 0.875) to study the effects of electron doping on the Kondo insulator YbB12. The Yb valences of Yb1−xZrxB12 at ...300 K estimated from the Yb 3d HAXPES spectra decreased after substituting Yb with Zr from 2.93 for YbB12 to 2.83 for Yb0.125Zr0.875B12. A temperature dependent valence decrease was found upon cooling for all doping concentrations. We found peak shifts of the B 1s and Zr 3d5/2, and Yb3+ 4f spectra toward the deeper binding-energy with increasing Zr concentration, which indicates a shift of the Fermi level to the higher energy and that of the Yb 4f hole level close to the Fermi level, respectively, due to electron doping. These results qualitatively show the enhanced hybridization between the Yb 4f and conduction-band states with Zr substitution, consistent with magnetic susceptibility measurements.
Recent studies suggest that an exemplary Kondo insulator SmB6 belongs to a new class of topological insulators (TIs), in which non-trivial spin-polarized metallic states emerge on surface upon the ...formation of Kondo hybridization gap in the bulk. Remarkably, the bulk resistivity reaches more than 20 Ω cm at 4 K, making SmB6 a candidate for a so-called bulk-insulating TI. We here investigate optical-pulse responses of SmB6 by pump-and-probe photoemission spectroscopy. Surface photovoltage effect is observed below ~90 K. This indicates that an optically-active band bending region develops beneath the novel metallic surface upon the bulk-gap evolution. The photovoltaic effect persists for >200 µs, which is long enough to be detected by electronics devices, and could be utilized for optical gating of the novel metallic surface.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Gastroesophageal reflux disease (GERD) is very prevalent in the general population, with a broad spectrum of clinical manifestations, requiring accurate diagnosis and treatment.
The aim of this ...expert review is to establish good clinical practice recommendations for the diagnosis and personalized treatment of GERD.
The good clinical practice recommendations were produced by a group of experts in GERD, members of the Asociación Mexicana de Gastroenterología (AMG), after carrying out an extensive review of the published literature and discussing each recommendation at a face-to-face meeting. This document does not aim to be a clinical practice guideline with the methodology such a document requires.
Fifteen experts on GERD formulated 27 good clinical practice recommendations for recognizing the symptoms and complications of GERD, the rational use of diagnostic tests and medical treatment, the identification and management of refractory GERD, the overlap with functional disorders, endoscopic and surgical treatment, and GERD in the pregnant woman, older adult, and the obese patient.
An accurate diagnosis of GERD is currently possible, enabling the prescription of a personalized treatment in patients with this condition. The goal of the good clinical practice recommendations by the group of experts from the AMG presented in this document is to aid both the general practitioner and specialist in the process of accurate diagnosis and treatment, in the patient with GERD.
La enfermedad por reflujo gastroesofágico (ERGE) es muy prevalente en población general, con un amplio espectro de manifestaciones clínicas que requiere de un diagnóstico y tratamiento de precisión.
Esta es una revisión de expertos que establece recomendaciones de buena práctica clínica para el diagnóstico y tratamiento personalizado de la ERGE.
Las recomendaciones de buena práctica clínica se generaron por un grupo de expertos en ERGE, miembros de la Asociación Mexicana de Gastroenterología (AMG), después de hacer una extensa revisión de la literatura publicada y la discusión de cada recomendación en una reunión presencial. Este documento no pretende ser una guía de práctica clínica con la metodología que este formato requiere.
Quince expertos en ERGE elaboraron 27 recomendaciones de buena práctica clínica para el reconocimiento de síntomas y complicaciones de la ERGE, uso racional de pruebas diagnósticas y tratamiento médico de los diferentes fenotipos, identificación y manejo de la ERGE refractaria, de la sobreposición con trastornos funcionales, del tratamiento endoscópico y quirúrgico y sobre la ERGE en el embarazo, adulto mayor y en el paciente obeso.
Actualmente es posible un diagnóstico de precisión en la ERGE que permite prescribir un tratamiento personalizado en los pacientes con esta condición. Las recomendaciones de buena práctica clínica del grupo de expertos de la AMG presentadas en este documento pretender ayudar al médico general y al especialista en el proceso del diagnóstico y tratamiento de precisión del paciente con ERGE.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We synthesized Ca1−xSrxFeO3 containing tetravalent iron Fe4+ with high valence by low temperature heat treatment along with ozone oxidization. We investigated the magnetic properties of perovskite ...Ca1−xSrxFeO3. The charge disproportionation transition temperature (TCD) of Ca1−xSrxFeO3 was observed from x = 0.0 to 0.6 in the magnetic susceptibility measurements. The decrease in TCD occurs is attributed to deformation of the crystal structure. The metamagnetic transitions with hysteresis were observed in the magnetization curves of all the compositions. The metamagnetic behavior is due to helical magnetism, which means that there are intermediate stable states before magnetization is saturated. In the Sr-rich region with x = 0.8 and 1.0, the saturation magnetization shows forced ferromagnetic order with a value of ∼3.2 μB at high magnetic field, H ∼ 60 T.
We report high-field magnetization and magnetostriction measurements on the rare-earth-metal tetraboride TbB4, in which the Tb moments form a Shastry-Sutherland lattice in the tetragonal basal plane. ...A number of magnetization plateaus appear when the magnetic field is perpendicular to the magnetic easy plane. We propose that the magnetization plateaus arise from the combined effect of magnetic frustration and quadrupole interaction in the unique two-dimensional network.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
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