A mechanism of superconductivity is proposed for the Kondo lattice which has semimetallic conduction bands with electron and hole Fermi surfaces. At high temperatures, the $f$ electron's localized spins/pseudospins are fluctuating between electron and hole Fermi surfaces to seek for a partner to couple with. This system tries to resolve this frustration at low temperatures and chooses to construct a quantum mechanically entangled state composed of the Kondo singlet with electron surface and that with hole surface, to break the U(1) gauge symmetry. The corresponding order parameter is given by a composite pairing amplitude as a three-body bound state of localized spin/pseudospin, electron and hole. The electromagnetic response is considered, where the composite pair itself does not contribute to the Meissner effect, but the induced pair between conduction electrons, which inevitably mixes due to, e.g., a band cutoff effect at high energies, carries the superconducting current under the external field. Possible applications to real heavy-electron materials are also discussed.
Abstract Background Extrinsic factors for erosive tooth wear (ETW) have been widely reported, but the intrinsic factors for wear remain unclear. Objectives The aim of this study was to evaluate the factors associated with the prevalence of ETW in patients with reflux oesophagitis (RO). To prevent severe ETW with RO, factors associated with severity of ETW were also evaluated. Methods A total of 270 patients with RO were recruited. A modified tooth wear index was used to evaluate the prevalence and severity of ETW. Salivary secretion and buffering capacity were assessed prior to endoscopy. Subjects were asked to complete a medical condition and oral self‐care questionnaire. Univariate and multivariate analyses were employed to identify factors collectively associated with the prevalence and severity of ETW. Results A total of 212 cases were categorized as patients with ETW (148 with mild ETW and 64 with severe ETW). Multivariate analyses indicated that saliva secretion, severity of RO and proton pump inhibitor (PPI) resistance were associated with the prevalence of ETW, whereas age, BMI and severity of RO were associated with the severity of ETW. The odds ratio of saliva secretion and BMI were less than 1, meaning that higher saliva secretion resulted in a lower prevalence of ETW and lower BMI was associated with severe ETW. Conclusion Saliva secretion, severity of RO and PPI resistance were associated with the prevalence of ETW, whereas age, BMI and severity of RO were associated with the severity of ETW. Lower saliva secretion and BMI were significant factors for ETW.
The effect of impurities on a superconductor with Bogoliubov Fermi surfaces (BFSs) is studied using a realistic tight-binding model. Based on the band structure composed of $d$-orbitals in tetragonal FeSe, whose S-doped sample is a potential material for BFS, we construct the superconducting state by introducing a time-reversal broken pair potential in terms of the band index. We further consider the effect of impurities on the BFS, where the impurity potential is defined as a local potential for the original $d$-orbitals. The self-energy is calculated using the (self-consistent) Born approximation, which shows an enhancement of the single-particle spectral weight on the Fermi surface. This is consistent with the previous phenomenological theory and is justified by the present more detailed calculation based on the FeSe-based material.
Magnetic and other unconventional electronic orders are discussed for heavy electrons. In addition to the ordinary Kondo lattice, we consider non-Kramers systems taking the two-channel Kondo lattice, and another lattice that consists of a singlet-triplet f2 configuration. The latter gives a scalar order with staggered sublattices of crystalline-electric-field (CEF) and Kondo singlets, which accounts for the observed order in PrFe4P12. In the two-channel Kondo lattice, an odd-frequency pairing is realized that becomes degenerate at half-filling with a composite order involving both localized and conduction electrons. The degeneracy is interpreted in terms of a hidden SO(5) symmetry. For the ordinary Kondo lattice with exchange interaction J, we take insulating ground states as reference. The metallic states are approached by infinitesimal doping of carriers either from the Kondo insulator or from the antiferromagnetic insulator. By adding intersite exchange we find that location of the band extremum of the heavy band depends on the value of J. The change of J gives topological change of the Fermi surface, which corresponds to a generalized version of the Lifshitz transition, and occurs separately from the quantum critical point of the antiferromagnetic order.
We study the controlled manipulation of the Jahn-Teller metal state of fulleride compounds using nonequilibrium dynamical mean-field theory. This anomalous metallic state is a spontaneous orbital-selective Mott phase, which is characterized by one metallic and two insulating orbitals. Using protocols based on transiently reduced hopping amplitudes or periodic electric fields, we demonstrate the possibility to switch orbitals between Mott insulating and metallic on a subpicosecond time scale, and to rotate the order parameter between three equivalent states that can be distinguished by their anisotropic conductance. The Jahn-Teller metal phase of alkali-doped fullerides thus provides a platform for ultrafast persistent memory devices.
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