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Register a new userElectronic-Structure-Driven Magnetic Ordering in a Kondo Semiconductor CeOs2Al10
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We report the anisotropic changes in the electronic structure of a Kondo semiconductor CeOs$_2$Al$_{10}$ across an anomalous antiferromagnetic ordering temperature ($T_0$) of 29 K, using optical conductivity spectra. The spectra along the $a$- and $c$-axes indicate that a $c$-$f$ hybridization gap emerges from a higher temperature continuously across $T_0$. Along the b-axis, on the other hand, a different energy gap with a peak at 20 meV appears below 39 K, which is higher temperature than $T_0$, because of structural distortion. The onset of the energy gap becomes visible below $T_0$. Our observation reveals that the electronic structure as well as the energy gap opening along the b-axis due to the structural distortion induces antiferromagnetic ordering below $T_0$.
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The lightly hole-doped system CeOs1.94Re0.06Al10 has been studied by muon spin relaxation and neutron diffraction measurements. A long-range antiferromagnetic ordering of the Ce-sublattice with substantially reduced value of the magnetic moment 0.18(1) mu_B has been found below T_N = 21 K. Similar to the undoped parent compound, the magnetic ground state of CeOs1.94Re0.06Al10 preserves the anomalous direction of the ordered moments along the c-axis. The obtained result reveals the crucial difference between electron- and hole-doping effects on the magnetic ordering in CeOs2Al10. The former suppresses the anisotropic c-f hybridization and promotes localized Ce moments. On the contrary, the latter increases the hybridization and shifts the system towards delocalized non-magnetic state.
We report temperature-dependent polarized optical conductivity [$sigma(omega)$] spectra of CeFe$_2$Al$_{10}$, which is a reference material for CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$ with an anomalous magnetic transition at 28 K. The $sigma(omega)$ spectrum along the b-axis differs greatly from that in the $ac$-plane, indicating that this material has an anisotropic electronic structure. At low temperatures, in all axes, a shoulder structure due to the optical transition across the hybridization gap between the conduction band and the localized $4f$ states, namely $c$-$f$ hybridization, appears at 55 meV. However, the gap opening temperature and the temperature of appearance of the quasiparticle Drude weight are strongly anisotropic indicating the anisotropic Kondo temperature. The strong anisotropic nature in both electronic structure and Kondo temperature is considered to be relevant the anomalous magnetic phase transition in CeRu$_2$Al$_{10}$ and CeOs$_2$Al$_{10}$.
The magnetic ground state of the antiferromagnet Kondo lattice compound Ce8Pd24Ga has been investigated using neutron powder diffraction, inelastic neutron scattering and zero-field muon spin relaxation measurements. The neutron diffraction analysis, below TN (3.6(0.2)K), reveals a commensurate type-C antiferromagnetic structure with the ordered state magnetic moment of ~0.36 mB/Ce-atom along the cubic <111> direction. The analysis of the inelastic neutron scattering (INS) data based on the crystal field (CF) model reveals a doublet ground state with a ground state moment of 1.29 mB/Ce-atom. The observed magnetic moment from neutron diffraction, which is small compared to the expected value from CF-analysis, is attributed to screening of the local Ce moment by the Kondo effect. This is supported by the observed Kondo-type resistivity and a small change in the entropy of Ce8Pd24Ga at TN. The zero-field muon spin relaxation rate exhibits a sharp increase below TN indicating ordering of Ce moments, in agreement with the neutron diffraction data. The present studies reveal that the physical properties of Ce8Pd24Ga are governed by the onsite Kondo compensation, the moment stabilizing intersite RKKY interaction and the crystal field effect.
The emergence of ferromagnetism in two-dimensional van der Waals materials has aroused broad interest. However, the ferromagnetic instability has been a problem remained. In this work, by using the first-principles calculations, we identified the critical ranges of strain and doping for the bilayer Cr2Ge2Te6 within which the ferromagnetic stability can be enhanced. Beyond the critical range, the tensile strain can induce the phase transition from the ferromagnetic to the antiferromagnetic, and the direction of magnetic easy axis can be converted from out-of-plane to in-plane due to the increase of compressive strain, or electrostatic doping. We also predicted an electron doping range, within which the ferromagnetism can be enhanced, while the ferromagnetic stability was maintained. Moreover, we found that the compressive strain can reverse the spin polarization of electrons at the conduction band minimum, so that two categories of half-metal can be induced by controlling electrostatic doping in the bilayer Cr2Ge2Te6. These results should shed a light on achieving ferromagnetic stability for low-dimensional materials.
Spin exchange between a single-electron charged quantum dot and itinerant electrons leads to an emergence of Kondo correlations. When the quantum dot is driven resonantly by weak laser light, the resulting emission spectrum allows for a direct probe of these correlations. In the opposite limit of vanishing exchange interaction and strong laser drive, the quantum dot exhibits coherent oscillations between the single-spin and optically excited states. Here, we show that the interplay between strong exchange and non-perturbative laser coupling leads to the formation of a new nonequilibrium quantum-correlated state, characterized by the emergence of a laser-induced secondary spin screening cloud, and examine the implications for the emission spectrum.
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