Evidence for gradual evolution of low-energy fluctuations underlying the first-order structural and valence order in YbPd

Unconventional Quantum Criticality due to Critical Valence Transition

Quantum criticality due to the valence transition in some Yb-based heavy fermion metals has gradually turned out to play a crucial role to understand the non-Fermi liquid properties that cannot be understood from the conventional quantum criticality theory due to magnetic transitions. Namely, critical exponents giving the temperature (T) dependence of the resistivity ρ(T), the Sommerfeld coefficient, C(T)/T, the magnetic susceptibility, χ(T), and the NMR relaxation rates, 1/(T_{1}T), can be understood as the effect of the critical valence fluctuations of f electrons in Yb ion in a unified way.…

Valence changes associated with the metal-insulator transition in Bi$_{1-x}$La$_x$NiO$_3$

Perovskite-type BiNiO$_3$ is an insulating antiferromagnet in which a charge disproportionation occurs at the Bi site. La substitution for Bi suppresses the charge disproportionation and makes the system metallic. We have measured the photoemission and x-ray absorption (XAS) spectra of Bi$_{1-x}$La$_{x}$NiO$_{3}$ to investigate how the electronic structure changes with La doping. From Ni $2p$ XAS, we observed an increase of the valence of Ni from 2+ toward 3+. Combined with the core-level photoemission study, it was found that the average valence of Bi remains $\sim 4+$ and that the Ni valence…

Eu valence transition behavior in the nano form of EuPd2Si2

The compound EuPd2Si2 is a well-known valence-fluctuating compound with a largest variation of Eu valence in a narrow temperature interval (around 150 K). The ball-milled form of this compound was investigated to understand the Eu valence behavior in the nanoform. The compound is found to retain the ThCr2Si2-type tetragonal structure after ball-milling leading to a reduction in particle size, typically falling in the range 10 - 100 nm. We find that there is a qualitative change in the temperature dependence of magnetic susceptibility for such small particles, with respect to that known for bul…

Strong magnetoelastic effect in CeCo$_{1-x}$Fe$_{x}$Si as Néel order is suppressed

A very strong magnetoelastic effect in the CeCo$_{1-x}$Fe$_{x}$Si alloys is reported. The strength of the magnetostrictive effect can be tuned upon changing $x$. The moderate low-temperature linear magnetostriction observed at low Fe concentrations becomes very large ($\frac {ΔL}{L} \left(16 T,2 K\right) =$ 3$\times$10$^{-3}$) around the critical concentration ($x_c \approx$ 0.23) at which the long-range antiferromagnetic order vanishes. Upon increasing doping through the non-magnetic region ($x > x_c$), the magnetostriction strength gradually weakens again. Remarkably the low-temperature magn…

揭示金属离子溶解的复杂性：来自混合第一性原理/连续介质计算的新见解

Unraveling the Complexity of Metal Ion Dissolution: Insights from Hybrid First-Principles/Continuum Calculations

本研究通过混合第一性原理/连续介质计算，揭示22种金属元素溶解的三种模型，提出离子价态选择的理论判据，深化原子层面溶解机制理解，助力高效电化学系统设计。

SU($\boldsymbol N$) Kondo-Heisenberg 链：相图、Ising 临界性及重准粒子与价键固体序的共存

SU($\boldsymbol N$) Kondo-Heisenberg chain: Phase diagram, Ising criticality, and the coexistence of heavy quasiparticles and valence bond solid order

本文绘制了一维 SU($N$) Kondo-Heisenberg 链的基态相图，利用 QMC 模拟揭示了 VBS 相与 Kondo 绝缘体相之间的量子相变，发现其临界性属于二维 Ising 普适类，并阐明了 VBS 序与重准粒子的共存与解耦机制。

Complementary views on electron spectra: From Fluctuation Diagnostics to real space correlations

We study the relation between the microscopic properties of a many-body system and the electron spectra, experimentally accessible by photoemission. In a recent paper [Phys. Rev. Lett. 114, 236402 (2015)], we introduced the "fluctuation diagnostics" approach, to extract the dominant wave vector dependent bosonic fluctuations from the electronic self-energy. Here, we first reformulate the theory in terms of fermionic modes, to render its connection with resonance valence bond (RVB) fluctuations more transparent. Secondly, by using a large-U expansion, where U is the Coulomb interaction, we rela…

Tunability of the k-space Location of the Dirac Cones in the Topological Crystalline Insulator Pb1-xSnxTe

We have performed systematic angle-resolved photoemission spectroscopy of the topological crystalline insulator (TCI) Pb1-xSnxTe to elucidate the evolution of its electronic states across the topological phase transition. As previously reported, the band structure of SnTe (x = 1.0) measured on the (001) surface possesses a pair of Dirac-cone surface states located symmetrically across the Xbar point in the (110) mirror plane. Upon approaching the topological phase transition into the trivial phase at x_c ~ 0.25, we discovered that Dirac cones gradually move toward the Xbar point with its spect…

Electron microscopy and spectroscopic study of structural changes, electronic properties and conductivity in annealed Li$_x$CoO$_2$

Chemically exfoliated nanoscale few-layer thin Li$_x$CoO$_2$ samples are studied as function of annealing at various temperatures, using transmission electron microscopy (TEM) and Electron Energy Loss Spectroscopies (EELS), probing the O-K, Co-L$_{2,3}$ spectra along with low energy interband transitions. These spectra are compared with first-principles DFT calculations of -Im$[\varepsilon^{-1}(q,ω)]$ and O-2p Partial Densities of States weighted by dipole matrix elements with the core wavefunction and including the O-1s core-hole and with known trends of the L$_2$/L$_3$ peak ratio to average …

常压下利用 $^{139}$La-NMR 探测多层镍酸盐 La$_3$Ni$_2$O$_7$ 和 La$_4$Ni$_3$O$_{10}$ 中的多带金属基态

Multiband Metallic Ground State in Multilayered Nickelates La$_3$Ni$_2$O$_7$ and La$_4$Ni$_3$O$_{10}$ Probed by $^{139}$La-NMR at Ambient Pressure

本文通过常压 $^{139}$La-NMR 研究多层镍酸盐 La$_3$Ni$_2$O$_7$ 和 La$_4$Ni$_3$O$_{10}$，发现密度波序下的多带金属基态及费米面附近平带特征，为理解其高压高温超导提供微观依据。