Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userOptical Conductivity Study of $f$ Electron States in YbCu$_2$Ge$_2$ at High Pressures to 20 GPa
115
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Optical conductivity [$sigma(omega)$] of YbCu$_2$Ge$_2$ has been measured at external pressures ($P$) to 20 GPa, to study the $P$ evolution of $f$ electron hybridized states. At $P$=0, $sigma(omega)$ shows a marked mid-infrared (mIR) peak at 0.37 eV, which is due to optical excitations from $f^{14}$ (Yb$^{2+}$) state located below the Fermi level. With increasing $P$, the mIR peak shows significant shifts to lower energy, reaching 0.18 eV at $P$=20 GPa. This result indicates that the $f^{14}$ energy level increases toward the Fermi level with $P$. Such a shift of the $f$ electron level with $P$ has been expected from theoretical considerations, but had never been demonstrated by spectroscopic experiment under high $P$. The obtained results are also analyzed in terms of the $P$ evolution of the conduction-$f$ electron hybridization.
rate research
Read More
We report Resonant inelastic x-ray scattering measurements (RIXS) in YbCu$_2$Si$_2$ at the Yb L$_{3}$ edge under high pressure (up to 22 GPa) and at low temperatures (down to 7 K) with emphasis on the vicinity of the transition to a magnetic ordered state. We find a continuous valence change towards the trivalent state with increasing pressure but with a pronounced change of slope close to the critical pressure. Even at 22 GPa the Yb$^{+3}$ state is not fully achieved. The pressure where this feature is observed decreases as the temperature is reduced to 9 GPa at 7K, a value close to the critical pressure (itshape{p ormalfont{$_c$}} ormalfont $approx$ 7.5 GPa) where magnetic order occurs. The decrease in the valence with decreasing temperature previously reported at ambient pressure is confirmed and is found to be enhanced at higher pressures. We also compare the f electron occupancy between YbCu$_2$Si$_2$ and its Ce-counterpart, CeCu$_2$Si$_2$.
Hidden order in URu$_2$Si$_2$ has remained a mystery now entering its 4th decade. The importance of resolving the nature of the hidden order has stimulated extensive research. Here we present a detailed characterization of different surface terminations in URu$_2$Si$_2$ by angle-resolved photoemission spectroscopy, in conjunction with scanning tunneling spectroscopy and DMFT calculations that may unveil a new piece of this puzzle. The U-terminated surface is characterized by an electron-like band around the $bar{X}$ point, while a hole-like band for the Si-terminated surface. We also investigate temperature evolution of the electronic structure around the $bar{X}$ point from 11 K up to 70 K, and did not observe any abrupt change of the electronic structure around the coherence temperature (55 K). The $f$ spectral weight gradually weakens upon increasing temperature, still some $f$ spectral weight can be found above this temperature. Our results suggest that surface terminations in URu$_2$Si$_2$ are an important issue to be taken into account in future work.
We have measured the resistivity, optical conductivity, and magnetic susceptibility of LaSb$_2$ to search for clues as to the cause of the extraordinarily large linear magnetoresistance and to explore the properties of the superconducting state. We find no evidence in the optical conductivity for the formation of a charge density wave state above 20 K despite the highly layered crystal structure. In addition, only small changes to the optical reflectivity with magnetic field are observed indicating that the MR is due to scattering rate, not charge density, variations with field. Although a superconducting ground state was previously reported below a critical temperature of 0.4 K, we observe, at ambient pressure, a fragile superconducting transition with an onset at 2.5 K. In crystalline samples, we find a high degree of variability with a minority of samples displaying a full Meissner fraction below 0.2 K and fluctuations apparent up to 2.5 K. The application of pressure stabilizes the superconducting transition and reduces the anisotropy of the superconducting phase.
Optical conductivity [$sigma(omega)$] of CeRhIn$_5$ and YbNi$_3$Ga$_9$ have been measured at external pressures to 10 GPa and at low temperatures to 6 K. Regarding CeRhIn$_5$, at ambient pressure the main feature in $sigma(omega)$ is a Drude peak due to free carriers. With increasing pressure, however, a characteristic mid-infrared (mIR) peak rapidly develops in $sigma(omega)$, and its peak energy and width increase with pressure. These features are consistent with an increased conduction ($c$)-$f$ electron hybridization at high pressure, and show that the pressure has tuned the electronic state of CeRhIn$_5$ from very weakly to strongly hybridized ones. As for YbNi$_3$Ga$_9$, in contrast, a marked mIR peak is observed already at ambient pressure, indicating a strong $c$-$f$ hybridization. At high pressures, however, the mIR peak shifts to lower energy and becomes diminished, and seems merged with the Drude component at 10 GPa. Namely, CeRhIn$_5$ and YbNi$_3$Ga$_9$ exhibit some opposite tendencies in the pressure evolutions of $sigma(omega)$ and electronic structures. These results are discussed in terms of the pressure evolutions of $c$-$f$ hybridized electronic states in Ce and Yb compounds, in particular in terms of the electron-hole symmetry often considered between Ce and Yb compounds.
Only several compounds bearing Ag(II) cation and other transition metal cation have been known. Herein, we predict stability and crystal structures of hypothetical ternary silver(II) fluorides with copper, nickel and cobalt in 1:1 stoichiometry at pressure range from 0 GPa up to 20 GPa within the frame of Density Functional Theory. Calculations show that AgCoF4 could be synthesized already at ambient conditions but this compound would host diamagnetic Ag(I) and high-spin Co(III). However, at increased pressure ternary fluorides of Ag(II) featuring Cu and Ni could be synthesized, in the pressure windows of 7-14 and 8-15 GPa, respectively. All title compounds would be semiconducting and magnetically ordered.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
