Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new user111Cd- TDPAC study of pressure-induced valence transition in YbAl2
104
0
0.0
(
0
)
Added by
Anatoly Tsvyashchenko
Publication date
2007
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
The quadrupole interaction at 111Cd impurity nuclei in the intermediate-valence compound YbAl2 has been measured under pressure up to 80 kbar by the TDPAC spectroscopy. It was found that the quadrupole frequency nQ measured on the 111Cd located at the Al sites in YbAl2, varies nonlinearly and increases by almost four times with the pressure increase up to 80 kbar. A linear correlation between the mean Yb valence, derived from Yb L3 OFY-XAS and RXES measurements, and the electric field gradient (the quadrupole frequency nQ=eQVzz/h) has been observed. The quadrupole frequencies on 111Cd in the GdAl2, YbAl3, TmAl3 and CaAl2 compounds have been measured, also. The possibility of determining the valence of Yb in the Yb compounds with p-metals from the relation nQ (u(P)) = n2 + (n3 - n2) u(P) has been considered.
rate research
Read More
The nuclear quadrupole interaction of the I=5/2 state of the nuclear probes 111Cd and 181Ta in the anatase and rutile polymorphs of bulk TiO2 was studied using the time differential perturbed angular correlation (TDPAC). The fast-slow coincidence setup is based on the CAMAC electronics. For anatase, the asymmetry of the electric field gradient was eta=0.22(1) and a quadrupole interaction frequency: 44.01(3) Mrad/s was obtained for 181Ta. For rutile, the respective values are eta=0.56(1) and quadrupole frequency=130.07(9) Mrad/s. The values for rutile match closely with the literature values. In case of the 111Cd probe produced from the beta decay of 111Ag, the quadrupole interaction frequency and the asymmetry parameter for anatase was negligible. This indicates an unperturbed angular correlation in anatase. On the other hand for rutile, the quadrupole frequency is 61.74(2) Mrad/s and the asymmetry is 0.23(1) for 111Cd probe. The results have been interpreted in terms of the surrounding atom positions in the lattice and the charge state of the probe nucleus.
In a semimetal, both electron and hole carriers contribute to the density of states at the Fermi level. The small band overlaps and multi-band effects give rise to many novel electronic properties, such as relativistic Dirac fermions with linear dispersion, titanic magnetoresistance and unconventional superconductivity. Black phosphorus has recently emerged as an exceptional semiconductor with high carrier mobility and a direct, tunable bandgap. Of particular importance is the search for exotic electronic states in black phosphorus, which may amplify the materials potential beyond semiconductor devices. Here we show that a moderate hydrostatic pressure effectively suppresses the band gap and induces a Lifshitz transition from semiconductor to semimetal in black phosphorus; a colossal magnetoresistance is observed in the semimetallic phase. Quantum oscillations in high magnetic field reveal the complex Fermi surface topology of the semimetallic black phosphorus. In particular, a Dirac-like fermion emerges at around 1.2 GPa, which is continuously tuned by external pressure. The observed semi-metallic behavior greatly enriches black phosphoruss material property, and sets the stage for the exploration of novel electronic states in this material. Moreover, these interesting behaviors make phosphorene a good candidate for the realization of a new two-dimensional relativistic electron system, other than graphene.
We report the high-pressure synthesis of novel superconductor MgB$_2$ and some related compounds. The superconducting transition temperature of our samples of MgB$_2$ is equal to 36.6 K. The MgB$_2$ lattice parameters determined via X-ray diffraction are in excellent agreement with results of our ab initio calculations. The time-differential perturbed angular correlation (TDPAC) experiments demonstrate a small increase in quadrupole frequency of $^111$Cd probe with decreasing temperature from 293 to 4.2 K. The electric field gradient (EFG) at the B site calculated from first principles is in fair agreement with EFG obtained from $^11$B NMR spectra of MgB$_2$ reported in the literature. It is also very close to EFG found in our $^111$Cd TDPAC measurements, which suggests that the $^111$Cd probe substitutes for boron in the MgB$_2$ lattice.
Recent progress in understanding the electronic band topology and emergent topological properties encourage us to reconsider the band structure of well-known materials including elemental substances. Controlling such a band topology by external field is of particular interest from both fundamental and technological view point. Here we report the pressure-induced topological phase transition from a semiconductor to a Weyl semimetal in elemental tellurium probed by transport measurements. Pressure variation of the periods of Shubnikov-de Haas oscillations, as well as oscillations phases, shows an anomaly around the pressure theoretically predicted for topological phase transition. This behavior can be well understood by the pressure-induced band deformation and resultant band crossing effect. Moreover, effective cyclotron mass is reduced toward the critical pressure, potentially reflecting the emergence of massless linear dispersion. The present result paves the way for studying the electronic band topology in well-known compounds and topological phase transition by the external field.
Given the consensus that pressure improves cation order in most of known materials, a discovery of pressure-induced disorder could require reconsideration of order-disorder transition in solid state physics/chemistry and geophysics. Double perovskites Y2CoIrO6 and Y2CoRuO6 synthesized at ambient pressure show B-site order, while the polymorphs synthesized at 6 and 15 GPa are partially-ordered and disordered respectively. With the decrease of ordering degrees, the lattices are shrunken and the crystal structures alter from monoclinic to orthorhombic symmetry. Correspondingly, long-range ferrimagnetic order in the B-site ordered phases are gradually overwhelmed by B-site disorder. Theoretical calculations suggest that unusual unit cell compressions under external pressures unexpectedly stabilize the disordered phases of Y2CoIrO6 and Y2CoRuO6.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
