ترغب بنشر مسار تعليمي؟ اضغط هنا

Orbital-Driven Electronic Structure Changes and the Resulting Optical Anisotropy of the Quasi-Two-Dimensional Spin Gap Compound La4Ru2O10

139   0   0.0 ( 0 )
 نشر من قبل Soon Jae Moon
 تاريخ النشر 2007
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We investigated the electronic response of the quasi-two-dimensional spin gap compound La4Ru2O10 using optical spectroscopy. We observed drastic changes in the optical spectra as the temperature decreased, resulting in anisotropy in the electronic structure of the spin-singlet ground state. Using the orbital-dependent hopping analysis, we found that orbital ordering plays a crucial role in forming the spin gap state in the non-one-dimensional material.



قيم البحث

اقرأ أيضاً

We report magnetization, nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and transmission electron microscopy (TEM) studies on the quasi-two-dimensional spin-gap system (CuCl)LaNb2O7, a possible candidate for the J1-J2 model on a square lattice. A sharp single NQR line is observed at the Cu and Cl sites, indicating that both Cu and Cl atoms occupy a unique site. However, the electric field gradient tensors at the Cu, Cl, and La sites do not have axial symmetry. This is incompatible with the reported crystal structure. Thus the J1-J2 model has to be modified. We propose alternative two-dimensional dimer models based on the NMR, NQR, and TEM results. The value of the hyperfine coupling constant at the Cu sites indicates that the spin density is mainly on the d(3z2-r2) orbital (z parallel c). At 1.5 K, Cu- and Nb-NMR signals disappear above the critical field Bc1 = 10.3 T determined from the onset of the magnetization, indicating a field-induced magnetic phase transition at Bc1.
We have studied the electronic structure of the two-dimensional Heisenberg antiferromagnet VOCl using photoemission spectroscopy and density functional theory including local Coulomb repulsion. From calculated exchange integrals and the observed ener gy dispersions we argue that the degree of one-dimensionality regarding both the magnetic and electronic properties is noticeably reduced compared to the isostructural compounds TiOCl and TiOBr. Also, our analysis provides conclusive justification to classify VOCl as a multi-orbital Mott insulator. In contrast to the titanium based compounds density functional theory here gives a better description of the electronic structure. However, a quantitative account of the low-energy features and detailed line shapes calls for further investigations including dynamical and spatial correlations.
The photoconductivity spectra of NbS_3 (phase I) crystals are studied. A drop of photoconductivity corresponding to the Peierls gap edge is observed. Reproducible spectral features are found at energies smaller the energy gap value. The first one is a peak at the energy 0.6 eV that is close to the midgap one. It has a threshold-like dependence of the amplitude on the electrical field applied. Another feature is a peak at the energy 0.9 eV near to the edge of the gap. We ascribe the origin of this peak to the stacking faults. The third one are continuous states between these peaks at energies 0.6-0.8 eV. We observed bleaching of the photoconductivity even below zero at this energies in the high electric field (700 V/cm) and under additional illumination applied.
Calcium vanadate CaV$_2$O$_4$ has a crystal structure of quasi-one-dimensional zigzag chains composed of orbital-active V$^{3+}$ ions and undergoes successive structural and antiferromagnetic phase transitions at $T_ssim 140$ K and $T_N sim 70$ K, re spectively. We perform ultrasound velocity measurements on a single crystal of CaV$_2$O$_4$. The temperature dependence of its shear elastic moduli exhibits huge Curie-type softening upon cooling that emerges above and below $T_s$ depending on the elastic mode. The softening above $T_s$ suggests the presence of either onsite Jahn-Teller-type or intersite ferro-type orbital fluctuations in the two inequivalent V$^{3+}$ zigzag chains. The softening below $T_s$ suggests the occurrence of a dimensional spin-state crossover, from quasi-one to three, that is driven by the spin-lattice coupling along the inter-zigzag-chain orthogonal direction. The successive emergence of the orbital- and spin-driven lattice instabilities above and below $T_s$, respectively, is unique to the orbital-spin zigzag chain system of CaV$_2$O$_4$.
273 - Yu Ni , Ya-Min Quan , Jingyi Liu 2019
The electronic states near the Fermi level of recently discovered superconductor Ba$_2$CuO$_{4-delta}$ consist primarily of the Cu $d_{x^2-y^2}$ and $d_{3z^2-r^2}$ orbitals. We investigate the electronic correlation effect and the orbital polarizatio n of an effective two-orbital Hubbard model mimicking the low-energy physics of Ba$_2$CuO$_{4-delta}$ in the hole-rich regime by utilizing the dynamical mean-field theory with the Lanczos method as the impurity solver. We find that the hole-overdoped Ba$_2$CuO$_{4-delta}$ with $3d^8$ (Cu$^{3+}$) is in the orbital-selective Mott phase (OSMP) at half-filling, and the typical two-orbital feature remains in Ba$_2$CuO$_{4-delta}$ when the electron filling approaches $n_esim 2.5$, which closely approximates to the experimental hole doping for the emergence of the high-$T_c$ superconductivity. We also obtain that the orbital polarization is very stable in the OSMP, and the multiorbital correlation can drive orbital polarization transitions. These results indicate that in hole-overdoped Ba$_2$CuO$_{4-delta}$ the OSMP physics and orbital polarization, local magnetic moment, and spin or orbital fluctuations still exist. We propose that our present results are also applicable to Sr$_2$CuO$_{4-delta}$ and other two-orbital cuprates, demanding an unconventional multiorbital superconducting scenario in hole-overdoped high-$T_c$ cuprates.
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا