اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدOptical study of phonons and electronic excitations in tetragonal Sr$_2$VO$_4$
204
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We report on the optical excitation spectra in Sr$_2$VO$_4$. The phonon modes are assigned and their evolution with temperature is discussed in the frame of the different phase transitions crossed upon cooling. Besides the expected infrared-active phonons we observe two additional excitations at about 290 cm$^{-1}$ and 840 cm$^{-1}$ which could correspond to electronic transitions of the V$^{4+}$ ions. Our experimental results are discussed in the context of recent experimental and theoretical studies of this material with a unique spin-orbital ground state.
قيم البحث
اقرأ أيضاً
Using high resolution X-Ray diffraction (XRD) on high purity powders, we resolved the structure and $ab$ symmetry of the intriguing compound svo$ $ from room temperature down to 20 K to an unprecedented level of accuracy. Upon cooling, this new set o
f data unambiguously reveals a second order phase transition lowering the symmetry from tetragonal to orthorhombic at a temperature $T_{c2}=136$ K. The observation of an orthorhombic distortion of the $ab$-plane is attributed to nematic phase formation supported by local Jahn-Teller (JT) dynamical instability. At $T_{N}=105$ K, spins order and at $T_{c1}=100$ K the tetragonal structure is recovered with an elongated c-axis.
Sr$_2$CuWO$_6$ is a double perovskite proposed to be at the border between two and three dimensional magnetism, with a square lattice of $S=frac{1}{2}$ Cu$^{2+}$ ions. We have used inelastic neutron scattering to investigate the spin wave excitations
of the system, to find out how they evolve as a function of temperature, as well as to obtain information about the magnetic exchange interactions. We observed well defined dispersive spin wave modes at $6$~K, which partially survive above the magnetic ordering temperature, $T_N=24$~K. Linear spin wave theory is used to determine the exchange interactions revealing them to be highly two-dimensional in nature. Density functional theory calculations are presented supporting this experimental finding, which is in contrast to a previous emph{ab-initio} study of the magnetic interactions. Our analysis confirms that not the nearest neighbour, but the next nearest neighbour interactions in the tetragonal $ab$ plane are the strongest. Low incident energy measurements reveal the opening of a $0.6(1)$~meV gap below $T_N$, which suggests the presence of a very weak single ion anisotropy term in the form of an easy axis along $hat{mathbf{a}}$.
We formulate and study an effective Hamiltonian for low-energy Kramers doublets of $d^1$-ions on a square lattice. We find that the system exhibits a magnetically hidden order in which the expectation values of the local spin and orbital moments both
vanish. The order parameter responsible for a time-reversal symmetry breaking has a composite nature and is a spin-orbital analog of a magnetic octupole. We argue that such a hidden order is realized in the layered perovskite Sr$_2$VO$_4$.
We present a theoretical investigation of the effects of correlations on the electronic structure of the Mott insulator Sr$_2$IrO$_4$ upon electron doping. A rapid collapse of the Mott gap upon doping is found, and the electronic structure displays a
strong momentum-space differentiation at low doping level: The Fermi surface consists of pockets centered around $(pi/2,pi/2)$, while a pseudogap opens near $(pi,0)$. Its physical origin is shown to be related to short-range spin correlations. The pseudogap closes upon increasing doping, but a differentiated regime characterized by a modulation of the spectral intensity along the Fermi surface persists to higher doping levels. These results, obtained within the cellular dynamical mean-field theory framework, are discussed in comparison to recent photoemission experiments and an overall good agreement is found.
We report on the electronic ground state of a layered perovskite vanadium oxide Sr$_2$VO$_4$ studied by the combined use of synchrotron radiation x-ray diffraction (SR-XRD) and muon spin rotation/relaxation ($mu$SR) techniques, where $mu$SR measureme
nts were extended down to 30 mK. We found an intermediate orthorhombic phase between $T_{rm c2} sim$~130 K and $T_{rm c1} sim$~100 K, whereas a tetragonal phase appears for $T > T_{rm c2}$ and $T < T_{rm c1}$. The absence of long-range magnetic order was confirmed by $mu$SR at the reentrant tetragonal phase below $T_{rm c1}$, where the relative enhancement in the $c$-axis length versus that of the $a$-axis length was observed. However, no clear indication of the lowering of the tetragonal lattice symmetry with superlattice modulation, which is expected in the orbital order state with superstructure of $d_{yz}$ and $d_{zx}$ orbitals, was observed by SR-XRD below $T_{rm c1}$. Instead, it was inferred from $mu$SR that a magnetic state developed below $T_{rm c0} sim$~10 K, which was characterized by the highly inhomogeneous and fluctuating local magnetic fields down to 30 mK. We argue that the anomalous magnetic ground state below $T_{rm c0}$ originates from the coexistence of ferromagnetic and antiferromagnetic correlations.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
