scholarly journals MEAN-FIELD APPROACH TO CHARGE, ORBITAL, AND SPIN ORDERING IN MANGANITES

2001 ◽  
Vol 15 (19n20) ◽  
pp. 2719-2726 ◽  
Author(s):  
SUDHAKAR YARLAGADDA ◽  
C. S. TING
Keyword(s):  
Nearest Neighbor ◽  
Mean Field Theory ◽  
Mean Field ◽  
Antiferromagnetic Coupling ◽  
Orbital Ordering ◽  
Teller Distortion ◽  
Spin Ordering ◽  
Jahn Teller ◽  
Jahn Teller Distortion ◽  
Doping Case

We present a mean-field theory of charge, orbital, and spin ordering in manganites at 50% and 0% dopings by considering Jahn–Teller interaction, nearest-neighbor repulsion, and no single-site double occupancy. For spinless fermions, we show that Jahn–Teller distortion and charge-orbital ordering occur simultaneously. In our two-dimensional model at 50% doping, for small nearest-neighbor repulsion the system is orbitally polarized while for larger repulsion the system undergoes CE type ordering. As for the 0% doping case, the ground state is orbitally antiferromagnetic. Upon including spin degree of freedom, at both 50% and 0% dopings the ordering remains the same at small antiferromagnetic coupling between adjacent core spins.

MICROSCOPIC APPROACH TO ELECTRON–PHONON INTERACTION PHYSICS IN HALF-DOPED MANGANITES

2001 ◽  
Vol 15 (27) ◽  
pp. 3529-3537 ◽  
Author(s):  
SUDHAKAR YARLAGADDA
Keyword(s):  
Two Dimensions ◽  
Antiferromagnetic Coupling ◽  
Orbital Ordering ◽  
Microscopic Approach ◽  
Teller Distortion ◽  
Electron Phonon Interaction ◽  
Spin Ordering ◽  
Jahn Teller ◽  
Doped Manganites ◽  
Jahn Teller Distortion

We present a microscopic picture of charge, orbital, and spin ordering in manganites at 50% doping by considering Jahn–Teller interaction. For spinless fermions, in two-dimensions and at 50% doping, we show that Jahn–Teller distortion and charge-orbital ordering occur simultaneously with the system in an essentially orbitally polarized state of dx2-y2 orbitals. Upon including spin degree of freedom, for small antiferromagnetic coupling, we obtain CE-type ordering.

Optical and magnetic studies of TmAsO 4

1984 ◽  
Vol 394 (1806) ◽  
pp. 69-85 ◽  
Keyword(s):  
Field Theory ◽  
Crystal Field ◽  
Mean Field Theory ◽  
Mean Field ◽  
Optical Measurements ◽  
Optical Absorption Spectroscopy ◽  
Magnetic Studies ◽  
Teller Distortion ◽  
Principal Axes ◽  
Jahn Teller

In the tetragonal paramagnet thulium arsenate, TmAsO 4 , the lowest manifold of the Tm 3+ ion, 4f 12 , 3 H 6 is split by the crystal field, which leaves a ground doublet with a nearby singlet at 13.8 cm -1 . Below a critical temperature T D = 6.13(3) K, a cooperative Jahn-Teller distortion splits the ground doublet, which produces domains with principal axes [110], [11̄0]. The behaviour of the three lowest levels has been studied by using high resolution optical absorption spectroscopy with magnetic fields up to 9 T along the [001] axis and in the (001) plane. Enhanced nuclear magnetic resonance of the single stable isotope 169 Tm has also been observed in these directions. Parallel to the c -axis the results confirm that from 1.6 to 4.2 K the magnitude of the Jahn-Teller splitting follows mean field theory to within 0.2 %. New values of the parameters give good agreement with mean field theory, but in the (001) plane the n. m. r. and optical measurements disagree with each other and with calculations based on the crystal field parameters of Bingham et al . (1984), which indicates that other interactions may be present.

scholarly journals Electric-Field Control of Magnetization, Jahn-Teller Distortion, and Orbital Ordering in Ferroelectric Ferromagnets

2019 ◽  
Vol 122 (24) ◽  
Author(s):  
Lan Chen ◽  
Changsong Xu ◽  
Hao Tian ◽  
Hongjun Xiang ◽  
Jorge Íñiguez ◽  
...  
Keyword(s):  
Electric Field ◽  
Orbital Ordering ◽  
Teller Distortion ◽  
Field Control ◽  
Jahn Teller ◽  
Jahn Teller Distortion

scholarly journals Magnetic structures and anisotropic excitations in Tb2Ti2O7spin liquid

2014 ◽  
Vol 70 (a1) ◽  
pp. C1543-C1543
Author(s):  
Isabelle Mirebeau ◽  
Sylvain Petit ◽  
Julien Robert ◽  
Solene Guitteny ◽  
Arsen Gukasov ◽  
...  
Keyword(s):  
Crystal Field ◽  
Ground State ◽  
Mean Field ◽  
Spin Liquid ◽  
Singlet Ground State ◽  
Field Calculation ◽  
Teller Distortion ◽  
Classical Spin ◽  
Jahn Teller ◽  
Jahn Teller Distortion

Geometrical frustration in the pyrochlore lattice of corner sharing tetrahedra yields exotic short range ordered ground states known as spin liquids or spin ices. Among them, Tb2Ti2O7 spin liquid (also called quantum spin ice) remains the most mysterious, in spite of 15 years of intense investigation. Our recent single crystal experiments using neutron diffraction and inelastic scattering down to 50 mK yield new insight on this question. By applying a high magnetic field along a [111] anisotropy axis [1], the Tb moments reorient gradually without showing the magnetization plateau observed in classical spin ices. Quantitative comparison with mean field calculation supports a dynamical symmetry breaking akin to a dynamic Jahn-Teller distortion, preserving the overall cubic symmetry. In the non-Kramers Tb ion this induce a quantum mixing of the wave-functions of the ground state crystal field doublet enabling the formation of a spin liquid, viewed as a non-magnetic two-singlet ground state in this mean-field picture [2]. The spin lattice coupling also shows up in the spin fluctuations in zero field [3]. Dispersive excitations emerge from pinch-points in the reciprocal space, with anisotropic spectral weight. This is the first evidence of them in a disordered ground state. They reveal the breaking of some conservation law ruling the relative orientations of the fluctuating magnetic moments in a given tetrahedron, as for the monopole excitations in classical spin ices. The algebraic character of the correlations shows that Tb2Ti2O7 ground state is akin to a Coulomb phase. Finally, the first excited crystal field level and an acoustic phonon mode interact, repelling each other. The whole results show that the magnetoelastic coupling is a key feature to understand the surprising spin liquid ground state. They call for an interaction between quadrupolar moments, whose Jahn-Teller distortion is the first (single site) approximation.

THE ORBITAL ORDERING OF THE CUBIC KCrF3

2012 ◽  
Vol 26 (04) ◽  
pp. 1150025 ◽  
Author(s):  
MINPING ZHANG ◽  
GUANGTAO WANG
Keyword(s):  
Electron Correlation ◽  
First Principles ◽  
Theoretical Calculations ◽  
Cubic Phase ◽  
Orbital Ordering ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Jahn Teller Distortion ◽  
First Principles Method

The electronic, magnetic and orbital structures of KCrF 3 in the cubic phase are studied by first principles method. In the cubic phase, the three Cr - F bonds distance are equal. If the Jahn–Teller distortion is the origin of the orbital polarization, the orbital ordering would disappear. However, our theoretical calculations show that the orbital ordering exists even without the Jahn–Teller distortion. By studying how the orbital polarization changes with the electron correlation and the Jahn–Teller distortion, we found that the origin of the orbital polarization should be the electron correlation and the Jahn–Teller distortion can reinforced such polarization.

scholarly journals Absence of Jahn−Teller transition in the hexagonal Ba3CuSb2O9 single crystal

2015 ◽  
Vol 112 (30) ◽  
pp. 9305-9309 ◽  
Author(s):  
Naoyuki Katayama ◽  
Kenta Kimura ◽  
Yibo Han ◽  
Joji Nasu ◽  
Natalia Drichko ◽  
...  
Keyword(s):  
Single Crystal ◽  
Liquid State ◽  
Electron Systems ◽  
Quantum Liquid ◽  
Orbital Ordering ◽  
Spin Orbital ◽  
Teller Distortion ◽  
Single Crystal Study ◽  
Jahn Teller ◽  
Jahn Teller Distortion

With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include Bose−Einstein condensation of cold atoms, superconductivity, quantum Hall state of electron systems, and quantum spin liquid state in the frustrated magnets. Moreover, recent studies have clarified the possibility of another exotic quantum liquid state based on the spin–orbital entanglement in FeSc2S4. To confirm this exotic ground state, experiments based on single-crystalline samples are essential. However, no such single-crystal study has been reported to date. Here, we report, to our knowledge, the first single-crystal study on the spin–orbital liquid candidate, 6H-Ba3CuSb2O9, and we have confirmed the absence of an orbital frozen state. In strongly correlated electron systems, orbital ordering usually appears at high temperatures in a process accompanied by a lattice deformation, called a static Jahn−Teller distortion. By combining synchrotron X-ray diffraction, electron spin resonance, Raman spectroscopy, and ultrasound measurements, we find that the static Jahn−Teller distortion is absent in the present material, which indicates that orbital ordering is suppressed down to the lowest temperatures measured. We discuss how such an unusual feature is realized with the help of spin degree of freedom, leading to a spin–orbital entangled quantum liquid state.

Formation of the C-type Orbital-Ordered State in the Simple Perovskite Manganite Sr1-xSmxMnO3

MRS Advances ◽  
2016 ◽  
Vol 1 (9) ◽  
pp. 615-620 ◽  
Author(s):  
Misato Yamagata ◽  
Ayumi Shiratani ◽  
Yasuhide Inoue ◽  
Yasumasa Koyama
Keyword(s):  
Electronic System ◽  
The State ◽  
Tetragonal Symmetry ◽  
Perovskite Manganite ◽  
Orbital Ordering ◽  
Teller Distortion ◽  
Rotational Displacement ◽  
Type Orbital ◽  
Jahn Teller ◽  
Jahn Teller Distortion

ABSTRACTThe simple perovskite manganite Sr1-xSmxMnO3 (SSMO) has been reported to have a highly-correlated electronic system for eg-electrons in a Mn ion. According to the previous studies, the C-type orbital-ordered (COO) state with the I4/mcm symmetry was found to be formed from the disordered-cubic (DC) state on cooling. The feature of the COO state is that its crystal structure involves both the Jahn-Teller distortion to orbital ordering and the R25-type rotational displacement of oxygen octahedra. Because of the involvement of both the distortion and the displacement, their competition should be expected in the formation of the COO state. However, the detailed features of the competition have not been understood yet. Thus, the crystallographic features of the COO state in SSMO have been examined by x-ray powder diffraction and transmission electron microscopy. It was found that, when the Sm content increased from x = 0 at room temperature, the DC state changed into the COO state with the tetragonal symmetry around x = 0.13. The notable feature of the COO state is that the state is characterized by a nanometer-scaled banded structure consisting of an alternating array of two tetragonal bands. One tetragonal band consisted of the COO state involving both the Jahn-Teller distortion and the R25-type rotational displacement. But, there was only the latter displacement in the other, the state of which could be identified as a disordered tetragonal (DT) state. Based on this, it is understood that the COO-state formation from the DC state should take place via the appearance of the DT state, which may involve fluctuations of the C-type orbital ordering.

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