Lattice distortion in the spin-orbital entangled state in RVO3 perovskites

Abstract

We report a thorough study of Y0.7La0.3VO3 single crystals by measuring magnetic properties, specific heat, thermal conductivity, x-ray and neutron diffraction with the motivation of revealing the lattice response to the spin-orbital entanglement in RVO3. Upon cooling from room temperature, the orbitally disordered paramagnetic state changes around T*∼220 K to spin-orbital entangled state which is then followed by a transition at TN =116 K to C-type orbital ordered (OO) and Gtype antiferromagnetic ordered (AF) ground state. In the temperature interval TN < T < T * , the VO 6/2 octahedra have two comparable in-plane V-O bonds which are longer than the out-of-plane V-O1 bond. This local structural distortion supports the spin-orbital entanglement of partially filled and degenerate yz/zx orbitals. However, this distortion is incompatible with the steric octahedral site distortion intrinsic to orthorhombic perovskites. Their competition induces a second order transition from the spin-orbital entangled state to C-OO/G-AF ground state where the long range OO suppresses the spin-orbital entanglement. Our analysis suggests that the spin-orbital entangled state and G-OO are comparable in energy and compete with each other. Rare earth site disorder favors the spin-orbital entanglement rather than a cooperative Jahn-Teller distortion. The results also indicate for LaVO3 a C-OO/G-AF state in Tt ≤ T ≤TN and an orbital flipping transition at Tt. arXiv:1809.03360v1 [cond-mat.str-el]

Orbital Rotations induced by Charges of Polarons and Defects in Doped Vanadates

“…Thus, the term ∝ V c weakens the superexchange orbital interaction ∝ Jr 1 , where J = 4t 2 /U and r 1 = (1 − 3η) −1 with η = J H /U [47]. One finds that for the present parameters (U = 4.5, t = 0.2, J H = 0.5, all in eV) Jr 1 = 53 meV, so taking V c = 50 meV one is indeed close to the switching of the orbital order observed in YVO 3 [45,46,54].…”

“…These orbital fluctuations lead to much stronger FM spin-couplings in the CS/GO phase [47][48][49] than expected for frozen orbitals, i.e., as assumed in Goodenough-Kanamori rules [50]. YVO 3 instead has a GS/CO ground state triggered by also present Jahn-Teller interactions that increase with decreasing R-ion radius [51][52][53][54]. Interestingly, already traces of Ca-doping switch the GS/CO ground state of YVO 3 to the CS/GO-phase [41,55,56], a feature that could be explained in a model for charged defects that we adopt here [57,58].…”

Evolution of Spin-Orbital Entanglement with Increasing Ising Spin-Orbit Coupling

“…Another experimental confirmation of spin-orbital entanglement is the evolution of the Néel temperature in the C-AF phase with decreasing ionic radius of R ions in RVO 3 , which is induced by the coupling to the orbital state [29]. Experimentally, the entanglement is observed in the critical competition between the two spin-orbital ordered states [30] and was investigated recently in Y 0.70 La 0.30 VO 3 single crystals [31]. Finally, entangled states play a role in the excited states [32] and may help to identify quantum phase transitions in spin-orbital models [8], including the transitions at finite magnetic field [33].…”

Magnetic order driven ultrafast phase transition in NdNiO3

“…Quite often, however, these DOF are deeply intertwined, leading to competing, coexisting, or even cooperative orders [1][2][3]. Such cooperative coupling between the lattice structure, electronic order, and the magnetic configuration occurs in a wide variety of transition metal oxides such as manganites [4], cobaltites [5], ferrites [6], vanadates [7], nickelates [8,9], and cuprates [10]. This arises due to the highly connected nature of the lattice [11][12][13][14] that results in an interplay between changes in electronic and magnetic order with many structural degrees of freedom such as distortions, octahedral rotations and cation displacements.…”