Jahn-Teller induced nematic orbital order in tetragonal Sr$_2$VO$_4$

TL;DR

This study uses high-resolution X-ray diffraction to uncover a Jahn-Teller driven nematic orbital order in Sr$_2$VO$_4$, revealing a sequence of structural phase transitions and spin ordering at low temperatures.

Contribution

It provides the first detailed structural analysis showing Jahn-Teller induced nematic order and associated phase transitions in Sr$_2$VO$_4$.

Findings

Tetragonal to orthorhombic transition at 136 K

Nematic phase formation due to Jahn-Teller instability

Spin ordering at 105 K and structural recovery at 100 K

Abstract

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 of 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.