Jahn-Teller induced nematic orbital order in tetragonalSr2VO4

Abstract

Using high resolution X-Ray diffraction (XRD) on high purity powders, we resolved the structure and ab symmetry of the intriguing compound Sr2VO4 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 Tc2 = 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 TN = 105 K, spins order and at Tc1 = 100 K the tetragonal structure is recovered with an elongated c-axis.

Competing magnetic interactions in a spin- 12 square lattice: Hidden order in Sr2VO4

“…To inspect the relation between magnetic and structural order we have fully relaxed the high-T tetragonal phase within DFT+U by imposing the ST order. As a result, we obtained a bifurcation of the lattice parameters (a=3.971 Å, b=3.960 Å) and the formation of an orthorhombic phase, in agreement with XRD measurements [23]. This transition is connected to the magnetostriction effect, namely the coupling between non-relativistic isotropic exchange and crystal structure.…”

“…No signals of spin-orbital order was detected down to low temperature but, rather, a possible existence of a nematic phase, originating from the competition between magnetic interaction and Jahn-Teller (JT) effect [23].…”

“…leads to more exotic states [11], for example the enigmatic nematic phases recently found in Fe-based superconductors which arises from the strong competition between the ST and Néel order [12][13][14][15].Tetragonal Sr 2 VO 4 , isostructural to the high-T c parent compound La 2 CuO 4 and similar to layered vanadate Li 2 VOSiO 4 [4], provides an opportunity to explore the role of the various types of magnetic interaction at play in a square lattice, owing to the presumably weak interplane interaction between spin-1/2 V 4+ (d 1 ) layers. The complicated structural, magnetic, and electronic transitions observed in Sr 2 VO 4 , in fact, suggests a competition and/or coexistence of different magnetic phases [16][17][18][19][20][21][22][23][24]. Upon cooling, the crystal structure evolves from tetragonal to an intermediate phase (at T c2 ∼ 140K), and again to a tetragonal phase (T c1 ∼ 100K) with a larger c/a ratio [16].…”

“…Upon cooling, the crystal structure evolves from tetragonal to an intermediate phase (at T c2 ∼ 140K), and again to a tetragonal phase (T c1 ∼ 100K) with a larger c/a ratio [16]. In the intermediate regime, an anomaly in the susceptibility is observed at T M ∼ 105K, which was initially thought to originate from magnetic order [16].No signals of spin-orbital order was detected down to low temperature but, rather, a possible existence of a nematic phase, originating from the competition between magnetic interaction and Jahn-Teller (JT) effect [23].Several proposals have been put forwarded for the elusive low-T ground state: orbitally ordered phase due to JT distortion [16], a competition between an orbitally ordered parquet-type and a double-stripe (DS) magnetic ordering [17,18] (DS10 in Fig. 1(a)), an octupolar order driven by spin-orbit coupling (SOC) [19], and a Néel order with muted magnetic moment, where the spin and orbital moments cancel each other [21].The magnetic properties are highly dependent on the sample quality [20].…”

“…Our proposed scenario is compatible with experimental data and call for a full verification by future experiments. For instance, we expect that nuclear magnetic resonance or inelastic neutron scattering experiments on Sr 2 VO 4 single crystals could allow for a conclusive identification of the origin of the low-T phases [23] and should reveal the character of the magnetic shortrange order effects in the three distinctive temperature intervals.…”