Singlet Orbital Ordering in Bilayer Sr3Cr2O7

Abstract

We perform an extensive study of Sr_{3}Cr_{2}O_{7}, the n=2 member of the Ruddlesden-Popper Sr_{n+1}Cr_{n}O_{3n+1} system. An antiferromagnetic ordering is clearly visible in the magnetization and the specific heat, which yields a huge transition entropy, Rln(6). By neutron diffraction as a function of temperature we have determined the antiferromagnetic structure that coincides with the one obtained from density functional theory calculations. It is accompanied by anomalous asymmetric distortions of the CrO_{6} octahedra. Strong coupling and Lanczos calculations on a derived Kugel-Khomskii Hamiltonian yield a simultaneous orbital and moment ordering. Our results favor an exotic ordered phase of orbital singlets not originated by frustration.

Structural and physical properties of the high pressure perovskite layered Sr 4 Cr 3 O 10 chromate

“…Extraction of reflection intensities of each PED pattern was performed by integrating the intensity of each reflection after subtracting the background noise. Consequently 5 different datasets were created from the zone axes PED patterns [010], , , [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20], [2-30] (Fig. 3) and merged using the common reflections between patterns.…”

“…Few reports exist in the literature on these chromates because High Pressure -High Temperature (HP-HT) is needed for their synthesis. In Sr 3 Cr 2 O 7 (n=2) we have reported an anomalous asymmetric distorsion of the CrO 6 octahedra associated to simultaneous orderings of the orbital and spin degrees of freedom [5]. We focus here on the isolation of the phase Sr 4 Cr 3 O 10 (n=3) and its structural and magnetic characterizations.…”

Origin of the Magnetic and Orbital ordering in $α$-Sr$_2$CrO$_4$

“…Recent developments in the chromium-based Ruddlesden-Popper (RP) series Sr n+1 Cr n O 3n+1 , provide an ideal playground for the spin and orbital degrees of freedom. Using X-rays and neutron diffraction, varying temperature, the simultaneous development of orbital and magnetic ordering has been observed for Sr 3 Cr 2 O 7 , the n = 2 member of the RP series [18]. In this compound, the spin ordering was found to be antiferromagnetic, while the orbital ordering was described as forming orbital singlet states [18,19].…”

“…Using X-rays and neutron diffraction, varying temperature, the simultaneous development of orbital and magnetic ordering has been observed for Sr 3 Cr 2 O 7 , the n = 2 member of the RP series [18]. In this compound, the spin ordering was found to be antiferromagnetic, while the orbital ordering was described as forming orbital singlet states [18,19]. The possibility of high-T c superconductivity in Sr 3 Cr 2 O 7 has been also proposed due to the hidden-ladder electronic structures [20] present in this compound.…”

Hidden Ladder in SrMoO3/SrTiO3 Superlattices: Experiments and Theoretical Calculations

“…21) Theoretical calculations on the basis of the fluctuation exchange approximation have shown the potential for high-T c superconductivity in this "hidden ladder" system. 21) Unfortunately, no sign of superconductivity has been observed experimentally in Sr 3 Cr 2 O 7 and Sr 3 Mo 2 O 7 , 22,23) although the incipient band is located close to the Fermi level. For Sr 3 Cr 2 O 7 , orbital ordering accompanied by an antiferromagnetic order at 210 K may prevent superconductivity, 22) while in the case of Sr 3 Mo 2 O 7 , oxygen deficiency is likely to be the main cause.…”