Anisotropic lattice compression and pressure-induced electronic phase transitions in Sr2IrO4

Abstract

The crystal lattice of Sr2IrO4 is investigated with synchrotron X-ray powder diffraction under hydrostatic pressures up to P = 43 GPa and temperatures down to 20 K. The tetragonal unit cell is maintained over the whole investigated pressure range, within our resolution and sensitivity. The c-axis compressibility κc(P, T ) ≡ −(1/c)(dc/dP ) presents an anomaly with pressure at P1 = 17 GPa at fixed T = 20 K that is not observed at T = 300 K, whereas κa(P, T ) is nearly temperatureindependent and shows a linear behavior with P . The anomaly in κc(P, T ) is associated with the onset of long-range magnetic order, as evidenced by an analysis of the temperature-dependence of the lattice parameters at fixed P = 13.7 ± 0.5 GPa. At fixed T = 20 K, the tetragonal elongation c/a(P, T ) shows a gradual increment with pressure and a depletion above P2 = 30 GPa that indicates an orbital transition and possibly marks the collapse of the J ef f = 1/2 spin-orbit-entangled state. Our results support pressure-induced phase transitions or crossovers between electronic ground states that are sensed, and therefore can be probed, by the crystal lattice at low temperatures in this prototype spin-orbit Mott insulator. arXiv:1912.07330v1 [cond-mat.str-el]

Quantum criticality in a layered iridate

“…Synchrotron X-ray powder diffraction measurements at ambient temperature were also carried out at the XDS beamline of the Brazilian Synchrotron Light Laboratory (LNLS) 67 with λ = 0.61986 Å employing the experimental setup described in ref. 27 . The structure illustrations in Fig.…”

“…The most obvious approach to access the possible quantum critical fluctuations (QCF) 22,23 associated with a metalinsulator transition would be to force the closure of the bandgap by application of external pressures. Nonetheless, the nonmetallic state persists up to at least 185 GPa despite the identification of exotic states at intermediate pressures [24][25][26][27][28][29] . The alternative approach employed here involves the quest for a specific dilute cationic substitution that induces acceptor or donor impurity levels within the bandgap without actually charge doping the Ir-derived bands at T = 0 K, as shown in Fig.…”

Low-field magnetic anisotropy of Sr2IrO4

“…DMI competes with the symmetric Heisenberg interaction and favors spin-canting in an otherwise AFM system. A spin-canting angle of ~12° results in a net magnetic moment in each domain; however, AFM ordering along the c axis leads to a zero net magnetization 28 . The fascinating feature of Sr 2 IrO 4 is that it exhibits both weak ferromagnetic (WFM) and AFM characteristics.…”

Quantum Criticality in a Layered Iridate

“…The most obvious approach to access the possible quantum critical fluctuations (QCF) [22,23] associated with a metal-insulator transition would be to force the closure of the bandgap by application of external pressures. Nonetheless, the nonmetallic state persists up to at least 185 GPa despite the identification of exotic states at intermediate pressures [24][25][26][27][28][29]. The alternative approach employed here involves the quest for a specific dilute cationic substitution that induces acceptor or donor impurity levels within the bandgap without actually charge doping the Ir-derived bands at T = 0 K, as shown in Fig.…”