Strong pseudospin-lattice coupling in Sr3Ir2O7 : Coherent phonon anomaly and negative thermal expansion

Abstract

The similarities to cuprates make iridates an interesting potential platform for investigating superconductivity. Equally attractive are their puzzling complex intrinsic interactions. Here, we report an ultrafast optical spectroscopy investigation of a coherent phonon mode in Sr 3 Ir 2 O 7 , a bilayer Ruddlesden-Popper perovskite iridate. An anomaly in the A 1g optical phonon (ν = 4.4 THz) is unambiguously observed below the Néel temperature (T N ), which we attribute to pseudospin-lattice coupling (PLC). Significantly, we find that PLC is the dominant interaction at low temperature, and we directly measure the PLC coefficient to be λ = 150 ± 20 cm -1 , which is two orders of magnitude higher than that in manganites (< 2.4 cm -1 ) and comparable to that in CuO (50 cm -1 , the strongest PLC or spin-lattice coupling (SLC) previously known). Moreover, we find that the strong PLC induces an anisotropic negative thermal expansion. Our findings highlight the key role of PLC in iridates and uncovers another intriguing similarity to cuprates. APPENDIX D: OBTAINING THE PLC COEFFICIENT  AND2 2 c J u  

Doping and temperature evolutions of optical response of Sr3(Ir1-xRux)2O7

“…The pseudospin-phonon coupling is manifested in previous spectroscopic studies on layered iridates. Raman 46 , 47 and ultrafast 48 spectroscopy studies of Sr 2 IrO 4 and Sr 3 Ir 2 O 7 show anomalies of the frequencies and the linewidths of phonon modes at T AF , which is similar with our observation summarized in Fig. 6 b,c.…”

Attosecond light source in material science investigation

“…功地应用于凝聚态物理和材料科学的研究中, 在高温 超导 [6] 、拓扑材料 [7,8] 、关联量子材料 [9,10] 、半导体材 料、2D材料、纳米结构、磁性材料 [11] 、软物质等凝聚 态物质的研究中取得了重要成果. 当飞秒泵浦-探测实 验方法与低温、强磁场、高压 [8] 在方 解石晶体中观察到了三次谐波.…”

Phase coexistence and negative thermal expansion in the triple perovskite iridate Ba3CoIr2O9

“…Compared to their 3d counterparts where spin (S) and orbital angular momentum (L) are considered to be good quantum * sunil@iiserpune.ac.in numbers, strong spin orbit coupling in the 5d compounds leads to the formation of J eff states, also called pseudospin states [21,22]. Many interesting ground states have been attributed to the presence of the pseudospin lattice (PSL) coupling which is two orders of magnitude higher compared to the manganites [23]. In compounds with strong spin orbit coupling, the high sensitivity of the ground state to local lattice distortions modifies the spin-phonon dynamics that are reflected through changes in the structural parameters and the magnetization response [20,24].…”

“…In compounds with strong spin orbit coupling, the high sensitivity of the ground state to local lattice distortions modifies the spin-phonon dynamics that are reflected through changes in the structural parameters and the magnetization response [20,24]. The presence of pseudospin in iridates has generated much curiosity and recent studies on single and bilayer Ruddlesden-Popper iridates of the form Sr n+1 Ir n O 3n+1 (n = 1, 2, inf) bear interesting results [23,[25][26][27][28][29]. These studies were focused on the J eff = 1/2 state for iridium where IrO 6 octahedra are connected via corners in the a-b plane and disconnected via a SrO layer along the c axis.…”

“…These studies were focused on the J eff = 1/2 state for iridium where IrO 6 octahedra are connected via corners in the a-b plane and disconnected via a SrO layer along the c axis. The pseudospin states coupled to lattice distortions have been speculated to promote tetragonal to orthorhombic distortions in the J eff = 1/2 Sr 2 IrO 4 system and anisotropic negative thermal expansion in the bilayered Sr 3 Ir 2 O 7 [23,25,26].…”