Strong spin-phonon coupling unveiled by coherent phonon oscillations in Ca2RuO4

Abstract

We utilize near-infrared femtosecond pulses to investigate coherent phonon oscillations of Ca2RuO4. The coherent Ag phonon mode of the lowest frequency changes abruptly not only its amplitude but also the oscillation-phase as the spin order develops. In addition, the phonon mode shows a redshift entering the magnetically ordered state, which indicates a spin-phonon coupling in the system. Density functional theory calculations reveal that the Ag oscillations result in octahedral tilting distortions, which are exactly in sync with the lattice deformation driven by the magnetic ordering. We suggest that the structural distortions by the spin-phonon coupling can induce the unusual oscillation-phase shift between impulsive and displacive type oscillations.

Simultaneous Observation of Carrier-Specific Redistribution and Coherent Lattice Dynamics in 2H-MoTe2 with Femtosecond Core-Level Spectroscopy

“…44 In the present work on MoTe2, the observed phases of the A1g and E1g frequency components (i.e. ~1 and 0, respectively) provide evidence for the "displacive" excitation of coherent phonons (DECP) mechanism, [45][46][47][48][49][50][51] which is schematically illustrated by the cartoon in the inset of Figure 5b. In the DECP mechanism, the redistribution of valence electrons (i.e.…”

“…excitation from VB to CB) suddenly alters the shape of the potential energy surface of the lattice, which produces a force that drives the coherent structural motion in the direction of the excited-state equilibrium. 48,50 Both fully symmetric (e.g. A1g) and non-totally symmetric (e.g.…”

Competition of three-dimensional magnetic phases in Ca$_2$Ru$_{1-x}$Fe$_x$O$_4$: A structural perspective

“…30,31 However, the nature of such magnetic competition has yet to be determined. As the structural carrier of such rich interplays among spin, charge and orbital degrees of freedom, RuO 6 octahedron becomes an effective control knob 4,13,[32][33][34][35][36] through its crucial role in SOC 20 , crystal field splitting 18 , Jahn Teller coupling 37 and spin-phonon coupling 37,38 . The distortions of the octahedra lie at the heart of electronic and magnetic phenomenology in CRO and its derived compounds.…”

Ultrafast signatures of spin and orbital order in antiferromagnetic $α$-Sr$_2$CrO$_4$

“…In this context, ultrafast optical spectroscopy (UOS) is a powerful tool for providing new insight into the intertwined spin and orbital DOFs in TM compounds [14]. By using femtosecond (fs) photoexcitation to drive the system out of equilibrium, the interplay among the competing charge, spin and orbital DOFs can be disentangled via their different timescales for returning to the initial ground state, as exemplified in previous studies of various TM oxides [16][17][18][19][20][22][23][24]. However, to the best of our knowledge this technique has not yet been used to study α-Sr 2 CrO 4 , providing an exciting opportunity to shed new light on the origin of the various order parameters present in this system.…”