Mott-to-Goodenough insulator-insulator transition inLiVO2

Efficient excitation of nonlinear phonons via chirped pulses: Induced structural phase transitions

“…Research in ultrafast light-control of materials have attracted a lot of interest recently [1][2][3][4][5][6][7][8][9]. Intense midinfrared pulses have been used to directly control the dynamical degrees of freedom of the crystal lattice [5][6][7][8][9], in particular, inducing melting of orbital and magnetic orders.…”

“…In all considered examples below, a phonon mode with (at least) quartic nonlinearity is driven by a laser pulse, creating effective potential for a coupled lower-frequency phonon mode those excitation triggers structural phase transition. Neglecting dissipation, our starting Hamiltonian H = P 2 2 + Ω 2 0 Q 2 2 + c 4 Q 4 + c 6 .. − QF 0 sin Φ(t), where Φ(t) is the phase of the drivingΦ(t) = Ω(t), Ω 0 is linear frequency of the driven phonon mode, c 4 , c 6 .. are anharmonic coefficients, F 0 (t) is the amplitude of the external field. Introducing symplectic coordinates…”

“…Ω0 sin φ we then make a transformation to the resonance phase γ = φ − Φ using the time-dependent generating function W = J(φ − Φ). The new Hamiltonian H ′ = H − JΩ can be averaged over the fast phase, with the result (neglecting nonlinearities higher than the quartic for a while) [2], Q1z was given a small initial excitation to initiate its dynamics (simulating temperature fluctuations). Strong driving of Q hx and corresponding excitation of Q1x modes almost do not affect decay of the transverse mode Q1z, and leaves it unexcited.…”

“…Excitation of Q hx mode should be done with a pulse of limited power and duration. When the driving frequency Ω is chosen close to the phonon mode frequency Ω h [2], the transverse mode Q 1z remains almost unaffected ( Fig. (2) due to insufficient amplitude of the Q hx mode.…”

“…Consider driving with sweeping frequency. A chirped pulse has the form F = F 0 (t) sin Φ(t), where Φ(t) = Ω 0 t + αt 2 2 , F 0 (t) = exp −t 2 /2(σ/2ln2) 2 . Time-dependence of the instantenious frequency and the amplitude translates into the dependence of parameters µ, λ of the Hamiltonian (1) on time.…”