Photoinduced $\ensuremath{\eta}$ pairing in the Kondo lattice model

Photoinduced $η$ pairing in the Kondo lattice model

Tomonori Shirakawa, Shohei Miyakoshi, and Seiji Yunoki

Phys. Rev. B 101, 174307 – Published 11 May 2020

Abstract

The previous theoretical study has shown that pulse irradiation to the Mott insulating state in the Hubbard model can induce the enhancement of superconducting correlation due to the generation of $η$ pairs [Kaneko et al., Phys. Rev. Lett. 122, 077002 (2019)]. Here, we show that the same mechanism can be applied to the Kondo lattice model, an effective model for heavy electron systems, by demonstrating that the pulse irradiation indeed enhances the $η$ -pairing correlation. As in the case of the Hubbard model, the nonlinear optical process is essential to increase the number of photoinduced $η$ pairs and thus the enhancement of the superconducting correlation. We also find the diffusive behavior of the spin dynamics after the pulse irradiation, suggesting that the increase of the number of $η$ pairs leads to the decoupling between the conduction band and the localized spins in the Kondo lattice model, which is inseparably related to the photodoping effect.

Received 24 February 2020
Revised 8 April 2020
Accepted 9 April 2020

DOI:https://doi.org/10.1103/PhysRevB.101.174307

Physics Subject Headings (PhySH)

Photoinduced effect

Kondo insulators Superconductivity

Kondo lattice model

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Tomonori Shirakawa ¹, Shohei Miyakoshi², and Seiji Yunoki^1,2,3

¹Computational Materials Science Research Team, RIKEN Center for Computational Science (R-CCS), Kobe, Hyogo 650-0047, Japan
²Computational Quantum Matter Research Team, RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198, Japan
³Computational Condensed Matter Physics Laboratory, RIKEN Cluster for Pioneering Research (CPR), Wako, Saitama 351-0198, Japan

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Vol. 101, Iss. 17 — 1 May 2020

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Figure 1
Schematic figures of possible transition processes by (a) a rank-1 tensor operator and (b) a rank-0 tensor operator, and (c) possible distribution of eigenstates for the final state. In (a) and (b), the vertical axis is the quantum number difference $Δ η$ and the horizontal axis is the energy difference $Δ E$ in unit of $ω_{p}$ (see the main text). Open green squares indicate transitions allowed in general while open green circles indicate transitions allowed only away from half filling. In (c), the vertical axis is the value of $η$ and the horizontal axis is the energy $E_{m}$ (in unit of $ω_{p})$ of eigenstates distributed in the final state. Here, we assume the energy distribution of the unperturbed Hamiltonian $\hat{H}$ as indicated by light-green shaded bars. The initial ground state is indicated by a black solid circle. Open blue squares indicate eigenstates allowed in general while open blue circles indicate eigenstates allowed only away from half filling.
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Figure 2
(a) Time-dependent external field $A (τ)$ used here with $A_{0} = 0.1, ω_{p} = 2.05 t, τ_{c} = 200 / t$ , and $τ_{w} = 50 / t$ [31]. (b) Time evolution of the on-site pair correlation function $\tilde{P} (q = π, τ)$ , the spin correlation function $\tilde{S} (q = π, τ)$ for mobile electrons, and the double occupancy $D (τ)$ for the 1D Kondo lattice model with $J = t$ and $L = 8$ at half filling. Momentum dependence of the on-site pair correlation function $\tilde{P} (q, τ)$ and the spin correlation functions $\tilde{S} (q, τ)$ and $\tilde{M} (q, τ)$ at (c) $τ = 0$ and (d) $τ = 400 / t$ for the same model parameters used in (b).
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Figure 3
(a) Contour plot of the on-site pair correlation function $\tilde{P} (q = π, τ)$ at $τ = 400 / t$ with varying $ω_{p}$ and $A_{0}$ . (b) On-site pair correlation function $\tilde{P} (π, τ = 400 / t)$ as a function of $ω_{p}$ for $A_{0} = 0.02$ and dynamical current correlation function $χ (ω)$ for the initial ground state. $ɛ$ in $χ (ω)$ is $0.01 t$ . The results are obtained for the 1D Kondo lattice model with $J = t$ and $L = 8$ at half filling. We use the external field $A (τ)$ with $τ_{c} = 200 / t$ and $τ_{ω} = 50 / t$ .
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Figure 4
Spectral function $P (η, ω, τ)$ in the photoexcited state $| ψ (τ) 〉$ at $τ = 400 / t$ for the half-filled 1D Kondo lattice model with $J = t$ and $L = 8$ under the external field $A (τ)$ with (a) $A_{0} = 0.1$ and $ω_{p} = 2.05 t$ , and (b) $A_{0} = 0.3$ and $ω_{p} = 3 t$ . The other parameters for $A (τ)$ are $τ_{c} = 200 / t$ and $τ_{ω} = 50 / t$ . For visibility, the spectral functions with different values of $η$ are shifted vertically. Black solid lines indicate the energy region where the eigenstates of $\hat{H}$ exist for each $η$ . Red arrows indicate the excitation energy of the vacuum state $| vac 〉$ . Crossing points between dashed lines and black solid lines indicate $ω = 2 n ω_{p}$ for $η$ even and $ω = (2 n + 1) ω_{p}$ for $η$ odd, where $n = 0, 1, 2, ...$ .
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Figure 5
(a), (b) Real part of dynamical correlation functions $M_{j^{'} j} (τ^{'}, τ)$ for (a) the initial state at $τ = 0$ and (b) the time-evolved state after the pulse irradiation at $τ = 400 / t$ . (c), (d) Imaginary part of $M_{j^{'} j} (τ^{'}, τ)$ for (c) the initial state $τ = 0$ and (d) the time-evolved state after the pulse irradiation at $τ = 400 / t$ . (e) Frequency-dependent dynamical correlation function ${\tilde{M}}_{j j} (ω, τ)$ at $τ = 0$ and $400 / t$ . The results are obtained for the half-filled 1D Kondo lattice model with $J = t$ and $L = 8$ under the external field $A (τ)$ with $A_{0} = 0.38, ω_{p} = 3 / t, τ_{w} = 50 / t$ , and $τ_{c} = 200 / t$ .
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Physical Review B

covering condensed matter and materials physics

Photoinduced $η$ pairing in the Kondo lattice model

Tomonori Shirakawa, Shohei Miyakoshi, and Seiji Yunoki

Phys. Rev. B 101, 174307 – Published 11 May 2020

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Physical Review B

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Photoinduced η pairing in the Kondo lattice model

Tomonori Shirakawa, Shohei Miyakoshi, and Seiji Yunoki

Phys. Rev. B 101, 174307 – Published 11 May 2020

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Photoinduced $η$ pairing in the Kondo lattice model