Quasi-Kondo Phenomenon due to the Dynamical Jahn-Teller Effect

A mechanism of the nonmagnetic Kondo effect is proposed on the basis of a multiorbital Anderson model coupled with dynamical Jahn-Teller (JT) phonons. An electron system coupled dynamically with JT phonons has a vibronic ground state with double degeneracy due to clockwise and anticlockwise rotational modes with entropy of $\log 2$. When a temperature is lower than a characteristic energy to turn the rotational direction, the rotational degree of freedom is eventually suppressed and the corresponding entropy $\log 2$ is released, leading to quasi-Kondo behavior. We discuss a simple relation between the “Kondo” temperature and the JT energy.

Figure 1

(a) $T{\chi }_a$ and (b) $S_{\mathrm{imp}}$ and $C_{\mathrm{imp}}$ vs temperature for $n=2$, $\Delta ={10}^{-5}$, $\omega =0.3$, $\alpha =0.5$, and $\beta =0$. (c) Local electron potential in an adiabatic approximation for $\beta =0$.

Figure 2

(a) Local electron potential in an adiabatic approximation for $\beta <0$. (b) $T{\chi }_a$ ($a=x$, $y$ and $z$), (c) $S_{\mathrm{imp}}$ and $C_{\mathrm{imp}}$, and (d) $⟨Q_i⟩$ and $\sqrt{⟨Q_i^2⟩}$ ($i=2$ and 3) vs temperature for $n=2$, $\Delta ={10}^{-5}$, $\omega =0.3$, $\alpha =0.5$, and $\beta =-0.006$. (e) Schematic views for displacements for $T>T^{*}$ and $T<T^{*}$.

Figure 3

Characteristic temperature $T^{*}$ vs $E_{\mathrm{JT}}$. Dashed line is a guide for eyes. Size of the symbol indicates the order of the precision of $T^{*}$ in the calculation.