Thermal Memory: A Storage of Phononic Information

Memory is an indispensible element for a computer in addition to logic gates. In this Letter we report a model of thermal memory. We demonstrate via numerical simulation that thermal (phononic) information stored in the memory can be retained for a long time without being lost and more importantly can be read out without being destroyed. The possibility of experimental realization is also discussed.

Figure 1

(a) Configuration of a thermal memory. Black wavy curve indicates the weak coupling between particle $O$ and segment $R$, which results in the negative differential thermal resistance (NDTR) here. (b) Heat currents, $J_L$, $J_R$ and $J_O$ versus temperature $T_O$. The NDTR between particle $O$ and segment $R$ makes $J_R$ increases in a wide region when $T_O$ is increased, thus makes the curve cross with $J_L$ at more than one values of temperature $T_O$. (c) PDF of the finite time temperature $T_O(t)$ of the central particle $O$ in the absence of control heat bath. Notice the clear correspondence of the two stable steady states in (b) and the two peaks in (c), which are indicated by the two vertical dot lines. Since $T_O(t)$ can only change continuously, the very low PDF in between clearly points out the low transition probability, thus implies the stability of the two states on and off.

Figure 2

A writing-reading process for an off state. Vertical dot lines separate different stages to guide eyes. (a) Illustration of the four stages. (b) Temperatures of the central particle $T_O(t)$, writer $T_{\mathrm{writer}}(t)$ and reader $T_{\mathrm{reader}}(t)$. (c) Heat currents through the two segments, $J_L$ and $J_R$. It can be seen that at the beginning of the reading stage, the net current $J_R-J_L$ changes to negative, namely, energy is absorbed from $O$; thus, $T_O(t)$ is cooled down back to the low temperature $T_{\mathrm{off}}$. (d) After the writing stage $r_{\mathrm{on}}(t)$ keeps very close to zero, namely, nearly all samples stay at the off state, even under the not-very-small perturbation from the hot reader.

Figure 3

A writing-reading process for an on state. (a) Illustration of the four stages. (b) Temperatures of the central particle $T_O(t)$, writer $T_{\mathrm{writer}}(t)$ and reader $T_{\mathrm{reader}}(t)$. (c) Heat currents through the two segments, $J_L$ and $J_R$. At the beginning of the reading stage, the net current $J_R-J_L$ is positive, namely, provides energy to $O$ thus warms it up back to the high level $T_{\mathrm{on}}$. (d) After the writing stage $r_{\mathrm{on}}(t)$ remains very close to 1, namely, nearly all samples stay at the on state, even under the not-very-small perturbation from the cold reader.