Disorder-Assisted Electron-Phonon Scattering and Cooling Pathways in Graphene

We predict that graphene is a unique system where disorder-assisted scattering (supercollisions) dominates electron-lattice cooling over a wide range of temperatures, up to room temperature. This is so because for momentum-conserving electron-phonon scattering the energy transfer per collision is severely constrained due to a small Fermi surface size. The characteristic $T^3$ temperature dependence and power-law cooling dynamics provide clear experimental signatures of this new cooling mechanism. The cooling rate can be changed by orders of magnitude by varying the amount of disorder providing means for a variety of new applications that rely on hot-carrier transport.

Figure 1

(a) Temperature dynamics obtained from Eq. (1) for the lattice temperature values matching those in (b). Parameter values used: doping $\mu =50\mathrm{meV}$ and disorder mean free path $k_F\ell =20$. (b) Carrier dynamics measured using the pump-probe technique for varying substrate temperatures [reproduced from Fig. 2(b) of Ref. 7].

Figure 2

(a) Kinematics of supercollisions and normal collisions at $T>T_{\mathrm{BG}}$. Phonon momenta ($q_{\mathrm{ph}}$) are constrained by the Fermi surface for normal collisions (white arrows), and totally unconstrained for supercollisions, with the recoil momentum ($q_{\mathrm{recoil}}$) transferred to the lattice via disorder scattering. The energy dissipated in supercollisions is much greater than that dissipated in normal collisions. (b) Feynman diagrams for disorder-assisted electron-phonon scattering processes, corresponding to the three terms in Eq. (6).