Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userIntervalley-Scattering Induced Electron-Phonon Energy Relaxation in Many-Valley Semiconductors at Low Temperatures
63
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We report on the effect of elastic intervalley scattering on the energy transport between electrons and phonons in many-valley semiconductors. We derive a general expression for the electron-phonon energy flow rate at the limit where elastic intervalley scattering dominates over diffusion. Electron heating experiments on heavily doped n-type Si samples with electron concentration in the range $3.5-16.0times 10^{25}$ m$^{-3}$ are performed at sub-1 K temperatures. We find a good agreement between the theory and the experiment.
rate research
Read More
We have measured directly the thermal conductance between electrons and phonons in ultra-thin Hf and Ti films at millikelvin temperatures. The experimental data indicate that electron-phonon coupling in these films is significantly suppressed by disorder. The electron cooling time $tau_epsilon$ follows the $T^{-4}$-dependence with a record-long value $tau_epsilon=25ms$ at $T=0.04K$. The hot-electron detectors of far-infrared radiation, fabricated from such films, are expected to have a very high sensitivity. The noise equivalent power of a detector with the area $1mum^2$ would be $(2-3)10^{-20}W/Hz^{1/2}$, which is two orders of magnitude smaller than that of the state-of-the-art bolometers.
We demonstrate significant modification of the electron-phonon energy loss rate in a many-valley semiconductor system due to lattice mismatch induced strain. We show that the thermal conductance from the electron system to the phonon bath in strained n + Si, at phonon temperatures between 200 mK and 450 mK, is more than an order of magnitude lower than that for a similar unstrained sample.
We consider electron-phonon (textit{e-ph}) energy loss rate in 3D and 2D multi-component electron systems in semiconductors. We allow general asymmetry in the textit{e-ph} coupling constants (matrix elements), i.e., we allow that the coupling depends on the electron sub-system index. We derive a multi-component textit{e-ph}power loss formula, which takes into account the asymmetric coupling and links the total textit{e-ph} energy loss rate to the density response matrix of the total electron system. We write the density response matrix within mean field approximation, which leads to coexistence of symmetric energy loss rate $F_{S}(T)$ and asymmetric energy loss rate $F_{A}(T)$ with total energy loss rate $ F(T)=F_{S}(T)+F_{A}(T)$ at temperature $T$. The symmetric component F_{S}(T) $ is equivalent to the conventional single-sub-system energy loss rate in the literature, and in the Bloch-Gr{u}neisen limit we reproduce a set of well-known power laws $F_{S}(T)propto T^{n_{S}}$, where the prefactor and power $n_{S}$ depend on electron system dimensionality and electron mean free path. For $F_{A}(T)$ we produce a new set of power laws F_{A}(T)propto T^{n_{A}}$. Screening strongly reduces the symmetric coupling, but the asymmetric coupling is unscreened, provided that the inter-sub-system Coulomb interactions are strong. The lack of screening enhances $F_{A}(T)$ and the total energy loss rate $F(T)$. Especially, in the strong screening limit we find $F_{A}(T)gg F_{S}(T)$. A canonical example of strongly asymmetric textit{e-ph} matrix elements is the deformation potential coupling in many-valley semiconductors.
The conductivity of an electron gas can be alternatively calculated either from the current--current or from the density--density correlation function. Here, we compare these two frequently used formulations of the Kubo formula for the two--dimensional Dirac electron gas by direct evaluations for several special cases. Assuming the presence of weak disorder we investigate perturbatively both formulas at and away from the Dirac point. While to zeroth order in the disorder amplitude both formulations give identical results, with some very strong assumptions though, they show significant discrepancies already in first order. At half filling we evaluate all second order diagrams. Virtually none of the topologically identical diagrams yield the same corrections for both formulations. We conclude that a direct comparison of conductivities of disordered system calculated in both formulas is not possible.
The notion of Thouless energy plays a central role in the theory of Anderson localization. We investigate the scaling of Thouless energy across the many-body localization (MBL) transition in a Floquet model. We use a combination of methods that are reliable on the ergodic side of the transition (e.g., spectral form factor) and methods that work on the MBL side (e.g. typical matrix elements of local operators) to obtain a complete picture of the Thouless energy behavior across the transition. On the ergodic side, the Thouless energy tends to a value independent of system size, while at the transition it becomes comparable to the level spacing. Different probes yield consistent estimates of the Thouless energy in their overlapping regime of applicability, giving the location of the transition point nearly free of finite-size drift. This work establishes a connection between different definitions of Thouless energy in a many-body setting, and yields new insights into the MBL transition in Floquet systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
