Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spatial-Temporal Imaging of Anisotropic Photocarrier Dynamics in Black
  Phosphorus   As an emerging single elemental layered material with a low symmetry in-plane
crystal lattice, black phosphorus (BP) has attracted significant research
interest owing to its unique electronic and optoelectronic properties,
including its widely tunable bandgap, polarization dependent photoresponse and
highly anisotropic in-plane charge transport. Despite extensive study of the
steady-state charge transport in BP, there has not been direct characterization
and visualization of the hot carriers dynamics in BP immediately after
photoexcitation, which is crucial to understanding the performance of BP-based
optoelectronic devices. Here we use the newly developed scanning ultrafast
electron microscopy (SUEM) to directly visualize the motion of photo-excited
hot carriers on the surface of BP in both space and time. We observe highly
anisotropic in-plane diffusion of hot holes, with a 15-times higher diffusivity
along the armchair (x-) direction than that along the zigzag (y-) direction.
Our results provide direct evidence of anisotropic hot carrier transport in BP
and demonstrate the capability of SUEM to resolve ultrafast hot carrier
dynamics in layered two-dimensional materials.

2
The categories of this paper are: math
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
37
The categories of this paper are: supr-con
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
13
The categories of this paper are: quant-ph
30
The categories of this paper are: q-alg
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
26
The categories of this paper are: bayes-an
33
The categories of this paper are: plasm-ph
3
The categories of this paper are: physics
6
The categories of this paper are: astro-ph