Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Revealing magnetoelectric coupling effect in polar antiferromagnet
  Fe$_2$Mo$_3$O$_8$ by static and time resolved second harmonic generation   We present both static and time-resolved second harmonic generation (SHG)
measurements on polar antiferromagnet Fe$_2$Mo$_3$O$_8$ to monitor the
evolution of the electric polarization change and its coupling to magnetic
order. We find that only one of the second order tensor elements,
$\chi_{ccc}^{(2)}$ ,shows a prominent change below the Neel temperature $T_N =
60$ K, indicating a magnetic order induced electric polarization change along
the c-axis. Time-resolved SHG measurement reveals an ultrafast recovery of the
second order tensor element upon the ultrashort laser excitation with fluence
above 0.3 $mJ/cm^2$, yielding evidence for a photoinduced ultrafast phase
transition from the AFM ordered state to the paramagnetic state. Our work will
help understand the spin induced polarization and the ultrafast optical tuning
effect in Fe$_{2}$Mo$_{3}$O$_{8}$.

16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
9
The categories of this paper are: nlin
27
The categories of this paper are: comp-gas
22
The categories of this paper are: chao-dyn
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
31
The categories of this paper are: ao-sci
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
24
The categories of this paper are: dg-ga
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
11
The categories of this paper are: hep-lat