Observations by GMRT at 323 MHz of radio-loud quasars at $z>5$
  We present Giant Metrewave Radio Telescope (GMRT) 323 MHz radio continuum
observations toward 13 radio-loud quasars at $z>5$, sampling the low-frequency
synchrotron emission from these objects. Among the 12 targets successfully
observed, we detected 10 above $4\sigma$ significance, while 2 remain
undetected. All of the detected sources appear as point sources. Combined with
previous radio continuum detections from the literature, 9 quasars have
power-law spectral energy distributions throughout the radio range; for some
the flux density drops with increasing frequency while it increases for others.
Two of these sources appear to have spectral turnover. For the power-law-like
sources, the power-law indices have a positive range between 0.18 and 0.67 and
a negative values between $-0.90$ and $-0.27$. For the turnover sources, the
radio peaks around $\sim1$ and $\sim10$ GHz in the rest frame, the optically
thin indices are $-0.58$ and $-0.90$, and the optically thick indices are 0.50
and 1.20. A magnetic field and spectral age analysis of SDSS
J114657.59+403708.6 at $z=5.01$ may indicate that the turnover is not caused by
synchrotron self-absorption, but rather by free-free absorption by the
high-density medium in the nuclear region. Alternatively, the apparent turnover
may be an artifact of source variability. Finally, we calculated the radio
loudness $R_{2500\rm\, \AA}$ for our sample, which spans a very wide range from
12$^{+13}_{-13}$ to 4982$^{+279}_{-254}$.
