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High redshift quasars ($z>5$) that also shine brightly at radio wavelengthsare unique signposts of supermassive black hole activity in the early universe.However, bright radio sources at $z\ge5$ are extremely rare and therefore wehave started a campaign to search for new high-$z$ quasars by combining anoptical dropout selection driven by the $g$, $r$, and $z$ bands from the DarkEnergy Spectroscopic Instrument (DESI) Legacy Imaging Surveys withlow-frequency radio observations from the LOFAR Two-metre Sky Survey (LoTSS).Currently, LoTSS covers a large fraction of the northern sky (5720 deg$^2$) tosuch a depth (median noise level of 83 $\mu$Jy beam$^{-1}$) that about 30% ofthe general quasar population is detected $-$ which is a factor of 5-10 morethan previous large sky radio surveys such as NVSS and FIRST, respectively. Inthis paper, we present the discovery of 20 new quasars (and the independentconfirmation of 4) between $4.9\leq z\leq 6.6$. Out of the 24 quasars, 21satisfy the traditional radio-loudness criterion of$R=f_{5\text{GHz}}/f_{4400A} > 10$, with the full sample spanning$R\sim$6-1000, thereby more than doubling the sample of known radio-loudquasars at $z \ge 5$. Our radio detection requirement strongly decreases thecontamination of stellar sources and allows one to select these quasars in abroad redshift range. Despite selecting our quasar candidates using fewer andless conservative colour restrictions, both the optical and near-infraredcolours, Ly$\alpha$ emission line properties, and dust reddening, $E(B-V)$,measurements of our quasar sample do not deviate from the known radio-quietquasar population, suggesting similar optical quasar properties of theradio-loud and radio-quiet quasar population at high-$z$. Our campaigndemonstrates the potential for discovering new high-$z$ quasar populationsthrough next generation radio continuum surveys.

Discovery of 24 radio-bright quasars at $4.9 \leq z \leq6.6$ using low-frequency radio observations