  Quantum liquids are characterized by the distinctive properties such as the
low temperature behavior of heat capacity and the spectrum of low-energy
quasiparticle excitations. In particular, at low temperature, Fermi liquids
exhibit the zero sound, predicted by L. D. Landau in 1957 and subsequently
observed in liquid He-3. In this paper, we ask a question whether such a
characteristic behavior is present in theories with holographically dual
description. We consider a class of gauge theories with fundamental matter
fields whose holographic dual in the appropriate limit is given in terms of the
Dirac-Born-Infeld action in AdS_{p+1} space. An example of such a system is the
N=4 SU(N_c) supersymmetric Yang-Mills theory with N_f massless N=2
hypermultiplets at strong coupling, finite baryon number density, and low
temperature. We find that these systems exhibit a zero sound mode despite
having a non-Fermi liquid type behavior of the specific heat. These properties
suggest that holography identifies a new type of quantum liquids.
