Title: Observation of a new field-induced phase transition and its concomitant quantum critical fluctuations in CeCo(In$_{1-x}$Zn$_x$)$_5$,
Abstract: We demonstrate a close connection between observed field-induced
antiferromagnetic (AFM) order and quantum critical fluctuation (QCF) in the
Zn7%-doped heavy-fermion superconductor CeCoIn5. Magnetization, specific heat,
and electrical resistivity at low temperatures all show the presence of new
field-induced AFM order under the magnetic field B of 5-10 T, whose order
parameter is clearly distinguished from the low-field AFM phase observed for B
< 5 T and the superconducting phase for B < 3 T. The 4f electronic specific
heat divided by the temperature, C_e/T, exhibits -lnT dependence at B~10 T (=
B_0), and furthermore, the C_e/T data for B >= B_0 are well scaled by the
logarithmic function of B and T: ln[(B-B_0)/T^{2.7}]. These features are quite
similar to the scaling behavior found in pure CeCoIn5, strongly suggesting that
the field-induced QCF in pure CeCoIn5 originates from the hidden AFM order
parameter equivalent to high-field AFM order in Zn7%-doped CeCoIn5.