  Silver nanowires have great application potential in fields like flexible
electronic devices, solar cells and transparent electrodes. It is critical and
fundamental to study the thermal and electrical transport properties in a
single silver nanowire. In this work, the thermal and electrical transport in
an individual silver nanowire is characterized down to 35 K with the steady
state electro-thermal technique. The results indicate that, at room
temperature, the electrical resistivity increases by around 4 folds compared
from that of its bulk counterpart. After fitting the temperature dependent
electrical resistivity curves with the Bloch-Gr\"uneisen formula, the Debye
temperature (151 K) of the silver nanowire is found 36% lower than that (235 K)
of bulk silver, confirming strong phonon softening. The thermal conductivity is
reduced by 55% compared with that of its bulk counterpart at room temperature
and this reduction becomes larger as the temperature goes down. To explain the
opposite trends of thermal conductivity (\k{appa}) ~ temperature (T) of silver
nanowire and bulk silver, a unified thermal resistivity is used to elucidate
the electron scattering mechanism. A large residual unified thermal resistivity
for the silver nanowire is observed while that of the bulk silver is almost
zero. The same trend of variation against T indicates that the silver nanowire
and bulk silver share the same phonon-electron scattering mechanism.
Additionally, due to phonon-assisted electron energy transfer across the grain
boundaries, the Lorenz number of the silver nanowire is found much larger than
that of bulk silver and decreases with decreasing temperature.
