Electronic properties of TiSi2 single crystals at low temperatures.

Abstract

We report measurements of Hall effect, transverse magnetoresistance, and specific heat on high-quality ${\mathrm{TiSi}}_{2}$ (C54 phase) single crystals at low temperatures. We used crystals with low residual resistivity (typically ${\mathrm{\ensuremath{\rho}}}_{4.2\phantom{\rule{0ex}{0ex}}\mathrm{K}}$=0.15 \ensuremath{\mu}\ensuremath{\Omega} cm) and magnetic fields (B) up to 20 T. These facts allowed us to study the electronic properties from the low (${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$\ensuremath{\tau}\ensuremath{\ll}1) to the high field regime (${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$\ensuremath{\tau}\ensuremath{\gtrsim}1, ${\mathrm{\ensuremath{\omega}}}_{\mathit{c}}$=eB/m* being the cyclotron frequency and \ensuremath{\tau} the electron relaxation time) as a function of magnetic-field strength and temperature. The low field Hall coefficient ${\mathit{R}}_{\mathit{H}}$ is negative, almost constant ${\mathit{R}}_{\mathit{H}}$=-(0.5\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}10}$ ${\mathrm{m}}^{3}$/C between 100 and 300 K and it changes sign at \ensuremath{\sim}30 K. The angular dependence of magnetoresistance shows either minima or maxima when the magnetic field is parallel to the principal crystallographic axes. These structures are, however, less pronounced than in other silicides, such as ${\mathrm{PdSi}}_{2}$ and ${\mathrm{NbSi}}_{2}$, and this suggests only a weak anisotropy of the ${\mathrm{TiSi}}_{2}$ Fermi surface. The galvanomagnetic properties behave consistently with band-structure calculations of Mattheiss and Hensel [Phys. Rev. B 39, 7754 (1989)] who found that ${\mathrm{TiSi}}_{2}$ is a compensated metal with only closed orbits for the Fermi electrons. Using a simple two-band model we estimated, from the low field magnetoresistance, carrier density ${\mathit{n}}_{\mathit{e}}$=${\mathit{n}}_{\mathit{h}}$=(0.45--0.52)\ifmmode\times\else\texttimes\fi{}${10}^{22}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ assuming equal concentration of electrons and holes. Low temperatures (1.6T22 K) specific-heat (${\mathit{C}}_{\mathit{p}}$) measurements fit a linear ${\mathit{C}}_{\mathit{p}}$/T=\ensuremath{\gamma}+\ensuremath{\beta}${\mathit{T}}^{2}$ dependence, with \ensuremath{\gamma}=3.35\ifmmode\pm\else\textpm\fi{}0.05 mJ/${\mathrm{K}}^{2}$ mol and \ensuremath{\beta}=0.0201\ifmmode\pm\else\textpm\fi{}0.0005 mJ/${\mathrm{K}}^{4}$ mol. From these parameters we estimated the Debye temperature ${\mathrm{\ensuremath{\Theta}}}_{\mathit{D}}$=662\ifmmode\pm\else\textpm\fi{}4 K and the renormalized electronic density of states at the Fermi surface N(${\mathrm{\ensuremath{\varepsilon}}}_{\mathit{F}}$)(1+\ensuremath{\lambda})=2.85 states/eV cell. \textcopyright{} 1996 The American Physical Society.