DYNAMIC STUDY OF THE TRANSPORT-PROPERTIES OF ETA-MO4O11 SINGLE-CRYSTALS BY USE OF THE PHOTOINDUCED TRANSIENT THERMOELECTRIC EFFECT

The pulsed-laser-induced transient thermoelectric effect (TTE) and the static transport properties (resistivity, Hall coefficient, magnetoresistance, and thermopower) of a quasi-two-dimensional eta-Mo4O11 crystal have been measured over the time range 50 ns-2 ms and temperature range 4.2-300 K. The observed TTE voltages decay exponentially with time, showing relaxation processes with multiple relaxation times tau(i) (i = 1-5) for thermal diffusions of photogenerated carriers (electrons and holes), from which we can evaluate the corresponding carrier mobilities mu(i). The temperature dependences of both dynamic and static transport quantities show anomalies around the characteristic temperatures T(c1) = 105 K and T(c2) = 35 K; T(c1) is the well-known charge-density-wave (CDW) transition temperature, but for the latter no definitive x-ray evidence for a CDW transition is reported. However, using our dynamic data and the existing two-dimensional tight-binding model, together with our proposed nesting model of the Fermi surfaces and the CDW-related modifications of the electron and hole bands at T(c1) and T(c2), we have self-consistently calculated the temperature dependence of the dc transport quantities, in satisfactory agreement with the experiments.