Phonon-drag thermopower and thermoelectric performance of MoS 2 monolayer in quantizing magnetic field.

We present a theory of phonon-drag thermopower,Sxxg, in MoS 2 monolayer at a low-temperature regime in the presence of a quantizing magnetic field B . Our calculations forSxxgconsider the electron-acoustic phonon interaction via deformation potential (DP) and piezoelectric (PE) couplings for longitudinal (LA) and transverse (TA) phonon modes. The unscreened TA-DP is found to dominateSxxgover other mechanisms. TheSxxgis found to oscillate with the magnetic field where the lifting effect of the valley and spin degeneracies in MoS 2 monolayer has been clearly observed. An enhancedSxxgwith a peak value of∼1mV K -1 at about T  = 10 K is predicted, which is closer to the zero field experimental observation. In the Bloch-Grüneisen regime the temperature dependence ofSxxggives the power-lawSxxg∝Tδe, where δ e varies marginally around 3 and 5 for unscreened and screened couplings, respectively. In addition,Sxxgis smaller for larger electron density n e . The power factor PF is found to increase with temperature T , decrease with n e , and oscillate with B . The prediction of an increase of thermal conductivity with temperature and the magnetic field is responsible for the limit of the figure of merit ( ZT ). At a particular magnetic field and temperature, ZT can be maximized by optimizing electron density. By fixingne=1012cm -2 , the highest ZT is found to be 0.57 at T  = 5.8 K and B  = 12.1 T. Our findings are compared with those in graphene and MoS 2 for the zero-magnetic field.