Hall effect and orbital diamagnetism in zerogap state of molecular conductor α-(BEDT-TTF)2I3

The apparent zerogap fermions in alpha-(BEDT-TTF)(2)I-3 are recently proposed to obey the tilted Weyl equation which is very unusual. The Hall conductivity, the conductivity and the orbital susceptibility are investigated theoretically for electrons described by this tilted Weyl equation. It is found that these quantities are enhanced due to tilting but keeping the same dependence on chemical potential as in the absence of tilting. Based on these results and expected temperature dependence of the chemical potential in alpha-(BEDT-TTF)(2)I-3, it is found that there will be the strong enhancement of the Hall coefficient toward low temperatures. Moreover, it is proposed that the sharp but continuous reversal of the sign of the Hall coefficient is possible at low temperatures if the extremely small amount of electron doping, about 1 ppm, exists. These results may explain very anomalous features of Hall coefficient observed in alpha-(BEDT-TTF)(2)I-3 and can be an unambiguous indication of the existence of the zerogap, fermions in alpha-(BEDT-TTF)(2)I-3. In addition, it is shown that the orbital diamagnetism can have a peak at the temperatures where the Hall coefficient changes sign. All these strong temperature dependences of both the Hall coefficient and the orbital diamagnetism are due to the inter-band effects of magnetic field.