Magnetoresistance negative

Bloom FL, Wagemans W, Kemerink M, Koopmans B (2007) Separating positive and negative magnetoresistance in organic semiconductor devices. Phys Rev Lett 99 257201... 

The temperature dependencies of the resistivity p in 200-nm thick layers of Gai xMnxAs with different Mn content x are displayed in fig. 14. In terms of the metal-insulator transition (MIT), these films can be cost into two categories. Low- and high-Mn composition samples (x < 0.03, x > 0.06) are on the insulator side of the MIT, whereas the layers containing intermediate Mn concentrations (0.03 < x 0.06) are metallic. All samples exhibit a negative magnetoresistance (MR) at low temperatures. Quite generally, the MIT occurs... 

Fig. 17. Magnetotransport properties of a 200-nm thick film of Ga -x Mnr As with x = 0.0S3 at 50 m K in high magnetic fields, (a) Hall resistance, which is a linear function of the magnetic field in the high-field region (inset), (b) Sheet resistance negative magnetoresistance tends to saturate in the high-field region (Omiya et al. 2000).

Anomalous Negative Magnetoresistance Caused by Non-Markovian Effects... 

So, the localized pairs display themselves at the stage when they become decoupled and contribute to the conductance. The negative magnetoresistance serves as an indirect manifestation of the specific insulating state destroyed by the field. However, as the theory [9, 10] relates only to the vicinity of the SIT, the negative magnetoresistance happens beyond the range of its action. 

Fig. 5. Set of isotherms R(T= const, B) of amorphous InOj, films [4]. (a) Magnetic field normal to the film (b) magnetic field parallel to the film. In the fields region I the material remains superconducting, label III marks the region of negative magnetoresistance. The theory [9, 10] relates to the vicinity of the boundary between the regions I and II in the geometry (a).

Finally, the situation looks as follows. Experiments concentrate on three specific properties as signs of the SIT fan-like temperature dependence scaling relation (1) negative magnetoresistance. The latter is very important... 

From here follow main goals in the SIT problem to find theoretical models which would lead to the negative magnetoresistance to trace how the specific SIT properties appear in the field-induced superconductor-normal metal transition while the normal metal is shifted toward the insulating state to find out whether the low dimensions of the films is crucial or the SIT can happen in 3D materials to find the explanation for the pair localization alternative to the boson-vortex duality. It seems that the first two goals are achieved. 

CMR colossal negative magnetoresistance QCP quantum critical point... 

---