Depolarizacijski prijelazi u mikrovalnom odzivu pločica silicijskog kristala

Microwave cavity perturbation measurements have been performed on several n-type silicon samples with different depolarization factors due to sample geometries. The general solution for the complex frequency shift in slab geometry is discussed for the specific case of semiconductors. The depolarization crossovers predicted by the theory have been experimentally observed. Their relative intensities suggest that the imaginary part of the complex conductivity of semiconductors has to be taken into account. Electron scattering time has been inferred from the microwave measurements.Načinili smo mjerenja učinka umetanja nekoliko silicijskih pločica tipa n u mikrovalni rezonator s različitim depolarizacijskim faktorima uzrokovanim oblikom pločica. Raspravljamo opće rješenje za kompleksan pomak frekvencije za poseban slučaj poluvodičke pločice. Teorijski predviđene depolarizacijske prijelaze smo eksperimentalno opazili. Njihove relativne jakosti ukazuju da se u poluvodičima mora uzeti u obzir imaginarni dio kompleksne vodljivosti. Na osnovi mikrovalnih mjerenja izveli smo vrijeme elektronskog raspršenja

Depolarizacijski prijelazi u mikrovalnom odzivu pločica silicijskog kristala

Microwave cavity perturbation measurements have been performed on several n-type silicon samples with different depolarization factors due to sample geometries. The general solution for the complex frequency shift in slab geometry is discussed for the specific case of semiconductors. The depolarization crossovers predicted by the theory have been experimentally observed. Their relative intensities suggest that the imaginary part of the complex conductivity of semiconductors has to be taken into account. Electron scattering time has been inferred from the microwave measurements.Načinili smo mjerenja učinka umetanja nekoliko silicijskih pločica tipa n u mikrovalni rezonator s različitim depolarizacijskim faktorima uzrokovanim oblikom pločica. Raspravljamo opće rješenje za kompleksan pomak frekvencije za poseban slučaj poluvodičke pločice. Teorijski predviđene depolarizacijske prijelaze smo eksperimentalno opazili. Njihove relativne jakosti ukazuju da se u poluvodičima mora uzeti u obzir imaginarni dio kompleksne vodljivosti. Na osnovi mikrovalnih mjerenja izveli smo vrijeme elektronskog raspršenja

Sliding spin-density waves: studies of conduction noise, magnetic field dependence and Hall resistivity

We have studied the current-voltage characteristics of the (TMTSF)_2PF_6 in the spin density state (SDW), and in zero and finite external magnetic field. For the oscillating part of the nonlinear voltage response to the applied DC electric field, the fundamental frequency distribution (as a function of this field) and a nonlinear relation between the frequency and the SDW current reveal the growth of parallel conduction channels characterized by lower velocities and larger cross-sections. The number of fundamental frequencies, their amplitude and the level of low-frequency noise as well as the depinning behaviour provide a consistent indication of the sample inhomogeneities and associated local field variations, and might be well understood within the framework of the phase slippage model. The increase of the threshold electric field with the applied magnetic filed can be explained by the Bjeli-Maki theory, if the imperfect nesting is taken into account. Finally, the electric-field dependence of the Hall resistivity is consistent with the sliding mechanism of the SDW conduction

Unconventional spin density wave in Bechgaard salt (TMTSF)2NO3

Among many Bechgaard salts, TMTSF2NO3 exhibits very anomalous low temperature properties. Unlike conventional spin density wave (SDW), TMTSF2NO3 undergoes the SDW transition at \T_SDW\approx 9.5 K and the low temperature quasiparticle excitations are gapless. Also, it is known that TMTSF2NO3 does not exhibit superconductivity even under pressure, while FISDW is found in TMTSF2NO3 only for P=8.5 kbar and B>20 T. Here we shall show that both the angle dependent magnetoresistance data and the nonlinear Hall resistance of TMTSF2NO3 at ambient pressure are interpreted satisfactory in terms of unconventional spin density wave (USDW). Based on these facts, we propose a new phase diagram for Bechgaards salts.Comment: 4 pages, 4 figs, RevTe

Unconventional spin density wave in (TMTSF)2PF6 below T* ~ 4K

The presence of subphases in spin-density wave (SDW) phase of (TMTSF)2PF6 below T* ~ 4K has been suggested by several experiments but the nature of the new phase is still controversial. We have investigated the temperature dependence of the angular dependence of the magnetoresistance in the SDW phase which shows different features for temperatures above and below T*. For T > 4K the magnetoresistance can be understood in terms of the Landau quantization of the quasiparticle spectrum in a magnetic field, where the imperfect nesting plays the crucial role. We propose that below T* ~ 4K the new unconventional SDW (USDW) appears modifying dramatically the quasiparticle spectrum. Unlike conventional SDW the order parameter of USDW depends on the quasiparticle momentum. The present model describes many features of the angular dependence of magnetoresistance reasonably well. Therefore, we may conclude that the subphase in (TMTSF)2PF6 below T* ~ 4K is described as SDW plus USDW.Comment: 7 pages, 9 figures, RevTeX4; misprint corrected, references updated, a few sentences adde

Sliding spin-density waves: studies of conduction noise, magnetic field dependence and Hall resistivity

We have studied the current-voltage characteristics of the (TMTSF)_2PF_6 in the spin density state (SDW), and in zero and finite external magnetic field. For the oscillating part of the nonlinear voltage response to the applied DC electric field, the fundamental frequency distribution (as a function of this field) and a nonlinear relation between the frequency and the SDW current reveal the growth of parallel conduction channels characterized by lower velocities and larger cross-sections. The number of fundamental frequencies, their amplitude and the level of low-frequency noise as well as the depinning behaviour provide a consistent indication of the sample inhomogeneities and associated local field variations, and might be well understood within the framework of the phase slippage model. The increase of the threshold electric field with the applied magnetic filed can be explained by the Bjeli-Maki theory, if the imperfect nesting is taken into account. Finally, the electric-field dependence of the Hall resistivity is consistent with the sliding mechanism of the SDW conduction

Unconventional charge density wave in the organic conductor alpha-(BEDT-TTF)_2KHg(SCN)_4

The low temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4 salt is known for its surprising angular dependent magnetoresistance (ADMR), which has been studied intensively in the last decade. However, the nature of the LTP has not been understood until now. Here we analyse theoretically ADMR in unconventional (or nodal) charge density wave (UCDW). In magnetic field the quasiparticle spectrum in UCDW is quantized, which gives rise to spectacular ADMR. The present model accounts for many striking features of ADMR data in alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 5 pages, 6 figure

High Mobility in LaAlO_3/SrTiO_3 Heterostructures: Origin, Dimensionality, and Perspectives

We have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures (PO2<10-5 mbar) and has a three-dimensional character. However, at higher PO2 the conduction is dramatically suppressed and nonmetallic behavior appears. Experimental data strongly support an interpretation of these properties based on the creation of oxygen vacancies in the SrTiO3 substrates during the growth of the LaAlO3 layer. When grown on SrTiO3 substrates at low PO2, other oxides generate the same high mobility as LaAlO3 films. This opens interesting prospects for all-oxide electronics