38 research outputs found
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
Transport, magnetic and superconducting properties of RuSr2RCu2O8 (R= Eu, Gd) doped with Sn
Ru{1-x}Sn{x}Sr2EuCu2O8 and Ru{1-x}Sn{x}Sr2GdCu2O8 have been comprehensively
studied by microwave and dc resistivity and magnetoresistivity and by the dc
Hall measurements. The magnetic ordering temperature T_m is considerably
reduced with increasing Sn content. However, doping with Sn leads to only
slight reduction of the superconducting critical temperature T_c accompanied
with the increase of the upper critical field B_c2, indicating an increased
disorder in the system and a reduced scattering length of the conducting holes
in CuO2 layers. In spite of the increased scattering rate, the normal state
resistivity and the Hall resistivity are reduced with respect to the pure
compound, due to the increased number of itinerant holes in CuO2 layers, which
represent the main conductivity channel. Most of the electrons in RuO2 layers
are presumably localized, but the observed negative magnetoresistance and the
extraordinary Hall effect lead to the conclusion that there exists a small
number of itinerant electrons in RuO layers that exhibit colossal
magnetoresistance.Comment: 10 pages, 9 figure
Klizni valovi spinske gustoce: prouÄavanje strujnog Å”uma, ovisnosti o magnetskom polju i Hallovog otpora
We have studied the current-voltage characteristics of the (TMTSF)2PF6 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.ProuÄavali smo karakteristike napon ā struja materijala (TMTSF)2PF6 u stanju valova spinske gustoÄe (SDW). Za oscilatorni dio nelinearnog naponskog odziva na istosmjerno elektriÄno polje, osnovna frekventna raspodjela (kao funkcija tog polja) i nelinearan odnos frekvencije i SDW struje pokazuju rast usporednih kanala voÄenja oznaÄenih manjim brzinama i veÄim udarnim presjecima. Broj osnovnih frekvencija, njihove amplitude i razina niskofrekventnog Å”uma, kao i otkoÄno ponaÅ”anje sustavno pokazuju na nehomogenosti uzorka i pridružene varijacije lokalnog polja, i mogu se shvatiti u okviru modela klizne faze. Rast praga elektriÄnog polja s magnetskim poljem može se protumaÄiti BjeliÅ”-Makijevom teorijom, ako se uzme u obzir ugniježdenje. KonaÄno, nalazimo da je ovisnost Hallovog otpora o elektriÄnom polju u skladu s kliznim mehanizmom SDW voÄenja struje
Klizni valovi spinske gustoce: prouÄavanje strujnog Å”uma, ovisnosti o magnetskom polju i Hallovog otpora
We have studied the current-voltage characteristics of the (TMTSF)2PF6 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.ProuÄavali smo karakteristike napon ā struja materijala (TMTSF)2PF6 u stanju valova spinske gustoÄe (SDW). Za oscilatorni dio nelinearnog naponskog odziva na istosmjerno elektriÄno polje, osnovna frekventna raspodjela (kao funkcija tog polja) i nelinearan odnos frekvencije i SDW struje pokazuju rast usporednih kanala voÄenja oznaÄenih manjim brzinama i veÄim udarnim presjecima. Broj osnovnih frekvencija, njihove amplitude i razina niskofrekventnog Å”uma, kao i otkoÄno ponaÅ”anje sustavno pokazuju na nehomogenosti uzorka i pridružene varijacije lokalnog polja, i mogu se shvatiti u okviru modela klizne faze. Rast praga elektriÄnog polja s magnetskim poljem može se protumaÄiti BjeliÅ”-Makijevom teorijom, ako se uzme u obzir ugniježdenje. KonaÄno, nalazimo da je ovisnost Hallovog otpora o elektriÄnom polju u skladu s kliznim mehanizmom SDW voÄenja struje
The angular dependent magnetoresistance in alpha-(BEDT-TTF)_2KHg(SCN)_4
In spite of extensive experimental studies of the angular dependent
magnetoresistance (ADMR) of the low temperature phase (LTP) of
alpha-(BEDT-TTF)_2KHg(SCN)_4 about a decade ago, the nature of LTP remains
elusive. Here we present a new study of ADMR of LTP in alpha-(ET)_2 salts
assuming that LTP is unconventional charge density wave (UCDW). In the presence
of magnetic field the quasiparticle spectrum in UCDW is quantized, which gives
rise to striking ADMR in UCDW. The present model appears to account for many
existing ADMR data of alpha-(BEDT-TTF)_2KHg(SCN)_4 remarkably well.Comment: 6 pages, 4 figure
Magnetotransport of lanthanum doped RuSr2GdCu2O8 - the role of gadolinium
Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied
by dc magnetization, microwave measurements, magnetoresistivity and Hall
resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron
doping by La reduces the hole concentration in the CuO2 planes and completely
suppresses superconductivity. Microwave absorption, dc resistivity and ordinary
Hall effect data indicate that the carrier concentration is reduced and a
semiconductor-like temperature dependence is observed. Two magnetic ordering
transitions are observed. The ruthenium sublattice orders antiferromagnetically
at 155 K for low applied magnetic field and the gadolinium sublattice
antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a
complicated temperature dependence due to the combination of the two magnetic
orderings and spin fluctuations. It is shown that the ruthenium magnetism
influences the conductivity in the RuO2 layers while the gadolinium magnetism
influences the conductivity in the CuO2 layers. The magnetoresistivity is
isotropic above 4 K, but it becomes anisotropic when gadolinium orders
antiferromagnetically.Comment: 7 pages, 9 figures, submitted to European Physical Journal
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
Threshold electric field in unconventional density waves
As it is well known most of charge density wave (CDW) and spin density wave
(SDW) exhibit the nonlinear transport with well defined threshold electric
field E_T. Here we study theoretically the threshold electric field of
unconventional density waves. We find that the threshold field increases
monotonically with temperature without divergent behaviour at T_c, unlike the
one in conventional CDW. The present result in the 3D weak pinning limit
appears to describe rather well the threshold electric field observed recently
in the low-temperature phase (LTP) of alpha-(BEDT-TTF)_2KHg(SCN)_4.Comment: 4 pages, 2 figure