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La1-xCaxMnO3 belongs to the family of manganites, with generalized chemical formula R1-xAxMnO3, where R element is a rare earth element, and A is alkaline, alkaline earth or Pb. These compounds became very interesting in 1994, due to the discovery of colossal magnetoresistance (CMR). CMR was originally found for 0.2 < x < 0.5, and therefore that part of the phase diagram was mostly investigated. Here we report our results obtained in the overdoped part of the diagram 0.5 ≤ x ≤ 0.75 on La1-xCaxMnO3 thin films grown on MgO substrate. We have found CMR and metastable behavior deep in the overdoped part, which we attributed the existence of FM clusters in the AFM / CO insulator state.

We investigate the dc resistivity and Hall effect of the quasi-two-dimensional organic materials κ–(ET)2X, where X=Ag2(CN)3 and B(CN)4 and compare them with the results for X=Cu2(CN)3. All three compounds are considered to be quantum-spin-disordered Mott insulators. Despite high similarities in chemical composition and crystal structure, large differences in the dc resistivity and Hall coefficient are found. While around room temperature the dc transport properties are dominantly determined by the strength of the electron correlations, upon reducing the temperature, dc transport happens by hopping due to inherent disorder. The most disordered compound with X=Cu2(CN)3 turns out to have the lowest dc resistivity and the highest charge carrier density, i.e., in the phase diagram it is located closest to the metal-insulator transition. The least disordered compound with X=B(CN)4 shows the highest resistivity and the lowest carrier density, i.e., lies farthest from the metal-insulator transition. We explain such counterintuitive behavior within the theory of Mott-Anderson localization as a consequence of disorder-induced localized states within the correlation gap.

The quest for exotic electronic orderings is driven by our ability to produce said states as cleanly as possible, in a tunable manner and preferably cheap. Organic conductors with reduced dimensionality offer all of these desirable properties as their rich phase diagrams are created by the competition between the tendency of electrons to delocalize and the pronounced interactions between charge, spin and lattice. We discuss here the organic charge-transfer salt α-(BEDT-TTF)2I3, a highly anisotropic material whose phase diagram features a number of intriguing quantum effects, most notably at ambient pressure it undergoes a metal-to-insulator transition into a charge-ordered (CO) state with CO-induced ferroelectricity. The electronic behavior in the CO phase and its exact microscopic underpinnings are however still under heated discussion. As an intriguing link to Mott-like spin-liquid systems from the same family of salts, the dielectric response and structural considerations point toward the important role of disorder. Here we show a detailed systematic study of the titular compound at ambient pressure above and below the CO phase transition, in particular of its dielectric properties both in-plane and out-of-plane, resistivity, Hall effect and magnetoresistance. In the high-temperature semimetallic phase, dominant inter-pocket scattering equalizes mobilities of the electrons and holes creating an almost temperature-independent conductivity as well as a low Hall effect. At low temperatures, within the insulating charge-ordered phase dc transport, magnetoresistance, as well as dielectric response show fingerprints of disorder whose origin is found in the anion layers tightly hydrogen-bonded to the conducting BEDT-TTF molecules.

Manganites R1−xAxMnO3, R and A being rare-earth and alkaline-earth ions respectively, show a wide variety of intriguing phenomena such as colossal magnetoresistance (CMR), multiferroicity, charge ordering, electronic phase separation, etc. Strong coupling of the spin, charge, orbital, and lattice degrees of freedom and the intense competition between the ferromagnetic (FM) metallic and antiferromagnetic (AFM) insulating phases cause very complicated phase diagrams. The exact phase depends on chemical substitution, level of doping, magnetic field, pressure, grain size, etc. La1−xCaxMnO3 is the most investigated member of the manganites family. Two phases dominate the well known phase diagram of La1−xCaxMnO3: a ferromagnetic metallic ground state for doping 0.2 < x < 0.5 and an antiferromagnetic (AFM) insulating charge order (CO) ground state for 0.5 < x < 0.9. However, the exact boundary between FM and CO/AFM phases is somehow sample dependent and it is believed that close to x = 0.5 the two dissimilar phases can coexist. In this work we show characterization of ceramic polycrystalline samples of La1-xCaxMnO3 with x = 0.5 using dc conductivity, ac susceptibility, magnetotransport and dielectric spectroscopy at low temperatures. Most importantly we find two prominent phase transitions, a high-temperature one corresponding to CO and a low-temperature transition with a FM fingerprint. Between these two features a metastable region is present both in charge as well as the spin sector. We discuss these findings in the context of phase separation and compare them with other La/Ca or Pr/Ca substitutions x.

The family of compounds based on bis-(ethylenedithio)tetrathiafulvalene (BEDT-TTF) molecule shows intriguing phenomena such as unconventional superconductivity, charge ordering, Mott transition, antiferromagnetism, incoherent metallic state etc. κ-(BEDT-TTF)2Cu2(CN)3 member is especially interesting because it is considered as one of the first realizations of a quantum spin liquid. It has a layered crystal structure consisting of conducting BEDT-TTF layers sandwiched between insulating Cu2(CN)3 layers and according to the phase diagram is in a Mott insulating state. However, approaching the spin liquid ground state various anomalies were observed showing that κ-(BEDT-TTF)2Cu2(CN)3 is not an ordinary Mott insulator. Here we present DC resistivity, Hall effect and magnetoresistance measurements for 10 K < T < 300 K and in magnetic fields up to 5 T on high quality κ-(BEDT-TTF)2Cu2(CN)3 single crystals. Our results clearly show that at lower temperatures (T < 130 K) charge transport takes place via variable range hopping, a mechanism typical for disordered systems. The origin of disorder, in nominally clean single crystals, can be found in insulating Cu2(CN)3 layers since some CN groups lie in centers of inversion and are therefore crystallographically disordered. The CN disorder affects conducting layers via hydrogen bonds between CN groups and ethylene groups of the BEDT-TTF molecules.

La1-xCaxMnO3 pripada obitelji manganovih oksida, preciznije manganita, s općenitom kemijskom formulom R1-xAxMnO3, gdje je R element rijetke zemlje, a A alkalni, zemnoalkalni metal ili Pb. Ovi spojevi se istražuju još od 1950., ali postaju posebno interesantni 1994., zbog otkrića kolosalnog magnetootpora (CMR). Osim toga, manganiti imaju vrlo bogate fazne dijagrame, s mnogim zanimljivim fenomenima. Istraživani spoj La1-xCaxMnO3 ima tri najvažnija (i najveća) dijela faznog dijagrama: paramagnetsko (PM) izolatorsko stanje na visokom temperaturama, feromagnetsko (FM) metalno stanjeza 0.2 < x < 0.5 (koje je povezano s CMR) i antiferomagnetsko (AFM) izolatorsko stanje, popraćeno uređenjem naboja (CO) za 0.5 < x < 0.87. Danas se vjeruje da u nekim dijelovima faznog dijagrama može doći do koegzistencije faza, posebno u blizini granice faza. Najzanimljivija je granica između FM metalnog stanja i AFM/CO izolatorskog stanja na x = 0.5. Nedavno smo objavili naše rezultate istraživanja magnetotransportnih svojstva tankih filmova manganita La1-xCaxMnO3, za x = 0.52, 0.58 i 0.75. Za koncentracije x = 0.52 i 0.58, opazili smo pojavu CMR (karakterističnu za x < 0.5), a koju smo pripisali postojanju FM klastera u AFM/CO izolatorskom stanju. Efekt je najizraženiji za x = 0.52, gdje dolazi do prijelaza u metalno stanje pod utjecajem magnetskog polja. Inače, ovisnost otpornosti o temperaturi bez primjene magnetskog polja, za sve tri koncentracije i na nižim temperaturama (T < TCO), slijedi režim trodimenzionalnog (3D) Mottovog preskoka promjenjivog dosega (VRH). Objavljeni rezultati su prošireni mjerenjima do nižih temperatura i jačih magnetskih polja, a također smo obuhvatili još različitih koncentracija, pri čemu su opažene i neke nove pojave: velike razlike između otpornih krivulja mjerenih u magnetskom polju, u slučajevima kad je uzorak hlađen u magnetskom polju (FC) i bez magnetskog polja (ZFC). Osim toga otporne krivulje pokazuju značajne efekte ovisne o povijesti mjerenja i neobične vremenske relaksacije.

Molecular solids are characterized by strong electronic correlations which may give rise to charge locali-zation. Due to an odd number of electrons per unit cell they are also considered as Mott insulators. At ambient pressure and low temperatures the antiferromagnetic ordering sets in but if the frustration due to triangular arrangement of molecular pairs is high enough, magnetic ordering is suppressed and the quantum spin liquid (QSL) ground state is expected. Three organic Mott systems with different degrees of cor-relations [1] exhibit QSL ground state: (i) kappa-(BEDT-TTF)2Cu2(CN)3, (ii) kappa-(BEDT-TTF)2 Ag2(CN)3 and (iii) beta’-EtMe3[Pd((dmit)2]2 [2]. In all of them the electrodynamic response is anomalous [3-5] and its full understanding is missing primarily due to a difficulty to reconcile the idea of exotic spin-charge coupling [10] with the experimentally evidenced absence of any considerable charge imbalance [5, 11]. In this presen¬tation we show how the dielectric, transport, optical and structural measure¬ments combined with the state-of-the-art DFT calculations provide evidence for the ground state involving several quasi-degenerate electronic states. These states reflect a random domain structure due to inherent disorder in the non-conducting anions/cations in the nominally clean single crystals of all three systems. This disorder is coupled to triangular charge and spin arrangements which give rise to the relaxor dielectric response and hopping dc transport and symmetry reduction, and thus may favour the formation of QSL. Single crystals provided by: J. Schlueter, K. Miyagawa, K. Kanoda, T. Hiramatsu, Y. Yoshida, G. Saito and R. Kato. [1] A. Pustogow et al., submitted to Science Advances (2017). [2] Y. Shimizu et al., Phys.Rev.Lett. 91, 107001 (2003) ; Phys.Rev.Lett. 117, 107203 (2016) ; T.Itou et al., Phys.Rev.B 77, 104413 (2008). [3] S. Tomic and M. Dressel, Rep. Prog. Phys. 78, 096501 (2015). [4] M.Abdel-Jawad et al., Phys.Rev.B 82, 125119 (2010) ; Phys.Rev.B 88, 075139 (2013). [5] M. Pinteric, M. Culo, O. Milat, M. Basletic, B. Korin-Hamzic, E. Tafra, A. Hamzic, T. Ivek, T. Peterseim, K. Miyagawa, K. Kanoda, J. A. Schlueter, M. Dressel, and S. Tomic, Phys.Rev.B 90, 195139 (2014). ; M. Pinteric, T. Ivek, M. Culo, O. Milat, M .Basletic, B. Korin-Hamzic, E. Tafra, A. Hamzic, M. Dressel, and S. Tomic, Physica B 460, 202 (2015) ; M. Culo, E. Tafra, M. Basletic, S.Tomic, A. Hamzic, B. Korin-Hamzic, M. Dressel, J.A. Schlueter, Physica B 460, 208 (2015). ; M. Dressel, P. Lazic, A. Pustogow, E. Zhukova, B. Gorshunov, J. A. Schlueter, O. Milat, B.Gumhalter, and S. Tomic, Phys. Rev. B 93, 081201(R) (2016) ; M. Pinteric, P. Lazic, A. Pustogow, T. Ivek, M. Kuvezdic, O. Milat, B.Gumhalter, M. Basletic, M. Culo, B. Korin-Hamzic, A. Loehle, R. Huebner, M. Sanz Alonso, T. Hiramatsu, Y.Yoshida, G.Saito, M.Dressel, and S.Tomic, Phys. Rev. B 94, 161105(R) (2016) ; M. Pinteric, P. Lazic, A. Pustogow, T. Ivek, D. Rivas Gongora, O. Milat, B.Gumhalter, M. Culo, B. Korin-Hamzic, R. Kato, M. Dressel, and S.Tomic, to be submitted (2017). [10] C. Hotta, Phys.Rev.B 82, 241104 (2010) ; S. Ishihara, J.Phys.Soc.Jpn 79, 011010 (2010). [11] K. Sedlmeier et al., Phys. Rev. B 86, 245103 (2012).

alpha-(BEDT-TTF)2I3, gdje BEDT-TTF označava organsku molekulu bis-(ethylenedithio)- tetrathiafulvalene, pokazuje mnoštvo intrigantnih fenomena kao što su metal-izolatorski prijelaz, uređenje naboja, elektronska feroelektričnost, nekonvencionalna supravodljivost, Diracovi fermioni itd. Prema faznom dijagramu alpha-(BEDT-TTF)2I3 pri atmosferskom tlaku na 135 K prelazi iz polumetalnog u stanje uređenja naboja (CO) što je popraćeno otvaranjem energijskog procjepa u nabojnom i spinskom sektoru. Mnoge fizikalne veličine doživljavaju skok na 135 K, a mjerenja specifične topline pokazuju divergenciju toplinskog kapaciteta te postojanje latentne topline što je snažna indikacija faznog prijelaza prvog reda. S druge strane, intenzitet drugog harmonika u optičkim mjerenjima i energijski procjep određen iz magnetske susceptibilnosti ispod 135 K slijede slično temperaturno ponašanje kao i parametar uređenja u BCS teoriji što bi pak upućivalo na fazni prijelaz drugog reda. Ovakvi kontradiktorni zaključci ukazuju na potrebu dodatnih eksperimentalnih i teorijskih rezultata ne bi li se riješila očito vrlo kompleksna priroda CO faznog prijelaza u alpha-(BEDT-TTF)2I3. Ovdje ćemo prikazati naše rezultate mjerenja dc otpornosti na monokristalima alpha-(BEDT-TTF)2I3 visoke kvalitete duž sva tri kristalografska smjera u temperaturnom području 30-300 K koji pokazuju odlike i faznog prijelaza prvog i faznog prijelaza drugog reda. Naime, otpornost duž sva tri smjera na 135 K pokazuje skok od oko tri reda veličine, a daljnjim snižavanjem temperature se jasno može prepoznati doprinos aktivacijskog ponašanja s odgovarajućim energijskim procjepom koji slijedi sličnu temperaturnu ovisnost kao i parametar uređenja u BCS teoriji. Dobivene rezultate ćemo diskutirati u odnosu na druge eksperimentalne činjenice i u svjetlu najnovijih DFT računa.

La1-xCaxMnO3 belongs to the family of manganese oxides, known as manganites, with a general chemical formula R1-xAxMnO3, where R is a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. These compounds have been investigated since 1950., but a huge interest started in 1994. with the discovery of the famous colossal magnetoresistance (CMR). Besides CMR, manganites are interesting because of their very rich phase diagrams which show plenty of intriguing phenomena such as metal- insulator transition, charge ordering, multiferroicity, magnetocaloric effect, colossal thermoelectric power, phase coexistence, etc. In the case of the investigated compound La1-xCaxMnO3 the phase diagram consists of the three large parts: a paramagnetic (PM) insulating phase at high temperatures for all x, a ferromagnetic (FM) metallic ground state for 0.2 < x < 0.5 and an antiferromagnetic (AFM) charge order (CO) insulating ground state for 0.5 < x < 0.87. CMR effect is closely related to the FM phase and has maximum value at the Curie temperature. At present, it is believed that across the phase diagram there are areas where two phases can coexist, particularly close to the boundary between the two phases. Especially interesting is the coexistence between the FM metallic and CO/AFM insulating phase which is believed to be the key for understanding the CMR effect. Our recent work on magnetotransport properties of manganites thin films La1-xCaxMnO3 for x > 0.5 has shown the existence of CMR, FM and metal- insulator transition, properties characteristic for x < 0.5, which has been ascribed to the presence of FM clusters in the CO/AFM background. Here we present a continuation of this research to lower temperatures and higher magnetic fields which reveals a huge difference between field- and zero-field cooled resistivity curve and unusual time relaxation of the resistivity after application of an external magnetic field. We discuss this features in terms of the FM/AFM phase separation scenario.

The Mott insulator κ-(BEDT-TTF)2Ag2(CN)3 forms a highly-frustrated triangular lattice of S = 1/2 dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response, and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasidegenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound κ-(BEDT-TTF)2Cu2(CN)3.

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1-xAxMnO3, where R represents a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. Replacement of trivalent R and divalent A introduces a mixed valence state Mn3+/Mn4+ and depending on the concentration x causes a presence of various phases in the phase diagrams of R1-xAxMnO3. A huge interest for this family of compounds started in 1994. when Jin et al. found a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). CMR is present in the part of the phase diagram with ferromagnetic metallic ground state which for the investigated system La1-xCaxMnO3 appears for concentrations 0.2 < x < 0.5. Here we focused on the poorly explored part of the phase diagram x > 0.5 with a paramagnetic insulating phase at high, charge order phase at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport and magnetization measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on thin film manganites for different concentrations 0.52 ≤ x ≤ 0.75. Our results show traces of CMR and ferromagnetism and a strong coupling between magnetic and transport properties which can be interpreted in terms of spin dependent variable range hopping mechanism and a coexistence of ferromagnetic and antiferromagnetic phase.

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1- xAxMnO3, where R represents a rare earth element or Bi and A an alkali or alkaline earth metal or Pb. Replacement of trivalent R and divalent A introduces a mixed valence state Mn3+/Mn4+ and depending on the concentration x causes a presence of various phases in the phase diagrams of R1-xAxMnO3. A huge interest for this family of compounds started in 1994. when Jin et al. found a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). CMR is present in the part of the phase diagram with ferromagnetic metallic ground state which for the investigated system La1-xCaxMnO3 appears for concentrations 0.2 < x < 0.5. Here we focused on the poorly explored part of the phase diagram x > 0.5 [3] with a paramagnetic insulating phase at high, charge order phase at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport and magnetization measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on thin film manganites for different concentrations 0.5 < x < 0.8. Our results show traces of CMR and ferromagnetism and a strong coupling between magnetic and transport properties which can be interpreted in terms of spin dependent variable range hopping mechanism and a coexistence of ferromagnetic and antiferromagnetic phase.

alpha-(BEDT-TTF)2I3 pripada familiji spojeva temeljenoj na organskoj molekuli bis-(ethylene-dithio)-tetrathiafulvalene (BEDT-TTF) koja se u novije vrijeme intenzivno istražuje zbog nekonvencionalne supravodljivosti, uređenja naboja, elektronske feroelektričnosti, stanja kvantne spinske tekućine itd. Kao i ostali pripadnici ove familije, i alpha-(BEDT-TTF)2I3 ima slojevitu kristalnu strukturu koja uzrokuje kvazidvodimenzionalna elektronska svojstva. Pri atmosferskom tlaku alpha-(BEDT-TTF)2I3 na visokim temperaturama pokazuje polumetalna svojstva s malim džepovima elektrona i šupljina, a na temperaturi TCO = 136 K prelazi u stanje uređenja naboja (CO) s feroelektričnim oznakama. Primjena tlaka uzrokuje postepeno potiskivanje CO faznog prijelaza, a pri određenim uvjetima i pojavu supravodljive faze ispod 7 K. Mjerenja Hallovog efekta i magnetootpora pri tlakovima većim od 1.5 GPa, kada je CO faza u potpunosti potisnuta, pokazuju da se koncentracija slobodnih nosioca naboja od 300 K do 2 K smanjuje 6 redova veličine, dok njihova pokretljivost raste 6 redova veličine. Ovi rezultati pokazuju da je alpha-(BEDT-TTF)2I3 iznad 1.5 GPa poluvodič s nultim energijskim procjepom čiji se nosioci naboja ponašaju kao Diracovi fermioni što je u skladu s najnovijim proračunima vrpci. Budući da su zbog spomenutih izrazito zanimljivih fizikalnih svojstava magnetotransportna istraživanja u literaturi uglavnom provedena uz primjenu visokih tlakova, proveli smo mjerenja pri atmosferskom tlaku koja nedostaju: dc otpornost, anizotropija dc otpornosti, magnetootpor i Hallov efekt u temperaturnom intervalu 40-300 K i u magnetskim poljima do 5 T. Dobivene rezultate usporedit ćemo s rezultatima magnetotransportnih istraživanja alpha-(BEDT-TTF)2I3 pod tlakom kao i s našim rezultatima magnetotransportnih istraživanja srodnog spoja kappa-(BEDT-TTF)2Cu2(CN)3 u kojem CO faza ne postoji.

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. Dimer Mott insulator with quantum spin-liquid phase κ-(BEDT-TTF)2Cu2(CN)3 shows variable-range hopping in dc limit and dielectric response featuring relaxor-like ferroelectricity [1, 2] despite missing symmetry-breaking evidences [3]. In this presentation we report our study of the anisotropic dc and ac charge response in a novel spin-liquid candidate κ-(BEDT-TTF)2Ag2(CN)3 [4]. The obtained results indicate the presence of an anomalous dielectric response, and we discuss and compare them with κ-(BEDT-TTF)2Cu2(CN)3. The importance of anion network geometry and cation-anion coupling is emphasized. [1] M. Abdel-Jawad et al., Phys.Rev.B 82, 125119 (2010). [2] M. Pinterić et al., Phys.Rev.B 90, 195139 (2014). [3] K. Sedlmeier et al., Phys.Rev.B 86, 245103 (2012). [4] M. Pinterić et al., in preparation (2015).

(TMTTF)2ReO4 i (TMTTF)2BF4 pripadaju u skupinu takozvanih Fabreovih soli koje pri sobnoj temperaturi većinski pokazuju kvazi 1D metalnu vodljivost. Variranjem raznih parametara poput tlaka, temperature te vrste aniona, dobiven je vrlo bogat fazni dijagram Fabreovih soli u kojem su neka od mogućih stanja: metalno stanje, stanje uređenja naboja, spin-Peierlsovo stanje, supravodljivo stanje i stanje vala gustoće spina[1]. Od prije je poznato da navedena dva spoja pri sobnoj temperaturi pokazuju kvazi 1D metalnu vodljivost te da spuštanjem temperature ispod 230 K za (TMTTF)2ReO4, odnosno 84 K za (TMTTF)2BF4, oba spoja prolaze kroz metal-izolatorski fazni prijelaz u izolatorsko stanje uređenja naboja. Također, oba spoja spadaju u skupinu soli s nesimetričnim anionima pa daljnjim spuštanjem temperature ispod 157 K za (TMTTF)2ReO4, odnosno 41.5 K za (TMTTF)2BF4, dolazi do zamrzavanja orijentacije aniona i loma simetrije pa oba spoja prolaze kroz izolator-izolatorski fazni prijelaz u stanje uređenja aniona[2]. U cilju boljeg razumijevanja transportnih mehanizama, mjerili smo otpornost i Hallov koeficijent RH u ovisnosti o temperaturi. Otpornost je mjerena u smjeru najveće vodljivosti, kao i RH (magnetsko polje je okomito na smjer struje) koji je mjeren AC kompenzacijskom metodom u magnetskim poljima do 9 T te za temperature 45 K< T < 300 K. Oba spoja pri sobnoj temperaturi imaju približno jednaku vrijednost RH koja je oko 3 puta veća od teorijski predviđene vrijednosti. RH je u oba spoja pozitivan što je u skladu s činjenicom da su nosioci naboja šupljine. Fazni prijelaz u stanje uređenja naboja posebno je naglašen u (TMTTF)2ReO4 gdje smo detektirali naglu promjenu predznaka RH u uskom intervalu temperatura. Daljnjim opadanjem temperature ispod faznog prijelaza u stanje uređenja naboja, porast RH u oba spoja prati eksponencijalni porast otpornosti što odgovara ponašanju izolatora kod kojih je ovakvo ponašanje posljedica smanjenja broja nosioca naboja sa snižavanjem temperature. Dobivene rezultate ćemo usporediti sa rezultatima srodnih spojeva te interpretirati u okviru postojećih teorijskih modela. [1] M. Dressel, Naturwissenschaften 94, 527 (2007). [2] B. Köhler, E. Rose, M. Dumm, G. Untereiner, and M. Dressel, Phys. Rev. B 84, 035124 (2011)

alpha-(BEDT-TTF)2I3 is a quasi-2D organic conductor most famous for its prominent charge order within molecular planes below TCO =136 K [1]. Due to the breaking of an inversion center, the response at the charge ordering transition should have a ferroelectric character [2, 3]. Puzzlingly, at the moment it is unclear whether the ferroelectric peak appears in the dielectric properties at all [4]. Furthermore, the low-lying excitations above the ground state seem to bring forth both a phason-like as well as a soliton-like relaxation, which have so far not been reported to appear together in similar systems [5]. In order to explore these open questions, we have carefully determined the direction-dependent (in-plane and out-of-plane) dielectric response in alpha-(BEDT-TTF)2I3 together with resistance and Hall effect measurements down to lowest temperatures. The temperature dependence of the Hall coefficient absolute value follows a similar behavior as the resistivity. An intriguing feature is found at TCO where the Hall coefficient changes sign. Another interesting property is a change in the in-plane transport activation energy around 60 K. On the other hand, dielectric measurements give strongly anisotropic and complex spectra. Our results are discussed within the wider context of strongly correlated systems with charge order. [1] T. Takahashi, Y. Nogami, and Kyuya Yakushi, J. Phys. Soc. Jpn. 75, 051008 (2006). [2] T. Kakiuchi, Y. Wakabayashi, H. Sawa, T. Takahashi, and T. Nakamura, J. Phys. Soc. Jpn. 76, 113702 (2007) [3] K. Yamamoto, A. A. Kowalska, and K. Yakushi, Appl. Phys. Lett. 96, 122901 (2010). [4] T. Ivek, B. Korin-Hamzić, O. Milat, S. Tomić, C. Clauss, N. Drichko, D. Schweitzer, and M. Dressel, Phys. Rev. Lett. 104, 206406 (2010) ; P. Monceau, private communication (2014). [5] T. Ivek, B. Korin-Hamzić, O. Milat, S. Tomić, C. Clauss, N. Drichko, D. Schweitzer, and M. Dressel, Phys. Rev. B 83, 165128 (2011).

Upon cooling the highly anisotropic organic conductors (TMTTF) 2 X undergo transitions to various ordered states in the charge and spin degrees of freedom and therefore turn out to be an excellent choice for exploring the phenomena of low-dimensional physics. In order to study the transport mechanism of these quasi-one-dimensional (1D) organic salts, the temperature-dependent Hall effect of (TMTTF) 2 X (X=BF 4 , ReO 4 , AsF 6 , SbF 6 ) has been measured by an AC compensation technique with current injection along the high-conducting a-axis. At elevated temperatures the Hall coefficient R H of all investigated compounds seems to be constant, positive and somehow enhanced compared to the calculated value for one hole per unit cell. Beyond the charge order phase transition the Hall coefficient follows similar exponential laws as the resistivity data. This indicates the behavior of a semiconductor, where the change in ρ(T) mainly originates from the change in the number of carriers. Here we discuss how the Hall coefficient is influenced by anisotropy, localization effects, anion symmetry and charge- as well as anion-ordering phenomena at low temperatures. We compare the results to resistivity studies and theoretical expectations.

We have in detail characterized the anisotropic charge response of the dimer Mott insulator κ−(BEDT-TTF)2Cu2(CN)3 by dc conductivity, Hall effect, and dielectric spectroscopy. At room temperature, the Hall coefficient is positive and close to the value expected from stoichiometry; the temperature behavior follows the dc resistivity ρ(T). Within the planes the dc conductivity is well described by variable-range hopping in two dimensions; this model, however, fails for the out-of-plane direction. An unusually broad in-plane dielectric relaxation is detected below about 60 K; it slows down much faster than the dc conductivity following an Arrhenius law. At around 17 K, we can identify a pronounced dielectric anomaly concomitantly with anomalous features in the mean relaxation time and spectral broadening. The out-of-plane relaxation, on the other hand, shows a much weaker dielectric anomaly; it closely follows the temperature behavior of the respective dc resistivity. At lower temperatures, the dielectric constant becomes smaller both within and perpendicular to the planes; also, the relaxation levels off. The observed behavior bears features of relaxorlike ferroelectricity. Because heterogeneities impede its long-range development, only a weak-tunneling-like dynamics persists at low temperatures. We suggest that the random potential and domain structure gradually emerge due to the coupling to the anion network.

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition [1, 2]. Conversely, the dielectric response observed in dimer Mott insulator phases with no charge ordering [3] is rather intriguing [4, 5, 6, 7]. In this presentation we review our in-depth study (dc conductivity, Hall effect and dielectric spectroscopy) of the anisotropic charge response in an unconventional Mott insulator with spin liquid kappa-(BEDT-TTF)2Cu2(CN)3. Variable-range hopping transport within molecular planes in dc limit and an anomalously broad anisotropic dielectric relaxation in audio-frequency range demonstrate the inherent heterogeneity present in nominally pure single crystals of kappa-(BEDT-TTF)2Cu2(CN)3. The relaxation bears fingerprints of relaxor ferroelectricity: a gradual slowing down becomes dominated by tunneling at low temperatures and at the bifurcation temperature anomalous features in dielectric constant, mean relaxation time and spectral broadening are detected. We argue that the observed behavior is due to a strong charge-spin-lattice coupling reflecting the gradual emergence of random potential and domain structure originated in the anion network. [1] T.Ivek et al., Phys.Rev.B83, 165128 (2011). [2] T.Ivek et al., Phys.Rev.B86, 245125 (2012). [3] K.Sedlmeier et al., Phys.Rev.B86, 245103 (2012). [4] M.Abdel-Jawad et al., Phys.Rev.B82, 125119 (2010). [5] S.Iguchi et al., Phys.Rev.B87, 075107 (2013). [6] P.Lunkenheimer et al., Nat. Mater. 11, 755 (2012). [7] S.Tomic et al., J.Phys.: Condens.Matter 25, 436004 (2013). [8] M.Pinteric et al., to be submitted (2014).

Novel forms of the low-temperature phases in the two-dimensional molecular solids with competing interactions between charges, spins and lattice, in particular those featuring anomalous dielectric relaxation, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations as well as their coupling to applied ac and dc electric fields. The charge response is reasonably well understood by now in the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition [1, 2]. Conversely, the dielectric response observed in dimer Mott insulator phases with no charge ordering is rather intriguing [3, 4, 5]. In this presentation we review our recent results of anisotropic complex conductivity (dc – MHz) in the magnetic phase of kappa-(BEDT-TTF)2Cu[N(CN)2]Cl and in the spin-liquid phase of kappa-(BEDT-TTF)2Cu2(CN)3 [6, 7]. We discuss possible explanations for the observed dynamics and compare them with the well-known fingerprints of the charge/spin density wave response to ac electric fields. [1] T.Ivek et al., Phys.Rev.B83, 165128 (2011). [2] T.Ivek et al., Phys.Rev.B86, 245125 (2012). [3] M.Abdel-Jawad et al., Phys.Rev.B82, 125119 (2010). [4] S.Iguchi et al., Phys.Rev.B87, 075107 (2013). [5] P.Lunkenheimer et al., Nat. Mater. 11, 755 (2012). [6] S.Tomic et al., J.Phys.: Condens.Matter 25, 436004 (2013). [7] M.Pinteric et al., in preparation (2014).

Manganites La1-xCaxMnO3 belong to the family of manganese oxides with a general chemical formula R1-xAxMnO3, where R stands for a rare earth element and A for an alkali or alkaline earth metal. One of the most prominent property of manganese oxides is a huge decrease of resistivity in external magnetic field close to Curie temperature known as colossal magnetoresistance (CMR). In these systems CMR can be as large as -99%, unlike magnetoresistance of most materials which is usually small (a few percent). Except CMR, manganese oxides are interesting because of their very rich phase diagrams as a consequence of the fine interplay of charge, spin, lattice and orbital interactions. CMR is present in the part of the phase diagram of manganese oxides with ferromagnetic metallic ground state and in the case of the investigated system La1-xCaxMnO3 for concentrations 0.2 < x < 0.5. While pure LaMnO3 and CaMnO3 are antiferromagnetic insulators and contain Mn3+, Mn4+ respectively, doped manganites La1-xCaxMnO3 have a variety of different phases and contain both Mn3+ and Mn4+ (a mixed valence state). Here we focused on the poorly explored part of the phase diagram x > 0.5 with a paramagnetic insulating phase at high, charge order phase (CO) at intermediate and antiferromagnetic insulating phase at low temperatures. We performed magnetotransport measurements in the temperature interval 4.2-300 K and magnetic fields up to 5 T on a series of thin film manganites (170 nm thick) of different concentrations 0.5 < x < 0.8 obtained by metalorganic aerosol deposition technique. We will show and discuss the results of magnetotransport properties by which we investigated the influence of the concentration x on resistivity, CO phase transition temperature, magnetoresistance and anisotropy of magnetoresistance.

Oksidi mangana R1−xAxMnO3 (gdje R označava element rijetke zemlje, A alkalijske elemente) predstavljaju jedinstveno područje za istraživanje utjecaja elektronskih korelacija u materijalima koje se odnose na naboj, spin, orbitalne stupnjeve slobode i stupnjeve slobode rešetke budući da su prisutne interakcije usporedive jakosti što ima za posljedicu vrlo bogati fazni dijagram. Naša istraživanja odnose se na seriju filmova manganita La1-xCaxMnO3 različitih koncentracija (x = 0.52, x = 0.58 i x = 0.75). Dok je početni spoj LaMnO3 izolator (s osnovnim antiferomagnetskim stanjem) i sadrži Mn3+ kation, dopiranje dvovalentnim Ca2+ kationom uzrokuje pojavu Mn4+ kationa te time i stanje „mješanih valencija“ Mn3+/Mn4+, a kao posljedicu veliku promjenu u fizikalnim svojstvima. Jedno od najpoznatijih svojstava manganovih oksida je kolosalni magnetootpor (CMR) koji se pojavljuje u La1-xCaxMnO3 za x ≈ 0.3 (veliko smanjenje otpornosti u vanjskom magnetskom polju u blizini Curieve temperature). Kako su do sada istraživanja uglavnom bila ograničena na koncentracije x < 0.5, a o prirodi samog spoja i pogotovo CMR još uvijek postoji čitav niz nepoznanica fokusirali smo se na koncentracije x > 0.5 gdje fazni dijagram karakterizira paramagnetsko stanje na visokim temperaturama, te sa snižavanjem temperature fazni prijelazi u stanje uređenja naboja (CO) i antiferomagnetsko stanje (AF). Mjerenja otpornosti, ovisnosti magnetootpornosti o temperaturi, jačini i smjeru vanjskog magnetskog polja te Hallovog efekta provedena su u širokom području temperatura 30 K < T < 300 K i u magnetskim poljima do 5 tesla. Prikazati ćemo i diskutirati rezultate mjerenja pomoću kojih smo odredili temperaturu faznog prijelaza u CO stanje za sve x, promjene u otpornosti u ovisnosti o x, promjene doprinosa CMR u ovisnosti o x, vrstu nosioca naboja na visokim temperaturama te promjenu predznaka Hallovog koeficijenta ispod TCO.

Mottov izolator kappa-(BEDT-TTF)2Cu2(CN)3 se sastoji od 2D slojeva molekulskih dimera raspoređenih u trokutastu rešetku. Usprkos jakom antiferomagnetskom vezanju J ~ 250 K, NMR mjerenja su pokazala da nema dugodosežnog magnetskog uređenja do 32 mK što ukazuje da je osnovno stanje sistema spinska tekućina. Optička vodljivost slijedi zakon potencija u terahertz području prividno u skladu s teorijskim očekivanjima za doprinos spinonskih pobuđenja unutar nabojskog procjepa, a uslijed vezanja na unutarnje baždarno polje. Međutim, eksponent je puno manji od teorijskog. Neki pak drugi teorijski modeli sugeriraju postojanje kvantnih električnih dipola koji su u drugom redu povezani sa spinom i vode na realizaciju dipolarno-spinske tekućine. Ujedno je sugerirano da su fluktuacije tih dipola u ishodištu dielektričnog odgovora. Unatoč velikom broju rezultata, mehanizam i porijeklo pobuđenja naboja su još uvijek nejasni. U ovom radu ćemo opisati i diskutirati rezultate naših galvanomagnetskih mjerenja te mjerenja dc otpornosti i dielektrične spektroskopije duž sva tri kristalografska smjera koji bacaju novo svjetlo na ovaj iznimno intrigantan fizikalni sistem.

A variety of organics with reduced dimensionality and competing interactions between charges, spins and lattice display a multiplicity of ordering phenomena and complex phase diagrams. Novel forms of the low-temperature phases, in particular those featuring ferroelectricity in the two-dimensional molecular solids, have been the focus of intense activity in recent years. Open issues concern the nature of collective charge excitations in the charge- and spin-ordered phases as well as their coupling to applied dc and ac fields. And while some of their features resemble the well-established electrodynamics of conventional charge-density waves in 1D, others appear quite different and have not been encountered until now. In the charge-ordered phase with the formation of ferroelectric-like domains below the metal-to-insulator phase transition, the charge response seems to be reasonably well understood now. Conversely, rather intriguing is the dielectric response in dimer Mott insulator phases with either canted antiferromagnetism or spin liquid. The result that neither charge disproportionation nor charge fluctuations could be detected by infrared vibrational spectroscopy leaves the proposal of ferroelectricity fully open. In order to explain the prominent dielectric relaxation we rather suggest an alternative scenario invoking collective excitations associated to domain walls or charge defects formed in an either magnetically ordered or intrinsically disordered background.

Much experimental and theoretical attention has been attracted by organic systems with reduced dimensionality and strong Coulomb interactions, and deservedly so due to their novel broken-symmetry phases and corresponding excitations. Here we take a detailed look at the electrodynamics of one of the most prominent charge-ordered systems, the quasi-2D conductor α (BEDT-TTF)2I3. A semimetal at high temperatures, at 136 K this particular system transitions into an insulating, diamagnetic ground state. Within the insulating phase a long-range commensurate ordering appears in the BEDT-TTF molecular planes, the so-called "horizontal stripe" charge order. [1, 2, 3] We characterize the charge response of the low-temperature phase using dc resistivity, dielectric and optical spectroscopy in different crystallographic directions within the BEDT-TTF layer. [4, 5] Interestingly, two dielectric relaxation modes appear in the kHz-MHz range. The large mode features an anisotropic phason-like behavior, while the small mode presents a soliton-like characteristic. The observed type of excitations agrees with the most relevant physical picture of this charge order as a cooperative bond-charge density wave with ferroelectric-like features. [6] On the other hand, puzzling phenomena including negative differential resistance and voltage oscillations have been reported under application of high electric fields. [7] Our carefully designed electric-field-dependent measurements of conductivity anisotropy within the molecular plane qualitatively confirm these findings ; additionally, they reveal novel intriguing behaviors. [8]. [1] Y. Takano et al., J. Phys. Chem. Solids 62, 393 (2001). [2] Organic Conductors, Special Topics Section, J. Phys. Soc. Jpn. 75, No. 5, (2006). [3] T. Kakiuchi et al., J. Phys. Soc. Jpn. 76, 113702 (2007). [4] T. Ivek et al., Phys. Rev. Lett. 104, 206406 (2010) [5] T. Ivek et al., Phys.Rev.B 83, 165128, (2011). [6] R. T. Clay et al., J. Phys. Soc. Jpn. 71, 1816 (2002). [7] K.Tamura et al., J. Appl.Phys.107, 103716(1-5), (2010). [8] T. Ivek et al., Phys. Rev. B 86, 245125 (2012).

A variety of organics with reduced dimensionality and strong Coulomb interactions between charges and spins display novel forms of ordering phenomena. These broken-symmetry phases and their excitations have been in the focus of intense activity in recent years. In this presentation we overview results of complex conductivity (Hz – MHz) and electric-field dependent measurements in the bond charge density wave phase of alpha-(BEDT-TTF)2I3 and in the canted antiferromagnetic phase of kappa-(BEDT-TTF)2Cu[N(CN)2]Cl. Observed dynamics is discussed within theoretical models for charge excitations and compared with the well-known fingerprints of the charge and spin density wave response to ac and dc electric fields.

Hallov koeficijent RH je bitna fizikalna veličina za karakterizaciju materijala, budući da odražava strukturu vrpce, koncentraciju i predznak nosioca naboja. U jako koreliranim sustavima RH pokazuje kompleksnu ovisnost o raznim parametrima (temperatura, magnetsko polje, dimenzionalnost sustava...). U slučaju reducirane dimenzionalnosti (visoko-anizotropni sustavi), elektronske korelacije postaju još istaknutije, što se jasno pokazuje i u Hallovom efektu. Za izotropne sustave mjerenja Hallovog efekta provode se u standardnoj geometriji, dok je u slučaju visoko-anizotropnih sustava nužan uvjet za dobivanje kvalitetnih i pouzdanih rezultata korištenje adekvatne geometrije mjerenja. U tu svrhu nužno je koristiti koncept ekvivalentnog izotropnog uzorka (EIS) [1]. Ovaj smo pristup detaljno primijenili pri mjerenjima Hallovog efekta kvazi-jednodimenzionalnog organskog vodiča TTF-TCNQ, za koji u literaturi postoje samo dva rezultata iz 1977. g., dobivena u ograničenom intervalu visokih temperatura, a koji se međusobno razlikuju i u iznosu i u predznaku [2] [3]. Kristalnu strukturu spoja TTF-TCNQ karakteriziraju odvojeni lanci u koje se slažu planarne TTF i TCNQ molekule. Uslijed prijenosa naboja s molekule TTF (kation) na TCNQ (anion) oba tipa lanca pokazuju metalno ponašanje: u TTF lancu nosioci naboja su šupljine, a u TCNQ lancu elektroni. Direktna posljedica ovakve strukture je izrazita anizotropija vodljivosti: σb>σc>σa pri čemu je σb/σc ≈ 102, σb/σa ≈ 103. Dok je na visokim temperaturama vodljivost za sva tri kristalografska smjera metalnog tipa, ispod 60K dolazi do serije faznih prijelaza te materijal postepeno prelazi u stanje izolatora. Mjerenja Hallovog efekta provedena su u širokom području temperatura 30K

$\alpha$-(BEDT-TTF)$_2$I$_3$ je kvazidvodimenzionalni organski polumetal kojem na $T_\mathrm{; ; CO}; ; = 136$\, K nastupa fazni prijelaz u izolator. U izolatorskoj fazi se unutar ravnina molekula BEDT-TTF razvija dugodosežno sumjerljivo uređenje, tzv.\ horizontalne pruge uređenog naboja.[1, 2, 3] Izvršili smo detaljnu karakterizaciju odziva naboja i rešetke s obje strane faznog prijelaza koristeći tehnike istosmjernog transporta i dielektrične spektroskopije, [4, 5] te pulsnog mjerenja nelinearne vodljivosti u širokom rasponu električnih polja. U izolatorskoj se fazi razvija temperaturno ovisna anizotropija istosmjerne vodljivosti i dielektričnog odziva unutar vodljivih ravnina. Kroz opis osnovnog stanja horizontalnih pruga uređenog naboja kao 2D vala gustoća naboja i veza [6] opaženu dielektričnu relaksaciju pripisujemo zasjenjenom niskofrekventnom fazonskom odzivu te nezasjenjenoj dinamici domenskih zidova. Budući da se kod standardnih 1D valova gustoće očekuje povećana vodljivost uslijed proklizavanja, diskutiramo nelinearne efekte u vodljivoj ravnini $\alpha$-(BEDT-TTF)$_2$I$_3$. Naši rezultati ukazuju određene sličnosti s dobro poznatim jednodimenzionalnim sustavima, no i na ključne razlike koje zahtijevaju daljnji teorijski i eksperimentalni napor. [1] Y. Takano et al., J. Phys. Chem. Solids {; ; \bf 62}; ; (2001) 393 [2] Organic Conductors, Special Topics Section, J. Phys. Soc. Jpn. {; ; \bf 75}; ; , No. 5, May 2006 [3] T. Kakiuchi et al., J. Phys. Soc. Jpn. {; ; \bf 76}; ; (2007) 113702 [4] T. Ivek et al., Phys. Rev. Lett. {; ; \bf 104}; ; (2010) 206406 [5] T. Ivek et al., prihvaćeno u Phys. Rev. B (2011) arXiv:1011.4912v2 [cond-mat.str-el] [6] R. T. Clay et al., J. Phys. Soc. Jpn. {; ; \bf 71}; ; (2002) 1816

We report on the anisotropic response, the charge and lattice dynamics of normal and charge-ordered phases with horizontal stripes in single crystals of the organic conductor alpha-(BEDT-TTF)2I3 determined by dc resistivity, dielectric and optical spectroscopy. An overdamped Drude response and a small conductivity anisotropy observed in optics is consistent with a weakly temperature dependent dc conductivity and anisotropy at high temperatures. The splitting of the molecular vibrations nu27(Bu) evidences the abrupt onset of static charge order below TCO=136 K. The drop of optical conductivity measured within the ab plane of the crystal is characterized by an isotropic gap that opens of approximately 75 meV with several phonons becoming pronounced below. Conversely, the dc conductivity anisotropy rises steeply, attaining at 50 K a value 25 times larger than at high temperatures. The dielectric response within this plane reveals two broad relaxation modes of strength Deltaepsilon_LD ~= 5000 and Deltaepsilon_SD ~= 400, centered at 1 kHz < f_LD < 100 MHz and f_SD ~= 1 MHz. The anisotropy of the large-mode (LD) mean relaxation time closely follows the temperature behavior of the respective dc conductivity ratio. We argue that this phason-like excitation is best described as a long-wavelength excitation of a 2kF bond-charge density wave expected theoretically for layered quarter-filled electronic systems with horizontal stripes. Conversely, based on the theoretically expected ferroelectric-like nature of the charge-ordered phase, we associate the small-mode (SD) relaxation with the motion of domain-wall pairs, created at the interface between two types of domains, along the a and b axes. We also consider other possible theoretical interpretations and discuss their limitations., 13 pages, 16 figures, resubmitted to Phys. Rev. B

The charge response of charge-ordered state in the organic conductor alpha-(BEDT-TTF)2I3 is characterized by dc resistivity, dielectric and optical spectroscopy in different crystallographic directions within the two-dimensional conduction layer. Two dielectric modes are detected. The large mode is related to the phason-like excitation of the 2kF bond-charge density wave which forms in the ab plane. The small dielectric mode is associated with the motion of domain-wall pairs along the a- and b-axes between two types of domains which are created due to inversion symmetry breaking., resubmitted to Phys. Rev. Lett.; 4 pages, 3 figures

The only published Hall effect measurements of TTF-TCNQ date back to 1977. They were performed in the high temperature metallic region above the phase transitions, and the results vary in their sign and values. The aim of the present work has been to extend the previous investigations to lower temperatures and higher magnetic fields and to compare the new data with the known results.

I will present our comparative study of the magnetotransport properties of organic conductors (TMTCF)2X (C= Se, S ; X=PF6, ReO4, AsF6..). Their phase diagram spanning from more anisotropic C = S to C = Se series shows the increasing interchain coupling that leads to the crossing-over of the dimensionality. Our results of the conductivity anisotropy, Hall effect and magnetoresistance enabled us to gain information about the spin density wave ground state at low temperature, Fermi liquid or Luttinger liquid behavior in the normal phase at high temperatures, possible dimensional crossover and phase transitions. The results are discussed in the framework of the existing theoretical models. I will also present our results of the Hall effect measurements of quasi-one-dimensional cuprates Sr14-xCaxCu24O41 ( 0 ≤ x ≤ 11.5) that have been conducted in order to determine the number of carriers participating in dc transport, and its relationship with doping.

alpha-(BEDT-TTF)2I3 je kvazi-dvodimenzionalan organski polumetal koji na TC = 136 K ima fazni prijelaz u izolator. U izolatorskoj fazi u ravninama BEDT-TTF molekula razvija se sumjerljivo uređenje naboja Wignerovog tipa s naizmjeničnim nabojem bogatim i nabojem siromašnim prugama [1, 2]. Izvršili smo detaljnu karakterizaciju kompleksnog dielektričnog odgovora izolatorske faze tehnikom niskofrekventne dielektrične spektroskopije (1 Hz - 10 MHz). Naši rezultati otkrivaju dva široka relaksacijska moda. Veliki dielektrični mod (LD) jakosti je \Delta \varepsilon LD ~= 5000, a njegovo srednje relaksacijsko vrijeme mijenja se s temperaturom proporcionalno istosmjernoj otpornosti. S druge strane, mali dielektrični mod (SD), vidljiv tek ispod 70 K, ne mijenja se s temperaturom: jakosti je \Delta \varepsilon SD ~= 400 i centriran na 1 MHz. LD i SD relaksaciju povezujemo s gibanjem parova domenskih zidova u fazi uređenja naboja. [1] Y. Takano et al., J. Phys. Chem. Solids 62, 393 (2001). [2] T. Kakiuchi et al., J. Phys. Soc. Jpn. 76, 113702 (2007).

We present Hall effect measurements of two-leg ladder Sr14-xCaxCu24O41 (0 10). They are the first superconducting copper oxides (superconductivity occurs under pressure for x>10) without the CuO2 planes, characteristic for high-temperature superconductors. The question of charge dynamics and hole distribution between the ladders and chains is still open. Our Hall effect results show typical semiconducting behavior for x

We present Hall-effect measurements of two-leg ladder compounds Sr14− xCaxCu24O41 (0

I will present our comparative study of the magnetotransport properties of organic conductors (TMTCF)2X (C= Se, S). Their phase diagram spanning from more anisotropic C = S to C = Se series shows the increasing interchain coupling that leads to the crossing-over of the dimensionality. Our results of the conductivity anisotropy, Hall effect and magnetoresistance enabled us to gain information about the spin density wave ground state at low temperature, Fermi liquid or Luttinger liquid behavior in the normal phase at high temperatures, possible dimensional crossover and phase transitions. The results are discussed in the framework of the existing theoretical models. The evidence that the 1D Luttinger liquid features appear in the transport properties at high temperatures in C=S series will be addressed. I will also present our results of the Hall effect measurements of quasi-one-dimensional cuprates Sr14-xCaxCu24O41 ( 0 ≤ x ≤ 11.5) that have been conducted in order to determine the number of carriers participating in dc transport, and its relationship with doping. Namely, a fair number of investigations were dedicated to the distribution of holes in the parent system at room temperature with contradictory results ; the reason for that has not been clarified.