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We present the result of a systematic study of electrical resistivity, superconductive transitions and Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals in a broad composition range x (0.1-0.5). All samples showed a high resistivity at room temperature (140-240 μΩ cm) and the superconducting transition temperatures decrease with increasing TL content, similar to binary amorphous [3] and crystalline HEA TE-TL alloys [4]. With the highest recorded transition for (TiZrNbCu)0.90Co0.10 at 1.94 K. The Hall coefficient RH is temperature independent and positive for all samples except for (TiZrNbCu)0.57Co0.43 with an interpolated critical concentration at xc=0.34, in good agreement with binary TE-TL alloys [1]. For the temperature dependence of resistivity, we discuss possible variable range hopping (VRH) like parallel conduction mode, in temperature range 30-150K, with an exponent p=1/2. We examine this in the context of VRH in granular materials [2]. References: [1] J. Ivkov and E. Babić, J. Phys.: Condens. Matter 2 (1990) 3891 [2] V. F. Gantmakher, Electrons and Disorder in Solids (OUP Oxford, 2005). [3] E. Babić et al, Solid State Commun. 39 (1981) 139 [4] K. Stolze et al, Chem. Mater. 30 (2018) 906

Despite a huge expansion of research on compositionally complex alloys, CCA (such as the entropy alloys, HEA and the corresponding glassy alloys) their comprehension is still limited, which is detrimental both for the design of CCAs and for their application. The broad compositional range in CCAs enables simple tuning of their properties by varying the contents of their constituent elements. Accordingly, the study of transition from CCA to conventional alloy, CA composed from the same constituents is important, both for understanding the formation of solid solutions in CCAs and for proper evaluation of their potential with respect to that of CAs. However, this transition has so far been studied systematically in only two types of alloys: isopleths of the Cantor alloy and glassy TiZrNbCuNi/Co alloys with variable Co, Ni or Cu content (Materials 14 (2021) 5824 and ref. therein). In both alloy systems the variation of a given property with composition depends sharply on the selected principal component and can be either monotonic (like that in the ideal solid solution) or non-monotonic. When the variation is non- monotonic, the maximum value of the selected property is usually outside of HEA composition range.

Using a He3 cryostat in a superconducting magnet with fields up to 16 T, superconductivity of (TiZrNbCu)1-xNix and (TiZrNbNi)1-xCux metallic glasses was studied over a broad concentration range from the high entropy alloys (HEA) region to the Ni- and Cu-rich alloys, respectively. We have observed that the upper critical fields of these alloys are Pauli limited and that the superconducting transition temperatures follow the behaviour of the dressed density of states at the Fermi level Nγ(EF), which is common in transition metals and their alloys [1]. In particular, we have shown that the electron-phonon coupling constant λe-p is proportional to the band density of the state at the Fermi level in our alloys, but also crystalline HEAs [2-4], and in other transition metal alloys. This addresses the problem of unusual superconductivity behaviour [4] which was attributed to the chemical complexity of HEAs but is shown to be inherent to transition metals. Although, minor complications do arise from combining metals of different transition series. [1] R. C. Dynes, C. M. Varma, J. Phys. F Met. Phys. 6 (7) (1976) L215-L219 [2] P. Koželj et al, Phys. Rev. Lett. 113 (10) (2014) 107001 [3] S. Vrtnik et al, J. Alloy. Compd. 695 (2017) 3530– 3540 [4] F. von Rohr et al, Proc. Natl. Acad. Sci. 113 (46) (2016) E7144–E7150

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.

We present the results of ongoing comprehensive study of the electronic properties of (TiZrNbCu)1- xNix metallic glasses performed in a broad composition range x encompassing both, the high entropy (HE) range, x ≤ 0.25, and conventional Ni- base alloy concentration range, x ≥ 0.35. The electronic structure (ES) studied by photoemission spectroscopy and low temperature specific heat (LTSH) [1] reveal the split-band structure of the density of states (DoS) inside the valence band with the d- electron of Ti, Zr, Nb and also Ni present in DoS at the Fermi level N(EF), whereas LTSH and present magnetoresistivity results show that variation of N(EF) with x changes in Ni-base regime. The variation of the superconducting transition temperatures, TC ≤ 1.6 K with x closely follows that of N(EF) as is usual in disordered transition metal alloys [2]. The electrical resistivities of all alloys are high (> 150 µΩ cm) and accordingly decrease with increasing temperature over most of the explored temperature range, and their temperature dependence seems dominated by the weak localization effects over a broad temperature range (10 – 300 K). The preliminary study of the Hall effect shows that the Hall coefficient RH > 0 and in the HE concentration range change little with x. The results are compared with these for corresponding binary metallic glasses. [1] I. A. Figueroa, et al., J. Alloys Compd. 745, 455 (2018) [2] E. Tafra, et al., J. Phys.: Condens. Matter 20, 425215 (2008)

Familija manganita kemijske formule La(1-x)Ca(x)MnO3 ima vrlo bogat fazni dijagram u kojem se glavna linija razgraničenja nalazi na koncentraciji x=0.5. Većina istraživanja na ovim sistemima bila je koncentrirana na tzv. poddopirane manganite (x0.5 (predopirani manganiti), je puno manje proučavan. Poznato je da u tom području dopiranja dolazi do formiranja kompleksnih (kolektivnih) osnovnih stanja za čije podrijetlo još uvijek ne postoji koncenzus u znanstvenoj literaturi [2], što je vjerojatno posljedica činjenice da su pojedine vrste interakcija - nabojne, spinske, orbitalne, fononske - usporedive po intenzitetu. Jedan od načina kojim možemo dobiti bolju uvid u karakter osnovnog stanja je proučavanje nelinearne električne vodljivosti, metode u kojoj se pobuđuju kolektivni modovi (fazoni). Npr. poznati su teorijski rezultati [3] koji predviđaju divergenciju, odnosno konačan porast graničnog električnog polja u CDW odnosno SDW stanju, kako se temperatura približava temperaturi prijelaza. Za mjerenje nelinearne električne vodljivosti koristimo nedavno razvijeni unaprijeđeni postav za mjerenje nelinearne električne vodljivosti [4] koji omogućuje mjerenje s puno većom osjetljivošću te na uzorcima puno većih otpora od ranijih mjerenja. U ovom radu ćemo prezentirati mjerenja nelinearne električne vodljivosti na tankim filmovima manganita u području koncentracija 0.5 ≤ x ≤ 0.75, pri električnim poljima do otprilike 50 V/cm. Dobiveni rezultati pokazuju da je nelinearnost prisutna u području koncentracija x ≤ 0.58 u temperaturnom području ispod oko 290K. Za ostale koncentracije nije zapažena ovisnost vodljivosti o primijenjenom električnom polju do na 0.2% što ukazuje na to da u njima ili nema nelinearne vodljivosti ili se pojavljuje pri većim električnim poljima. Također, opaženo je da granično polje ET, koje je reda veličine 10V/cm, na pojedinim temperaturama ne pokazuje ovisnost o magnetskom polju (B ≤ 5T), premda je poznato da se otpor znatno mijenja s magnetskim poljem. Navedene rezultate ćemo usporediti s postojećim teorijskim modelima. [1] A. P. Ramirez, Journal of Physics: Condensed Matter 9, 39 (1997) 8171 [2] S. Mori, C. H. Chen, S. W. Cheong, Nature, 392 (1998) 473-476 [3] K. Maki, A. Virosztek, Phys. Rev. B, 42 (1990) 655 [4] B. Mihaljević, M. Basletić, T. Ivek, B. Hamzić, D. Altus, S. Tomić, 10. znanstveni sastanak Hrvatskog fizikalnog društva, Baška, Hrvatska (2017)

Heuslerove slitine na bazi Co privukle su veliki interes kao kandidati za primjenu u spintronici. Neki od ovih materijala karakteriziraju se kao polu-metalni (half-metal) feromagneti s visokom Curievom temperaturom i polarizacijom spina struje [1]. Jedan od takvih je Co_2TiSn [2, 3]. Za ovaj materijal teorijska istraživanja predvidjela su postojanje topološkog semimetalnog stanja s Weylovim čvorovima koji se javljaju za određene smjerove magnetizacije, što bi trebalo rezultirati velikim magnetootporom i anomalnim Hallovim efektom [4] te da je glavni doprinos intrinsičnom anomalnom Hallovom efektu rezultat pojave Berryeve zakrivljenosti [5]. U ovom radu predstavljamo sistematsko istraživanje otpornosti, magnetootpora i Hallovog efekta Co_2TiSn i Co_2Ti_0.6V_0.4Sn tankih filmova na više temperatura i za magnetska polja do 16 T primijenjena duž odabranih kristalografskih smjerova. Oba sustava pokazuju veliki anomalni Hallov efekt, ali ipak manji nego što je za neke standardne feromagnetske slitine. Izmjerena anomalna Hallova vodljivost za Co_2TiSn manja je od drugih rezultata [5], ali još uvijek u skladu sa teorijski izračunatom vrijednošću [5]. Za Co_2Ti_0.6V_0.4Sn anomalna Hallova vodljivost je znatno niža. Za oba sustava dominantni doprinos anomalnom Hallovom efektu dolazi od intrinsičnog side-jump efekta, što je u skladu sa teorijskim predviđanjima [6] za sustave s visokom otpornošću. Magnetoopor za oba sustava je malog iznosa (

α-(BEDT-TTF)2I3 is a prominent example of charge ordering among organic conductors. In this work, we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly interpocket scattering which equalizes mobilities of the two types of charge carriers. At low temperatures, within the insulating charge-ordered phase two channels of conduction can be discerned: a temperature-dependent activation, which follows the mean-field behavior, and a nearest-neighbor-hopping contribution. Together with negative magnetoresistance, the latter relies on the presence of disorder. The charge-ordered phase also features a prominent dielectric peak which bears a similarity to relaxor ferroelectrics. Its dispersion is determined by free-electron screening and pushed by disorder well below the transition temperature. The source of this disorder can be found in the anion layers which randomly perturb BEDT-TTF molecules through hydrogen bonds.

U radu je prikazan unaprijeđeni postav za mjerenje nelinearne električne vodljivosti pomoću diferencijalnog buffera domaće izrade, pulsnom metodom. Prikazani su preliminarni rezultati na nekoliko materijala (poglavito tanki filmovi LCMO ; DCNQI) gdje se vidi da je osjetljivost postava manja od 0.5% što je značajno unapređenje u odnosu na prijašnje eksperimentalne postave.

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.

Ferromagnetic Heusler alloys are characterized by high Curie temperatures and a great variety of electronic and magnetic properties. The Co-based Heusler alloys are of a particular interest, as half-metallic ferromagnets with a high spin polarization at Fermi energy they have a great potential for spintronic applications (for example, as magnetic electrodes in magnetic tunnel junctions). Recently, a theoretical study [1] has predicted a topological semimetal state in Co2TiSn with Weyl nodes appearing for certain magnetization directions, which could result in a large magnetoresistance and anomalous Hall effect. We have performed a detailed study of the resistivity, magnetoresistance, and Hall effect of Co2TiSn and Co2Ti0.6V0.4Sn Heusler alloys at several temperatures and with the magnetic field applied along selected crystallographic directions. Our data show that the anomalous Hall effect conductivity is large, in the range of the AHE conductivity found in Mn3Ge [2], while the magnetoresistance is small and quasi-isotropic without any unusual dependences on the field orientation with respect to the crystal axes. Although the results do not show a specific and clear signature of a Weyl character, they recognize the potential of the Co2TixV1-xSn system for future spintronic device applications. [1] G. Chang et al, Sci. Rep. 6 (2016) 38839. [2] A. K. Nayak et al, Sci. Adv. 2 (2016) e1501870.

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).

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.

Većina konvencionalnih slitina sastoji se od jednog, ili u rijetkim slučajevima dva, osnovna metala kojima se dodaju male količine drugih metala i/ili nemetala kako bi se poboljšala njihova svojstva. U posjednih nekoliko godina veliku pažnju pak privlači novi tip slitina, tzv. slitine visoke entropije (eng. High-entropy alloys - HEA). Ove slitine su građene od velikog broja (=>5) elemenata u približno ekvimolarnom omjeru [1, 2]. Ovakva građa otvara potencijal za istraživanje velikog broja novih slitina raznih struktura i svojstava [3]. Nedavno su objavljeni rezultati [4] opsežnih istraživanja četiri (TiZrNbCu)_1-xNi_x(x

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.

The Mott insulator $\kappa$-(BEDT-TTF)$_2$\-Ag$_2$(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 quasi-degenerate 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 $\kappa$-(BEDT-TTF)$_2$\-Cu$_2$(CN)$_3$.

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)