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We report on linear magnetoelectric effect observed by the static electric polarization measurements in external magnetic field up to 12 T on topological multidomain antiferromagnet Cu$_3$TeO$_6$. The polarization is non-zero only below the N\'{e}el temperature and for $\mathbf{E}\perp \mathbf{H}$. The magnetization data show spin reorientation taking place already in $H, Comment: 6 pages, 4 figures

The family of antiferromagnets (AFM) with multidomain structure is of particular importance in the fundamental research of multiferroics because they represent an opportunity to examine the dynamics of domains and domain walls, their motion, creation, or destruction, as well to examine the role of magnetoelectric (ME) effect. Here the ME effect is investigated in copper tellurium oxide, Cu3TeO6, with cubic unit cell and 3D AFM order in which copper ions form hexagons with shared vertices. Below TN = 61 K multiple domains develop with easy axes pointing along diagonals of the unit cell, resulting in 8 (4x2) AFM domains.We present ME properties of Cu3TeO6by the results of static electric polarization measurements in an external magnetic field up to 16 T for a few different orientations of electric polarization P and magnetic field H. Below TN P-E hysteresis opens (Fig. 2) by the magnetic field applied in perpendicular direction to the electric field, with saturation polarization increasing linearly with the magnetic field and behaving BCS- like with temperature. Since the symmetry analysis shows that the observed ME effect is not in agreement with the symmetry-determined ME tensor we consider two possible explanations: i) the actual symmetry of the ordered state is different than expected from neutron diffraction experiment, ii) spin reorientation within domains takes place. We analyze both and investigate possibility of ferrotoroidal order. Analysis of magnetic symmetry by studying magnetic anisotropy will be shown.

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

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

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)

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 (

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

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).

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.

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.

Izvršena su mjerenja otpornosti i dielektrična spektroskopija pri niskim temperaturama na uzorcima kvazi-dvodimenzionalnih organskih vodiča koji su bazirani na organskoj molekuli bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF). Istraživanje spoja α -ET_2I_3 je provedeno kako bi se bolje razumjela feroelektrična priroda metalno-izolatorskog prijelaza na T_MI = 135K te pojava relaksacijskih modova u smjeru okomitom na vodljivu ravninu ispod tog prijelaza. Transportna mjerenja su pokazala promjenu vrijednosti energijskog procjepa na niskim temperaturama koja dosad nije razmatrana u literaturi. Također je izvedeno istraživanje svojstava nedavno sintetiziranog spoja κ-ET_2Ag_2(CN)_3 da bismo bolje razumjeli ponašanje srodnog κ -ET_2Cu_2(CN)_3 koji je istaknuti kandidat za pronalaženje osnovnog stanja kvantne spinske tekućine. U ovom radu je prezentirana prva dielektrična karakterizacija uzorka κ-ET_2Ag_2(CN)_3 koja je zabilježila pojavu većeg broja relaksacijskih modova. Resistance measurements and dielectric spectroscopy at low temperatures were performed on samples of quasi-two-dimensional organic conductors based on the organic molecule bis(ethylenedithio)-tetrathiafulvalene (BEDT-TTF). An investigation on the α – ET_2I_3 compound was conducted in order to better understand the ferroelectric nature of the metal-insulator transition at T_MI = 135K, as well as the appearance of out-of-plane relaxation modes below this transition temperature. Transport measurements have shown a change in energy gap values at low temperatures, which was not previously discussed in the literature. The properties of the newly synthesised compound κ – ET_2Ag_2(CN)_3 were also explored in order to better comprehend the behaviour of the related κ – ET_2Cu_2(CN)_3 which is a prominent candidate for finding a quantum spin liquid ground state. In this work the first dielectric characterization of a sample of κ – ET_2Ag_2(CN)_3 is presented which recorded an occurrence of multiple relaxation modes.

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).

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).