Nuclear Magnetic Resonance in High Magnetic Field: Application to Condensed Matter Physics

In this review, we describe the potentialities offered by the nuclear magnetic resonance (NMR) technique to explore at a microscopic level new quantum states of condensed matter induced by high magnetic fields. We focus on experiments realised in resistive (up to 34~T) or hybrid (up to 45~T) magnets, which open a large access to these quantum phase transitions. After an introduction on NMR observable, we consider several topics: quantum spin systems (spin-Peierls transition, spin ladders, spin nematic phases, magnetisation plateaus and Bose-Einstein condensation of triplet excitations), the field-induced charge density wave (CDW) in high $T_c$~superconductors, and exotic superconductivity including the Fulde-Ferrel-Larkin-Ovchinnikov superconducting state and the field-induced superconductivity due to the Jaccarino-Peter mechanism.Comment: 19 pages, 6 figure

Dynamics of Bound Magnon Pairs in the Quasi-One-Dimensional Frustrated Magnet LiCuVO_4

We report on the dynamics of the spin-1/2 quasi-one-dimensional frustrated magnet LiCuVO$\mathrm{_4}$ measured by nuclear spin relaxation in high magnetic fields 10--34 T, in which the ground state has spin-density-wave order. The spin fluctuations in the paramagnetic phase exhibit striking anisotropy with respect to the magnetic field. The transverse excitation spectrum probed by $^{51}$V nuclei has an excitation gap, which increases with field. On the other hand, the gapless longitudinal fluctuations sensed by $^7$Li nuclei grow with lowering temperature, but tend to be suppressed with increasing field. Such anisotropic spin dynamics and its field dependence agree with the theoretical predictions and are ascribed to the formation of bound magnon pairs, a remarkable consequence of the frustration between ferromagnetic nearest neighbor and antiferromagnetic next-nearest-neighbor interactions.Comment: 7 pages, 6 figure

Preliminarni podaci o fauni kornjaša (Coleoptera) Turopoljskog luga

Wetlands provide many important ecosystem services, e.g. serving as natural retention areas to prevent flooding and they can be recreational areas for the general public. They also represent vital habitats for many animal species and many are protected nature areas. In spite of this, the fauna of many wetlands in Croatia is still mostly unknown, especially when it comes to beetles. Not knowing the fauna of a particular habitat hinders management efforts. One such location is Turopoljski Lug forest, south-east from the capital Zagreb. The fieldwork was done from March till September 2017, utilising four methods: sweep netting, baited traps on tree trunks, light trapping with UV light traps at night, and collecting by hand. Additionally, several records from earlier visits are included. The total number of currently known species for the forest is raised from 51 to 133. A total of nine species are near threatened (NT), seven of which are saproxylic. Three species listed in Annexes II and IV of the Habitats Directive occur in the area, of which only Cerambyx cerdo had been recorded. Additionally, a neglected literature record of a fourth, Phryganophilus ruficollis, has been discovered. Current management practices for the forest should be re-evaluated and modified if necessary. Future research targeting specific beetle groups should yield further increases in the number of species known for the area, while a targeted mapping of the distribution of species listed on the Annexes should yield much-needed conservation information.Vlažna staništa pružaju mnoge usluge ekosustava, npr. služe kao prirodne retencije poplavnih voda, a mogu biti i područja za rekreaciju šire javnosti. Predstavljaju i životno važna staništa za brojne životinjske vrste, stoga su mnoga vlažna staništa pod nekim stupnjem zaštite. Unatoč tomu, fauna mnogih vlažnih staništa i dalje je većinom nepoznata, posebice po pitanju kornjaša. Nepoznavanje faune određenog područja otežava upravljanje istim. Jedna takva lokacija je šuma Turopoljski lug, smještena jugoistočno od glavnog grada Zagreba. Terensko istraživanje provedeno je od ožujka do rujna 2017. Koristile su se četiri metode: kečiranje, zamke s mamcima na stablima, svjetlosne zamke s UV žaruljama po noći i sakupljanje rukom. Rezultatima je pridodano i nekoliko nalaza od ranije. Ukupan broj poznatih vrsta kornjaša za Turopoljski lug podignut je s 51 na 133. Devet vrsta imaju gotovo ugrožen IUCN status ugroženosti, od kojih je sedam saproksilnog načina života. Iz područja su poznate tri vrste navedene u Dodacima II i IV Direktive o staništima, od kojih smo zabilježili samo Cerambyx cerdo. Također, pronađen je zanemaren nalaz iz literature za četvrtu – Phryganophilus ruficollis. Potrebno je preispitati i, po potrebi, izmijeniti dosadašnji način upravljanja šumom. Buduća usmjerena istraživanja određenih skupina kornjaša trebala bi uroditi dodatnim povećanjem broja vrsta poznatih za lug, dok bi ciljano kartiranje prisutnosti vrsta s Dodataka iznjedrilo prijeko potrebne podatke za zaštitu prirode

Catalogue of the entomological collection of the Division of Zoology of the Faculty of Science in Zagreb, collection of family Coccinellidae (Insecta: Coleoptera)

Entomological collections are an invaluable source of data, due to the variety of species they contain, capturing the biodiversity of a given time. Thus, the entomology part of the Division of Zoology Collection (Faculty of Science, Department of Biology), in Zagreb, established in 1890, is an important asset for all faunistic research and any overview of historical changes in species composition, as well as an important resource in the education of young scientists. Here we provide records of 198 ladybird specimens belonging to five tribes and 24 taxa. Coccinella septempunctata Linnaeus, 1758 and Hippodamia (Hemisphaerica) tredecimpunctata (Linnaeus, 1758) were the most abundant species in the collection, with 59 and 40 specimens respectively. The altitudinal range for the specimens in the collection is 10–1031 m a.s.l., with most records having been found between 10 and 199 m a.s.l. Due to the educational and scientific importance of entomological collections, it is recommended that the review and inventory of the entomological material within the Division of Zoology Collection be continued

Incomplete devil's staircase in the magnetization curve of SrCu2(BO3)2

We report on NMR and torque measurements on the frustrated quasi-two-dimensional spin-dimer system SrCu2(BO3)2 in magnetic fields up to 34 T that reveal a sequence of magnetization plateaus at 1/8, 2/15, 1/6, and 1/4 of the saturation and two incommensurate phases below and above the 1/6 plateau. The magnetic structures determined by NMR involve a stripe order of triplets in all plateaus, suggesting that the incommensurate phases originate from proliferation of domain walls. We propose that the magnetization process of SrCu2(BO3)2 is best described as an incomplete devil's staircase.Comment: 21 pages, 9 figures (main: 12 pages, 4 figures/supplemental material: 9 pages, 5 figures

Nuclear magnetic resonance study of the magnetic-field-induced ordered phase in the NiCl2-4SC(NH2)2 compound

Nuclear magnetic resonance (NMR) study of the high magnetic field (H) part of the Bose-Einstein condensed (BEC) phase of the quasi-onedimensional (quasi-1D) antiferromagnetic quantum spin-chain compound NiCl2-4SC(NH2)2 (DTN) was performed. We precisely determined the phase boundary, Tc(H), down to 40 mK; the critical boson density, n_c(Tc); and the absolute value of the BEC order parameter S_perp at very low temperature (T = 0.12 K). All results are accurately reproduced by numerical quantum Monte Carlo simulations of a realistic three-dimensional (3D) model Hamiltonian. Approximate analytical predictions based on the 1D Tomonaga-Luttinger liquid description are found to be precise for Tc(H), but less so for S_perp(H), which is more sensitive to the strength of 3D couplings, in particular close to the critical field. A mean-field treatment, based on the Hartree-Fock-Popov description, is found to be valid only up to n_c = 4% (T < 0.3 K), while for higher n_c boson interactions appear to modify the density of states.Comment: Manuscript (6 pages, 3 figures) and the corresponding Supplemental material (5 pages, 6 figures), altogether 11 pages and 9 figure