10 research outputs found
Spin Squeezing as a Probe of Emergent Quantum Orders
Nuclear magnetic resonance (NMR) experiments can reveal local properties in
materials, but are often limited by the low signal-to-noise ratio. Spin
squeezed states have an improved resolution below the Heisenberg limit in one
of the spin components, and have been extensively used to improve the
sensitivity of atomic clocks, for example. Interacting and entangled spin
ensembles with non-linear coupling are a natural candidate for implementing
squeezing. Here, we propose measurement of the spin-squeezing parameter that
itself can act as a local probe of emergent orders in quantum materials. In
particular, we demonstrate how to investigate an anisotropic electric field
gradient via its coupling to the nuclear quadrupole moment. While squeezed spin
states are pure, the squeezing parameter can be estimated for both pure and
mixed states. We evaluate the range of fields and temperatures for which a
thermal-equilibrium state is sufficient to improve the resolution in an NMR
experiment and probe relevant parameters of the quadrupole Hamiltonian,
including its anisotropy
PULSEE: A software for the quantum simulation of an extensive set of magnetic resonance observables
We present an open-source software for the simulation of observables in
magnetic resonance experiments, including nuclear magnetic/quadrupole resonance
NMR/NQR and electron spin resonance (ESR), developed to assist experimental
research in the design of new strategies for the investigation of fundamental
quantum properties of materials, as inspired by magnetic resonance protocols
that emerged in the context of quantum information science (QIS). The package
introduced here enables the simulation of both standard NMR spectroscopic
observables and the time-evolution of an interacting single-spin system subject
to complex pulse sequences, i.e. quantum gates. The main purpose of this
software is to facilitate in the development of much needed novel NMR-based
probes of emergent quantum orders, which can be elusive to standard
experimental probes. The software is based on a quantum mechanical description
of nuclear spin dynamics in NMR/NQR experiments and has been widely tested on
available theoretical and experimental results. Moreover, the structure of the
software allows for basic experiments to easily be generalized to more
sophisticated ones, as it includes all the libraries required for the numerical
simulation of generic spin systems. In order to make the program easily
accessible to a large user base, we developed a user-friendly graphical
interface, Jupyter notebooks, and fully-detailed documentation. Lastly, we
portray several examples of the execution of the code that illustrate the
potential of a novel NMR paradigm, inspired by QIS, for efficient investigation
of emergent phases in strongly correlated materials.Comment: 51 page
Electron-hole asymmetry in the phase diagram of carrier-tuned CsVSb
Here we study the effect of electron doping the kagome superconductor
CsVSb. Single crystals and powders of CsVSbTe are
synthesized and characterized via magnetic susceptibility, nuclear quadrupole
resonance, and x-ray diffraction measurements, where we observe a slight
suppression of the charge density wave transition temperature and
superconducting temperature with the introduction of electron dopants. In
contrast to hole-doping, both transitions survive relatively unperturbed up to
the solubility limit of Te within the lattice. A comparison is presented
between the electronic phase diagrams of electron- and hole-tuned
CsVSb.Comment: 11 pages, 4 figure
Petrographical and organic geochemical study of the lignite from the Smederevsko Pomoravlje field (Kostolac Basin, Serbia)
Three Upper Miocene (Pontian) lignite seams are present in the Smederevsko Pomoravlje field (Kostolac Basin, Serbia). The origin of their organic matter (OM), the characteristics of the depositional environment and certain utilisation properties have been evaluated based on petrographic data, bulk organic geochemical parameters, biomarker patterns and their isotope signatures. Moreover, results of isotopic analysis were used for the investigation of the influence of diagenetic aromatisation on delta C-13 signatures of biomarkers. The studied lignites are typical humic coals. The OM of lignites is derived from woody vegetation and herbaceous peat-forming plants, with a strong prevalence of the former. The peat-forming vegetation is dominated by decay resistant conifers, including gymnosperm families Cupressaceae, Taxodiaceae, and Pinaceae. Angiosperms occurred in lower amounts. Minor contribution of ferns, fungi and emergent aquatic macrophyta to the biomass is also evident. Chemoautotrophic- and heterotrophic bacteria played an import role during diagenesis. Diagenetic alterations, associated with change in the number of carbon atoms, influence delta C-13 ratios. Diagenetic aromatisation of di- and non-hopanoid triterpenoids is accompanied with C-13 depletion, whereas aromatisation of hopanoids displays the opposite trend. Peatification proceeded in a fresh water environment under variable, anoxic to slightly oxic redox conditions. The lowermost coal seam III accumulated in a topogenous fresh water peat mire with open water areas, which changed occasionally into a wet forest swamp. This resulted in the deposition of mineral-rich coal. The characteristics of lignite in coal seam II are similar to those of coal seam III. This is supported also by generally similar delta C-13 values of individual biomarkers. Coal seam I is dominated by xylite-rich coal, formed under mesotrophic to ombrotrophic conditions. Rapid flooding of the bogs stopped peat growth in all three coal seams. The ratios of ring-A-degraded and non-degraded aromatic diterpenoids and non-hopanoid triterpenoids, proposed in this study, as well as degree of aromatisation of these biomarkers, reflect changes in the water table. Calorific values of the samples indicate that they meet basic requirements for utilisation in the thermal power plants. None of the lignite samples is suitable for coal briquetting, whereas, based on petrographic data, lignite from coal seam I possesses certain potential for fluidized bed gasification
Entanglement between Muon and I > 1/2 Nuclear Spins as a Probe of Charge Environment
We report on the first example of quantum coherence between the spins of muons and quadrupolar nuclei. We reveal that these entangled states are highly sensitive to a local charge environment and thus, can be deployed as a functional quantum sensor of that environment. The quantum coherence effect was observed in vanadium intermetallic compounds which adopt the A15 crystal structure, and whose members include all technologically pertinent superconductors. Furthermore, the extreme sensitivity of the entangled states to the local structural and electronic environments emerges through the quadrupolar interaction with the electric field gradient due to the charge distribution at the nuclear (I >1/2) sites. This case study demonstrates that positive muons can be used as a quantum sensing tool to also probe structural and charge-related phenomena in materials, even in the absence of magnetic degrees of freedom
Spin-orbital Jahn-Teller bipolarons
Polarons and spin-orbit (SO) coupling are distinct quantum effects that play
a critical role in charge transport and spin-orbitronics. Polarons originate
from strong electron-phonon interaction and are ubiquitous in polarizable
materials featuring electron localization, in particular
transition metal oxides (TMOs). On the other hand, the relativistic coupling
between the spin and orbital angular momentum is notable in lattices with heavy
atoms and develops in TMOs, where electrons are spatially
delocalized. Here we combine ab initio calculations and magnetic measurements
to show that these two seemingly mutually exclusive interactions are entangled
in the electron-doped SO-coupled Mott insulator
(), unveiling the formation of
spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller
lattice activity, converts the Os spin-orbital
levels, characteristic of the parent compound
(BNOO), into a bipolaron
manifold, leading to the coexistence of different
J-effective states in a single-phase material. The gradual increase of
bipolarons with increasing doping creates robust in-gap states that prevents
the transition to a metal phase even at ultrahigh doping, thus preserving the
Mott gap across the entire doping range from BNOO to
(BCOO)
Doping Evolution of the Local Electronic and Structural Properties of the Double Perovskite BaNaCaOsO
We present a combined experimental and computational study of the effect of charge doping in the osmium based double perovskite BaNaCaOsO for 0 ≤ x ≤ 1 in order to provide a structural and electronic basis for understanding this complex Dirac–Mott insulator material. Specifically, we investigate the effects of the substitution of monovalent Na with divalent Ca, a form of charge doping or alloying that nominally tunes the system from Os with a 5d configuration to Os with 5d configuration. After an X-ray diffraction characterization, the local atomic and electronic structure has been experimentally probed by X-ray absorption fine structure at all the cation absorption edges at room temperature; the simulations have been performed using ab initio density functional methods. We find that the substitution of Na by Ca induces a linear volume expansion of the crystal structure which indicates an effective alloying due to the substitution process in the whole doping range. The local structure corresponds to the expected double perovskite one with rock-salt arrangement of Na/Ca in the B site and Os in the B′ one for all the compositions. X-ray absorption near edge structure measurements show a smooth decrease of the oxidation state of Os from 7+ (5d) to 6+ (5d) with increasing Ca concentration, while the oxidation states of Ba, Na, and Ca are constant. This indicates that the substitution of Na by Ca gives rise to an effective electron transfer from the B to the B′ site. The comparison between X-ray absorption measurements and ab initio simulations reveals that the expansion of the Os–O bond length induces a reduction of the crystal field splitting of unoccupied Os derived d states