510 research outputs found
Impact of disorder on dynamics and ordering in the honeycomb-lattice iridate Na2IrO3
Kitaev's honeycomb spin-liquid model and its proposed realization in materials such as α-RuCl3, Li2IrO3, and Na2IrO3 continue to present open questions about how the dynamics of a spin liquid are modified in the presence of non-Kitaev interactions as well as the presence of inhomogeneities. Here we use Na23 nuclear magnetic resonance to probe both static and dynamical magnetic properties in single-crystal Na2IrO3. We find that the NMR shift follows the bulk susceptibility above 30 K but deviates from it below; moreover below TN the spectra show a broad distribution of internal magnetic fields. Both of these results provide evidence for inequivalent magnetic sites at low temperature, suggesting inhomogeneities are important for the magnetism. The spin-lattice relaxation rate is isotropic and diverges at TN, suggesting that the Kitaev cubic axes may control the critical quantum spin fluctuations. In the ordered state, we observe gapless excitations, which may arise from site substitution, emergent defects from milder disorder, or possibly be associated with nearby quantum paramagnetic states distinct from the Kitaev spin liquid
Impurities near an Antiferromagnetic-Singlet Quantum Critical Point
Heavy fermion systems, and other strongly correlated electron materials,
often exhibit a competition between antiferromagnetic (AF) and singlet ground
states. Using exact Quantum Monte Carlo (QMC) simulations, we examine the
effect of impurities in the vicinity of such AF- singlet quantum critical
points, through an appropriately defined impurity susceptibility, .
Our key finding is a connection, within a single calculational framework,
between AF domains induced on the singlet side of the transition, and the
behavior of the nuclear magnetic resonance (NMR) relaxation rate . We
show that local NMR measurements provide a diagnostic for the location of the
QCP which agrees remarkably well with the vanishing of the AF order parameter
and large values of . We connect our results with experiments on
Cd-doped CeCoIn
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Molecular madeling of amorphous polymers in the condensed phase
We have developed a tractable computational approach, PRISM theory (polymer Reference Interaction Site Model), for modeling structure and thermodynamics of polymer liquids and alloys. PRISM theory allows one to predict the effect of polymer architecture and monomer structure on the intermolecular packing in the condensed phase. Three applications of this method are discussed: phase behavior of polymer blends, solubility of gases in polymers, and structure of polymers near walls and interfaces. In these applications, nonrandom mixing effects (not included in previous theories) play an important role in the macroscopic properties of importance to the materials scientist
Specific heat at the transition in a superconductor with fluctuating magnetic moments
In the heavy-fermion materials CeCoIn and UBe, the superconducting
order parameter is coupled to flucutating magnetization of the uncompensated
part of the localized -moments. We find that this coupling decreases the
superconducting transition temperature and increases the jump of the
specific-heat coefficient, which indicates entropy transfer from the magnetic
to the superconducting degree of freedom at the transition temperature. Below
the transition, we find that the magnetic fluctuations are suppressed. We
discuss the relation of our results to experiments on CeCoIn under
pressure.Comment: 4 pages, 1 figur
Acupuncture in the treatment of temporomandibular disorders, facial pain, and postural neuromuscular disorders. Presentation of a clinical case
Background and objectives: Temporomandibular disorders have a multifactorial etiology and involve the masticatory muscles, temporomandibular joint and associated structures. Therefore, different treatments are proposed and used. The aim of this paper is the use of acupuncture to treat temporomandibular disorders and associated symptoms. This article presents a clinical case study of a 39-year-old patient who presented temporomandibular disorders and headache of muscular origin. Results: After 10 acupuncture sessions, the results were highly satisfactory, with complete relief of headache pain and absence of joint disorders. These results suggest the efficacy of acupuncture in the symptomatic relief of temporomandibular disorders. Conclusions: It is concluded that acupuncture is an alternative method to conventional stomatognathic treatment for individuals with craniomandibular disorders of muscular origin
Mast cells, microRNAs and others: The role of translational research on colorectal cancer in the forthcoming era of precision medicine
Colorectal cancer (CRC) is a heterogeneous disease, molecularly and anatomically, that develops in a multi-step process requiring the accumulation of several genetic or epigenetic mutations that lead to the gradual transformation of normal mucosa into cancer. In fact, tumorigenesis is extremely complex, with many immunologic and non-immunologic factors present in the tumor microenvironment that can influence tumorigenesis. In the last few years, a role for mast cells (MCs), microRNAs (miRNAs), Kirsten rat sarcoma (KRAS) and v-raf murine sarcoma viral oncogene homologue B (BRAF) in cancer development and progression has been suggested, and numerous efforts have been made to thoroughly assess their correlation with CRC to improve patient survival and quality of life. The identification of easily measurable, non-invasive and cost-effective biomarkers, the so-called “ideal biomarkers”, for CRC screening and treatment remains a high priority. The aim of this review is to discuss the emerging role of mast cells (MCs), microRNAs (miRNAs), KRAS and BRAF as diagnostic and prognostic biomarkers for CRC, evaluating their influence as potential therapy targets in the forthcoming era of precision medicine
Stripes Disorder and Correlation lengths in doped antiferromagnets
For stripes in doped antiferromagnets, we find that the ratio of spin and
charge correlation lenghts, , provide a sharp criterion for
determining the dominant form of disorder in the system. If stripes disorder is
controlled by topological defects then . In contast,
if stripes correlations are disordered primarily by non-topological elastic
deformations (i.e., a Bragg-Glass type of disorder) then is expected. Therefore, the observation of in and in invariably implies that the stripes
are in a Bragg glass type state, and topological defects are much less relevant
than commonly assumed. Expected spectral properties are discussed. Thus, we
establish the basis for any theoretical analysis of the experimentally
obsereved glassy state in these material.Comment: 4 pages, 2 figure
As NMR studies of superconducting LaOFFeAs
We have performed 75As Nuclear Magnetic Resonance (NMR) measurements on
aligned powders of the new LaO0.9F0.1FeAs superconductor. In the normal state,
we find a strong temperature dependence of the spin shift and Korringa behavior
of the spin lattice relaxation rate. In the superconducting state, we find
evidence for line nodes in the superconducting gap and spin-singlet pairing.
Our measurements reveal a strong anisotropy of the spin lattice relaxation
rate, which suggest that superconducting vortices contribute to the relaxation
rate when the field is parallel to the c-axis but not for the perpendicular
direction
Anomalous NMR Magnetic Shifts in CeCoIn_5
We report ^{115}In and ^{59}Co Nuclear Magnetic Resonance (NMR) measurements
in the heavy fermion superconductor CeCoIn_5 above and below T_c. The hyperfine
couplings of the In and Co are anisotropic and exhibit dramatic changes below
50K due to changes in the crystal field level populations of the Ce ions. Below
T_c the spin susceptibility is suppressed, indicating singlet pairing.Comment: 4 pages, 4 figure
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