457 research outputs found
Systematic Cu-63 NQR studies of the stripe phase in La(1.6-x)Nd(0.4)Sr(x)CuO(4) for 0.07 <= x <= 0.25
We demonstrate that the integrated intensity of Cu-63 nuclear quadrupole
resonance (NQR) in La(1.6-x)Nd(0.4)Sr(x)CuO(4) decreases dramatically below the
charge-stripe ordering temperature T(charge). Comparison with neutron and X-ray
scattering indicates that the wipeout fraction F(T) (i.e. the missing fraction
of the integrated intensity of the NQR signal) represents the charge-stripe
order parameter. The systematic study reveals bulk charge-stripe order
throughout the superconducting region 0.07 <= x <= 0.25. As a function of the
reduced temperature t = T/T(charge), the temperature dependence of F(t) is
sharpest for the hole concentration x=1/8, indicating that x=1/8 is the optimum
concentration for stripe formation.Comment: 10 pages of text and captions, 11 figures in postscript. Final
version, with new data in Fig.
Mechanism of metallization and superconductivity suppression in YBaCuZnO revealed by Zn NQR
We measure the nuclear quadrupole resonance (NQR) signal on the Zn site in
nearly optimally doped YBaCuO, when Cu is substituted by 3\%
of isotopically pure Zn. We observe that Zn creates large insulating
islands, confirming two earlier conjectures: that doping provokes an orbital
transition in the CuO plane, which is locally reversed by Zn substitution,
and that the islands are antiferromagnetic. Also, we find that the Zn impurity
locally induces a breaking of the D symmetry. Cluster and DFT calculations
show that the D symmetry breaking is due to the same partial lifting of
degeneracy of the nearest-neighbor oxygen sites as in the LTT transition in
LaBaCuO, similarly well-known to strongly suppress
superconductivity. These results show that in-plane oxygen orbital
configurations are principally involved in the metallicity and
superconductivity of all high-T cuprates, and provide a qualitative
symmetry-based constraint on the SC mechanism.Comment: extended version, to appear in New Journal of Physic
Design of probe for NQR/NMR detection
Nuclear Magnetic Resonance (NMR) is a RF technique that is able to detect any compound by sensing the excited resonance signals from atomic nuclei having non-zero spin. NQR is similar to NMR but the only difference is NMR needs a DC magnetic field and due to this its application in the field is limited. A FPGA based NQR spectrometer is designed using a single FPGA chip to perform the digital tasks required for NQR spectrometer. Design of Probe for NMR/NQR spectrometer is researched. Parallel tuned and series tuned Probes are discussed and simulated.14N NQR from NaNO2 is observed from spectrometer designed with parallel tuned probe
Phase separation and suppression of critical dynamics at quantum transitions of itinerant magnets: MnSi and (SrCa)RuO
Quantum phase transitions (QPTs) have been studied extensively in correlated
electron systems. Characterization of magnetism at QPTs has, however, been
limited by the volume-integrated feature of neutron and magnetization
measurements and by pressure uncertainties in NMR studies using powderized
specimens. Overcoming these limitations, we performed muon spin relaxation
(SR) measurements which have a unique sensitivity to volume fractions of
magnetically ordered and paramagnetic regions, and studied QPTs from itinerant
heli/ferro magnet to paramagnet in MnSi (single-crystal; varying pressure) and
(SrCa)RuO (ceramic specimens; varying ). Our results
provide the first clear evidence that both cases are associated with
spontaneous phase separation and suppression of dynamic critical behavior,
revealed a slow but dynamic character of the ``partial order'' diffuse spin
correlations in MnSi above the critical pressure, and, combined with other
known results in heavy-fermion and cuprate systems, suggest a possibility that
a majority of QPTs involve first-order transitions and/or phase separation.Comment: 11 pages, 4 figures, 21 authors, to appear in Nature Physic
A Cryogenically-Cooled High-Sensitivity Nuclear Quadrupole Resonance Spectrometer
The paper describes a radio frequency (RF) spectrometer for 14N nuclear
quadrupole resonance (NQR) spectroscopy that uses a detector coil cooled to 77
K to maximize measurement sensitivity. The design uses a minimally-intrusive
network of active duplexers and mechanical contact switches to realize a
digitally reconfigurable series/parallel coil tuning network that allows
transmit- and receive-mode performance to be independently optimized. The
design is battery-powered and includes a mixed-signal embedded system to
monitor and control secondary processes, thus enabling autonomous operation.
Tests on an acetaminophen sample show that cooling both the detector and sample
increases the signal-to-noise ratio (SNR) per scan by a factor of approximately
88 (in power units), in good agreement with theoretical predictions.Comment: Submitted to Review of Scientific Instrument
Rapid detection of arsenic minerals using portable broadband NQR
The remote real-time detection of specific arsenic species would significantly benefit in minerals processing to mitigate the release of arsenic into aquatic environments and aid in selective mining. At present, there are no technologies available to detect arsenic minerals in bulk volumes outside of laboratories. Here we report on the first room-temperature broadband 75As nuclear quadrupole resonance (NQR) detection of common and abundant arsenic ores in the Earth crust using a large sample (0.78 L) volume prototype sensor. Broadband excitation aids in detection of natural minerals with low crystallinity. We briefly discuss how the proposed NQR detector could be employed in mining operations. Key Points Transformation of chemical analysis method to geophysical detection technologyFirst NQR ore characterization of selected arsenic minerals in bulk volumesBroadband NQR sensor to detect arsenic minerals with low crystallinit
Cu-63 NQR Measurement of Stripe Order Parameter in La(2-x)Sr(x)CuO(4)
We demonstrate that one can measure the charge-stripe order parameter in the
hole-doped CuO(2) planes of La(1.875)Ba(0.125)CuO(4),
La(1.48)Nd(0.4)Sr(0.12)CuO(4) and La(1.68)Eu(0.2)Sr(0.12)CuO(4) utilizing the
wipeout effects of Cu-63 NQR. Application of the same approach to
La(2-x)Sr(x)CuO(4) reveals the presence of similar stripe order for the entire
underdoped superconducting regime 1/16 < x < 1/8.Comment: 4 pages in RevTex, 3 figures in postscript. Minor changes have been
made to increase readability. This manuscript has been accepted for
publication in Physical Review Letter
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