2,467 research outputs found
Measurement of the ionization yield of nuclear recoils in liquid argon at 80 and 233 keV
The energy calibration of nuclear recoil detectors is of primary importance
to rare-event experiments such as those of direct dark matter search and
coherent neutrino-nucleus scattering. In particular, such a calibration is
performed by measuring the ionization yield of nuclear recoils in liquid Ar and
Xe detection media, using neutron elastic scattering off nuclei. In the present
work, the ionization yield for nuclear recoils in liquid Ar has for the first
time been measured in the higher energy range, at 80 and 233 keV, using a
two-phase Cryogenic Avalanche Detector (CRAD) and DD neutron generator. The
ionization yield in liquid Ar at an electric field of 2.3 kV/cm amounted to
7.8+/-1.1 and 9.7+/-1.3 e-/keV at 80 and 233 keV respectively. The Jaffe model
for nuclear recoil-induced ionization, in contrast to that Thomas-Imel, can
probably consistently describe the energy dependence of the ionization yield.Comment: 6 pages, 6 figures. Fig. 6 changed. Submitted to EP
An Electron Spin Resonance Selection Rule for Spin-Gapped Systems
The direct electron spin resonance (ESR) absorption between a singlet ground
state and the triplet excited states of spin gap systems is investigated. Such
an absorption, which is forbidden by the conservation of the total spin quantum
number in isotropic Hamiltonians, is allowed by the Dzyaloshinskii-Moriya
interaction. We show a selection rule in the presence of this interaction,
using the exact numerical diagonalization of the finite cluster of the
quasi-one-dimensional bond-alternating spin system. The selection rule is also
modified into a suitable form in order to interpret recent experimental results
on CuGeO and NaVO.Comment: 5 pages, Revtex, with 6 eps figures, to appear in J. Phys. Soc. Jpn.
Vol. 69 No. 11 (2000
Weak ferromagnetism and field-induced spin reorientation in K2V3O8
Magnetization and neutron diffraction measurements indicate long-range
antiferromagnetic ordering below TN=4 K in the 2D, S=1/2 Heisenberg
antiferromagnet K2V3O8. The ordered state exhibits ``weak ferromagnetism'' and
novel, field-induced spin reorientations. These experimental observations are
well described by a classical, two-spin Heisenberg model incorporating
Dzyaloshinskii-Moriya interactions and an additional c-axis anisotropy. This
additional anisotropy can be accounted for by inclusion of the symmetric
anisotropy term recently described by Kaplan, Shekhtman, Entin-Wohlman, and
Aharony. This suggests that K2V3O8 may be a very unique system where the
qualitative behavior relies on the presence of this symmetric anisotropy.Comment: 5 pages, 4 ps figures, REVTEX, submitted to PR
Dzyaloshinsky-Moriya antisymmetric exchange coupling in cuprates: Oxygen effects
We revisit a problem of Dzyaloshinsky-Moriya antisymmetric exchange coupling
for a single bond in cuprates specifying the local spin-orbital contributions
to Dzyaloshinsky vector focusing on the oxygen term. The Dzyaloshinsky vector
and respective weak ferromagnetic moment is shown to be a superposition of
comparable and, sometimes, competing local Cu and O contributions. The
intermediate oxygen O Knight shift is shown to be an effective tool to
inspect the effects of Dzyaloshinsky-Moriya coupling in an external magnetic
field. We predict the effect of oxygen weak antiferromagnetism in
edge-shared CuO chains due to uncompensated oxygen Dzyaloshinsky vectors.
Finally, we revisit the effects of symmetric spin anisotropy, in particular,
those directly induced by Dzyaloshinsky-Moriya coupling.Comment: 12 pages, 2 figures, submitted to JET
Effects of anisotropic spin-exchange interactions in spin ladders
We investigate the effects of the Dzialoshinskii-Moriya (DM) and
Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) interactions on various
thermodynamic and magnetic properties of a spin 1/2 ladder. Using the Majorana
fermion representation, we derive the spectrum of low energy excitations for a
pure DM interaction and in presence of a superimposed KSEA interaction. We
calculate the various correlation functions for both cases and discuss how they
are modified with respect to the case of an isotropic ladder. We also discuss
the electron spin resonance (ESR) spectrum of the system and show that it is
strongly influenced by the orientation of the magnetic field with respect to
the Dzialoshinskii-Moriya vector. Implications of our calculations for NMR and
ESR experiments on ladder systems are discussed.Comment: 14 pages, 4 eps figures, corrected calculation of NMR rate (v3
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