176 research outputs found
Spin susceptibility of charge ordered YBa2Cu3Oy across the upper critical field
The value of the upper critical field Hc2, a fundamental characteristic of
the superconducting state, has been subject to strong controversy in high-Tc
copper-oxides. Since the issue has been tackled almost exclusively by
macroscopic techniques so far, there is a clear need for local-probe
measurements. Here, we use 17O NMR to measure the spin susceptibility
of the CuO2 planes at low temperature in charge ordered
YBa2Cu3Oy. We find that increases (most likely linearly) with
magnetic field H and saturates above field values ranging from 20 to 40 T. This
result is consistent with Hc2 values claimed by G. Grissonnanche et al. [Nat.
Commun. 5, 3280 (2014)] and with the interpretation that the
charge-density-wave (CDW) reduces Hc2 in underdoped YBa2Cu3Oy. Furthermore, the
absence of marked deviation in at the onset of long-range CDW
order indicates that this Hc2 reduction and the Fermi-surface reconstruction
are primarily rooted in the short-range CDW order already present in zero
field, not in the field-induced long-range CDWorder. Above Hc2, the relatively
low values of at T=2 K show that the pseudogap is a ground-state
property, independent of the superconducting gap.Comment: To appea
Thermodynamics of mixing in diopside-jadeite, CaMgSi2O6-NaAlSi2O6, solid solution from staticlattice energy calculations
Static lattice energy calculations (SLEC), based on empirical interatomic potentials, have beenperformed for a set of 800 different structures in a 2 2 4 supercell of C2/c diopside with compositionsbetween diopside and jadeite, and with different states of order of the exchangeable Na/Ca and Mg/Al cations. Excess static energies of these structures have been cluster expanded in a basis set of 37 pair-interaction parameters. These parameters have been used to constrain Monte Carlo simulations of temperature-dependent properties in the range of 273?2,023 K and to calculate a temperature?composition phase diagram. The simulations predict the order?disorder transition in omphacite at1,150 20C in good agreement with the experimental data of Carpenter (Mineral Petrol 78:433?440, 1981). The stronger ordering of Mg/Al within the M1 site than of Ca/Na in the M2 site is attributed to the shorter M1?M1 nearest-neighbor distance, and, consequently, the stronger ordering force. The comparison of the simulated relationship between the order parameters corresponding to M1 and M2 sites with the X-ray refinement data on natural omphacites (Boffa Ballaran et al. in Am Mineral83:419?433, 1998) suggests that the cation ordering becomes kinetically ineffective at about 600C
Spin-echo and quantum versus classical critical fluctuations in TmVO
Using spin-echo Nuclear Magnetic Resonance in the model Transverse-Field
Ising system TmVO, we show that low frequency quantum fluctuations at the
quantum critical point have a very different effect on V nuclear-spins
than classical low-frequency noise or fluctuations that arise at a finite
temperature critical point. Spin-echos filter out the low frequency classical
noise but not the quantum fluctuations. This allows us to directly visualize
the quantum critical fan and demonstrate the persistence of quantum
fluctuations at the critical coupling strength in TmVO to high temperatures
in an experiment that remains transparent to finite temperature classical phase
transitions. These results show that while dynamical decoupling schemes can be
quite effective in eliminating classical noise in a qubit, a quantum critical
environment may lead to rapid entanglement and decoherence.Comment: 10 pages, 5 figure
Second order Zeeman interaction and ferroquadrupolar order in TmVO
TmVO exhibits ferroquadrupolar order of the Tm 4f electronic orbitals
at low temperatures, and is a model system for Ising nematicity that can be
tuned continuously to a quantum phase transition via magnetic fields along the
-axis. Here we present V nuclear magnetic resonance data in magnetic
fields perpendicular to the -axis in a single crystal that has been
carefully cut by a plasma focused ion beam to an ellipsoidal shape to minimize
the inhomogeneity of the internal demagnetization field. The resulting dramatic
increase in spectral resolution enabled us to resolve the anisotropy of the
electric field gradient and to measure the magnetic and quadrupolar relaxation
channels separately. Perpendicular magnetic fields nominally do not couple to
the low energy degrees of freedom, but we find a significant nonlinear
contribution for sufficiently large fields that give rise to a rich phase
diagram. The in-plane magnetic field can act either as an effective transverse
or longitudinal field to the Ising nematic order, depending on the orientation
relative to the principle axes of the quadrupole order, and leads to a marked
in-plane anisotropy in both relaxation channels. We find that the small
in-plane transverse fields initially enhance the ferroquadrupolar ordering
temperature but eventually suppress the long-range order. We tentatively
ascribe this behavior to the competing effects of field-induced mixing of
higher energy crystal field states and the destabilizing effects of
field-induced quantum fluctuations.Comment: 15 pages, 13 figure
Competition between spin ordering and superconductivity near the pseudogap boundary in La2âxSrxCuO4: Insights from NMR
When superconductivity is suppressed by high magnetic fields in La2âxSrxCuO4, striped antiferromagnetic (AFM) order becomes the magnetic ground state of the entire pseudogap regime, up to its end at the doping pâ [Frachet, Vinograd et al., Nat. Phys. 16, 1064 (2020)]. Glass-like freezing of this state is detected in 139La NMR measurements of the spin-lattice relaxation rate Tâ11. Here, we present a quantitative analysis of Tâ11 data in the hole-doping range p=x=0.12â0.171, based on the Bloembergen-Purcell-Pound (BPP) theory, modified to include statistical distribution of parameters arising from strong spatial inhomogeneity. We observe spin fluctuations to slow down at temperatures T near the onset of static charge order and, overall, the effect of the field B may be seen as equivalent to strengthening stripe order by approaching p=0.12 doping. In details, however, our analysis reveals significant departure from usual field-induced magnetic transitions. The continuous growth of the amplitude of the fluctuating moment with increasing B suggests a nearly-critical state in the Bâ0 limit, with very weak quasistatic moments possibly confined in small areas like vortex cores. Further, the nucleation of spin order in the vortex cores is shown to account quantitatively for both the value and the p dependence of a field scale characterizing bulk spin freezing. The correlation time of the fluctuating moment appears to depend exponentially on B/T (over the investigated range). This explains the timescale dependence of various experimental manifestations, including why, for transport measurements, the AFM moments may be considered static over a considerable range of B and T. These results make the high-field magnetic ground state up to pâ an integral part of the discussion on putative quantum criticality
Unusual interplay between superconductivity and field-induced charge order in YBa2Cu3Oy
We present a detailed study of the temperature (T) and magnetic field (H)
dependence of the electronic density of states (DOS) at the Fermi level, as
deduced from specific heat and Knight shift measurements in underdoped
YBa2Cu3Oy. We find that the DOS becomes field-independent above a
characteristic field H_{DOS} and that the H_{DOS}(T) line displays an unusual
inflection near the onset of the long range 3D charge-density wave order. The
unusual S-shape of H_{DOS}(T) is suggestive of two mutually-exclusive orders
that eventually establish a form of cooperation in order to coexist at low T.
On theoretical grounds, such a collaboration could result from the
stabilisation of a pair-density wave state, which calls for further
investigations in this region of the phase diagramComment: 6 pages, 4 figure
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