24 research outputs found
Nuclear Magnetic Resonance in High Magnetic Field: Application to Condensed Matter Physics
In this review, we describe the potentialities offered by the nuclear
magnetic resonance (NMR) technique to explore at a microscopic level new
quantum states of condensed matter induced by high magnetic fields. We focus on
experiments realised in resistive (up to 34~T) or hybrid (up to 45~T) magnets,
which open a large access to these quantum phase transitions. After an
introduction on NMR observable, we consider several topics: quantum spin
systems (spin-Peierls transition, spin ladders, spin nematic phases,
magnetisation plateaus and Bose-Einstein condensation of triplet excitations),
the field-induced charge density wave (CDW) in high ~superconductors, and
exotic superconductivity including the Fulde-Ferrel-Larkin-Ovchinnikov
superconducting state and the field-induced superconductivity due to the
Jaccarino-Peter mechanism.Comment: 19 pages, 6 figure
Nuclear magnetic resonance study of the magnetic-field-induced ordered phase in the NiCl2-4SC(NH2)2 compound
Nuclear magnetic resonance (NMR) study of the high magnetic field (H) part of
the Bose-Einstein condensed (BEC) phase of the quasi-onedimensional (quasi-1D)
antiferromagnetic quantum spin-chain compound NiCl2-4SC(NH2)2 (DTN) was
performed. We precisely determined the phase boundary, Tc(H), down to 40 mK;
the critical boson density, n_c(Tc); and the absolute value of the BEC order
parameter S_perp at very low temperature (T = 0.12 K). All results are
accurately reproduced by numerical quantum Monte Carlo simulations of a
realistic three-dimensional (3D) model Hamiltonian. Approximate analytical
predictions based on the 1D Tomonaga-Luttinger liquid description are found to
be precise for Tc(H), but less so for S_perp(H), which is more sensitive to the
strength of 3D couplings, in particular close to the critical field. A
mean-field treatment, based on the Hartree-Fock-Popov description, is found to
be valid only up to n_c = 4% (T < 0.3 K), while for higher n_c boson
interactions appear to modify the density of states.Comment: Manuscript (6 pages, 3 figures) and the corresponding Supplemental
material (5 pages, 6 figures), altogether 11 pages and 9 figure
Locally commensurate charge-density wave with three-unit-cell periodicity in YBCO
In order to identify the mechanism responsible for the formation of
charge-density waves (CDW) in cuprate superconductors, it is important to
understand which aspects of the CDW's microscopic structure are generic and
which are material-dependent. Here, we show that, at the local scale probed by
NMR, long-range CDW order in YBa2Cu3Oy is unidirectional with a commensurate
period of three unit cells (lambda = 3b), implying that the incommensurability
found in X-ray scattering is ensured by phase slips (discommensurations).
Furthermore, NMR spectra reveal a predominant oxygen character of the CDW with
an out-of-phase relationship between certain lattice sites but no specific
signature of a secondary CDW with lambda = 6b associated with a putative
pair-density wave. These results shed light on universal aspects of the cuprate
CDW. In particular, its spatial profile appears to generically result from the
interplay between an incommensurate tendency at long length scales, possibly
related to properties of the Fermi surface, and local commensuration effects,
due to electron-electron interactions or lock-in to the lattice.Comment: Original submission (revised version available upon request
Hidden magnetism at the pseudogap critical point of a high temperature superconductor
The mysterious pseudogap phase of cuprate superconductors ends at a critical
hole doping level p* but the nature of the ground state below p* is still
debated. Here, we show that the genuine nature of the magnetic ground state in
La2-xSrxCuO4 is hidden by competing effects from superconductivity: applying
intense magnetic fields to quench superconductivity, we uncover the presence of
glassy antiferromagnetic order up to the pseudogap boundary p* ~ 0.19, and not
above. There is thus a quantum phase transition at p*, which is likely to
underlie highfield observations of a fundamental change in electronic
properties across p*. Furthermore, the continuous presence of quasi-static
moments from the insulator up to p* suggests that the physics of the doped Mott
insulator is relevant through the entire pseudogap regime and might be more
fundamentally driving the transition at p* than just spin or charge ordering.Comment: 26 pages, supplementary info include
Magnetic-field-induced charge-stripe order in the high temperature superconductor YBa2Cu3Oy
Electronic charges introduced in copper-oxide planes generate high-transition
temperature superconductivity but, under special circumstances, they can also
order into filaments called stripes. Whether an underlying tendency of charges
to order is present in all cuprates and whether this has any relationship with
superconductivity are, however, two highly controversial issues. In order to
uncover underlying electronic orders, magnetic fields strong enough to
destabilise superconductivity can be used. Such experiments, including quantum
oscillations in YBa2Cu3Oy (a notoriously clean cuprate where charge order is
not observed) have suggested that superconductivity competes with spin, rather
than charge, order. Here, using nuclear magnetic resonance, we demonstrate that
high magnetic fields actually induce charge order, without spin order, in the
CuO2 planes of YBa2Cu3Oy. The observed static, unidirectional, modulation of
the charge density breaks translational symmetry, thus explaining quantum
oscillation results, and we argue that it is most likely the same 4a-periodic
modulation as in stripe-ordered cuprates. The discovery that it develops only
when superconductivity fades away and near the same 1/8th hole doping as in
La2-xBaxCuO4 suggests that charge order, although visibly pinned by CuO chains
in YBa2Cu3Oy, is an intrinsic propensity of the superconducting planes of high
Tc cuprates.Comment: For a final version, see
http://www.nature.com/nature/journal/v477/n7363/full/nature10345.htm
NMR and NQR study of the tetrahedral frustrated quantum spin system Cu2Te2O5Br2 in its paramagnetic phase
The quantum antiferromagnet Cu2Te2O5Br2 was investigated by NMR and nuclear quadrupole resonance (NQR). The Te-125 NMR investigation showed that there is a magnetic transition around 10.5 K at 9 T, in agreement with previous studies. From the divergence of the spin-lattice relaxation rate, we ruled out the possibility that the transition could be governed by a one-dimensional divergence of the spin-spin correlation function. The observed anisotropy of the Te-125 shift was shown to be due to a spin polarization of the 5s(2) "E" doublet of the [TeO3E] tetrahedra, highlighting the importance of tellurium in the exchange paths. In the paramagnetic state, Br NQR and NMR measurements led to the determination of the Br hyperfine coupling and the electric field gradient tensor, and to the spin polarization of Br p orbitals. The results demonstrate the crucial role of bromine in the interaction paths between Cu spins
Detection of a Disorder-Induced Bose-Einstein Condensate in a Quantum Spin Material at High Magnetic Fields
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Nuclear Magnetic Resonance Reveals Disordered Level-Crossing Physics in the Bose-Glass Regime of the Br-Doped Ni(Cl_{1-x}Br_{x})_{2}-4SC(NH_{2})_{2} Compound at a High Magnetic Field.
By measuring the nuclear magnetic resonance (NMR) T_{1}^{-1} relaxation rate in the Br (bond) doped DTN compound, Ni(Cl_{1-x}Br_{x})_{2}-4SC(NH_{2})_{2}(DTNX), we show that the low-energy spin dynamics of its high magnetic field "Bose-glass" regime is dominated by a strong peak of spin fluctuations found at the nearly doping-independent position H^{*}≅13.6  T. From its temperature and field dependence, we conclude that this corresponds to a level crossing of the energy levels related to the doping-induced impurity states. Observation of the local NMR signal from the spin adjacent to the doped Br allowed us to fully characterize this impurity state. We have thus quantified a microscopic theoretical model that paves the way to better understanding of the Bose-glass physics in DTNX, as revealed in the related theoretical study [M. Dupont, S. Capponi, and N. Laflorencie, Phys. Rev. Lett. 118, 067204 (2017).PRLTAO0031-900710.1103/PhysRevLett.118.067204]