arXiv subjects

C. Payen

Publications and source records attributed to C. Payen.

7 recordsLinked to original sources

arXiv2017

Evidence for a spinon Fermi surface in the triangular S=1 quantum spin liquid Ba$_3$NiSb$_2$O$_9$

Inelastic neutron scattering is used to study the low-energy magnetic excitations in the spin-1 triangular lattice of the 6H-B phase of Ba$_3$NiSb$_2$O$_9$. We study two powder samples: Ba$_3$NiSb$_2$O$_9$ synthesized under high pressure and Ba$_{2.5}$Sr$_{0.5}$NiSb$_2$O$_9$ in which chemical pressure stabilizes the 6H-B structure. The measured excitation spectra show broad gapless and nondispersive continua at characteristic wave vectors. Our data rules out most theoretical scenarios that have previously been proposed for this phase, and we find that it is well described by an exotic quantum spin liquid with three flavors of unpaired fermionic spinons, forming a large spinon Fermi surface.

cond-mat.str-el↗

arXiv2012

Singlet Ground State of the Quantum Antiferromagnet Ba3CuSb2O9

We present local probe results on the honeycomb lattice antiferromagnet Ba3CuSb2O9. Muon spin relaxation measurements in zero field down to 20 mK show unequivocally that there is a total absence of spin freezing in the ground state. Sb NMR measurements allow us to track the intrinsic susceptibility of the lattice, which shows a maximum at around 55 K and drops to zero in the low-temperature limit. The spin-lattice relaxation rate shows two characteristic energy scales, including a field-dependent crossover to exponential low-temperature behavior, implying gapped magnetic excitations.

cond-mat.str-el↗

arXiv2009

Phonon Control of Magnetic Relaxation in the Pyrochlore Slab Compounds SCGO and BSZCGO

We are interested in the phonon response in the frustrated magnets SrCr$_{9x}$Ga$_{12-9x}$O$_{19}$ (SCGO) and Ba$_{2}$Sn$_{2}$ZnCr$_{7x}$Ga$_{10-7x}$O$_{22}$ (BSZCGO). The motivation of the study is the recently discovered, phonon-driven, magnetic relaxation in the SCGO compound [Mutka et al. PRL {\bf 97} 047203 (2006)] pointing out the importance of a low-energy ($\hbarω\sim$7 meV) phonon mode. In neutron scattering experiments on these compounds the phonon signal is partly masked by the magnetic signal from the Cr moments and we have therefore examined in detail the non-magnetic isostructural counterparts SrGa$_{12}$O$_{19}$ (SGO) and Ba$_{2}$Sn$_{2}$ZnGa$_{10}$O$_{22}$ (BSZGO). Our {\it ab-initio} lattice dynamics calculations on SGO reveal a peak in the vibrational density of states matching with the neutron observations on SGO and SCGO. A strong contribution in the vibrational density of states comes from the partial contribution of the Ga atoms on the 2b and 12k sites, involving modes at the M--point of the hexagonal system. These modes comprise dynamics of the kagomé planes of the pyrochlore slab magnetic sub-lattice, 12k sites, and therefore can drive magnetic relaxation via spin-phonon coupling. Both BSZCGO and BSZGO show a similar low-energy Raman peak but no corresponding peak in the neutron determined density of states of BSZGO is seen. However, a strong non-Debye enhancement of low-energy phonon response is observed. We attribute this particular feature to the Zn/Ga disorder on the 2$d$ -site, already evoked earlier to affect the magnetic properties of BSZCGO. We propose that this disorder-induced phonon response explains the absence of a characteristic energy scale and the much faster magnetic relaxation observed in BSZCGO.

cond-mat.mtrl-sci↗

arXiv2002

Anomalous spectral weight in photoemission spectra of the hole doped Haldane chain Y2-xSrxBaNiO5

In this paper, we present photoemission experiments on the hole doped Haldane chain compound $Y_{2-x}Sr_xBaNiO_5$. By using the photon energy dependence of the photoemission cross section, we identified the symmetry of the first ionisation states (d type). Hole doping in this system leads to a significant increase in the spectral weight at the top of the valence band without any change in the vicinity of the Fermi energy. This behavior, not observed in other charge transfer oxides at low doping level, could result from the inhomogeneous character of the doped system and from a Ni 3d-O 2p hybridization enhancement due to the shortening of the relevant Ni-O distance in the localized hole-doped regions.

cond-mat.str-el↗

arXiv2001

Unconventional antiferromagnetic correlations of the doped Haldane gap system Y$_2$BaNi$_{1-x}$Zn$_x$O$_5$

We make a new proposal to describe the very low temperature susceptibility of the doped Haldane gap compound Y$_2$BaNi$_{1-x}$Zn$_x$O$_5$. We propose a new mean field model relevant for this compound. The ground state of this mean field model is unconventional because antiferromagnetism coexists with random dimers. We present new susceptibility experiments at very low temperature. We obtain a Curie-Weiss susceptibility $χ(T) \sim C / (Θ+T)$ as expected for antiferromagnetic correlations but we do not obtain a direct signature of antiferromagnetic long range order. We explain how to obtain the ``impurity'' susceptibility $χ_{imp}(T)$ by subtracting the Haldane gap contribution to the total susceptibility. In the temperature range [1 K, 300 K] the experimental data are well fitted by $T χ_{imp}(T) = C_{imp} (1 + T_{imp}/T )^{-γ}$. In the temperature range [100 mK, 1 K] the experimental data are well fitted by $T χ_{imp}(T) = A \ln{(T/T_c)}$, where $T_c$ increases with $x$. This fit suggests the existence of a finite Néel temperature which is however too small to be probed directly in our experiments. We also obtain a maximum in the temperature dependence of the ac-susceptibility $χ'(T)$ which suggests the existence of antiferromagnetic correlations at very low temperature.

cond-mat.str-el↗

arXiv2001

Random interactions and spin-glass thermodynamic transition in the hole-doped Haldane system Y$_{2-x}$Ca$_x$BaNiO$_5$

Magnetization, DC and AC bulk susceptibility of the $S$=1 Haldane chain system doped with electronic holes, Y$_{2-x}$Ca$_x$BaNiO$_5$ (0$\leq$x$\leq$0.20), have been measured and analyzed. The most striking results are (i) a sub-Curie power law behavior of the linear susceptibility, $χ(T)$$\sim $ $T$$^{-α}$, for temperature lower than the Haldane gap of the undoped compound (x=0) (ii) the existence of a spin-glass thermodynamic transition at $T$$_g$ = 2-3 K. These findings are consistent with (i) random couplings within the chains between the spin degrees of freedom induced by hole doping, (ii) the existence of ferromagnetic bonds that induce magnetic frustration when interchain interactions come into play at low temperature.

cond-mat.str-el↗

arXiv2000

Evidence of quantum criticality in the doped Haldane system Y2BaNiO5

Experimental bulk susceptibility X(T) and magnetization M(H,T) of the S=1-Haldane chain system doped with nonmagnetic impurities, Y2BaNi1-xZnxO5 (x=0.04,0.06,0.08), are analyzed. A numerical calculation for the low-energy spectrum of non-interacting open segments describes very well experimental data above 4 K. Below 4 K, we observe power-law behaviors, X(T)=T^-alpha and M(H,T)/T^(1-alpha)=f(alpha,(H/T)), with alpha (<1) depending on the doping concentration x.This observation suggests the appearance of a gapless quantum phase due to a broad distribution of effective couplings between the dilution-induced moments.

cond-mat.str-el↗