arXiv subjects

Philippe Mendels

Publications and source records attributed to Philippe Mendels.

9 recordsLinked to original sources

arXiv2025

Emergence of a Fluctuating Ground State in Y-kapellasite under Pressure

Y-kapellasite (Y$_3$Cu$_9$(OH)$_{19}$Cl$_8$), which hosts an original anisotropic kagome sublattice, is a promising candidate for studying elusive and complex correlated physics. It exhibits a theoretically predicted in-plane $(1/3, 1/3)$ magnetic order [1] but its magnetic interaction values place it close to a phase boundary to a spin liquid state [2]. Our $\mu$SR measurements under hydrostatic pressure demonstrate the complete suppression of static magnetism in favor of a fully dynamical ground state at $2.3$~GPa. Complementary high-pressure x-ray and optical phonon measurements reveal a gradual reduction of the kagome anisotropy, enhancing magnetic frustration without structural transitions. Our results establish Y-kapellasite as a rare clean kagome model in which long-range order is suppressed by pressure-tuned frustration, the first fingerprint for the realization of a quantum spin liquid without strong disorder.

cond-mat.str-el↗

arXiv2024

NMR study of the local magnetic order in the kagome Weyl semimetal Co$_3$Sn$_2$S$_2$

A magnetic Weyl semimetal presents the intriguing possibility of controlling topological properties through magnetic order. The kagome compound \CoSnS~has emerged as one of the most thoroughly characterized magnetic Weyl semimetals, yet the potential coexistence of a ferromagnetic state below $T_c$ = 172~K with a non-collinear antiferromagnetic phase or a glassy state remains unresolved. We employ $^{59}$Co NMR to gain a local perspective on the magnetic order. The magnetic and electric field gradient tensors at room temperature are determined by fitting the NMR spectra using evolutionary algorithms. Zero-field NMR measurements reveal that all Co sites are equivalent in the magnetic phase at low temperatures and up to 90~K. The local magnetic field follows in intensity the macroscopic magnetization as a function of temperature and is tilted from the c-axis by a few degrees toward the nearest triangle center. Above 90~K, a shoulder appears on the low-field side, which we attribute to a preferential tilting of the local field in one direction, breaking the equivalence between the three Co sites of the kagome structure. We rule out any coexistence with an in-plane antiferromagnetic phase and suggest instead that in-plane ferromagnetic-like moments appear above 90~K and play an increasing role in the magnetic order up to the magnetic transition.

cond-mat.str-el↗

arXiv2019

Local study of the insulating quantum kagome antiferromagnets YCu3(OH)6OxCl3-x (x=0,1/3)

The quantum kagome antiferromagnets YCu3(OH)6OxCl3-x (x=0,1/3) are produced using a unified solid state synthesis route for polycrystalline samples. From structural refinements based on neutron diffraction data, we clarify the structure of the Y3Cu9(OH)18OCl8 (x=1/3) compound and provide a revised chemical formula. We use muon spin relaxation, as a local probe of magnetism, to investigate the exotic low temperature properties in the two compounds. In agreement with the low temperature neutron diffraction data, we find no evidence for long range ordering in both materials but they exhibit distinct ground states: while disordered static magnetism develops in the x=0 compound, we conclude on the stabilization of a quantum spin liquid in the x=1/3 one, since the local fields remain fully dynamical. Our findings are in contrast to previous reports based on thermodynamical measurements only. We then discuss their origin on the basis of structural details and specific heat measurements. In particular, the x=1/3 compound appears to realize an original spatially anisotropic kagome model.

cond-mat.str-el↗

arXiv2017

Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO$_4$: an NMR investigation

The frustrated one-dimensional (1D) quantum magnet LiCuSbO$_4$ is one rare realization of the $J_1-J_2$ spin chain model with an easily accessible saturation field, formerly estimated to 12~T. Exotic multipolar nematic phases were theoretically predicted in such compounds just below the saturation field, but without unambiguous experimental observation so far. In this paper we present extensive experimental research of the compound in the wide temperature (30mK$-$300K) and field (0$-$13.3T) range by muon spin rotation ($μ$SR), $^7$Li nuclear magnetic resonance (NMR) and magnetic susceptibility (SQUID). $μ$SR experiments in zero magnetic field demonstrate the absence of long range 3D ordering down to 30mK. Together with former heat capacity data [S.E. Dutton \emph{et al}, Phys. Rev. Lett. 108, 187206 (2012)], magnetic susceptibility measurements suggest short range correlated vector chiral phase in the field range $0-4$T. In the intermediate field values (5$-$12T), the system enters in a 3D ordered spin density wave phase with 0.75$μ_B$ per copper site at lowest temperatures (125mK), estimated by NMR. At still higher field, the magnetization is found to be saturated above 13T where the spin lattice $T_1^{-1}$ relaxation reveals a spin gap estimated to 3.2(2)K. We narrow down the possibility of observing a multipolar nematic phase to the range 12.5$-$13T.

cond-mat.str-el↗

arXiv2010

Interplay of thermal and quantum spin fluctuations on the kagome lattice

We present a Raman spectroscopic investigation of the Herbertsmithite ZnCu3(OH)6Cl2, the first realization of a Heisenberg s=1/2 antiferromagnet on a perfect kagome lattice. The magnetic excitation spectrum of this compound is dominated by two components, a high temperature quasi elastic signal and a low temperature, broad maximum. The latter has a linear low energy slope and extends to high energy. We have investigated the temperature dependence and symmetry properties of both signals. Our data agree with previous calculations and point to a spin liquid ground state.

cond-mat.str-el↗

arXiv2010

Quantum Kagome antiferromagnet ZnCu3(OH)6Cl2

The frustration of antiferromagnetic interactions on the loosely connected kagome lattice associated to the enhancement of quantum fluctuations for S=1/2 spins was acknowledged long ago as a keypoint to stabilize novel ground states of magnetic matter. Only very recently, the model compound Herbersmithite, ZnCu3(OH)6Cl2, a structurally perfect kagome antiferromagnet, could be synthesized and enables a close comparison to theories. We review and classify various experimental results obtained over the past years and underline some of the pending issues.

cond-mat.str-el↗

arXiv2005

Correlations, spin dynamics, defects: the highly-frustrated Kagomé bilayer

The SrCr$\_{9p}$Ga$\_{12-9p}$O$\_{19}$ and Ba$\_{2}$Sn$\_{2}$ZnGa$\_{10-7p}$Cr$\_{7p}$O$\_{22}$ compounds are two highly-frustrated magnets possessing a quasi-two-dimensional Kagomé bilayer of spin 3/2 chromium ions with antiferromagnetic interactions. Their magnetic susceptibility was measured by local Nuclear Magnetic Resonance and non-local (SQUID) techniques, and their low-temperature spin dynamics by Muon Spin Resonance. Consistent with the theoretical picture drawn for geometrically frustrated systems, the Kagomé bilayer is shown here to exhibit: (i) short range spin-spin correlations down to a temperature much lower than the Curie-Weiss temperature, no conventional long-range transition occurring; (ii) a Curie contribution to the susceptibility from paramagnetic defects generated by spin vacancies; (iii) low-temperature spin fluctuations, at least down to 30 mK, which are a trademark of a dynamical ground state. These properties point to a spin-liquid ground state, possibly built on Resonating Valence Bonds with unconfined spinons as the magnetic excitations.

cond-mat.str-el↗

arXiv2004

Intrinsic susceptibility and bond defects in the novel 2D frustrated antiferromagnet Ba$_{2}$Sn$_{2}$ZnCr$_{7p}$Ga$_{10-7p}$O$_{22}$

We present microscopic and macroscopic magnetic properties of the highly frustrated antiferromagnet Ba$_{2}$Sn$_{2}$ZnCr$_{7p}$Ga$_{10-7p}$O$_{22}$, respectively probed with NMR and SQUID experiments. The $T$-variation of the intrinsic susceptibility of the Cr$^{3+}$ frustrated kagomé bilayer, $χ_{kag}$, displays a maximum around 45 K. The dilution of the magnetic lattice has been studied in detail for $0.29 \leq p \leq0.97$. Novel dilution independent defects, likely related with magnetic bond disorder, are evidenced and discussed. We compare our results to SrCr$_{9p}$Ga$_{12-9p}$O$_{19}$. Both bond defects and spin vacancies do not affect the average susceptibility of the kagomé bilayers.

cond-mat.str-el↗

arXiv2002

Dynamics at T -> 0 in the half-integer isotropic high spin molecules

We investigate the dynamical spin-spin auto-correlation function of the isotropic high spin molecules CrCu$_{6}$ (S=9/2), CrNi$_{6}$ (S=15/2) and CrMn$_{6}$ (S=27/2), using magnetization, $μ$SR and NMR measurements. We find that the field autocorrelation time $τ$ of the molecule's spin at zero and low fields is nearly temperature independent as $T\to 50$ mK. The high temperatures $τ$ is very different between the molecules. Surprisingly, it is identical ($\sim$ 10 nsec) at low temperature. This suggests that $τ$ is governed by hyperfine interactions.

cond-mat.mes-hall↗