Maxime Dupont

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 one-dimensional (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, nc(Tc), and the absolute value of the BEC order parameter Sp at very low temperature (T = 0.12 K). All results are accurately reproduced by numerical quantum Monte Carlo simulations of a realistic 3D model Hamiltonian. Approximate analytical predictions based on 1D Tomonaga- Luttinger liquid description are found to be precise for Tc(H), but less so for Sp(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 nc = 4% (T < 0.3 K), while for higher nc boson interactions appear to modify the density of states.

Temperature dependence of the NMR relaxation rate

We present results of numerical simulations performed on one-dimensional spin chains in order to extract the so-called relaxation rate

1/T_1

1/T_1

for quantum spin chains

accessible through NMR experiments. Building on numerical tensor network methods using the Matrix Product States (MPS) formalism, we can follow the non-trivial crossover occurring in critical chains between the high-temperature diffusive classical regime and the low-temperature response described by the Tomonaga-Luttinger liquid (TLL) theory, for which analytical expressions are known. In order to compare analytics and numerics, we focus on a generic spin-

Competing Bose-glass physics with disorder-induced Bose-Einstein condensation in the doped S=1 antiferromagnet Ni(Cl1−xBrx)2−4SC(NH2)2 at high magnetic fields

1/2

Dimensional modulation of spontaneous magnetic order in quasi-two-dimensional quantum antiferromagnets

XXZ chain which is a paradigm of gapless TLL, as well as a more realistic spin-

Nuclear Magnetic Resonance Reveals Disordered Level-Crossing Physics in the Bose-Glass Regime of the Br-Doped Ni(Cl1−xBrx)2−4SC(NH2)2 Compound at a High Magnetic Field

1

Disorder-Induced Revival of the Bose-Einstein Condensation in Ni(Cl1−xBrx)2−4SC(NH2)2 at High Magnetic Fields

anisotropic chain, modelling the DTN material, which can be either in a trivial gapped phase or in a TLL regime induced by an external magnetic field. Thus, by monitoring the finite temperature crossover, we provide quantitative limits on the range of validity of TLL theory, that will be useful when interpreting experiments on quasi one-dimensional materials.

Many-body localization as a large family of localized groundstates

Author(s): Dupont, Maxime; Capponi, Sylvain; Horvatic, Mladen; Laflorencie, Nicolas | Abstract: We study the interplay between disorder and interactions for emergent bosonic degrees of freedom induced by an external magnetic field in the Br-doped spin-gapped antiferromagnetic material Ni(Cl

Detection of a Disorder-Induced Bose-Einstein Condensate in a Quantum Spin Material at High Magnetic Fields

_{1-x}