Olivo Piovesana

NUCLEAR MAGNETIC RESONANCE STUDY OF THE S = 1/2 HEISENBERG LADDER CU2(C5HJ2N2)2C14 : QUANTUM PHASE TRANSITION AND CRITICAL DYNAMICS

We present an extensive NMR study of the spin-1/2 antiferromagnetic Heisenberg ladder Cu2(C5H12N2)2Cl4 in a magnetic field range 4.5 - 16.7 T. By measuring the proton NMR relaxation rate 1/T_1 and varying the magnetic field around the critical field H_c1 = Delta / g\mu_B = 7.5 T, we have studied the transition from a gapped spin liquid ground state to a gapless magnetic regime which can be described as a Luttinger liquid. We identify an intermediate regime T > |H-H_c1|, where the spin dynamics is (possibly) only controlled by the T=0 critical point H_c1.

Controlling Luttinger liquid physics in spin ladders under a magnetic field.

We present a 14N nuclear magnetic resonance study of a single crystal of CuBr4(C5H12N)2 (BPCB) consisting of weakly coupled spin-1/2 Heisenberg antiferromagnetic ladders. Treating ladders in the gapless phase as Luttinger liquids, we are able to fully account for (i) the magnetic field dependence of the nuclear spin-lattice relaxation rate T1(-1) at 250 mK and for (ii) the phase transition to a 3D ordered phase occurring below 110 mK due to weak interladder exchange coupling. BPCB is thus an excellent model system where the possibility to control Luttinger liquid parameters in a continuous manner is demonstrated and the Luttinger liquid model tested in detail over the whole fermion band.

Zero temperature phase transitions in spin-ladders: Phase diagram and dynamical studies of Cu2(C5H12N2)2Cl4>

Abstract:In a magnetic field, spin-ladders undergo two zero-temperature phase transitions at the critical fields Hc1 and Hc2. An experimental review of static and dynamical properties of spin-ladders close to these critical points is presented. The scaling functions, universal to all quantum critical points in one-dimension, are extracted from (a) the thermodynamic quantities (magnetization) and (b) the dynamical functions (NMR relaxation). A simple mapping of strongly coupled spin ladders in a magnetic field on the exactly solvable XXZ model enables to make detailed fits and gives an overall understanding of a broad class of quantum magnets in their gapless phase (between Hc1 and Hc2). In this phase, the low temperature divergence of the NMR relaxation demonstrates its Luttinger liquid nature as well as the novel quantum critical regime at higher temperature. The general behavior close these quantum critical points can be tied to known models of quantum magnetism.

Identification of Nuclear Relaxation Processes in a Gapped Quantum Magnet: 1 H NMR in the S = 1 2 Heisenberg Ladder Cu 2 ( C 5 H 12 N 2 ) 2 Cl 4

The proton hyperfine shift K and NMR relaxation rate

Quantum-critical spin dynamics in quasi-one-dimensional antiferromagnets.

1/T_1

Thermodynamic properties of the spin-1/2 antiferromagnetic ladder \(\) under magnetic field

have been measured as a function of temperature in the S=1/2 Heisenberg antiferromagnetic ladder Cu2(C5H12N2)2Cl4. The presence of a spin gap

New pentanuclear mixed valence Co(II)–Co(III) complexes of “short” salen homologues

\Delta \simeq J_\perp-J_\parallel

Structure and Magnetism of a New 2-D Bimetallic Compound of Mn(II) and Cu(II)

in this strongly coupled ladder (

Field-induced staggered magnetization and magnetic ordering in Cu2(C5H12N2)2Cl4.

J_\parallel < J_\perp

Binuclear Co(II)Co(II), Co(II)Co(III) and Co(III)Co(III) complexes of “short” salen homologues derived from the condensation of salicylaldehyde and methanediamine or phenylmethanediamines. Synthesis, structures and magnetism

) is supported by the K and