Laurent. P. Levy

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.

New Phase Transition between Partially and Fully Polarized Quantum Hall States with Charge and Spin Gaps at nu = (2/3)

The average electron spin polarization Rho of a two-dimensional electron gas confined in GaAs/GaAlAs multiple quantum wells was measured by NMR near the fractional quantum Hall state with filling factor nu = 2/3. Above this filling factor (2/3< or = nu < 0.85), a strong depolarization is observed corresponding to two spin flips per additional flux quantum. The most remarkable behavior of the polarization is observed at nu = 2/3, where a quantum phase transition from a partially polarized (Rho approximately 3/4) to a fully polarized (Rho = 1) state can be driven by increasing the ratio between the Zeeman and the Coulomb energy above a critical value eta(c) = Delta(Z)/Delta(C) = 0.0185.

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

High-field magnetic phases of a two-leg spin ladder: Cu2(C5H12N2)2Cl4

1/T_1

Magnetization of an incompressible two-dimensional electron gas.

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

MAGNETIZATION AND INCOMPRESSIBILITY OF A HIGH MOBILITY 2D ELECTRON GAS IN THE IQHE

\Delta \simeq J_\perp-J_\parallel

Tunnel spectroscopy of a double superconducting island qubit

in this strongly coupled ladder (

Magnetization and Orbital Properties of the Two-Dimensional Electron Gas in the Quantum Limit

J_\parallel < J_\perp

MAGNETIZATION AND ENERGY GAPS OF A HIGH-MOBILITY 2D ELECTRON GAS IN THE QUANTUM LIMIT

) is supported by the K and

NMR determination of 2D electron spin polarization at nu = 1/2.

1/T_1