L2C - Laboratoire Charles Coulomb

Spin physics

These activities are funded by :

  • CONUS (ANR-Russian Science Fundation project, 2022-2025) : COrrelated NUclear Spin states in n-GaAs and nanostructures
  • Bourse Vernadski (Ambassade de France en Fédération de Russie, 2021-2025, PhD in co-tutelle de Boris Gribakin)

Spin dynamics :

Concerning spin dynamics, the most outstanding results were obtained on the dynamics of collective excitations in n-type CdMnTe quantum wells, in which we have observed in the time-domain the signature of mixed electron-Mn precession modes.

This is an example of strong coupling between conduction band electron spins and Mn spins, which manifests itself via the appearance of spin beatings (see Figure 6). This observation gives a new independent mean to determine the spin polarisation of the 2DEG, and look for its enhancement due to Coulomb interactions. In addition Mn spin excitations uncoupled to the 2DEG have been discovered.

Time-resolved Kerr rotation (black curve) and fit with 3 damped cosines (red curve) (left a). FFT of the Kerr rotation exhibiting the existence of three modes, two broadened mixed modes and one narrow uncoupled mode (left b)). Precession frequencies and relaxation times of the three modes as a function of magnetic field (right a and b).

Spin Noise spectroscopy and Nuclear spin :

    Spin noise spectroscopy (SNS) is a powerful new method for studying magnetic resonance and spin dynamics. It is based on measuring magnetization noise of a paramagnet using the Faraday rotation technique. We have contributed to the development of this technique, by increasing both its sensitivity and accessible frequency range using heterodyne detection scheme [Cronenberger2016].

    The SNS implemented in L2C allowed, in particular, for the detection of atomic-like spin fluctuations of Mn ions diluted in CdTe, while previously SNS was limited to carriers in semiconductor heterostructures [Cronenberger2015]. More recently we implemented spatiotemporal spin noise spectroscopy and applied it to n-CdTe, reaching spatial resolutions down to ∼λ/10 [Cronenberger2019,Cronenberger2021]. This activity benefits from long-standing fruitful collaboration with institute Néel.

    In a set of theoretical and experimental works we have established the potential of the SNS for probing nuclear spin polaron, a collective electron-nuclei spin state which is specific to semiconductors [Vladimirova2021]. To do so, we have addressed experimentally and theoretically nuclear spin relaxation in both n and p-type GaAs, as a function of impurity concentration and magnetic field (collaboration with C2N and SpinOptics Lab in St-Petersburg). The adiabatic demagnetization of nuclei to zero magnetic field, detected by SNS, provided us with a first direct confirmation of the nuclear spin temperature hypothesis, and a direct measurement of the nuclear heat capacity field [Vladimirova2018].

    Later on we proposed and implemented nuclear magnetic resonance experiments detected by electron spin noise. These experiments allowed us to establish a connection between the residual strain in n-GaAs giving rise to quadrupole splittings, the increased heat capacity and nuclear spin relaxation rates at low and zero field [Vladimirova2021].

    This topic has been initially developed in the framework ANR SNS and PRC Russie SpinCool. It is now supported by ANR-RNF CONUS : COrrelated NUclear Spin states in n-GaAs and nanostructures.

    Atomic-like spin noise in solid-state demonstrated with manganese in cadmium telluride :