QDev Seminar: Trevor Rhone – University of Copenhagen

QDev Seminar: Trevor Rhone

NMR probing of spin and charge order in two dimensional electron systems

Trevor D. Rhone1,2, Lars Tiemann1,2, Koji Muraki1,2

1. NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi, 243-0198, Japan
2. ERATO Nuclear Spin Electronics Project, Japan Science and Technology Agency (JST)

We probe the spin signatures of a two-dimensional electron system, confined to a GaAs quantum well, around filling factors v = 2, 5/2 and 3, using resistively detected nuclear magnetic resonance (RDNMR) spectroscopy at milliKelvin temperatures. NMR can be used to study the spin properties for delicate states such as the one at v = 5/2 - the investigation of which is at the forefront of quantum Hall research. We find the state at v = 5/2 to be fully spin polarized.
In addition, we report striking anomalies in the RDNMR spectral line shape in the vicinity of integer quantum Hall states, v ~ 2 and v ~ 3. Using NMR as a local probe of the 2DES together with simulations based on microscopic wavefunctions, we find the anomalous line shape to be due to the presence of correlated electron solids in the vicinity of integer filling.
The existence of spin textures, known as skyrmions, around odd-integer states in the excited Landau levels is a debated issue. Using NMR we probe spin signatures at v ~ 3 - measuring the T1 spin-lattice relaxation time and the Knight shift. T1 is sensitive to spin textures as they trigger a rapid nuclear spin relaxation. Our T1 measurements around v = 3 show long spin-lattice relaxation times, suggesting the absence of skyrmions. Knight shift measurements show the 2DES is maximally spin polarized, corroborating this interpretation.
Interestingly, the 2DES at v ~ 3 is fully spin polarized in the presence of domains of electron solids which could engender the collapse of the ferromagnetic spin wave observed in recent light scattering experiments. This work shows that NMR is capable of exploring both spin and charge order of a 2DES and could be employed to investigate the existence of skyrmions and solid phases near v = 5/2. This work also encourages the study of exotic phenomena such as bubble phases, stripe phases and quantum Hall nematic phases where work on broken translation symmetry in quantum Hall systems is becoming of increasing interest.