CPM Seminar

Dynamic nuclear polarization and resistively-detected NMR in semiconductor two-dimensional systems

Yoshiko Hirayama

Tohoku University

Recent progress of resistively-detected nuclear-magnetic-resonance (RDNMR) provides us a versatile tool to study physics in two-dimensional systems [1]. The RDNMR needs dynamic nuclear polarization (DNP) and sensitive detection of nuclear polarization. In semiconductor two-dimensional systems, the DNP is achieved by a current flow through a domain structure appearing in the quantum Hall ferromagnet (QHF) at the spin phase transition of ν = 2/3 (GaAs) or ν = 2 (InSb) [1,2]. The DNP can also be achieved by a quantum Hall breakdown [3] and irradiation of a circularly polarized light [4]. The situation necessary for the DNP also provides us sensitive detection of the nuclear polarization. Especially, a modulation of the domain structure by the DNP changes resistance value dramatically in the QHF [1]. The important role of the chiral edge channel on RDNMR is also addressed by using the InSb ν = 2 QHF [5].

We can clarify many interesting physics from RDNMR measurements. The Knight shift provides us information of electron spin polarization [6] and/or charge/spin ordering [7]. The nuclear relaxation (T1) includes information of electron spin fluctuation [1]. The quadrupolar splitting gives us a microscopic information of the strain. The novel Dicke-type interaction is suggested between ensemble of nuclear spins and ensemble of electron spins with a linear dispersion mode [8].

The nuclear resonance measurement has been extended to a microscopic imaging by a combination of the RDNMR and a sophisticated scanning-nanoprobe system operating at dilution temperatures. A quadrupolar coupling enables us rf electric field manipulation of nuclear spins [9]. This manipulation has an advantage of the higher spatial resolution than the conventional manipulation by rf magnetic field [10]. Successful mapping of NMR signal intensity and Knight shift has been demonstrated in the quantum Hall breakdown regime [11].

[1] Y. Hirayama et al., Semicond. Sci. Technol. 24, 023001 (2009); Y. Hirayama, Chapter 38, Quantum Hall Effects (3rd Edition) (World Scientific, 2013).
[2] M. Korkusinski et al., Scientific Reports 7, 43553 (2017).
[3] M. Kawamura et al., Appl. Phys. Lett. 90, 022102 (2007); T. Tomimatsu et al., Appl. Phys. Lett. 103, 082108 (2013).
[4] K. Akiba et al., Appl. Phys. Lett. 99, 112106 (2011); K. Akiba et al., Phys. Rev. B87, 235309 (2013); K. Akiba et al., Phys. Rev. Lett. 115, 026804 (2015)
[editor's Suggestion].
[5] K. F. Yang et al., Nature Comm., DOI: 10.1038/ncomms15084 (2017).
[6] L. Tiemann et al., Science 335, 828 (2012); R. Higashida et al., HMF2016.
[7] L. Tiemann et al., Nature Physics 10, 648 (2014).
[8] M. H. Fauzi et al., Phys. Rev. B90, 235308 (2014); Y. Hama et al., New J. Physics 18, 023027 (2016).
[9] T. Tomimatsu et al., AIP Advance 5, 087156 (2015).
[10] K. Hashimoto et al., AIP Advances 6, 075024 (2016).
[11] K. Hashimoto et al., ICPS2016 (invited); manuscript is in preparation.