NMR response of nuclear-spin helix in quantum wires with hyperfine and spin-orbit interaction

Stano, Peter; Loss, Daniel

doi:10.1103/physrevb.90.195312

Cited by 11 publications

(14 citation statements)

References 47 publications

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“…111 Indirect experimental signatures of the nuclear spin order, however, can be searched for below the transition temperature. As discussed in the literature, these include: (1) the reduction of conductance by a factor of 2 due to the opening of the partial gap; 37,38,47,112 (2) the anisotropic spin susceptibilityχ x αβ (q) =χ z αβ (q) due to the formation of the nuclear spin order; 95 (3) NMR response at the frequency set by the RKKY exchange due to the singular RKKY peak; 113 (4) the unusual temperature dependence of the nuclear spin relaxation rate due to the Luttinger liquid parameters modified by the Overhauser field; 114 (5) the reentrant behavior in the conductance as a function of gate voltage due to the nuclear spin induced gap; 115 (6) the dynamical nuclear polarization at zero external magnetic field. 42 Furthermore, experimental probes can be implemented to observe the distinct pairing gaps, ∆ (e/i) s…”

Section: Discussionmentioning

confidence: 99%

Antiferromagnetic nuclear spin helix and topological superconductivity inC13nanotubes

et al. 2015

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We investigate the RKKY interaction arising from the hyperfine coupling between localized nuclear spins and conduction electrons in interacting 13 C carbon nanotubes. Using the Luttinger liquid formalism, we show that the RKKY interaction is sublattice dependent, consistent with the spin susceptibility calculation in noninteracting carbon nanotubes, and it leads to an anti-ferromagnetic nuclear spin helix in finite-size systems. The transition temperature reaches up to tens of millikelvins, due to a strong boost by a positive feedback through the Overhauser field from ordered nuclear spins. Similar to GaAs nanowires, the formation of the helical nuclear spin order gaps out half of the conduction electrons, and is therefore observable as a reduction of conductance by a factor of two in a transport experiment. The nuclear spin helix leads to a density wave combining spin and charge degrees of freedom in the electron subsystem, resulting in synthetic spin-orbit interaction, which induces non-trivial topological phases. As a result, topological superconductivity with Majorana fermion bound states can be realized in the system in the presence of proximity-induced superconductivity without the need of fine tuning the chemical potential. We present the phase diagram as function of system parameters, including the pairing gaps, the gap due to the nuclear spin helix, and the Zeeman field perpendicular to the helical plane.

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Section: Discussionmentioning

confidence: 99%

Antiferromagnetic nuclear spin helix and topological superconductivity inC13nanotubes

et al. 2015

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“…However, NMR or other direct evidence showing involvement of nuclear spins has not been presented so far. NMR signal detection in the QPC conductance would constitute a novel experimental technique to probe spin properties of QPCs or nanowires [32,33].In this Letter, we report an electronic magnetization measurement of a QPC defined in a GaAs/AlGaAs heterostructure based on NMR spectroscopy. We find that the QPC differential conductance changes when the frequency of an applied oscillating magnetic field matches the NMR frequencies of 69 Ga, 71 Ga, and 75 As.…”

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confidence: 99%

Electronic Magnetization of a Quantum Point Contact Measured by Nuclear Magnetic Resonance

Kawamura¹,

Ono²,

Stano³

et al. 2015

Phys. Rev. Lett.

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We report an electronic magnetization measurement of a quantum point contact (QPC) based on nuclear magnetic resonance (NMR) spectroscopy. We find that NMR signals can be detected by measuring the QPC conductance under in-plane magnetic fields. This makes it possible to measure, from Knight shifts of the NMR spectra, the electronic magnetization of a QPC containing only a few electron spins. The magnetization changes smoothly with the QPC potential barrier height and peaks at the conductance plateau of 0.5 × 2e 2 /h. The observed features are well captured by a model calculation assuming a smooth potential barrier, supporting a no bound state origin of the 0.7 structure.Quantum point contact (QPC) is a short onedimensional (1D) channel connecting two electron reservoirs. Its conductance is quantized to integer multiples of 2e 2 /h, where e is electron charge and h is Planck's constant [1,2]. The conductance quantization is well understood within a model of non-interacting electrons [3]. However, experiments have shown an additional conductance feature, a shoulder-like structure at around 0.7 × 2e 2 /h termed as 0.7 structure [4,5]. Despite the simplicity of a QPC, a comprehensive understanding of the 0.7 structure is still lacking [6][7][8][9][10][11][12][13][14][15][16][17][18][19].Theories proposed to explain the 0.7 structure can be discriminated according to their predictions on the electron spin arrangement, which include spontaneous spin polarization [6,7], antiferromagnetic Wigner crystal [8], Kondo screening [9][10][11], and local spin fluctuations accompanied by van Hove singularity [12,13]. Especially in the Kondo scenario, the existence of a localized magnetic moment in the QPC is an inevitable ingredient. On one hand, early experiments observing Fano resonances suggested such presence of a local single spin trapped in a bound state regardless of magnetic fields [14]. On the other hand, an experiment measuring compressibility contradicts such bound state formation [18]. Thus, the degree of spin polarization of a QPC is one of the central issues to understand the origin of the 0.7 structure.However, most experiments[4, 5, 14-17] to date have focused on transmission properties, without the QPC spin polarization being addressed directly. Despite the recent progress in magnetic sensors [20], the magnetization measurement of a QPC containing only a few electrons is still very challenging. Recently, small magnetizations of two-dimensional electron systems (2DESs) embedded in GaAs have been measured [21][22][23] by combining techniques of current-induced nuclear spin polarization [24][25][26][27][28] and resistance (conductance) detection of nuclear magnetic resonance (NMR) signals of Ga and As nuclei [27][28][29]. Because of the hyperfine interaction between electronic and nuclear spins, an electronic magnetization produces an effective magnetic field for nuclei, resulting in the shift of the NMR frequency, the Knight shift. From the Knight shift, the electronic magnetization can be determined [30].A recent...

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“…It is natural to expect that high temperature destroys the nuclear helical order. 15,16,34,36 Indeed, Fig. 4 shows that the heli- cal polarization p h decays with temperature and then drops in magnitude around T 109 mK.…”

Section: Resulting Polarizationsmentioning

confidence: 97%

Voltage-induced conversion of helical to uniform nuclear spin polarization in a quantum wire

et al. 2015

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We study the effect of bias voltage on the nuclear spin polarization of a ballistic wire, which contains electrons and nuclei interacting via hyperfine interaction. In equilibrium, the localized nuclear spins are helically polarized due to the electron-mediated Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Focusing here on non-equilibrium, we find that an applied bias voltage induces a uniform polarization, from both helically polarized and unpolarized spins available for spin flips. Once a macroscopic uniform polarization in the nuclei is established, the nuclear spin helix rotates with frequency proportional to the uniform polarization. The uniform nuclear spin polarization monotonically increases as a function of both voltage and temperature, reflecting a thermal activation behavior. Our predictions offer specific ways to test experimentally the presence of a nuclear spin helix polarization in semiconducting quantum wires.

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NMR response of nuclear-spin helix in quantum wires with hyperfine and spin-orbit interaction

Cited by 11 publications

References 47 publications

Antiferromagnetic nuclear spin helix and topological superconductivity inC13nanotubes

Antiferromagnetic nuclear spin helix and topological superconductivity inC13nanotubes

Electronic Magnetization of a Quantum Point Contact Measured by Nuclear Magnetic Resonance

Voltage-induced conversion of helical to uniform nuclear spin polarization in a quantum wire

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