Interaction-Induced Spin Polarization in Quantum Dots

Rogge, M.; Räsänen, E.; Haug, Rolf J.

doi:10.1103/physrevlett.105.046802

Cited by 28 publications

(23 citation statements)

References 32 publications

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“…Within perturbation theory, the effective interaction strength is enhanced by the presence of disorder, leading to a ferromagnetic instability already below the Stoner threshold [51]. Observations of the spin polarization for a few electrons system confined in quantum dots were reported in several experiments [52,53] and are considered as evidence of interaction-induced collective spin polarization transition. …”

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Novel energy scale in the interacting two-dimensional electron system evidenced from transport and thermodynamic measurements

2016

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We study how the non-Fermi-liquid two-phase state reveals itself in transport properties of highmobility Si-MOSFETs. We have found features in zero-field transport, magnetotransport, and thermodynamic spin magnetization in a 2D correlated electron system that may be directly related with the two-phase state. The features manifest above a density dependent temperature T * that represents a novel high-energy scale, apart from the Fermi energy. More specifically, in magnetoconductivity, we found a sharp onset of the novel regime δσ(B, T ) ∝ (B/T ) 2 above a density-dependent temperature T kink (n), a high-energy behavior that "mimics" the low-temperature diffusive interaction regime. The zero-field resistivity temperature dependence exhibits an inflection point T infl (n). In thermodynamic magnetization, the weak-field spin susceptibility per electron, ∂χ/∂n changes sign at T dM/dn (n). All three notable temperatures, T kink , T infl , and T dM/dn , behave critically ∝ (n − nc), are close to each other, and are intrinsic to high-mobility samples solely; we therefore associate them with an energy scale T * caused by interactions in the 2DE system. [5][6][7], metal-insulator transition (MIT) [1,5,[8][9][10], strong positive magnetoresistance (MR) in parallel field [11][12][13][14][15][16][17][18], strong renormalization of the effective mass and spin susceptibility [2,[19][20][21][22][23][24], etc.Far away from the critical MIT density n c , in the well "metallic regime," these effects are explained within the framework of the Fermi liquid theory -either in terms of interaction quantum corrections (IC) [25,26], or temperaturedependent screening of the disorder potential [27][28][29][30][31]. Both theoretical approaches so far are used to treat the experimental data on transport, and the former one -also to determine the Fermi liquid coupling constants from fitting the transport and magnetotransport data to the IC theory. In the close vicinity of the critical region, conduction is treated within the renormalization group [32][33][34][35][36], or the Wigner-Mott approach [37,38].On the other side, a number of theories predicts breakdown of the uniform paramagnetic 2D Fermi liquid state due to instability in the spin or charge channel, developing as interaction strength increases [39][40][41][42][43]. However, how the potential instabilities reveal themselves in charge transport remains an almost unexplored question.On the spin polarization of the 2D electron system Spin fluctuations are believed to play an important role in the 2DE system, especially near the apparent metalinsulator transition. Ferromagnetic instabilities result from the interplay of the electronic interactions and the Pauli principle. The interaction energy can be minimized when the fermion antisymmetry requirement is satisfied by the spatial wave function resulting in the alignment of spins and a large ground-state spin magnetization. In clean metals, the long-range part of the Coulomb interaction is screened, whereas its short-range part leads to s...

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Novel energy scale in the interacting two-dimensional electron system evidenced from transport and thermodynamic measurements

2016

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“…The constant gaps between adjacent Coulomb peaks due to the Coulomb repulsion energy are removed following the procedure presented in detail in Ref. 22. The states of the excitation spectrum can thereby be followed over several electron numbers.…”

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Spin-dependent shot noise enhancement in a quantum dot

et al. 2013

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The spin-dependent dynamical blockade was investigated in a lateral quantum dot in a magnetic field. Spinpolarized edge channels in the two-dimensional leads and the spatial distribution of Landau orbitals in the dot modulate the tunnel coupling of the quantum dot level spectrum. In a measurement of the electron shot noise we observe a pattern of super-Poissonian noise which is correlated to the spin-dependent competition between different transport channels. DOI: 10.1103/PhysRevB.88.041304 PACS number(s): 72.70.+m, 72.25.−b, 73.23.Hk, 73.63.Kv The prospect of using the electron spin as a basic element of information for quantum computation and new semiconductor devices has stimulated the study of spindependent phenomena. Many of these applications require control of the spin-dependent dynamics in the transfer of charge through single electron devices. Fluctuations of the current contain information about these dynamics and the underlying mechanisms can be probed in a measurement of the electron shot noise. In particular, the bunching of tunneling events, observable as an increased shot noise power, can characterize the Coulomb interaction in the transport through multilevel quantum dots.1-8 The sequence of tunneling events is correlated by the Coulomb blockade and depends on the effective tunneling rates and internal level structure, which allows for the detection of spin-dependent tunneling through quantum dots.9 Injection of electrons from spin-polarized leads may result in a spin-dependent blockade as shown by Ciorga et al. [10][11][12] The spin blockade effect 13 has been observed in the addition spectrum of a quantum dot in a magnetic field 14,15 as a modulation of the Coulomb blockade peak amplitude or in the occurrence of negative differential resistance. 16 While these measurements studied the average conductance, additional dynamical information can be obtained by shot noise detection techniques.In this Rapid Communication we present our measurements of the electron shot noise in the spin blockade regime. At finite bias we observe super-Poissonian noise at the Coulomb blockade peak. The shot noise enhancement follows a regular pattern correlated to the crossing Landau levels in a magnetic field. Interpretation in terms of the dynamical channel blockade mechanism suggests an underlying competition between transport channels with different spin.The quantum dot is defined by local anodic oxidation of a GaAs/AlGaAs heterostructure with a two-dimensional electron system 34 nm below the surface. 16 The electron density of the heterostructure is 4.6 × 10 11 cm −2 and the mobility is 6.4 × 10 5 cm 2 /V s. Measurements were performed in a 3 He/ 4 He dilution refrigerator at a temperature of 100 mK. Current fluctuations are converted to voltage fluctuations by RLC circuits in a cross-correlation configuration [ Fig. 1(a)] centered at 1 MHz. The voltage fluctuations are amplified by cryogenic high-electron-mobility transistor (Refs. 17 and 18) and digitized at room temperature. The real part of the cross-corr...

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“…To calculate exchangecorrelation energy E xc , we use the local spin density approximation (LSDA) with a parametrization provided by Attaccalite et al 34 . The SDFT scheme together with LSDA leads to good numerical accuracy and produce reliable results in comparision with quantum Monte Carlo calculations in quantum dot systems 16,20,35 . In the SDFT calculations, we utilise the OCTOPUS 36,37 code package (published under the General Public License) built on the real space grid discretization method which allows realistic modeling of two dimensional systems.…”

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Formation of spin droplet atν=52in an asymmetric quantum dot under quantum Hall conditions

Atci

Siddiki

2017

Phys. Rev. B

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In this work, a quantum dot that is defined asymmetrically by electrostatic means induced on a GaAs/AlGaAs heterostructure is investigated to unravel the effect of geometric constrains on the formation of spin droplets under quantised Hall conditions. The incompressibility of exciting ν = 5/2 state is explored by solving the Schrödinger equation within spin density functional theory, where the confinement potential is obtained self-consistently utilising the Thomas-Fermi approximation. Our numerical investigations show that the spatial distribution of the ν = 2 incompressible strips and electron occupation in the second lowest Landau level considerably differ from the results of the laterally symmetric quantum dots. Our findings yield two important consequences, first the incompressibility of the intriguing ν = 5/2 state is strongly affected by the asymmetry, and second, since the Aharonov-Bohm interference patterns depend on the velocity of the particles, asymmetry yields an additional parameter to adjust the oscillation period, which imposes a boundary condition dependency in observing quasi-particle phases.

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Interaction-Induced Spin Polarization in Quantum Dots

Cited by 28 publications

References 32 publications

Novel energy scale in the interacting two-dimensional electron system evidenced from transport and thermodynamic measurements

Novel energy scale in the interacting two-dimensional electron system evidenced from transport and thermodynamic measurements

Spin-dependent shot noise enhancement in a quantum dot

Formation of spin droplet atν=52in an asymmetric quantum dot under quantum Hall conditions

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