Single-electron capacitance spectroscopy of discrete quantum levels

Ashoori, R. C.; Störmer, H. L.; Weiner, J. S.; Pfeiffer, L. N.; Pearton, S. J.; Baldwin, K. W.; West, K. W.

doi:10.1103/physrevlett.68.3088

Cited by 476 publications

(393 citation statements)

References 10 publications

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“…To measure capacitance, we used a HEMT-based amplifier to construct a low temperature capacitance bridge-on-achip 34 . A schematic representation of the bridge geometry and electronics appears in Supplementary Figure S6.…”

Section: Capacitance Measurementsmentioning

confidence: 99%

Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state

Young

Sanchez-Yamagishi

Hunt

et al. 2013

Nature

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276

349

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Low-dimensional electronic systems have traditionally been obtained by electrostatically confining electrons, either in heterostructures or in intrinsically nanoscale materials such as single molecules, nanowires, and graphene. Recently, a new paradigm has emerged with the advent of symmetry-protected surface states on the boundary of topological insulators, enabling the creation of electronic systems with novel properties. For example, time reversal symmetry (TRS) endows the massless charge carriers on the surface of a three-dimensional topological insulator with helicity, locking the orientation of their spin relative to their momentum 1,2 . Weakly breaking this symmetry generates a gap on the surface, 3 resulting in charge carriers with finite effective mass and exotic spin textures 4 . Analogous manipulations of the one-dimensional boundary states of a two-dimensional topological insulator are also possible, but have yet to be observed in the leading candidate materials 5,6 . Here, we demonstrate experimentally that charge neutral monolayer graphene displays a new type of quantum spin Hall (QSH) effect 7,8 , previously thought to exist only in time reversal invariant topological insulators 5,9-11 , when it is subjected to a very large magnetic field angled with respect to the graphene plane. Unlike in the TRS case 5,9,10 , the QSH presented here is protected by a spin-rotation symmetry that emerges as electron spins in a half-filled Landau level are polarized by the large in-plane magnetic field. The properties of the resulting helical edge states can be modulated by balancing the applied field against an intrinsic antiferromagnetic instability [12][13][14] , which tends to spontaneously break the spin-rotation symmetry. In the resulting canted antiferromagnetic (CAF) state, we observe transport signatures of gapped edge states, which constitute a new kind of one-dimensional electronic system with tunable band gap and associated spin-texture 15 .In the integer quantum Hall effect, the topology of the bulk Landau level (LL) energy bands 16 requires the existence of gapless edge states at any interface with the vacuum. The metrological precision of the Hall quantization can be traced to the inability of these edge states to backscatter due to the physical separation of modes with opposite momentum by the insulating sample bulk 17 . In contrast, counterpropagating boundary states in a symmetry-protected topological (SPT) insulator coexist spatially but are prevented from backscattering by a symmetry of the experimental system 1,2 . The local symmetry that protects transport in SPT surface states is unlikely to be as robust as the inherently nonlocal physical separation that protects the quantum Hall effect. However, it enables the creation of new electronic systems in which momentum and some quantum number such as spin are coupled, potentially leading to devices with new functionality. Most experimentally realized SPT phases are based on TRS, with counterpropagating states protected from intermixing by the Kram...

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Section: Capacitance Measurementsmentioning

confidence: 99%

Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state

Young

Sanchez-Yamagishi

Hunt

et al. 2013

Nature

Self Cite

276

349

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“…Typically, neighboring energy levels do not cross each other, but rather come close and then repel in an "avoided crossing". However, if there is an exact symmetry, neighboring levels can have different symmetries uncoupled by the perturbation, and in this special case they can cross.A new and powerful way of studying parametric evolution in many-body quantum systems is through the Coulomb blockade peaks that occur in mesoscopic quantum dots [2,3,4,5]. The electrostatic energy of an additional electron on a quantum dot-an island of confined charge with quantized states-blocks the flow of current through the dot-the Coulomb blockade [6,7].…”

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confidence: 99%

Interactions and interference in quantum dots: Kinks in Coulomb-blockade peak positions

2000

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We investigate the spin of the ground state of a geometrically confined many-electron system. For atoms, shell structure simplifies this problem-the spin is prescribed by the well-known Hund's rule. In contrast, quantum dots provide a controllable setting for studying the interplay of quantum interference and electron-electron interactions in general cases. In a generic confining potential, the shell-structure argument suggests a singlet ground state for an even number of electrons. The interaction among the electrons produces, however, accidental occurrences of spin-triplet ground states, even for weak interaction, a limit which we analyze explicitly. Variaton of an external parameter causes sudden switching between these states and hence a kink in the conductance. Experimental study of these kinks would yield the exchange energy for the "chaotic electron gas".The evolution of the properties of a system as a continuous change is made to it is a ubiquitous topic in quantum physics. The classic example is the evolution of energy levels as the strength of a perturbation is varied [1]. Typically, neighboring energy levels do not cross each other, but rather come close and then repel in an "avoided crossing". However, if there is an exact symmetry, neighboring levels can have different symmetries uncoupled by the perturbation, and in this special case they can cross.A new and powerful way of studying parametric evolution in many-body quantum systems is through the Coulomb blockade peaks that occur in mesoscopic quantum dots [2,3,4,5]. The electrostatic energy of an additional electron on a quantum dot-an island of confined charge with quantized states-blocks the flow of current through the dot-the Coulomb blockade [6,7]. Current can flow only if two different charge states of the dot are tuned to have the same energy; this produces a peak in the conductance through the dot. The position of the Coulomb blockade peak depends on the difference in ground state energy upon adding an electron, E gr (N + 1) − E gr (N ). Thus, the evolution of the peak position reflects the evolution of these many-body energy levels as a parameter, such as magnetic field or gate voltage, is varied.Since quantum dots are generally irregular in shape, the orbital levels have no symmetry and so avoid crossing. However, the spin degrees of freedom are often decoupled from the rest of the system, so states of different total spin can cross. Such a crossing will cause an abrupt change in the evolution of the Coulomb blockade peak position-a kink-as the spin of the ground state changes, even though there is no crossing in the singleparticle states. Such kinks have been observed in small circular dots-"artificial atoms"-because of their special circular symmetry [5]. More generally, kinks should occur in generic quantum dots with no special symmetries [8]. In fact, the data of Ref. [4] show evidence for kinks in large dots, though they were not the subject of that investigation.Small circular dots behave much like atoms (hence "artificial atoms"): ...

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“…In quantum dots electrostatically produced, both their size and separation can be controlled by variable gate voltages through metallic electrodes deposited on the heterostructure interface. The eventual existence of doping hydrogenic impurities, probably arising from Si dopant atoms in the GaAs quantum well, have been experimentally studied [45]. These impurities have been theoretically analyzed with a superimposed attractive 1/r-type potential [46,47].…”

Section: Model and Calculation Methodsmentioning

confidence: 99%

“…Recent works [42,43,44,45,46,47,48] studied the effects of having unintentional charged impurities in two-electron laterally coupled two-dimensional double quantum-dot systems. They analyzed the effects of quenched random-charged impurities on the singlet-triplet exchange coupling and spatial entanglement in two-electron double quantum-dots.…”

Section: Introductionmentioning

confidence: 99%

Optimal control of a charge qubit in a double quantum dot with a Coulomb impurity

Coden

Romero

Ferrón

et al. 2017

Physica E: Low-dimensional Systems and Nanostructures

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Abstract. We study the efficiency of modulated laser pulses to produce efficient and fast charge localization transitions in a two-electron double quantum dot. We use a configuration interaction method to calculate the electronic structure of a quantum dot model within the effective mass approximation. The interaction with the electric field of the laser is considered within the dipole approximation and optimal control theory is applied to design high-fidelity ultrafast pulses in pristine samples. We assessed the influence of the presence of Coulomb charged impurities on the efficiency and speed of the pulses. A protocol based on a two-step optimization is proposed for preserving both advantages of the original pulse. The processes affecting the charge localization is explained from the dipole transitions of the lowest lying two-electron states, as described by a discrete model with an effective electron-electron interaction.

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Single-electron capacitance spectroscopy of discrete quantum levels

Cited by 476 publications

References 10 publications

Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state

Tunable symmetry breaking and helical edge transport in a graphene quantum spin Hall state

Interactions and interference in quantum dots: Kinks in Coulomb-blockade peak positions

Optimal control of a charge qubit in a double quantum dot with a Coulomb impurity

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