Observation of the Kondo effect in a spin-32 hole quantum dot

Abstract

We report the observation of Kondo physics in a spin-3 2 hole quantum dot. The dot is formed close to pinch-off in a hole quantum wire defined in an undoped AlGaAs/GaAs heterostructure. We clearly observe two distinctive hallmarks of quantum dot Kondo physics. First, the Zeeman spin-splitting of the zero-bias peak in the differential conductance is independent of gate voltage. Second, this splitting is twice as large as the splitting for the lowest one-dimensional subband. We show that the Zeeman splitting of the zero-bias peak is highly-anisotropic, and attribute this to the strong spin-orbit interaction for holes in GaAs.PACS numbers: 72.15. Qm, 75.70.Tj The observation of an unexpected minimum in the low temperature resistance of metals by de Haas in 1933 was ultimately explained thirty years later by Kondo as being due to interactions between a single magnetic impurity and the sea of conduction electrons in a metal [1,2]. More recently there has been a resurgence of interest in the Kondo effect, following the discovery that the conductance of a few electron quantum dot in the Coulomb blockade regime is enhanced when the dot contains an odd number of electrons [3][4][5]. There is a direct analogy with the Kondo effect in metals, with the localized electron in the quantum dot acting as a magnetic impurity that interacts with the two-dimensional sea of electrons in the source and drain reservoirs.Studies of the Kondo effect in bulk systems have progressed since the 1960s, with the focus shifting towards manifestations of Kondo physics in the strongly correlated electron systems formed in cuprates and heavyfermion metals [6]. More precise control via improved electrostatic gate design has similarly allowed progress towards the study of more exotic manifestations of Kondo phenomena in quantum dots such as the integer-spin [7][8][9], two-impurity [10], and orbital Kondo effects [11]. Thus far all quantum dot Kondo studies have involved electrons, and GaAs hole quantum dots present an interesting next step. Holes in GaAs originate from p-like orbitals and behave as spin-3 2 particles due to strong spinorbit coupling [12]. In two-and one-dimensional systems, the spin-3 2 nature of holes leads to remarkable, highlyanisotropic phenomena [13-17] not observed in electron systems, and new physics is expected for hole quantum dots also [18]. Studies of Kondo physics in hole quantum dots may also provide useful connections to recent studies in bulk strongly correlated systems [19,20].Here we report the observation of the Kondo effect in a GaAs hole quantum dot. Due to the poor stability of conventional gate-defined modulation doped struc- * klochan@phys.unsw.edu. A key advantage to this approach is the ability to obtain an independent estimate of the effective Landé g-factor g * . Using this we have fabricated a small hole quantum dot and conclusively demonstrate the "smoking gun" for Kondo physics [23] -a splitting of the zero-bias peak in the differential conductance that opens as 2g * µ B B in response to an in-plane...

Extreme Sensitivity of the Spin-Splitting and 0.7 Anomaly to Confining Potential in One-Dimensional Nanoelectronic Devices

“…In Figure , we plot G ′( V sd ) versus V sd for BT and PI-0, with V t settings chosen to best isolate the effect of differences in Δ E 1,2 and n (the corresponding data points are indicated (a–c) in Figure ). PI-0 shows a clear zero-bias peak (ZBP) over the entire range 0 < G < G 0 ; this ZBP behavior is consistent with most previous reports. ,,− The ZBP amplitude and width for a given G are relatively independent of density (Figure b,c); similar behavior is found for PI-375. In comparison, the ZBP for BT is heavily suppressed (Figure a); while evident as a smaller amplitude peak for 0.4 G 0 < G < 0.8 G 0 , it vanishes in the limits G → 0 and G → G 0 .…”

“…One possible explanation for our observations, in particular the link between the 0.7 anomaly behavior and Δ E 1,2 but also the sensitivity of g 1 * , is the formation of a quantum-dot-like localized charge state within the QPC due to the 1D–2D mismatch at the QPC openings. There is strong experimental evidence that this can occur in QPCs including observations of Kondo-like behavior, ,,− Fano resonances, − and Fabry–Pérot oscillations on the integer conductance plateaus by other authors. [We also observe weak Fabry–Pérot-like structure along V sd = 0 in some of our source-drain bias plots (see Supplementary Figure 4, Supporting Information); it is much stronger in ref , presumably due to the stronger 1D confinement (Δ E 1,2 ∼ 5 meV).]…”

Towards low-dimensional hole systems in Be-doped GaAs nanowires

“…Holes in GaAs exhibit strong spin-orbit effects, behaving like spin- 3 2 particles, by virtue of the p-like nature of GaAs valence band states [33]. This led to the observation of highly anisotropic Zeeman spin-splitting in 1D hole systems [34][35][36] and correspondingly anisotropic Kondo physics in hole quantum dots [37] made using conventional planar p-type AlGaAs/GaAs heterostructures. A major difficulty in these devices is the ability to achieve strong confinement and access the few-electron limit [38].…”

Tuning the Fano Resonance with an Intruder Continuum

“…Our experiments make use of the peculiar properties of QPCs close to pinch-off, where strongly enhanced carrier interactions can spontaneously distort their self-consistent potential. The distortion is associated with Friedel oscillations generated by scattering from the QPC barrier and is thought to lead to the formation of a narrow well that may support a quasi-localized state (LS) near the center of the QPC. − Several studies have been undertaken to explore the structure of this unusual microscopic feature, − and we have revealed its presence by using it as the discrete level in a FR geometry. − In these experiments (see the Supporting Information for further details on the measurement procedure), two QPCs are formed in close proximity and are allowed to interact via an intervening region of two-dimensional electron gas (Figure a). By suitable variation of the voltage ( V s ) applied to the gates of one of the QPCs (referred to hereafter as the “swept-QPC”, and denoted by the subscript “s”) we form a LS inside it by pinching it off.…”