Non-Kondo zero-bias anomaly in quantum wires

T.-M. Chen, A. C. Graham, M. Pepper, I. Farrer, and D. A. Ritchie

Phys. Rev. B 79, 153303 – Published 14 April 2009

Abstract

It has been suggested that a zero-bias conductance peak in quantum wires signifies the presence of Kondo spin-correlations, which might also relate to an intriguing one-dimensional (1D) spin effect known as the 0.7 structure. These zero-bias anomalies (ZBA) are strongly temperature dependent, and have been observed to split into two peaks in magnetic field, both signatures of Kondo correlations in quantum dots. We present data in which ZBAs in general do not split as magnetic field is increased up to 10 T. A few of our ZBAs split in magnetic field but by significantly less than the Kondo splitting value, and evolve back to a single peak upon moving the 1D constriction laterally. The ZBA therefore does not appear to have a Kondo origin, and instead we propose a simple phenomenological model to reproduce the ZBA which is in agreement mostly with observed characteristics.

Received 3 March 2009

DOI:https://doi.org/10.1103/PhysRevB.79.153303

Authors & Affiliations

T.-M. Chen, A. C. Graham, M. Pepper, I. Farrer, and D. A. Ritchie

Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom

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Issue

Vol. 79, Iss. 15 — 15 April 2009

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Images

Figure 1
(a) Differential conductance vs dc bias for fixed split-gate voltages, at $B = 0$ and $B = 7.6 T$ , both showing a clear zero-bias anomaly (ZBA). (b) Differential conductance vs split-gate voltage for $B = 0 \to 16 T$ . (c) dc-bias data showing the evolution of the ZBA with increasing field.Reuse & Permissions
Figure 2
(Color online) (a) Temperature dependence of differential conductance vs dc bias at $B = 0$ . (b) Linear conductance as a function of scaled temperature $T / T_{K}$ at various $V_{g}$ , where the Kondo temperature $T_{K}$ is the fit parameter in the modified Kondo function. (c) The same experimental data shown in an Arrhenius plot: $ln {[1 - G (T)] / C_{A}}$ as a function of scaled temperature $T_{A} / T$ , where the activation temperature $T_{A}$ and $C_{A}$ are the fit parameters in Arrhenius function. (d) $T_{K}$ (solid symbols) and $T_{A}$ (open symbols) extracted from the fits of both models, along with the conductance at 60 mK (solid), 230 mK (dashed), and 800 mK (dotted).Reuse & Permissions
Figure 3
(a) Differential conductance vs split-gate voltage at $B = 0$ , 2, 4, and 6 T. (b) Differential conductance vs dc bias for fixed split-gate voltages, at $B = 0$ , 2, 4, and 6 T, showing a clear ZBA which splits into two with increasing $B$ . [(c) and (d)] Same as (a) and (b) but with a difference of $d V_{g} = + 0.3 V$ between the voltages on the two split-gates—the splitting of the ZBA with increasing $B$ is even clearer. [(e) and (f)] Same as (a) and (b) but for $d V_{g} = - 0.6 V$ —the ZBA is stronger for all $B$ , but no longer exhibits any splitting. [(g) and (h)] Same as (a) and (b) but for $d V_{g} = + 0.6 V$ —these data are very different to (e) and (f), indicating that disorder strongly affects ZBAs.Reuse & Permissions
Figure 4
(Color online) (a) Calculated differential conductance vs dc bias, assuming subband energy, $E_{s} = E_{s 0}$ , is fixed with respect to the average of the source and drain chemical potentials, where $E_{s 0}$ is the subband energy at zero dc bias. (b) Differential conductance vs dc bias, calculated in the same way, but including a linear increase, $E (V_{s d})$ , in the subband energy $E_{s}$ , as a function of dc bias. A zero-bias anomaly is present. (c) Variation in subband energy required to keep density fixed as function of dc bias, for $k T = 0.02 - 0.16 meV$ . Curves at $y > 0$ $(y < 0)$ are for the subband sitting above (below) $E_{f}$ at $V_{s d} = 0$ . (d) The temperature variation in the characteristics in (b). (e) Same as (d), but now using a linear increase $E (V_{s d}, T)$ in subband energy, which decreases with increasing temperature. (f) Comparison of subband energy used in (e) to calculate $d I / d V_{s d}$ (bottom) to curves for fixed density (top) taken from (c).Reuse & Permissions

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