Orbital effect of an in-plane magnetic field on quantum transport in chaotic lateral dots

Abstract

We show how the in-plane magnetic field, which breaks time-reversal and rotational symmetries of the orbital motion of electrons in a heterostructure due to the momentumdependent inter-subband mixing, affects weak localisation correction to conductance of a large-area chaotic lateral quantum dot and parameteric dependences of universal conductance fluctuations in it.A high sensitivity of phase-coherent transport through quantum dots to external perturbations has recently enabled one to transform studies of mesoscopic effects [1][2][3] into a spectroscopic tool for detecting tiny energetic changes in the electron gas [4] and for studying electron dephasing and inelastic relaxation rates [5,6]. A convenient object [7], once used as a mesoscopic thermometer [8], consists of a lateral semiconductor dot weakly coupled to the reservoirs via two leads, l and r, each with N l,r 1 open conducting channels, and, therefore, quantum conductances g l,r = 2e 2 h N l,r . Information concerning fine energetic characteristics of singleparticle electron states in a dot can be extracted from the variance and parametric correlations of universal conductance fluctuations (UCF), δg = g − g , measured as random oscillations of the dot conductance, g around the mean value, g = g l g r /(g l + g r ), upon variation of a perpendicular magnetic field [1,3], the Fermi energy [2,3] or the dot shape [7].Energetic resolution of such a spectroscopy is set by the level broadening of single-particle states in a particular device, which is limited by the carrier escape into the leads,where ∆ = 2π 2 /mS is the mean level spacing of singleparticle states of spin-polarized electrons with mass m in a dot with area S. The use of larger dots with weaker coupling to the leads increases the sensitivity of the dot conductance to the variation of external parameters. The use of larger dots also enables one to assess directly the low excitation energy characteristics of the 2D electron gas, since the electron properties in 1÷10µm 2 -area dots containing 10 3 −10 4 particles are less affected by the confinement effects. Recently, large area dots were used for studying spin-polarisation of a 2D electron gas [4]. In order to enhance coupling between a magnetic field and electron spin, J.Folk et al [4] used a magnetic field finely tuned to be orientated exactly parallel to the plane of 2D electrons. One observed a strong suppression of the variance δg 2 (B ) by an in-plane field B interpreted in terms of a spin-orbit coupling in the 2D gas [9]. This feature has also been accompanied by an observation [10] of such a negative weak localisation (WL) magnetoresistance caused by an in-plane field B that one would relate to the time-reversal symmetry breaking in the orbital motion of electrons. In the present publication, we assess to which extent one can reduce the influence of an ideally in-plane tuned magnetic field on quantum transport in lateral semiconductor dots to spin effects alone, that is, we determine the range of fields B that would affect WL and UCF's i...

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