No abstract

No abstract

We use magnetoconductance fluctuation measurements of phase-coherent semiconductor billiards to quantify the contributions to the nonlinear electric conductance that are asymmetric under reversal of magnetic field. We experimentally determine that the average asymmetric contribution is linear in magnetic field (for magnetic flux much larger than one flux quantum) and that its magnitude depends on billiard geometry. In addition, we find an unexpected asymmetry in the power spectrum characteristics of the magnetoconductance with respect to reversal of magnetic field and bias voltage.PACS numbers: 73.63. Kv, 73.23.Ad, 73.50.Fq Electron transport in linear response is characterized by a high degree of symmetry with respect to the direction of an applied magnetic field, B, as described by the Onsager-Casimir relations σ αβ (B) = σ βα (-B) in terms of the local conductivity tensor [1]. For the case of two-terminal mesoscopic conductors, this corresponds to the reciprocity theorem, which predicts the conductance to be an even function of B in linear response [2]. At zero magnetic field, it is well known that the absence of spatial symmetry leads to nonlinear terms in the conductance that are asymmetric in V [3]. Only very recently has a distinct nonlinear term attracted attention that leads to an asymmetry of the conductance in the presence of both finite B and V [4,5]. The contribution of electron-electron interaction to this asymmetry was calculated to lowest order for disordered [6] and ballistic [7] phase-coherent conductors for a magnetic flux smaller than one flux quantum Φ o = h/e, and for bias voltages, V smaller than the characteristic energy scale of the system (typically µeV in semiconductor billiards).Here we quantitatively investigate conductance asymmetries in a new regime, namely for magnetic B fields much greater than one flux quantum threaded through the device area, A, and for significant bias voltages (on order of mV) using billiards of varying geometry.Using measurements of magnetoconductance fluctuations (MCF) we quantify, for the first time, the lowest nonlinear conductance term that leads to the breakdown of the Onsager-Casimir relations in this regime, and show that its magnitude is related to billiard geometry. In addition we have discovered that not only individual features of the MCF, but, unexpectedly, the characteristics of the MCF power spectrum are asymmetric in B and V, and that they depend on device asymmetry.The nonlinear differential conductance, g (B, V) = dI/dV, can be approximated by an expansion in V,

The well-established symmetry relations for linear transport phenomena cannot, in general, be applied in the nonlinear regime. Here we propose a set of symmetry relations with respect to bias voltage and magnetic field for the nonlinear conductance of two-terminal electric conductors. We experimentally confirm these relations using phase-coherent, semiconductor quantum dots.

The strength of the Zeeman splitting induced by an applied magnetic field is an important factor for the realization of spin-resolved transport in mesoscopic devices. We measure the Zeeman splitting for a quantum point contact etched into a Ga0.25In0.75As quantum well, with the field oriented parallel to the transport direction. We observe an enhancement of the Lande g-factor from |g*|=3.8 +/- 0.2 for the third subband to |g*|=5.8 +/- 0.6 for the first subband, six times larger than in GaAs. We report subband spacings in excess of 10 meV, which facilitates quantum transport at higher temperatures.Comment: [Version 2] Revtex4, 11 pages, 3 figures, accepted for publication in Applied Physics Letter