S. T. Herbert

Publications (7)31.11 Total impact

• Source

  Available from: M. Cahay

  Article: Spin Polarization in a AlGaAs/GaAs Quantum Point Contact with in-plane side gates

  N. Bhandari, P. P. Das, M. Cahay, R. S. Newrock, S. T. Herbert
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  ABSTRACT: We report the observation of an anomalous conductance plateau near G = 0.5 G0 (G0 = 2e2/h) in asymmetrically biased AlGaAs/GaAs quantum point contacts (QPCs), with in-plane side gates in the presence of lateral spin-orbit coupling. This is a signature of spin polarization in the narrow portion of the QPC. The appearance and evolution of the conductance anomaly has been studied at T=4.2K as a function of the potential asymmetry between the side gates. The observation of spontaneous spin polarization in a side-gated GaAs QPC could eventually lead to the realization of an all-electric spin-valve at tens of degrees Kelvin.
  04/2012;
• Article: Understanding the anomalous conductance plateau in asymmetrically biased InAs/In0.52Al0.48As quantum point contacts—A step towards a tunable all electric spin valve

  P. P. Das, K. B. Chetry, N. Bhandari, J. Wan, M. Cahay, R. S. Newrock, S. T. Herbert
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  ABSTRACT: The appearance and evolution of an anomalous conductance plateau at 0.4(2e2/h) in an In0.52Al0.48As/InAs quantum point contact (QPC), in the presence of lateral spin-orbit coupling, has been studied at T = 4.2 K as a function of the potential asymmetry between the in-plane gates of the QPC. The anomalous plateau, a signature of spin polarization in the channel, appears only over an intermediate range (around 3 V) of bias asymmetry. It is quite robust, being observed over a maximum range of nearly 1 V of the sweep voltage common to the two in-plane gates. The conductance measurements show evidence of surface roughness and dangling bond scattering from the side walls of the QPC.
  Applied Physics Letters 09/2011; 99(12):122105-122105-3. · 3.84 Impact Factor
• Article: Anamolous conductance plateau in an asymmetrically biased InAs/InAlAs quantum point contact

  P. P. Das, K. B. Chetry, N. Bhandari, J Wan, M. Cahay, R. S. Newrock, S. T. Herbert
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  ABSTRACT: The appearance and evolution of an anomalous conductance plateau at 0.4 (in units of 2e2/h) in an In0.52Al0.48As/InAs quantum point contact (QPC), in the presence of lateral spin-orbit coupling, has been studied at T=4.2K as a function of the potential asymmetry between the in-plane gates of the QPC. The anomalous plateau, a signature of spin polarization in the channel, appears only over an intermediate range (around 3 V) of bias asymmetry. It is quite robust, being observed over a maximum range of nearly 1V of the sweep voltage common to the two in-plane gates. Our conductance measurements show evidence of surface roughness scattering from the side walls of the QPC. We show that a strong perpendicular magnetic field leads to magnetic confinement in the channel which reduces the importance of scattering from the side walls and favors the onset of near ballistic transport through the QPC.
  07/2011;
• Article: All-electric quantum point contact spin-polarizer.

  P Debray, S M S Rahman, J Wan, R S Newrock, M Cahay, A T Ngo, S E Ulloa, S T Herbert, M Muhammad, M Johnson
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  ABSTRACT: The controlled creation, manipulation and detection of spin-polarized currents by purely electrical means remains a central challenge of spintronics. Efforts to meet this challenge by exploiting the coupling of the electron orbital motion to its spin, in particular Rashba spin-orbit coupling, have so far been unsuccessful. Recently, it has been shown theoretically that the confining potential of a small current-carrying wire with high intrinsic spin-orbit coupling leads to the accumulation of opposite spins at opposite edges of the wire, though not to a spin-polarized current. Here, we present experimental evidence that a quantum point contact -- a short wire -- made from a semiconductor with high intrinsic spin-orbit coupling can generate a completely spin-polarized current when its lateral confinement is made highly asymmetric. By avoiding the use of ferromagnetic contacts or external magnetic fields, such quantum point contacts may make feasible the development of a variety of semiconductor spintronic devices.
  Nature Nanotechnology 11/2009; 4(11):759-64. · 27.27 Impact Factor
• Article: All-Electric Quantum Point Contact Spin Valve

  P. Debray, J Wan, S. M. S. Rahman, R. S. Newrock, M. Cahay, A. T. Ngo, S. E. Ulloa, S. T. Herbert, M. Muhammad, M. Johnson
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  ABSTRACT: This paper has been withdrawn by the author because in the main text some discussion parts were inadvertently added by mistake. Comment: This paper has been withdrawn
  01/2009;
• Source

  Available from: Jenny R Holzer

  Article: Finite-Size Effects and Dynamical Scaling in Two-Dimensional Josephson Junction Arrays

  J. Holzer, R. S. Newrock, C. J. Lobb, T. Aouaroun, S. T. Herbert
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  ABSTRACT: In recent years many groups have used Fisher, Fisher, and Huse (FFH) dynamical scaling to investigate and demonstrate details of the superconducting phase transition. Some attention has been focused on two dimensions where the phase transition is of the Kosterlitz-Thouless-Berezinskii (KTB) type. Pierson et al. used FFH dynamical scaling almost exclusively to suggest that the dynamics of the two-dimensional superconducting phase transition may be other than KTB-like. In this work we investigate the ability of scaling behavior by itself to yield useful information on the nature of the transition. We simulate current-voltage (IV) curves for two-dimensional Josephson junction arrays with and without finite-size-induced resistive tails. We find that, for the finite-size effect data, the values of the scaling parameters, specifically the transition temperature and the dynamical scaling exponent z, depend critically on the magnitude of the contribution that the resistive tails make to the IV curves. In effect, the values of the scaling parameters depend on the noise floor of the measuring system. Comment: 24 pages, 8 figures; submitted to Physical Review B
  11/2000;
• Article: Effect of finite size on the Kosterlitz-Thouless transition in two-dimensional arrays of proximity-coupled junctions

  S. T. Herbert, Y. Jun, C. J. Lobb, H.-K. Shin K. Ravindran
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  ABSTRACT: We have investigated the Kosterlitz-Thouless (KT) transition in a series of proximity-coupled Josephson junction arrays of varying widths. Our results indicate that the KT transition in any experimentally realizable sample is almost always obscured by the presence of thermally generated, finite-size-induced free vortices. While the existence of these finite-size-induced free vortices has been known for some time, our work suggests that they are much more prevalent and thus have a far greater effect on the transition than had been previously thought. As a consequence of this, the vortex-unbinding transition temperature TKT may not occur when the experimentally measured current-voltage exponent a(T)=3, but in fact may occur at significantly higher temperatures. We present a detailed picture of these finite-size effects applied specifically to arrays, but which may have implications for other two-dimensional systems.
  Phys. Rev. B. 12/1997; 57(2).