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Evidence for universality of tunable-barrier electron pumps
Giblin, Stephen P,Fujiwara, Akira,Yamahata, Gento,Bae, Myung-Ho,Kim, Nam,Rossi, Alessandro,Mö,ttö,nen, Mikko,Kataoka, Masaya BUREAU INTERNATIONAL DES POIDS ET MESURES 2019 METROLOGIA -BERLIN- Vol.56 No.4
<P>We review recent precision measurements on semiconductor tunable-barrier electron pumps operating in a ratchet mode. Seven studies on five different designs of pumps have reported measurements of the pump current with relative total uncertainties around 10<SUP>−6</SUP> or less. Combined with theoretical models of electron capture by the pumps, these experimental data exhibits encouraging evidence that the pumps operate according to a universal mechanism, independent of the details of device design. Evidence for robustness of the pump current against changes in the control parameters is at a more preliminary stage, but also encouraging, with two studies reporting robustness of the pump current against three or more parameters in the range of ∼<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0026-1394/56/4/044004/metab29a5ieqn001.gif'/> to ∼<img ALIGN='MIDDLE' ALT='' SRC='http://ej.iop.org/images/0026-1394/56/4/044004/metab29a5ieqn002.gif'/>. This review highlights the need for an agreed protocol for tuning the electron pump for optimal operation, as well as more rigorous evaluations of the robustness in a wide range of pump designs.</P>
Robust operation of a GaAs tunable barrier electron pump
Giblin, S P,Bae, M-H,Kim, N,Ahn, Ye-Hwan,Kataoka, M BUREAU INTERNATIONAL DES POIDS ET MESURES 2017 METROLOGIA -BERLIN- Vol.54 No.3
<P>We demonstrate the robust operation of a gallium arsenide tunable-barrier single-electron pump operating with 1 part-per-million accuracy at a temperature of 1.3 K and a pumping frequency of 500 MHz. The accuracy of current quantisation is investigated as a function of multiple control parameters, and robust plateaus are seen as a function of three control gate voltages and RF drive power. The electron capture is found to be in the decay-cascade, rather than the thermally-broadened regime. The observation of robust plateaus at an elevated temperature which does not require expensive refrigeration is an important step towards validating tunable-barrier pumps as practical current standards.</P>
P. G. Freeman,S. R. Giblin,K. Hradil,R. A. Mole,D. Prabhakaran 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.10
The magnetic excitation spectrums of charge stripe ordered La2−xSrxNiO4 x = 0.45 and x = 0.4were studied by inelastic neutron scattering. We found the magnetic excitation spectrum of x = 0.45from the ordered Ni2+ S = 1 spins to match that of checkerboard charge ordered La1.5Sr0.5NiO4. The distinctive asymmetry in the magnetic excitations above 40meV was observed for both doping levels, but an additional ferromagnetic mode was observed in x = 0.45 and not in the x = 0.4. We discuss the origin of crossover in the excitation spectrum between x = 0.45 and x = 0.4 with respect to discommensurations in the charge stripe structure.
Stabilization of single-electron pumps by high magnetic fields
Fletcher, J. D.,Kataoka, M.,Giblin, S. P.,Park, Sunghun,Sim, H.-S.,See, P.,Ritchie, D. A.,Griffiths, J. P.,Jones, G. A. C.,Beere, H. E.,Janssen, T. J. B. M. American Physical Society 2012 Physical review. B, Condensed matter and materials Vol.86 No.15
Precision measurement of a potential-profile tunable single-electron pump
Bae, Myung-Ho,Ahn, Ye-Hwan,Seo, Minky,Chung, Yunchul,Fletcher, J D,Giblin, S P,Kataoka, M,Kim, Nam BUREAU INTERNATIONAL DES POIDS ET MESURES 2015 METROLOGIA -BERLIN- Vol.52 No.2
<P>We performed a precision measurement of the current from a single-parameter electron pump, where the potential-profile for a quantum dot was manipulated by multiple top-metal gates. In an optimally tuned condition, driven with a sinusoidal-waveform microwave at <I>f</I> = 0.95 GHz, <I>B</I> = 11 T, and <I>T</I> = 0.3 K, the relative deviation of the pump current from <I>ef</I>, <I>δI</I><SUB><I>p</I></SUB>/<I>ef</I>?≡?(<I>I</I><SUB><I>p</I></SUB>?−?<I>ef</I>)/<I>ef</I> was measured to be (−0.92 ??? 1.37) ppm. Our experiment reproduces the current quantisation accuracy of a previous measurement of a single-parameter pump, but in a device fabricated using very different geometry, thereby indicating that accurate single-parameter pumping is insensitive to device details.</P>