Giant Oscillations of Acoustoelectric Current in a Quantum Channel

A theory of d.c. electric current induced in a quantum channel by a propagating surface acoustic wave (acoustoelectric current) is worked out. The first observation of the acoustoelectric current in such a situation was reported by J. M. Shilton et al., Journ. Phys. C (to be published). The authors observed a very specific behavior of the acoustoelectric current in a quasi-one-dimensional channel defined in a GaAs-AlGaAs heterostructure by a split-gate depletion -- giant oscillations as a function of the gate voltage. Such a behavior was qualitatively explained by an interplay between the energy-momentum conservation law for the electrons in the upper transverse mode with a finite temperature splitting of the Fermi level. In the present paper, a more detailed theory is developed, and important limiting cases are considered.Comment: 7 pages, 2 Postscript figures, RevTeX 3.

Acoustoelectric effects in quantum constrictions

A dc current induced in a quantum constriction by a traveling acoustic wave (or by non-equilibrium ballistic phonons) is considered. We show that in many important situations the effect is originated from acoustically-induced scattering between the propagating and reflecting states in the constriction. Two particular regimes corresponding to relatively high and low acoustic frequencies are discussed. In the first regime, the acoustoelectric effect in a smooth constriction can be understood by semi-classical considerations based on local conservation laws. For the low frequency regime, we show that the acousto-conductance is closely related to the zero field conductance. The qualitative considerations are confirmed by numerical calculations both for smooth and abrupt channels.Comment: 10 pages, RevTeX, 9 postscript figures, submitted to Phys. Rev.

Surface acoustic wave solid-state rotational micromotor

Surface acoustic waves (SAWs) are used to drive a 1mm diameter rotor at speeds exceeding 9000 rpm and torque of nearly 5 nNm. Unlike recent high-speed SAW rotary motors, however, the present design does not require a fluid coupling layer but interestingly exploits adhesive stiction as an internal preload, a force usually undesirable at these scales; with additional preloads, smaller rotors can be propelled to 15 000 rpm. This solid-state motor has no moving parts except for the rotor and is sufficiently simple to allow integration into miniaturized drive systems for potential use in microfluidic diagnostics, optical switching and microrobotics

Non-adiabaticity and single-electron transport driven by surface acoustic waves

Single-electron transport driven by surface acoustic waves (SAW) through a narrow constriction, formed in two-dimensional electron gas, is studied theoretically. Due to long-range Coulomb interaction, the tunneling coupling between the electron gas and the moving minimum of the SAW-induced potential rapidly decays with time. As a result, nonadiabaticiy sets a limit for the accuracy of the quantization of acoustoelectric current

Acoustoelectric effect in a finite-length ballistic quantum channel

The dc current induced by a coherent surface acoustic wave (SAW) of wave vector q in a ballistic channel of length L is calculated. The current contains two contributions, even and odd in q. The even current exists only in a asymmetric channel, when the electron reflection coefficients r_1 and r_2 at both channel ends are different. The direction of the even current does not depend on the direction of the SAW propagation, but is reversed upon interchanging r_1 and r_2. The direction of the odd current is correlated with the direction of the SAW propagation, but is insensitive to the interchange of r_1 and r_2. It is shown that both contributions to the current are non zero only when the electron reflection coefficients at the channel ends are energy dependent. The current exhibits geometric oscillations as function of qL. These oscillations are the hallmark of the coherence of the SAW and are completely washed out when the current is induced by a flux of non-coherent phonons. The results are compared with those obtained previously by different methods and under different assumptions.Comment: 7 pages, 2 figure

The Ursinus Weekly, March 9, 1959

J. Robbins is \u2759 May queen; Court, committees are picked • Folk song concert presented, Mar. 21 • Juniors plan to present prom • Dr. Helen Cam to speak at Forum Wed. • Junior men should apply for Cub and Key • 90th anniversary of its charter celebrated by Ursinus on Feb. 19 • Campus Chest opens annual charity drive • APO plans for future events • SEAP hears pupils discuss teachers • Editorial: Giving? • Weavers • Letters to the editor • Sun dial was fast • Intramural night to be held Tuesday, March 24 • Badminton team wins third in row • Courtmen end season; Lose 2 more contests • Grapplers end season with 3-5 record • Religion in life week presented • Curtain Club begins tryouts for Spring play • Student faculty show to be new & different • Sophs present dancehttps://digitalcommons.ursinus.edu/weekly/1379/thumbnail.jp

The Ursinus Weekly, December 8, 1958

Daniels, Brenner chosen king and queen at prom • Rev. O. Rowland to speak at marriage seminar • SEAP shows movie; Plans convention • Stars and Players awards points • MS-WSGA hold annual banquet; Plan Christmas dance December 17 • Handel\u27s Messiah to be presented Dec. 11 • Bob Petersen picked for 1958 ECAC football • Ruby assignments listed; Deadline near • Editorial: Isolation • Work camps • Guardian angels • Futility • Comparisons • Word • Wrestling team begins practice for \u2759 season • Schmoyer places on MAC 2nd team; Drexel\u27s 1st team • Courtmen win first game of season, 78-46 • Girls begin practice for basketball • Bears end season with 0-8 record; \u2759 looks better • Ursinus grad gains position in Ghana • Art news • Ursinus host to CDA last weekhttps://digitalcommons.ursinus.edu/weekly/1373/thumbnail.jp

Acoustoelectric current and pumping in a ballistic quantum point contact

The acoustoelectric current induced by a surface acoustic wave (SAW) in a ballistic quantum point contact is considered using a quantum approach. We find that the current is of the "pumping" type and is not related to drag, i.e. to the momentum transfer from the wave to the electron gas. At gate voltages corresponding to the plateaus of the quantized conductance the current is small. It is peaked at the conductance step voltages. The peak current oscillates and decays with increasing SAW wavenumber for short wavelengths. These results contradict previous calculations, based on the classical Boltzmann equation.Comment: 4 pages, 1 figur

Weiss Oscillations in Surface Acoustic Wave Propagation

The interaction of a surface acoustic wave (SAW) with a a two-dimensional electron gas in a periodic electric potential and a classical magnetic field is considered. We calculate the attenuation of the SAW and its velocity change and show that these quantities exhibit Weiss oscillations.Comment: 4 pages REVTEX, 2 figures included as eps file