2,118 research outputs found
Nuclear spin coherence in a quantum wire
We have observed millisecond-long coherent evolution of nuclear spins in a
quantum wire at 1.2 K. Local, all-electrical manipulation of nuclear spins is
achieved by dynamic nuclear polarization in the breakdown regime of the Integer
Quantum Hall Effect combined with pulsed Nuclear Magnetic Resonance. The
excitation thresholds for the breakdown are significantly smaller than what
would be expected for our sample and the direction of the nuclear polarization
can be controlled by the voltage bias. As a four-level spin system, the device
is equivalent to two qubits.Comment: 5 pages, 5 figure
The effect of screening long-range Coulomb interactions on the metallic behavior in two-dimensional hole systems
We have developed a technique utilizing a double quantum well heterostructure
that allows us to study the effect of a nearby ground-plane on the metallic
behavior in a GaAs two-dimensional hole system (2DHS) in a single sample and
measurement cool-down, thereby maintaining a constant disorder potential. In
contrast to recent measurements of the effect of ground-plane screening of the
long-range Coulomb interaction in the insulating regime, we find surprisingly
little effect on the metallic behavior when we change the distance between the
2DHS and the nearby ground-plane.Comment: 5 pages, 4 figures, accepted for publication in PR
The Psychopharmacology of Agitation: Consensus Statement of the American Association for Emergency Psychiatry Project BETA Psychopharmacology Workgroup
Agitation is common in the medical and psychiatric emergency department, and appropriate management of agitation is a core competency for emergency clinicians. In this article, the authors review the use of a variety of first-generation antipsychotic drugs, second-generation antipsychotic drugs, and benzodiazepines for treatment of acute agitation, and propose specific guidelines for treatment of agitation associated with a variety of conditions, including acute intoxication, psychiatric illness, delirium, and multiple or idiopathic causes. Pharmacologic treatment of agitation should be based on an assessment of the most likely cause of the agitation. If agitation results from a delirium or other medical condition, clinicians should first attempt to treat the underlying cause instead of simply medicating with antipsychotics or benzodiazepines
Metal-insulator transition at B=0 in a dilute two dimensional GaAs-AlGaAs hole gas
We report the observation of a metal insulator transition at B=0 in a high
mobility two dimensional hole gas in a GaAs-AlGaAs heterostructure. A clear
critical point separates the insulating phase from the metallic phase,
demonstrating the existence of a well defined minimum metallic conductivity
sigma(min)=2e/h. The sigma(T) data either side of the transition can be
`scaled' on to one curve with a single parameter (To). The application of a
parallel magnetic field increases sigma(min) and broadens the transition. We
argue that strong electron-electron interactions (rs = 10) destroy phase
coherence, removing quantum intereference corrections to the conductivity.Comment: 4 pages RevTex + 4 figures. Submitted to PRL. Originally posted 22
September 1997. Revised 12 October 1997 - minor changes to referencing,
figure cations and figure
Local transport in a disorder-stabilized correlated insulating phase
We report the experimental realization of a correlated insulating phase in 2D
GaAs/AlGaAs heterostructures at low electron densities in a limited window of
background disorder. This has been achieved at mesoscopic length scales, where
the insulating phase is characterized by a universal hopping transport
mechanism. Transport in this regime is determined only by the average electron
separation, independent of the topology of background disorder. We have
discussed this observation in terms of a pinned electron solid ground state,
stabilized by mutual interplay of disorder and Coulomb interaction.Comment: 4+delta pages, 4 figures, To appear in the Physical Review B (Rapid
Comm
'Mine's a Pint of Bitter': Performativity, gender, class and representations of authenticity in real-ale tourism
Leisure choices are expressive of individual agency around the maintenance of taste, boundaries, identity and community. This research paper is part of a wider project designed to assess the social and cultural value of real ale to tourism in the north of England. This paper explores the performativity of real-ale tourism and debates about belonging in northern English real-ale communities. The research combines an ethnographic case study of a real-ale festival with semi-structured interviews with organisers and volunteers, northern English real-ale brewers and real-ale tourists visiting the festival. It is argued that real-ale tourism, despite its origins in the logic of capitalism, becomes a space where people can perform Habermasian, communicative leisure, and despite the contradictions of preferring some capitalist industries over others on the basis of their perceived smaller size and older age, real-ale fans demonstrate agency in their performativity
Back gating of a two-dimensional hole gas in a SiGe quantum well
A device comprising a low-resistivity, n-type, Si substrate as a back gate to a p-type (boron), remote-doped, SiGe quantum well has been fabricated and characterized. Reverse and forward voltage biasing of the gate with respect to the two-dimensional hole gas in the quantum well allows the density of holes to be varied from 8 × 1011 cm–2 down to a measurement-limited value of 4 × 1011 cm–2. This device is used to demonstrate the evolution with decreasing carrier density of a re-entrant insulator state between the integer quantum Hall effect states with filling factors 1 and 3
Tunneling Between Two-Dimensional Electron Gases in a Strong Magnetic Field
We have measured the tunneling between two two-dimensional electron gases at
high magnetic fields , when the carrier densities of the two electron layers
are matched. For filling factors , there is a gap in the current-voltage
characteristics centered about , followed by a tunneling peak at ~mV. Both features have been observed before and have been attributed to
electron-electron interactions within a layer. We have measured high field
tunneling peak positions and fitted gap parameters that are proportional to
, and independent of the carrier densities of the two layers. This suggests
a different origin for the gap to that proposed by current theories, which
predict a dependence.Comment: 9 pages, cond-mat/yymmnn
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