arXiv subjects

I. Bar-Joseph

Publications and source records attributed to I. Bar-Joseph.

At least 19 recordsLinked to original sources

arXiv2012

NMR probing of the spin polarization of the nu=5/2 quantum Hall state

Resistively detected nuclear magnetic resonance is used to measure the Knight shift of the As nuclei and determine the electron spin polarization of the fractional quantum Hall states of the second Landau level. We show that the 5/2 state is fully polarized within experimental error, thus confirming a fundamental assumption of the Moore-Read theory. We measure the electron heating under radio frequency excitation, and show that we are able to detect NMR at electron temperatures down to 30 mK.

cond-mat.str-el↗

arXiv2010

Optical Probing of the Spin Polarization of the nu=5/2 Quantum Hall State

We apply polarization resolved photoluminescence spectroscopy to measure the spin polarization of a two dimensional electron gas in perpendicular magnetic field. In the vicinity of filling factor nu=5/2, we observe a sharp discontinuity in the energy of the zero Landau level emission line. We find that the splitting between the two circular polarizations exhibits a sharp drop at nu=5/2 and is equal to the bare Zeeman energy, which resembles the behavior at even filling factors. We show that this behavior is consistent with filling factor nu=5/2 being unpolarized.

cond-mat.mes-hall↗

arXiv2009

Optical absorption to probe the quantum Hall ferromagnet at filling factor $ν=1$

Optical absorption measurements are used to probe the spin polarization in the integer and fractional quantum Hall effect regimes. The system is fully spin polarized only at filling factor $ν=1$ and at very low temperatures($\sim40$ mK). A small change in filling factor ($δν\approx\pm0.01$) leads to a significant depolarization. This suggests that the itinerant quantum Hall ferromagnet at $ν=1$ is surprisingly fragile against increasing temperature, or against small changes in filling factor.

cond-mat.mes-hall↗

arXiv2007

The Fermi edge singularity of spin polarized electrons

We study the absorption spectrum of a two-dimensional electron gas (2DEG) in a magnetic field. We find that that at low temperatures, when the 2DEG is spin polarized, the absorption spectra, which correspond to the creation of spin up or spin down electron, differ in magnitude, linewidth and filling factor dependence. We show that these differences can be explained as resulting from creation of a Mahan exciton in one case, and of a power law Fermi edge singularity in the other.

cond-mat.mes-hall↗

arXiv2006

Absorption in the fractional quantum Hall regime: trion dichroism and spin polarization

We present measurements of optical interband absorption in the fractional quantum Hall regime in a GaAs quantum well in the range 0 < nu < 1. We investigate the mechanism of singlet trion absorption, and show that its circular dichroism can be used as a probe of the spin polarization of the ground state of the two-dimensional electron system (2DES). We find that at nu = 1/3 the 2DES is fully spin-polarized. Increasing the filling factor results in a gradual depolarization, with a sharp minimum in the dichroism near nu = 2/3. We find that in the range 0.5 < nu < 0.85 the 2DES remains partially polarized for the broad range of magnetic fields from 2.75 to 11 Tesla. This is consistent with the presence of a mixture of polarized and depolarized regions.

cond-mat.mes-hall↗

arXiv2005

Sensing electric and magnetic fields with Bose-Einstein Condensates

We discuss the application of Bose-Einstein condensates (BECs) as sensors for magnetic and electric fields. In an experimental demonstration we have brought one-dimensional BECs close to micro-fabricated wires on an atom chip and thereby reached a sensitivity to potential variations of ~10e-14eV at 3 micron spatial resolution. We demonstrate the versatility of this sensor by measuring a two-dimensional magnetic field map 10 micron above a 100-micron-wide wire. We show how the transverse current-density component inside the wire can be reconstructed from such maps. The field sensitivity in dependence on the spatial resolution is discussed and further improvements utilizing Feshbach resonances are outlined.

cond-mat.other↗

arXiv2005

Matter-wave interferometry in a double well on an atom chip

Matter-wave interference experiments enable us to study matter at its most basic, quantum level and form the basis of high-precision sensors for applications such as inertial and gravitational field sensing. Success in both of these pursuits requires the development of atom-optical elements that can manipulate matter waves at the same time as preserving their coherence and phase. Here, we present an integrated interferometer based on a simple, coherent matter-wave beam splitter constructed on an atom chip. Through the use of radio-frequency-induced adiabatic double-well potentials, we demonstrate the splitting of Bose-Einstein condensates into two clouds separated by distances ranging from 3 to 80 microns, enabling access to both tunnelling and isolated regimes. Moreover, by analysing the interference patterns formed by combining two clouds of ultracold atoms originating from a single condensate, we measure the deterministic phase evolution throughout the splitting process. We show that we can control the relative phase between the two fully separated samples and that our beam splitter is phase-preserving.

quant-ph↗

arXiv2005

Disorder Potentials near Lithographically Fabricated Atom Chips

We show that previously observed large disorder potentials in magnetic microtraps for neutral atoms are reduced by about two orders of magnitude when using atom chips with lithographically fabricated high quality gold layers. Using one dimensional Bose-Einstein condensates, we probe the remaining magnetic field variations at surface distances down to a few microns. Measurements on a 100 um wide wire imply that residual variations of the current flow result from local properties of the wire.

cond-mat.other↗

arXiv2004

The absorption spectrum around nu=1: evidence for a small size Skyrmion

We measure the absorption spectrum of a two-dimensional electron system (2DES) in a GaAs quantum well in the presence of a perpendicular magnetic field. We focus on the absorption spectrum into the lowest Landau Level around nu=1. We find that the spectrum consists of bound electron-hole complexes, trion and exciton like. We show that their oscillator strength is a powerful probe of the 2DES spatial correlations. We find that near nu=1 the 2DES ground state consists of Skyrmions of small size (a few magnetic lengths).

cond-mat.str-el↗

arXiv2004

Atom Chips: Fabrication and Thermal Properties

Neutral atoms can be trapped and manipulated with surface mounted microscopic current carrying and charged structures. We present a lithographic fabrication process for such atom chips based on evaporated metal films. The size limit of this process is below 1$μ$m. At room temperature, thin wires can carry more than 10$^7$A/cm$^2$ current density and voltages of more than 500V. Extensive test measurements for different substrates and metal thicknesses (up to 5 $μ$m) are compared to models for the heating characteristics of the microscopic wires. Among the materials tested, we find that Si is the best suited substrate for atom chips.

cond-mat.mtrl-sci↗

arXiv2003

An atom fiber for guiding cold neutral atoms

We present an omnidirectional matter wave guide on an atom chip. The rotational symmetry of the guide is maintained by a combination of two current carrying wires and a bias field pointing perpendicular to the chip surface. We demonstrate guiding of thermal atoms around more than two complete turns along a spiral shaped 25mm long curved path (curve radii down to 200$μ$m) at various atom--surface distances (35-450$μ$m). An extension of the scheme for the guiding of Bose-Einstein condensates is outlined.

quant-ph↗

arXiv2003

Resonant Enhancement of Inelastic Light Scattering in the Fractional Quantum Hall Regime at $ν=1/3$

Strong resonant enhancements of inelastic light scattering from the long wavelength inter-Landau level magnetoplasmon and the intra-Landau level spin wave excitations are seen for the fractional quantum Hall state at $ν= 1/3$. The energies of the sharp peaks (FWHM $\lesssim 0.2meV$) in the profiles of resonant enhancement of inelastic light scattering intensities coincide with the energies of photoluminescence bands assigned to negatively charged exciton recombination. To interpret the observed enhancement profiles, we propose three-step light scattering mechanisms in which the intermediate resonant transitions are to states with charged excitonic excitations.

cond-mat.mes-hall↗

arXiv2003

Trapping and manipulating neutral atoms with electrostatic fields

We report on experiments with cold thermal $^7$Li atoms confined in combined magnetic and electric potentials. A novel type of three-dimensional trap was formed by modulating a magnetic guide using electrostatic fields. We observed atoms trapped in a string of up to six individual such traps, a controlled transport of an atomic cloud over a distance of 400$μ$m, and a dynamic splitting of a single trap into a double well potential. Applications for quantum information processing are discussed.

quant-ph↗

arXiv2002

Bose-Einstein Condensation in a simple Microtrap

A Bose-Einstein condensate is created in a simple and robust miniature Ioffe-Pritchard trap, the so-called Z trap. This trap follows from the mere combination of a Z-shaped current carrying wire and a homogeneous bias field. The experimental procedure allows condensation of typically 3x10^5 Rb-87 atoms in the |F=2, m_F=2> state close to any mirroring surface, irrespective of its structure, thus it is ideally suited as a source for cold atom physics near surfaces.

cond-mat.soft↗

arXiv2002

Long-range spatial correlations in the exciton energy distribution in GaAs/AlGaAs quantum-wells

Variations in the width of a quantum well (QW) are known to be a source of broadening of the exciton line. Using low temperature near-field optical microscopy, we have exploited the dependence of exciton energy on well-width to show that in GaAs QWs, these seemingly random well-width fluctuations actually exhibit well-defined order -- strong long-range correlations appearing laterally, in the plane of the QW, as well as vertically, between QWs grown one on top of the other. We show that these fluctuations are correlated with the commonly found mound structure on the surface. This is an intrinsic property of molecular beam epitaxial growth.

cond-mat↗

arXiv2002

Anisotropy and periodicity in the density distribution of electrons in a quantum-well

We use low temperature near-field optical spectroscopy to image the electron density distribution in the plane of a high mobility GaAs quantum well. We find that the electrons are not randomly distributed in the plane, but rather form narrow stripes (width smaller than 150 nm) of higher electron density. The stripes are oriented along the [1-10 ] crystal direction, and are arranged in a quasi-periodic structure. We show that elongated structural mounds, which are intrinsic to molecular beam epitaxy, are responsible for the creation of this electron density texture.

cond-mat.mes-hall↗

arXiv2001

Charged exctions in the fractional quantum Hall regime

We study the photoluminescence spectrum of a low density ($ν<1$) two-dimensional electron gas at high magnetic fields and low temperatures. We find that the spectrum in the fractional quantum Hall regime can be understood in terms of singlet and triplet charged-excitons. We show that these spectral lines are sensitive probes for the electrons compressibility. We identify the dark triplet charged-exciton and show that it is visible at the spectrum at $T<2$ K. We find that its binding energy scales like $e^{2}/l $, where $l$ is the magnetic length, and it crosses the singlet slightly above 15 T.

cond-mat.mes-hall↗

arXiv2000

Excitonic emission in the presence of a two dimensional electron gas: a microscopic understanding

The near- and far-field photoluminescence spectra of a gated two-dimensional electron gas have been measured. Spatial fluctuations in the electron density are found to be manifested as spatial fluctuations in the emission amplitude of the negatively charged exciton (X$^{-}$) and in the peak energy of the neutral exciton (X). Consequently, the far-field X$^{-}$ spectrum is a homogoneously broadened Lorentzian, while the X lineshape exhibits substantial inhomogenous broadening. We present a novel and simple technique to extract the electron density from the X$^{-}$ spectrum. We show that width of the far-field X line is proportional to the electron density fluctuations; hence it can be used to characterize the inhomogeneity in the electron density.

cond-mat↗