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High-resolution tunnelling spectroscopy of a graphene quartet
Song, Young Jae,Otte, Alexander F.,Kuk, Young,Hu, Yike,Torrance, David B.,First, Phillip N.,de Heer, Walt A.,Min, Hongki,Adam, Shaffique,Stiles, Mark D.,MacDonald, Allan H.,Stroscio, Joseph A. Nature Publishing Group, a division of Macmillan P 2010 Nature Vol.467 No.7312
Electrons in a single sheet of graphene behave quite differently from those in traditional two-dimensional electron systems. Like massless relativistic particles, they have linear dispersion and chiral eigenstates. Furthermore, two sets of electrons centred at different points in reciprocal space (??valleys??) have this dispersion, giving rise to valley degeneracy. The symmetry between valleys, together with spin symmetry, leads to a fourfold quartet degeneracy of the Landau levels, observed as peaks in the density of states produced by an applied magnetic field. Recent electron transport measurements have observed the lifting of the fourfold degeneracy in very large applied magnetic fields, separating the quartet into integer and, more recently, fractional levels. The exact nature of the broken-symmetry states that form within the Landau levels and lift these degeneracies is unclear at present and is a topic of intense theoretical debate. Here we study the detailed features of the four quantum states that make up a degenerate graphene Landau level. We use high-resolution scanning tunnelling spectroscopy at temperatures as low as 10??mK in an applied magnetic field to study the top layer of multilayer epitaxial graphene. When the Fermi level lies inside the fourfold Landau manifold, significant electron correlation effects result in an enhanced valley splitting for even filling factors, and an enhanced electron spin splitting for odd filling factors. Most unexpectedly, we observe states with Landau level filling factors of 7/2, 9/2 and 11/2, suggestive of new many-body states in graphene.
Invited Review Article: A 10 mK scanning probe microscopy facility.
Song, Young Jae,Otte, Alexander F,Shvarts, Vladimir,Zhao, Zuyu,Kuk, Young,Blankenship, Steven R,Band, Alan,Hess, Frank M,Stroscio, Joseph A American Institute of Physics 2010 Review of scientific instruments Vol.81 No.12
<P>We describe the design, development and performance of a scanning probe microscopy (SPM) facility operating at a base temperature of 10 mK in magnetic fields up to 15 T. The microscope is cooled by a custom designed, fully ultra-high vacuum (UHV) compatible dilution refrigerator (DR) and is capable of in situ tip and sample exchange. Subpicometer stability at the tip-sample junction is achieved through three independent vibration isolation stages and careful design of the dilution refrigerator. The system can be connected to, or disconnected from, a network of interconnected auxiliary UHV chambers, which include growth chambers for metal and semiconductor samples, a field-ion microscope for tip characterization, and a fully independent additional quick access low temperature scanning tunneling microscope (STM) and atomic force microscope (AFM) system. To characterize the system, we present the cooling performance of the DR, vibrational, tunneling current, and tip-sample displacement noise measurements. In addition, we show the spectral resolution capabilities with tunneling spectroscopy results obtained on an epitaxial graphene sample resolving the quantum Landau levels in a magnetic field, including the sublevels corresponding to the lifting of the electron spin and valley degeneracies.</P>
Christel Braaksma,Jill Otte,Ronald N. Wessel,Nienke Wolterbeek 대한견주관절학회 2022 대한견주관절의학회지 Vol.25 No.1
Background: There are various conservative treatment options for lateral epicondylitis (LE). The aim is to evaluate pain, daily functioning, and complications after ultrasound-standardized autologous blood injections in patients with LE. Methods: For this prospective cohort study, consecutive patients (>18 years) diagnosed with LE were included. Autologous blood was injected using a medical device containing an injection disposable with 12 small needles (Instant Tennis Elbow Cure [ITEC]) device. Patient-Rated Tennis Elbow Evaluation (PRTEE), subjective elbow score (SES), palpation and provocation pain, satisfaction, and complications of treatment were measured at baseline and two months after treatment. Paired t-tests and Fisher’s exact tests were used for calculating the difference between pre- and post-treatment outcomes. Results: Fifty-five elbows were analyzed. Mean time between pre- and post-treatment was 11.1 weeks (standard deviation [SD], 8.9 weeks). The mean PRTEE score decreased from 68.2 (SD, 15.7) before surgery to 53.2 (SD, 25.9; p<0.001) after. The mean SES improved from 36.9 (SD, 20.8) to 51.7 (SD, 27.4; p<0.001). Despite this improvement, only 44.7% of patients showed relevant clinical improvement in PRTEE, and 37.3% showed significant clinical improvement based on SES. Four patients reported a complication and the injection disposable failed three times. Conclusions: Ultrasound-standardized autologous blood injection using the ITEC device is not an effective tool in reducing symptoms related to LE. This study showed that only half of all patients experienced a positive effect. In this heterogeneous cohort of patients, we showed no added value of ultrasound standardization.
Time resolved coherence-imaging spectrometer on WEGA stellarator
Chung, Jinil,Kö,nig, Ralf,Howard, John,Otte, Matthias,Klinger, Thomas Published jointly by The Institute of Physics and 2005 Plasma physics and controlled fusion Vol.47 No.6
<P>Imaging sensor technologies such as charge coupled devices and complementary metal-oxide-semiconductor have made remarkable progress in recent years. Fast imaging systems based on these new technologies are now being routinely employed for advanced fusion diagnostics. Since two-dimensional imaging considerably improves the investigation of three-dimensional structural physics, we have installed and operated the first high-speed two-dimensional coherence imaging camera system for the study of ion temperatures and flow velocities in the WEGA stellarator based on the Doppler broadening of 468.6 nm He II line emission. The coherence imaging camera was able to image the complete plasma poloidal cross-section over a toroidal region spanning 10°. The camera was used for basic plasma studies, including electron cyclotron resonance heating (ECRH) power step experiments. The ion temperature of helium plasmas in WEGA is found to be 1.5–2.0 eV at maximum (26 kW) ECRH power. The plasma rotates in the <I>E</I> × <I>B</I> direction with speeds between 500 and 1000 m s<SUP>−1</SUP>, increasing at higher ECRH power. It was confirmed that the flow direction reverses with the direction of the magnetic field. The observed ion temperatures and flows were cross checked against a multi-channel Echelle spectrometer and satisfactory agreement obtained.</P>